sterror(3): added library for C-like error messages; Makefile: some efficiency changes

Makefile

@@ -13,8 +13,11 @@
 
 PREFIX=/usr/local
 
-CC=cc
+CC != command -v "$$CC" || printf 'cc\n'
-RUSTC=rustc
+RUSTC != command -v "$$RUSTC" || printf 'rustc\n'
+RUSTLIBS=--extern getopt=build/o/libgetopt.rlib \
+	--extern sysexits=build/o/libsysexits.rlib \
+	--extern strerror=build/o/libstrerror.rlib
 
 .PHONY: all
 all: dj false fop hru intcmp rpn scrut str strcmp true
@@ -43,6 +46,18 @@ test: build
 	tests/posix-compat.sh
 	$(RUSTC) --test src/getopt-rs/lib.rs -o build/test/getopt
 
+.PHONY: rustlibs
+rustlibs: build/o/libsysexits.rlib build/o/libgetopt.rlib \
+	build/o/libstrerror.rlib
+
+build/o/libgetopt.rlib: build src/getopt-rs/lib.rs
+	$(RUSTC) $(RUSTFLAGS) --crate-type=lib --crate-name=getopt \
+		-o $@ src/getopt-rs/lib.rs
+
+build/o/libstrerror.rlib: build src/strerror.rs
+	$(RUSTC) $(RUSTFLAGS) --crate-type=lib -o $@ \
+		src/strerror.rs
+
 build/o/libsysexits.rlib: build
 	# bandage solution until bindgen(1) gets stdin support
 	printf '#define EXIT_FAILURE 1\n' | cat - include/sysexits.h \
@@ -51,11 +66,7 @@ build/o/libsysexits.rlib: build
 		"$$(printf '#include <sysexits.h>\n' \
 			| cpp -M -idirafter "build/include" - \
 			| sed 's/ /\n/g' | grep sysexits.h)" \
-		| $(RUSTC) $(RUSTFLAGS) --crate-type lib -o build/o/libsysexits.rlib -
+		| $(RUSTC) $(RUSTFLAGS) --crate-type lib -o $@ -
-
-build/o/libgetopt.rlib: src/getopt-rs/lib.rs
-	$(RUSTC) $(RUSTFLAGS) --crate-type=lib --crate-name=getopt \
-		-o build/o/libgetopt.rlib src/getopt-rs/lib.rs
 
 .PHONY: dj
 dj: build/bin/dj
@@ -69,17 +80,13 @@ build/bin/false: src/false.c build
 
 .PHONY: fop
 fop: build/bin/fop
-build/bin/fop: src/fop.rs build build/o/libgetopt.rlib build/o/libsysexits.rlib
+build/bin/fop: src/fop.rs build rustlibs
-	$(RUSTC) $(RUSTFLAGS) --extern getopt=build/o/libgetopt.rlib \
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/fop.rs
-		--extern sysexits=build/o/libsysexits.rlib \
-		-o $@ src/fop.rs
 
 .PHONY: hru
 hru: build/bin/hru
-build/bin/hru: src/hru.rs build build/o/libgetopt.rlib build/o/libsysexits.rlib
+build/bin/hru: src/hru.rs build rustlibs 
-	$(RUSTC) $(RUSTFLAGS) --extern getopt=build/o/libgetopt.rlib \
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/hru.rs
-		--extern sysexits=build/o/libsysexits.rlib \
-		-o $@ src/hru.rs
 
 .PHONY: intcmp
 intcmp: build/bin/intcmp
@@ -88,10 +95,8 @@ build/bin/intcmp: src/intcmp.c build
 
 .PHONY: rpn
 rpn: build/bin/rpn
-build/bin/rpn: src/rpn.rs build build/o/libsysexits.rlib
+build/bin/rpn: src/rpn.rs build rustlibs
-	$(RUSTC) $(RUSTFLAGS) \
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/rpn.rs
-		--extern sysexits=build/o/libsysexits.rlib \
-		-o $@ src/rpn.rs
 
 .PHONY: scrut
 scrut: build/bin/scrut

src/strerror.rs

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: FSFAP
+ *
+ * Copying and distribution of this file, with or without modification, are
+ * permitted in any medium without royalty provided the copyright notice and
+ * this notice are preserved.  This file is offered as-is, without any warranty.
+ */
+
+use std::ffi::{ c_int, c_char, CStr };
+
+/* binding to strerror(3p) */
+extern "C" { fn strerror(errnum: c_int) -> *mut c_char; }
+
+/* wrapper function for use in Rust */
+pub fn c_error(err: std::io::Error) -> String {
+	/* Get the raw OS error. If it’s None, what the hell is going on‽ */
+	let error = err.raw_os_error().unwrap_or_else(|| { panic!() }) as c_int;
+
+	/* Get a CStr from the error message so that it’s referenced and then
+	 * convert it to an owned value. If the string is not valid UTF-8, return
+	 * that error instead. */
+	match unsafe { CStr::from_ptr(strerror(error)) }.to_str() {
+		Ok(s) => s.to_owned(), // yay!! :D
+		Err(e) => e.to_string(), // awww :(
+	}
+}