added arg crate source for potential argument parsing

src/env/derive/mod.rs

@@ -0,0 +1,799 @@
+/* 
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * This file is part of SPD.
+ *
+ * SPD is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * SPD is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with SPD. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and permission
+ * notice:
+ *
+ *     Copyright 2017 Douman
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+
+//! Command line argument parser derive
+
+extern crate alloc;
+extern crate proc_macro;
+
+mod utils;
+use utils::*;
+
+use crate::println;
+
+use proc_macro::TokenStream;
+use quote::quote;
+
+use alloc::{
+    string::String,
+    borrow::ToOwned,
+    vec,
+    vec::*,
+};
+use core::fmt::Write;
+
+struct Argument {
+    field_name: String,
+    name: String,
+    desc: String,
+    required: bool,
+    is_optional: bool,
+    default: Option<String>,
+}
+
+#[derive(PartialEq, Eq, Debug)]
+enum OptValueType {
+    Help,
+    Bool,
+    Value,
+    MultiValue,
+}
+
+struct Opt {
+    arg: Argument,
+    long: String,
+    short: Option<String>,
+    typ: OptValueType,
+}
+
+struct Command {
+    variant_name: String,
+    command_name: String,
+    desc: String,
+}
+
+const FROM_FN: &str = "core::str::FromStr::from_str";
+const TAB: &str = "    ";
+const PARSER_TRAIT: &str = "arg::Args";
+const DEFAULT_INIT: &str = "Default::default()";
+const INVALID_ARG_TYPE_STRING: &str = "Attribute accepts only str";
+const INVALID_REQUIRED_BOOL: &str = "Attribute required cannot be applied to bool switch";
+const UNKNOWN_ARG_ATTR: &str = "Unknown attribute is used";
+const ARG_INVALID_CHARS: &[char] = &[' ', '\t'];
+const ARG_NAME_SPACE_ERROR: &str = "Name contains space character";
+
+fn parse_segment(segment: &syn::PathSegment) -> OptValueType {
+    if segment.ident == "bool" {
+        OptValueType::Bool
+    } else if segment.ident == "Vec" {
+        OptValueType::MultiValue
+    } else {
+        OptValueType::Value
+    }
+}
+
+fn from_enum(ast: &syn::DeriveInput, payload: &syn::DataEnum) -> TokenStream {
+    let mut about_prog = String::new();
+    for attr in ast.attrs.iter() {
+        let attr = match attr.parse_meta() {
+            Ok(attr) => attr,
+            Err(error) => {
+                return syn::Error::new_spanned(attr, format!("cannot parse attribute: {error}")).to_compile_error().into()
+            }
+        };
+
+        match attr {
+            syn::Meta::NameValue(value) => if value.path.is_ident("doc") {
+                if let syn::Lit::Str(ref text) = value.lit {
+                    about_prog.push_str(&text.value());
+                    about_prog.push_str("\n");
+                }
+            } else {
+            },
+            _ => (),
+        }
+    }
+    about_prog.pop();
+
+    let mut commands = Vec::new();
+    for variant in payload.variants.iter() {
+        let mut desc = String::new();
+        let variant_name = variant.ident.to_string();
+        if variant_name.is_empty() {
+            return syn::Error::new_spanned(&variant.ident, "Oi, mate, You cannot have enum variant without name").to_compile_error().into()
+        }
+        let command_name = to_hyphenated_lower_case(&variant_name);
+        if command_name.eq_ignore_ascii_case("help") {
+            return syn::Error::new_spanned(&variant.ident, "Oi, mate, You cannot use variant 'Help'").to_compile_error().into()
+        }
+
+        for attr in variant.attrs.iter() {
+            let attr = match attr.parse_meta() {
+                Ok(attr) => attr,
+                Err(error) => {
+                    return syn::Error::new_spanned(attr, format!("cannot parse attribute: {error}")).to_compile_error().into()
+                }
+            };
+
+            match attr {
+                syn::Meta::NameValue(value) => if value.path.is_ident("doc") {
+                    if let syn::Lit::Str(ref text) = value.lit {
+                        desc.push_str(&text.value());
+                        desc.push_str(" ");
+                    }
+                },
+                _ => continue
+            }
+        }
+
+        let field = match &variant.fields {
+            syn::Fields::Unit => return syn::Error::new_spanned(&variant.fields, "Unit variant cannot be used").to_compile_error().into(),
+            syn::Fields::Named(_) => return syn::Error::new_spanned(&variant.fields, "I'm too lazy to support named variant").to_compile_error().into(),
+            syn::Fields::Unnamed(fields) => {
+                if fields.unnamed.empty_or_trailing() {
+                    return syn::Error::new_spanned(&fields, "MUST specify single field").to_compile_error().into();
+                } else if fields.unnamed.len() > 1 {
+                    return syn::Error::new_spanned(&fields, "MUST not specify more than 1 field").to_compile_error().into();
+                } else {
+                    fields.unnamed.first().unwrap()
+                }
+            },
+        };
+
+        match &field.ty {
+            syn::Type::Path(ref ty) => {
+                let ty = ty.path.segments.last().expect("To have at least one segment");
+                if ty.ident == "Option" {
+                    return syn::Error::new_spanned(&ty, "Command cannot be optional").to_compile_error().into()
+                } else {
+                    match parse_segment(ty) {
+                        OptValueType::Bool => return syn::Error::new_spanned(&ty, "Command value cannot be boolean").to_compile_error().into(),
+                        OptValueType::MultiValue => return syn::Error::new_spanned(&ty, "Command value Vec<_>").to_compile_error().into(),
+                        _ => (),
+                    }
+                }
+            },
+            ty => {
+                return syn::Error::new_spanned(&ty, "Expected simple ident or path").to_compile_error().into()
+            }
+        }
+
+        commands.push(Command {
+            command_name,
+            variant_name,
+            desc
+        })
+    }
+
+    if commands.is_empty() {
+        return syn::Error::new_spanned(&ast, "Enum must have at least one variant").to_compile_error().into()
+    }
+
+    let (impl_gen, type_gen, where_clause) = ast.generics.split_for_impl();
+
+    let help_msg = {
+        use std::io::Write;
+        use tabwriter::TabWriter;
+
+        let mut tw = TabWriter::new(vec![]);
+
+        let _ = write!(tw, "COMMANDS:\n");
+        for command in commands.iter() {
+            let _ = write!(tw, "\t{}\t{}\n", command.command_name, command.desc);
+        }
+
+        let _ = tw.flush();
+
+        String::from_utf8(tw.into_inner().unwrap()).unwrap()
+    };
+
+    let mut result = String::new();
+    let _ = writeln!(result, "{} {} for {}{} {{", quote!(impl #impl_gen), PARSER_TRAIT, ast.ident, quote!(#type_gen #where_clause));
+
+    let _ = writeln!(result, "{}const HELP: &'static str = \"{}\";", TAB, help_msg);
+
+    //from_args START
+    let _ = writeln!(result, "{}fn from_args<'a, T: IntoIterator<Item = &'a str>>(_args_: T) -> Result<Self, arg::ParseKind<'a>> {{", TAB);
+
+    let _ = writeln!(result, "{0}{0}let mut _args_ = _args_.into_iter();\n", TAB);
+
+    //args START
+    let _ = writeln!(result, "{0}{0}while let Some(_arg_) = _args_.next() {{", TAB);
+
+    //help
+    let _ = writeln!(result, "{0}{0}{0}if _arg_.eq_ignore_ascii_case(\"help\") {{", TAB);
+    let _ = writeln!(result, "{0}{0}{0}{0}return Err(arg::ParseKind::Top(arg::ParseError::HelpRequested(Self::HELP)));", TAB);
+    let _ = write!(result, "{0}{0}{0}}}", TAB);
+
+    for command in commands.iter() {
+        //arg START
+        let _ = writeln!(result, " else if _arg_.eq_ignore_ascii_case(\"{}\") {{", command.command_name);
+
+        let _ = writeln!(result, "{0}{0}{0}{0}match {1}::from_args(_args_) {{", TAB, PARSER_TRAIT);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Ok(res) => return Ok(Self::{1}(res)),", TAB, command.variant_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Err(arg::ParseKind::Top(error)) => return Err(arg::ParseKind::Sub(\"{1}\", error)),", TAB, command.command_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Err(arg::ParseKind::Sub(name, error)) => return Err(arg::ParseKind::Sub(name, error)),", TAB);
+        let _ = writeln!(result, "{0}{0}{0}{0}}}", TAB);
+
+        //arg END
+        let _ = write!(result, "{0}{0}{0}}}", TAB);
+    }
+
+    //args END
+    let _ = writeln!(result, "\n{0}{0}}}", TAB);
+
+    let _ = writeln!(result, "{0}{0}Err(arg::ParseKind::Top(arg::ParseError::RequiredArgMissing(\"command\")))", TAB);
+
+    //from_args END
+    let _ = writeln!(result, "{}}}", TAB);
+
+    let _ = writeln!(result, "}}");
+
+    if let Ok(val) = std::env::var("ARG_RS_PRINT_PARSER") {
+        match val.trim() {
+            "0" | "false" => (),
+            _ => println!("{result}"),
+        }
+    }
+    result.parse().expect("To parse generated code")
+}
+
+fn from_struct(ast: &syn::DeriveInput, payload: &syn::DataStruct) -> TokenStream {
+    let mut about_prog = String::new();
+    for attr in ast.attrs.iter() {
+        let attr = match attr.parse_meta() {
+            Ok(attr) => attr,
+            Err(error) => {
+                return syn::Error::new_spanned(attr, format!("cannot parse attribute: {error}")).to_compile_error().into()
+            }
+        };
+
+        match attr {
+            syn::Meta::NameValue(value) => if value.path.is_ident("doc") {
+                if let syn::Lit::Str(ref text) = value.lit {
+                    about_prog.push_str(&text.value());
+                    about_prog.push_str("\n");
+                }
+            } else {
+            },
+            _ => (),
+        }
+    }
+
+    about_prog.pop();
+
+    let mut options = Vec::new();
+    let mut arguments = Vec::new();
+
+    options.push(Opt {
+        arg: Argument {
+            field_name: "_".to_owned(),
+            name: "help".to_owned(),
+            desc: "Prints this help information".to_owned(),
+            required: false,
+            is_optional: false,
+            default: None,
+        },
+        short: Some("h".to_owned()),
+        long: "help".to_owned(),
+        typ: OptValueType::Help,
+    });
+
+    let mut sub_command = None;
+    let mut multi_argument = None;
+
+    for field in payload.fields.iter() {
+        let field_name = field.ident.as_ref().unwrap().to_string();
+        let name = field.ident.as_ref().unwrap().to_string().trim_matches(|ch| !char::is_alphanumeric(ch)).to_owned();
+        let mut desc = String::new();
+        let mut short = None;
+        let mut long = None;
+        let mut required = false;
+        let mut is_sub = false;
+
+        let (is_optional, typ) = match field.ty {
+            syn::Type::Path(ref ty) => {
+                let ty = ty.path.segments.last().expect("To have at least one segment");
+
+                if ty.ident == "Option" {
+                    let ty = match &ty.arguments {
+                        syn::PathArguments::AngleBracketed(ref args) => match args.args.len() {
+                            0 => return syn::Error::new_spanned(&ty.ident, "Oi, mate, Option is without type arguments. Fix it").to_compile_error().into(),
+                            1 => match args.args.first().unwrap() {
+                                syn::GenericArgument::Type(syn::Type::Path(ty)) => parse_segment(ty.path.segments.last().expect("To have at least one segment")),
+                                _ => return syn::Error::new_spanned(&ty.ident, "Oi, mate, Option should have type argument, but got some other shite. Fix it").to_compile_error().into(),
+                            },
+                            _ => return syn::Error::new_spanned(&ty.ident, "Oi, mate, Option has too many type arguments. Fix it").to_compile_error().into()
+                        },
+                        syn::PathArguments::None => return syn::Error::new_spanned(&ty.ident, "Oi, mate, Option is without type arguments. Fix it").to_compile_error().into(),
+                        syn::PathArguments::Parenthesized(_) => return syn::Error::new_spanned(&ty.ident, "Oi, mate, you got wrong brackets for your Option . Fix it").to_compile_error().into(),
+                    };
+
+                    (true, ty)
+                } else {
+                    (false, parse_segment(ty))
+                }
+            },
+            _ => (false, OptValueType::Value),
+        };
+
+        if is_optional && typ == OptValueType::MultiValue {
+            return syn::Error::new_spanned(field, "Option<Vec<_>> makes no sense. Just use plain Vec<_>").to_compile_error().into();
+        }
+
+        let mut default = None;
+
+        for attr in field.attrs.iter() {
+            let attr = match attr.parse_meta() {
+                Ok(attr) => attr,
+                Err(error) => {
+                    return syn::Error::new_spanned(attr, format!("cannot parse attribute: {error}")).to_compile_error().into()
+                }
+            };
+
+            match attr {
+                syn::Meta::NameValue(value) => if value.path.is_ident("doc") {
+                    if let syn::Lit::Str(ref text) = value.lit {
+                        desc.push_str(&text.value());
+                        desc.push_str(" ");
+                    }
+                },
+                syn::Meta::List(value) => if value.path.is_ident("arg") {
+                    for value_attr in value.nested.iter() {
+                        match value_attr {
+                            syn::NestedMeta::Meta(value_attr) => {
+                                match value_attr {
+                                    syn::Meta::Path(value_attr) => if value_attr.is_ident("short") {
+                                        short = Some(format!("{}", name.chars().next().unwrap()).to_lowercase());
+                                    } else if value_attr.is_ident("long") {
+                                        long = Some(name.to_lowercase());
+                                    } else if value_attr.is_ident("default_value") {
+                                        default = Some(DEFAULT_INIT.to_owned());
+                                    } else if value_attr.is_ident("required") {
+                                        if typ != OptValueType::Bool {
+                                            required = true
+                                        } else {
+                                            return syn::Error::new_spanned(value_attr, INVALID_REQUIRED_BOOL).to_compile_error().into();
+                                        }
+                                    } else if value_attr.is_ident("sub") {
+                                        if typ == OptValueType::Value {
+                                            is_sub = true;
+                                        } else {
+                                            return syn::Error::new_spanned(value_attr, "Sub-command must be simple value").to_compile_error().into();
+                                        }
+                                    }
+                                    syn::Meta::NameValue(value_attr) => if value_attr.path.is_ident("short") {
+                                        if let syn::Lit::Str(ref text) = value_attr.lit {
+                                            let value_attr_text = text.value();
+
+                                            if value_attr_text.contains(ARG_INVALID_CHARS) {
+                                                return syn::Error::new_spanned(value_attr.lit.clone(), ARG_NAME_SPACE_ERROR).to_compile_error().into();
+                                            }
+
+                                            short = Some(value_attr_text);
+                                        } else {
+                                            return syn::Error::new_spanned(value_attr.path.clone(), INVALID_ARG_TYPE_STRING).to_compile_error().into();
+                                        }
+                                    } else if value_attr.path.is_ident("long") {
+                                        if let syn::Lit::Str(ref text) = value_attr.lit {
+                                            let value_attr_text = text.value();
+
+                                            if value_attr_text.contains(ARG_INVALID_CHARS) {
+                                                return syn::Error::new_spanned(value_attr.lit.clone(), ARG_NAME_SPACE_ERROR).to_compile_error().into();
+                                            }
+
+                                            long = Some(value_attr_text)
+                                        } else {
+                                            return syn::Error::new_spanned(value_attr.path.clone(), INVALID_ARG_TYPE_STRING).to_compile_error().into();
+                                        }
+                                    } else if value_attr.path.is_ident("default_value") {
+                                        if let syn::Lit::Str(ref text) = value_attr.lit {
+                                            default = Some(text.value());
+                                        } else {
+                                            return syn::Error::new_spanned(value_attr.path.clone(), INVALID_ARG_TYPE_STRING).to_compile_error().into();
+                                        }
+                                    } else {
+                                        return syn::Error::new_spanned(value_attr.path.clone(), UNKNOWN_ARG_ATTR).to_compile_error().into();
+                                    }
+                                    _ => {
+                                    },
+                                }
+                            },
+                            syn::NestedMeta::Lit(_) => (),
+                        }
+                    }
+                },
+                _ => (),
+            }
+        }
+
+        desc.pop();
+
+        if required && default.is_some() {
+            return syn::Error::new_spanned(field.ident.clone(), "Marked as required, but default value is provided?").to_compile_error().into();
+        } else if is_optional && default.is_some() {
+            return syn::Error::new_spanned(field.ident.clone(), "Optional, but default value is provided?").to_compile_error().into();
+        } else if is_sub && is_optional {
+            return syn::Error::new_spanned(field.ident.clone(), "Sub-command cannot be optional").to_compile_error().into();
+        } else if is_sub && default.is_some() {
+            return syn::Error::new_spanned(field.ident.clone(), "Sub-command cannot have default value").to_compile_error().into();
+        } else if !required && !is_optional && default.is_none() {
+            default = Some(DEFAULT_INIT.to_owned());
+        }
+
+        if short.is_none() && long.is_none() {
+            if typ == OptValueType::MultiValue {
+                if multi_argument.is_some() {
+                    return syn::Error::new_spanned(field.ident.clone(), "Second argument collection. There can be only one").to_compile_error().into();
+                } else if sub_command.is_some() {
+                    return syn::Error::new_spanned(field.ident.clone(), "Multi-argument collection and sub-command are mutually exclusive").to_compile_error().into();
+                }
+
+                multi_argument = Some(Argument {
+                    field_name,
+                    name,
+                    desc,
+                    required,
+                    is_optional,
+                    default,
+                });
+
+            } else if is_sub {
+                if sub_command.is_some() {
+                    return syn::Error::new_spanned(field.ident.clone(), "Second sub-command. There can be only one").to_compile_error().into();
+                } else if multi_argument.is_some() {
+                    return syn::Error::new_spanned(field.ident.clone(), "Sub-command and multi-argument collection are mutually exclusive").to_compile_error().into();
+                }
+
+                sub_command = Some(Argument {
+                    field_name,
+                    name,
+                    desc,
+                    required: true,
+                    is_optional: false,
+                    default: None,
+                });
+            } else {
+                arguments.push(Argument {
+                    field_name,
+                    name,
+                    desc,
+                    required,
+                    is_optional,
+                    default,
+                })
+            }
+
+        } else {
+            let long = match long {
+                Some(long) => long,
+                None => name.clone()
+            };
+
+            options.push(Opt {
+                arg: Argument {
+                    field_name,
+                    name,
+                    desc,
+                    required,
+                    is_optional,
+                    default,
+                },
+                short,
+                long,
+                typ
+            })
+        }
+    }
+
+    let (impl_gen, type_gen, where_clause) = ast.generics.split_for_impl();
+
+    let help_msg = {
+        use std::io::Write;
+        use tabwriter::TabWriter;
+
+        let mut tw = TabWriter::new(vec![]);
+
+        let _ = write!(tw, "{}
+USAGE:", about_prog);
+
+        if !options.is_empty() {
+            let _ = write!(tw, " [OPTIONS]");
+        }
+
+        for argument in arguments.iter() {
+            let _ = if argument.required {
+                write!(tw, " <{}>", argument.name)
+            } else {
+                write!(tw, " [{}]", argument.name)
+            };
+        }
+
+        if let Some(argument) = multi_argument.as_ref() {
+            let _ = if argument.required {
+                write!(tw, " <{}>...", argument.name)
+            } else {
+                write!(tw, " [{}]...", argument.name)
+            };
+        } else if let Some(argument) = sub_command.as_ref() {
+            let _ = write!(tw, " <{}>", argument.name);
+        }
+
+        if !options.is_empty() {
+            let _ = write!(tw, "\n\nOPTIONS:\n");
+        }
+
+        for option in options.iter() {
+            let _ = write!(tw, "\t");
+            if let Some(short) = option.short.as_ref() {
+                let _ = write!(tw, "-{},", short);
+            }
+            let _ = write!(tw, "\t");
+
+            let _ = write!(tw, "--{}", option.long);
+
+            let _ = match option.typ {
+                OptValueType::MultiValue => write!(tw, " <{}>...", option.arg.name),
+                OptValueType::Value => write!(tw, " <{}>", option.arg.name),
+                _ => Ok(()),
+            };
+
+            let _ = write!(tw, "\t{}\n", option.arg.desc);
+        }
+
+        if !arguments.is_empty() || multi_argument.is_some() || sub_command.is_some() {
+            let _ = write!(tw, "\nARGS:\n");
+        }
+
+        for argument in arguments.iter() {
+            let _ = if argument.required {
+                writeln!(tw, "\t<{}>\t{}", argument.name, argument.desc)
+            } else {
+                writeln!(tw, "\t[{}]\t{}", argument.name, argument.desc)
+            };
+        }
+
+        if let Some(argument) = multi_argument.as_ref() {
+            let _ = writeln!(tw, "\t<{}>...\t{}", argument.name, argument.desc);
+        } else if let Some(command) = sub_command.as_ref() {
+            let _ = writeln!(tw, "\t<{}>\t{}", command.name, command.desc);
+        }
+
+        let _ = tw.flush();
+
+        String::from_utf8(tw.into_inner().unwrap()).unwrap()
+    };
+
+    let mut result = String::new();
+    let _ = writeln!(result, "{} {} for {}{} {{", quote!(impl #impl_gen), PARSER_TRAIT, ast.ident, quote!(#type_gen #where_clause));
+    let _ = writeln!(result, "{}const HELP: &'static str = \"{}\";", TAB, help_msg);
+
+    let _ = writeln!(result, "{}fn from_args<'a, T: IntoIterator<Item = &'a str>>(_args_: T) -> Result<Self, arg::ParseKind<'a>> {{", TAB);
+
+    for option in options.iter() {
+        if option.arg.field_name == "_" {
+            continue;
+        }
+
+        let _ = match option.typ {
+            OptValueType::MultiValue => writeln!(result, "{0}{0}let mut {1} = Vec::new();", TAB, option.arg.field_name),
+            OptValueType::Bool => writeln!(result, "{0}{0}let mut {1} = false;", TAB, option.arg.field_name),
+            _ => writeln!(result, "{0}{0}let mut {1} = None;", TAB, option.arg.field_name),
+        };
+    }
+
+    for argument in arguments.iter() {
+        let _ = writeln!(result, "{0}{0}let mut {1} = None;", TAB, argument.field_name);
+    }
+
+    if let Some(argument) = multi_argument.as_ref() {
+        let _ = writeln!(result, "{0}{0}let mut {1} = Vec::new();", TAB, argument.field_name);
+    } else if let Some(command) = sub_command.as_ref() {
+        let _ = writeln!(result, "{0}{0}let mut {1} = None;", TAB, command.field_name);
+    }
+
+    let _ = writeln!(result, "{0}{0}let mut _args_ = _args_.into_iter();\n", TAB);
+    let _ = writeln!(result, "{0}{0}while let Some(_arg_) = _args_.next() {{", TAB);
+
+    //options
+    let _ = writeln!(result, "{0}{0}{0}if let Some(_arg_) = _arg_.strip_prefix('-') {{", TAB);
+    let _ = writeln!(result, "{0}{0}{0}{0}match _arg_ {{", TAB);
+    let _ = writeln!(result, "{0}{0}{0}{0}{0}\"h\" | \"-help\" => return Err(arg::ParseKind::Top(arg::ParseError::HelpRequested(Self::HELP))),", TAB);
+    let _ = writeln!(result, "{0}{0}{0}{0}{0}\"\" => (),", TAB);
+
+    for option in options.iter() {
+        if option.arg.field_name == "_" {
+            continue;
+        }
+
+        let _ = write!(result, "{0}{0}{0}{0}{0}", TAB);
+
+        if let Some(short) = option.short.as_ref() {
+            let _ = write!(result, "\"{}\" | ", short);
+        }
+
+        let _ = write!(result, "\"-{}\" => ", option.long);
+
+        let _ = match option.typ {
+            OptValueType::Help => panic!("Option Help is invalid here. Bug report it"),
+            OptValueType::Bool => write!(result, "{{ {0} = !{0}; continue }},", option.arg.field_name),
+            OptValueType::Value => write!(result, "match _args_.next() {{
+{0}{0}{0}{0}{0}{0}Some(_next_arg_) => match {1}(_next_arg_) {{
+{0}{0}{0}{0}{0}{0}{0}Ok(value) => {{ {2} = Some(value); continue }},
+{0}{0}{0}{0}{0}{0}{0}Err(_) => return Err(arg::ParseKind::Top(arg::ParseError::InvalidFlagValue(\"{3}\", _next_arg_))),
+{0}{0}{0}{0}{0}{0}}},
+{0}{0}{0}{0}{0}{0}None => return Err(arg::ParseKind::Top(arg::ParseError::MissingValue(\"{3}\"))),
+{0}{0}{0}{0}{0}}}", TAB, FROM_FN, option.arg.field_name, option.arg.name),
+            OptValueType::MultiValue => write!(result, "match _args_.next() {{
+{0}{0}{0}{0}{0}{0}Some(_next_arg_) => match {1}(_next_arg_) {{
+{0}{0}{0}{0}{0}{0}{0}Ok(value) => {{ {2}.push(value); continue }},
+{0}{0}{0}{0}{0}{0}{0}Err(_) => return Err(arg::ParseKind::Top(arg::ParseError::InvalidFlagValue(\"{3}\", _next_arg_))),
+{0}{0}{0}{0}{0}{0}}},
+{0}{0}{0}{0}{0}{0}None => return Err(arg::ParseKind::Top(arg::ParseError::MissingValue(\"{3}\"))),
+{0}{0}{0}{0}{0}}}", TAB, FROM_FN, option.arg.field_name, option.arg.name),
+        };
+        let _ = writeln!(result, "");
+    }
+    let _ = writeln!(result, "{0}{0}{0}{0}{0}_ => return Err(arg::ParseKind::Top(arg::ParseError::UnknownFlag(_arg_))),", TAB);
+
+    let _ = writeln!(result, "{0}{0}{0}{0}}}", TAB);
+    let _ = writeln!(result, "{0}{0}{0}}}", TAB);
+    //rest args
+    for (idx, arg) in arguments.iter().enumerate() {
+        if idx == 0 {
+            let _ = writeln!(result, "{0}{0}{0}if {1}.is_none() {{", TAB, arg.field_name);
+        } else {
+            let _ = writeln!(result, "{0}{0}{0}}} else if {1}.is_none() {{", TAB, arg.field_name);
+        }
+        let _ = writeln!(result, "{0}{0}{0}{0}match {1}(_arg_) {{", TAB, FROM_FN);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Ok(_res_) => {1} = Some(_res_),", TAB, arg.field_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Err(_) => return Err(arg::ParseKind::Top(arg::ParseError::InvalidArgValue(\"{1}\", _arg_))),", TAB, arg.field_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}}}", TAB);
+    }
+    //too many args?
+    if !arguments.is_empty() {
+        let _ = writeln!(result, "{0}{0}{0}}} else {{", TAB);
+    }
+
+    if let Some(arg) = multi_argument.as_ref() {
+        let _ = writeln!(result, "{0}{0}{0}{0}match {1}(_arg_) {{", TAB, FROM_FN);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Ok(_res_) => {1}.push(_res_),", TAB, arg.field_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Err(_) => return Err(arg::ParseKind::Top(arg::ParseError::InvalidArgValue(\"{1}\", _arg_))),", TAB, arg.field_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}}}", TAB);
+    } else if let Some(command) = sub_command.as_ref() {
+        let _ = writeln!(result, "{0}{0}{0}{0}match {1}::from_args(core::iter::once(_arg_).chain(_args_)) {{", TAB, PARSER_TRAIT);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Ok(_res_) => {{ {1} = Some(_res_); break; }},", TAB, command.field_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Err(arg::ParseKind::Top(_)) => return Err(arg::ParseKind::Top(arg::ParseError::RequiredArgMissing(\"{1}\"))),", TAB, command.field_name);
+        let _ = writeln!(result, "{0}{0}{0}{0}{0}Err(arg::ParseKind::Sub(name, error)) => return Err(arg::ParseKind::Sub(name, error)),", TAB);
+        let _ = writeln!(result, "{0}{0}{0}{0}}}", TAB);
+    } else {
+        let _ = writeln!(result, "{0}{0}{0}{0} return Err(arg::ParseKind::Top(arg::ParseError::TooManyArgs));", TAB);
+    }
+    //exit args
+    if !arguments.is_empty() {
+        let _ = writeln!(result, "{0}{0}{0}}}", TAB);
+        let _ = writeln!(result, "{0}{0}}}", TAB);
+    } else {
+        let _ = writeln!(result, "{0}{0}}}", TAB);
+    }
+
+    //Set defaults
+    for option in options.iter() {
+        if option.arg.field_name == "_" {
+            continue;
+        }
+
+        let _ = match option.typ {
+            OptValueType::MultiValue => Ok(()),
+            OptValueType::Bool => Ok(()),
+            _ => match option.arg.default {
+                Some(ref default) => writeln!(result, "{0}{0}let {1} = if let Some(value) = {1} {{ value }} else {{ {2} }};", TAB, option.arg.field_name, default),
+                None => match option.arg.is_optional {
+                    true => Ok(()),
+                    false => writeln!(result, "{0}{0}let {1} = if let Some(value) = {1} {{ value }} else {{ return Err(arg::ParseKind::Top(arg::ParseError::RequiredArgMissing(\"{2}\"))) }};", TAB, option.arg.field_name, option.arg.name),
+                },
+            },
+        };
+    }
+
+    for arg in arguments.iter() {
+        let _ = match arg.default {
+            Some(ref default) => writeln!(result, "{0}{0}let {1} = if let Some(value) = {1} {{ value }} else {{ {2} }};", TAB, arg.field_name, default),
+            None => match arg.is_optional {
+                true => Ok(()),
+                false => writeln!(result, "{0}{0}let {1} = if let Some(value) = {1} {{ value }} else {{ return Err(arg::ParseKind::Top(arg::ParseError::RequiredArgMissing(\"{2}\"))) }};", TAB, arg.field_name, arg.name),
+            }
+        };
+    }
+
+    if let Some(command) = sub_command.as_ref() {
+        let _ = writeln!(result, "{0}{0}let {1} = if let Some(value) = {1} {{ value }} else {{ return Err(arg::ParseKind::Top(arg::ParseError::RequiredArgMissing(\"{2}\"))) }};", TAB, command.field_name, command.name);
+    }
+
+    //Fill result
+    let _ = writeln!(result, "{0}{0}Ok(Self {{", TAB);
+
+    for option in options.iter() {
+        if option.arg.field_name == "_" {
+            continue;
+        }
+
+        let _ = if option.arg.is_optional && option.typ == OptValueType::Bool {
+            writeln!(result, "{0}{0}{0}{1}: Some({1}),", TAB, option.arg.field_name)
+        } else {
+            writeln!(result, "{0}{0}{0}{1},", TAB, option.arg.field_name)
+        };
+    }
+
+    for arg in arguments.iter() {
+        let _ = writeln!(result, "{0}{0}{0}{1},", TAB, arg.field_name);
+    }
+
+    if let Some(arg) = multi_argument.as_ref() {
+        let _ = writeln!(result, "{0}{0}{0}{1},", TAB, arg.field_name);
+    } else if let Some(arg) = sub_command.as_ref() {
+        let _ = writeln!(result, "{0}{0}{0}{1},", TAB, arg.field_name);
+    }
+
+    let _ = writeln!(result, "{0}{0}}})", TAB);
+
+    //Exit fn
+    let _ = writeln!(result, "{}}}", TAB);
+
+    let _ = writeln!(result, "}}");
+
+    if let Ok(val) = std::env::var("ARG_RS_PRINT_PARSER") {
+        match val.trim() {
+            "0" | "false" => (),
+            _ => println!("{result}"),
+        }
+    }
+    result.parse().expect("To parse generated code")
+}
+
+#[proc_macro_derive(Args, attributes(parser, arg))]
+pub fn parser_derive(input: TokenStream) -> TokenStream {
+    const INVALID_INPUT_TYPE: &str = "Unsupported parser input type. Expect: struct";
+    let ast: syn::DeriveInput = syn::parse(input).unwrap();
+
+    match ast.data {
+        syn::Data::Struct(ref data) => from_struct(&ast, data),
+        syn::Data::Enum(ref data) => from_enum(&ast, data),
+        _ => syn::Error::new_spanned(ast.ident, INVALID_INPUT_TYPE).to_compile_error().into(),
+    }
+}

src/env/derive/utils.rs

@@ -0,0 +1,76 @@
+/* 
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * This file is part of SPD.
+ *
+ * SPD is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * SPD is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with SPD. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and permission
+ * notice:
+ *
+ *     Copyright 2017 Douman
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+extern crate alloc;
+use alloc::string::String;
+
+pub fn to_hyphenated_lower_case(input: &str) -> String {
+    let mut output = String::with_capacity(input.len());
+
+    let mut chars = input.chars();
+    let mut prev_upper = false;
+    if let Some(ch) = chars.next() {
+        if ch.is_uppercase() {
+            prev_upper = true;
+            for ch in ch.to_lowercase() {
+                output.push(ch);
+            }
+        } else {
+            output.push(ch);
+        }
+    }
+
+    for ch in chars {
+        if ch.is_uppercase() {
+            if !prev_upper {
+                output.push('-');
+            }
+
+            for ch in ch.to_lowercase() {
+                output.push(ch);
+            }
+
+            prev_upper = true;
+        } else {
+            output.push(ch);
+
+            prev_upper = false;
+        }
+    }
+
+    output
+}

src/env/mod.rs

@@ -0,0 +1,157 @@
+/* 
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * This file is part of SPD.
+ *
+ * SPD is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * SPD is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with SPD. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and permission
+ * notice:
+ *
+ *     Copyright 2017 Douman
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+#![no_std]
+#![warn(missing_docs)]
+#![cfg_attr(feature = "cargo-clippy", allow(clippy::style))]
+#![cfg_attr(feature = "cargo-clippy", allow(clippy::needless_lifetimes))]
+
+use core::fmt;
+
+mod derive;
+mod split;
+
+use derive::*;
+use split::Split;
+
+
+#[derive(PartialEq, Eq, Debug)]
+///Parse errors
+pub enum ParseKind<'a> {
+    ///Main command result
+    Top(ParseError<'a>),
+    ///Sub-command name and result
+    Sub(&'static str, ParseError<'a>),
+}
+
+impl<'a> ParseKind<'a> {
+    #[inline]
+    ///Returns whether help is requested
+    pub fn is_help(&self) -> bool {
+        match self {
+            Self::Top(err) => err.is_help(),
+            Self::Sub(_, err) => err.is_help(),
+        }
+    }
+}
+
+impl<'a> PartialEq<ParseError<'a>> for ParseKind<'a> {
+    #[inline(always)]
+    fn eq(&self, right: &ParseError<'a>) -> bool {
+        match self {
+            Self::Top(left) => PartialEq::eq(left, right),
+            Self::Sub(_, left) => PartialEq::eq(left, right),
+        }
+    }
+}
+
+#[derive(PartialEq, Eq, Debug)]
+///Parse errors
+pub enum ParseError<'a> {
+    ///User requested help.
+    ///
+    ///Contains slice with `Args::HELP`
+    HelpRequested(&'static str),
+    ///Too many arguments are specified.
+    TooManyArgs,
+    ///Argument is required, but missing
+    ///
+    ///Contains name of argument
+    RequiredArgMissing(&'a str),
+    ///Flag is specified, but value is missing.
+    ///
+    ///Contains full flag name.
+    MissingValue(&'a str),
+    ///Flag is specified with invalid value
+    ///
+    ///Contains full flag name and provided value.
+    InvalidFlagValue(&'a str, &'a str),
+    ///Argument is supplied with invalid vlaue
+    ///
+    ///Contains argument name and provided value.
+    InvalidArgValue(&'a str, &'a str),
+    ///Unknown flag is specified.
+    UnknownFlag(&'a str)
+}
+
+impl<'a> ParseError<'a> {
+    ///Returns whether help is requested
+    pub fn is_help(&self) -> bool {
+        match self {
+            ParseError::HelpRequested(_) => true,
+            _ => false,
+        }
+    }
+}
+
+impl<'a> fmt::Display for ParseError<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ParseError::HelpRequested(help) => f.write_str(help),
+            ParseError::TooManyArgs => f.write_str("Too many arguments are provided"),
+            ParseError::RequiredArgMissing(arg) => write!(f, "Argument '{}' is required, but not provided", arg),
+            ParseError::MissingValue(arg) => write!(f, "Flag '{}' is provided without value", arg),
+            ParseError::InvalidFlagValue(arg, value) => write!(f, "Flag '{}' is provided with '{}' which is invalid", arg, value),
+            ParseError::InvalidArgValue(arg, value) => write!(f, "Argument '{}' is provided with '{}' which is invalid", arg, value),
+            ParseError::UnknownFlag(flag) => write!(f, "Unknown flag '{}' is provided", flag),
+        }
+    }
+}
+
+impl<'a> fmt::Display for ParseKind<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ParseKind::Top(res) => fmt::Display::fmt(res, f),
+            ParseKind::Sub(name, res) => write!(f, "{name}: {res}"),
+        }
+    }
+}
+
+
+///Describers command line argument parser
+pub trait Args: Sized {
+    ///Help message for parser.
+    const HELP: &'static str;
+
+    ///Parses arguments from iterator of strings
+    fn from_args<'a, T: IntoIterator<Item = &'a str>>(args: T) -> Result<Self, ParseKind<'a>>;
+
+    ///Parses arguments from string, which gets tokenized and passed to from.
+    fn from_text<'a>(text: &'a str) -> Result<Self, ParseKind<'a>> {
+        Self::from_args(Split::from_str(text))
+    }
+}

src/env/split.rs

@@ -0,0 +1,88 @@
+/* 
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * This file is part of SPD.
+ *
+ * SPD is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * SPD is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with SPD. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and permission
+ * notice:
+ *
+ *     Copyright 2017 Douman
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+///Simple split of string into arguments
+pub struct Split<'a> {
+    string: &'a str,
+}
+
+impl<'a> Split<'a> {
+    ///Creates new instance
+    pub const fn from_str(string: &'a str) -> Self {
+        Self {
+            string
+        }
+    }
+
+    #[inline(always)]
+    ///Retrieves next argument
+    pub fn next_arg(&mut self) -> Option<&str> {
+        self.next()
+    }
+}
+
+impl<'a> Iterator for Split<'a> {
+    type Item = &'a str;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.string = self.string.trim_start();
+
+        if self.string.is_empty() {
+            return None;
+        }
+
+        let (end_char, from) = match self.string.get(0..=0) {
+            Some("'") => ('\'', 1),
+            Some("\"") => ('"', 1),
+            _ => (' ', 0),
+        };
+
+        match self.string[from..].find(end_char) {
+            Some(end_idx) => {
+                let end_idx = end_idx + from;
+                let result = &self.string[from..end_idx];
+                self.string = &self.string[end_idx+1..];
+                Some(result.trim_start())
+            },
+            None => {
+                let result = &self.string[from..];
+                self.string = "";
+                Some(result.trim())
+            }
+        }
+    }
+}

tests/args.rs

@@ -0,0 +1,222 @@
+/* 
+ * Copyright (c) 2023 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * This file is part of SPD.
+ *
+ * SPD is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * SPD is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with SPD. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * This file incorporates work covered by the following copyright and permission
+ * notice:
+ *
+ *     Copyright 2017 Douman
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+use crate::env::args::Args;
+
+#[allow(unused)]
+#[derive(Args, Debug)]
+struct Test4 {
+}
+
+#[allow(unused)]
+#[derive(Args, Debug)]
+struct Test3 {
+  paths: Vec<String>,
+}
+
+#[allow(unused)]
+#[derive(Args, Debug)]
+struct Test2 {
+  #[arg(short = "u")]
+  u: bool,
+
+  paths: Vec<String>,
+}
+
+
+#[derive(Debug, Args)]
+///my_exe 0.1.0
+///About my program
+///
+///About my program
+struct MyArgs {
+    #[arg(short, long, required)]
+    ///Required argument
+    required: u32,
+
+    #[arg(short, long)]
+    ///Optional argument
+    optional: Option<u32>,
+
+    #[arg(short, long)]
+    ///About this flag
+    flag: bool,
+
+    #[arg(long = "verbose")]
+    ///Verbose mode
+    verbose: bool,
+
+    #[arg(short = "v", long = "velocity", default_value = "42")]
+    ///This is felocity. Default value is 42.
+    speed: u32,
+
+    #[arg(short = "g", long = "gps")]
+    ///GPS coordinates.
+    gps: Vec<u32>,
+
+    #[arg(required)]
+    ///To store path
+    path: String,
+
+    #[arg(required)]
+    ///To store path 2
+    path2: String,
+
+    ///To store rest of paths
+    remain_paths: Vec<String>,
+}
+
+#[derive(Debug, Args)]
+///My subcommand
+enum BigSubArgs {
+    ///my arguments
+    MyArgs(MyArgs),
+    ///test args
+    Test(Test2),
+}
+
+#[derive(Debug, Args)]
+struct BigArgs {
+    #[arg(long = "verbose")]
+    ///Verbose mode
+    verbose: bool,
+    #[arg(sub)]
+    cmd: BigSubArgs,
+}
+
+#[test]
+fn should_error_on_missing_args() {
+    let result = MyArgs::from_text("-f --verbose path1").unwrap_err();
+    assert_eq!(result, arg::ParseError::RequiredArgMissing("required"));
+
+    let result = MyArgs::from_text("-f -r 5 --verbose path1").unwrap_err();
+    assert_eq!(result, arg::ParseError::RequiredArgMissing("path2"));
+
+    let result = MyArgs::from_text("-f -r 5 --verbose").unwrap_err();
+    assert_eq!(result, arg::ParseError::RequiredArgMissing("path"));
+}
+
+#[test]
+fn should_error_on_missing_flag_value() {
+    let result = MyArgs::from_text("-f -r").unwrap_err();
+    assert_eq!(result, arg::ParseError::MissingValue("required"));
+}
+
+#[test]
+fn should_error_on_invalid_flag_value() {
+    let result = MyArgs::from_text("-f -r gg").unwrap_err();
+    assert_eq!(result, arg::ParseError::InvalidFlagValue("required", "gg"));
+}
+
+
+#[test]
+fn should_handle_all_flags() {
+    let result = MyArgs::from_text("-f -r 5 --verbose -v 32 -g 1 --gps 55 path1 path2 rest1 rest2").unwrap();
+    assert!(result.flag);
+    assert!(result.verbose);
+    assert_eq!(result.optional, None);
+    assert_eq!(result.required, 5);
+    assert_eq!(result.speed, 32);
+    assert_eq!(result.gps, &[1, 55]);
+    assert_eq!(result.path, "path1");
+    assert_eq!(result.path2, "path2");
+    assert_eq!(result.remain_paths, &["rest1", "rest2"]);
+
+    let result = MyArgs::from_text("-f -r 5 --verbose -o 13 -v 32 -g 1 --gps 55 path1 path2 rest1 rest2").unwrap();
+    assert!(result.flag);
+    assert!(result.verbose);
+    assert_eq!(result.optional, Some(13));
+    assert_eq!(result.required, 5);
+    assert_eq!(result.speed, 32);
+    assert_eq!(result.gps, &[1, 55]);
+    assert_eq!(result.path, "path1");
+    assert_eq!(result.path2, "path2");
+    assert_eq!(result.remain_paths, &["rest1", "rest2"]);
+}
+
+#[test]
+fn should_fail_invalid_sub_command() {
+    let result = BigArgs::from_text("--verbose my-invalid-args -f -r 5 --verbose -v 32 -g 1 --gps 55 path1 path2 rest1 rest2").unwrap_err();
+    assert_eq!(result, arg::ParseKind::Top(arg::ParseError::RequiredArgMissing("cmd")));
+}
+
+#[test]
+fn should_fail_sub_command_with_wrong_args() {
+    let result = BigArgs::from_text("--verbose my-args -f -r 5 --verbose -v 32 -g 1 --gps lolka path1 path2 rest1 rest2").unwrap_err();
+    assert_eq!(result, arg::ParseKind::Sub("my-args", arg::ParseError::InvalidFlagValue("gps", "lolka")));
+}
+
+#[test]
+fn should_handle_all_flags_as_sub_command() {
+    let result = BigArgs::from_text("--verbose my-args -f -r 5 --verbose -v 32 -g 1 --gps 55 path1 path2 rest1 rest2").unwrap();
+    assert!(result.verbose);
+    let result = match result.cmd {
+        BigSubArgs::MyArgs(args) => args,
+        unexpected => panic!("invalid sub command result: {:?}", unexpected),
+    };
+    assert!(result.flag);
+    assert!(result.verbose);
+    assert_eq!(result.optional, None);
+    assert_eq!(result.required, 5);
+    assert_eq!(result.speed, 32);
+    assert_eq!(result.gps, &[1, 55]);
+    assert_eq!(result.path, "path1");
+    assert_eq!(result.path2, "path2");
+    assert_eq!(result.remain_paths, &["rest1", "rest2"]);
+
+    let result = BigArgs::from_text("--verbose test -u path1 path2 rest1 rest2").unwrap();
+    assert!(result.verbose);
+    let result = match result.cmd {
+        BigSubArgs::Test(args) => args,
+        unexpected => panic!("invalid sub command result: {:?}", unexpected),
+    };
+    assert!(result.u);
+    assert_eq!(result.paths, &["path1", "path2", "rest1", "rest2"]);
+}
+
+#[test]
+fn should_supply_default_value() {
+    let result = MyArgs::from_text("-f -r 5 --verbose -g 1 --gps 55 path1 path2 rest1 rest2").unwrap();
+    assert_eq!(result.speed, 42);
+}
+
+#[test]
+fn shoukd_handle_dash() {
+    let result = MyArgs::from_text("-f -r 5 --verbose -g 1 --gps 55 path1 path2 rest1 -").unwrap();
+    assert_eq!(result.remain_paths[1], "-");
+}
+