harakit/STYLE

“Everyone knows that debugging is twice as hard as writing a program in the
first place. So if you’re as clever as you can be when you write it, how
will you ever debug it?”
	– Brian Kernighan, The Elements of Programming Style


The following guidelines are conducive to clear and readable code that is
consistent with the style of the rest of the Bonsai Computer System.


Use
===

 0. A single line for control flow statements short enough to be easily
 understood at a glance:

	if !(argc < 0) { usage(program_name); }

 This applies to C switch statements and cases and Rust match statements, as
 well:

	switch (value) { /* aligning stuff to make it easier to read is fine */
		case possibility: variable = foo;  break;
		default:          variable = NULL; break;
	}

 1. Switch cases in C and match arms in Rust should start another level of
 indentation:

	switch (value) {
		case possibility:
			statement;
			break;
		case default:
			statement;
			break;
	}

	match result {
		Ok(n) => variable = n,
		Err(e) => error = e,
	}

 2. Braces in control flow where their inclusion is left optional in C:

	if (condition) { statement; }

 3. Empty lines between different kinds of statements:

	int t;

	assert(io->bufuse > 0);
	assert(io->bufuse <= io->bs);

	if ((t = write(io->fd, io->buf, io->bufuse)) < 0) {
		io->error = errno;
		t = 0;
	} else if (t > 0) {
		memmove(io->buf, &(io->buf)[t], (io->bufuse -= t));
	}

	io->bytes += t;
	io->prec  += (t > 0 && io->bufuse > 0);
	io->rec   += (t > 0 && io->bufuse == 0);

	return io;

 4. Compiler options that yield the most useful warnings, such as -Wpedantic in
 a lot of C compilers. Fix the warnings, too [0].

 5. Fixed bounds for loops [0].

 6. One more level of indentation and one argument per line when a function
 call or statement header is too long to fit on one line:

	let usage = format!(
		"Usage: {} [-d delimiter] index command [args...]",
		argv[0],
	);

 7. One more level of indentation than the keyword that initiated a multi-line
 block.

	if (condition) {
		statement;
		statement;
	}

 8. The return value of all non-void functions, or explicitly ignore them (like
 casting to void in C) [0]:

	if ((a = malloc(sizeof char)) == NULL) {          /* handle this error */
		(void)fprintf(stderr, "oh noes!");   /* explicitly ignore this one */
		return EX_OSERR;       /* ...because the program is exiting anyway */
	}

 9. The smallest possible scope for data [0].

 10. Comments noting all the symbols and macros used from a C header file, next
 to its include macro:

	#include <unistd.h> /* close(2), getopt(3), lseek(2), read(2), write(2),
	(space-aligned)      * optarg, optind, STDIN_FILENO, STDOUT_FILENO */

 11. Spaces in control flow statements, after the keyword and before the
 opening brace:

	for (i = 2; i < argc; ++i) {


 12. In Rust, a trailing comma on all arguments or fields that are on their own
 lines:

	return Err(EvaluationError {
		message: format!("{}: Invalid token", i),
		code: EX_DATAERR,
	})

 13. In Rust, place extern statements after use statements that include standard
 library crates. Group like statements:

	use std::fs::Path;

	extern crate strerror;
	extern crate sysexits;

	use strerror::StrError;
	use sysexits::{ EX_OSERR, EX_USAGE };

 14. If text is on the same line as a brace, spaces after an opening brace and
 before a closing one:

	use sysexits::{ EX_DATAERR, EX_IOERR, EX_UNAVAILABLE, EX_USAGE };

 15. Alphabetic sorting, where applicable:

	use std::io::{ BufWriter, Read, Write, stderr, stdin, stdout }

 16. In Rust, use the to_owned() method on string types (str, OsStr, CStr, etc.)
 and the to_string() method on other types.


Avoid
=====

 17. Function pointers [0].

 18. Heap memory allocation [0].

 19. Using too much nested logic (within reason).

 20. Too many levels of dereferences [0]:

	/* do not do this */
	for (size_t i = 0; i < sizeof a / sizeof *a; ++i) {
		if (a[i].id == MATCH) { a[i].val = 0; }
	}

	/* do this */
	for (struct MadeUp *s = &a[0]; *s != NULL; s = &s[1]) {
		if (s->id == MATCH) { s->val = 0; }
	}

 21. Using C preprocessor macros; the fewer, the better [0].

 22. The exit(3p) and std::process::exit() functions; returning from the main
 function skips a system call.


Do Not Use
==========

 23. More than the length of one printed page for a function [0].

 24. Recursion, as it’s complex and can unexpectedly overflow the stack [0].

 25. Any functionality not in the POSIX C specification and language features not
 in C99.

 26. Do-while loops, as they’re unique to C and confusing for casual programmers.

 27. Labels and goto statements; use sensible flow control [0].

 28. Pointer arithmetic, as it tends to be confusing and unnecessary; use
 index-reference patterns like &p[1] instead of p + 1. &p[n] is the address at
 p + sizeof p * n, not p + n, like pointer arithmetic suggests.

 29. C struct bitfields in unions, to access certain bits of bigger data types,
 as it’s poorly defined in the C standards; use bit arithmetic.

 30. C trigraphs.

 31. Inclusions in C header files, to prevent multiple file inclusions.

 32. C preprocessor variables to prevent multiple inclusions of the same file,
 such as:

	#ifdef _FILE
	#define _FILE
	/* file body */
	#endif /* ifdef _FILE */

 Instead, take the time to ensure other files aren’t including any files twice.

 33. The gets(3p) function from <stdio.h>, as it’s impossible to prevent buffer
 overflows when it's used; use fgets(3p) from <stdio.h>.

 34. The scanf(3p) function from <stdio.h> [1].

 35. Any functionality not described in the latest POSIX make(1) specification.

 36. Macros which panic on failure in Rust (such as the print!() and println!()
 macros). Use a function and handle any errors. However, do use the eprintln!()
 macro for error messages. Handling an error for writing an error message is
 redundant.


Usage Text
==========

This section is adapted from the NetBSD style guide [2].

When programs are invoked incorrectly and in the synopsis of manual pages, uasge
text should be provided to the user. The following is the format used by this
project for this purpose:

All optional arguments are to be placed in square brackets (U+005B, U+005D).
Mutually exclusive arguments can be separated by a vertical line (U+007C).
Groups of arguments should be specified in alphabetical order in most cases. The
order of arguments and an example of these rules follows:

 0. Options with no option arguments.
 1. Options with option arguments. Arguments should be specified inside the same
 square brackets as the options.
 3. Non-option arguments.

	"usage: f [-aDde] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\n"
	"usage: f [-a | -b] [-c [-de] [-n number]]\n"


References
==========

[0] <https://web.eecs.umich.edu/~imarkov/10rules.pdf>
[1] <http://sekrit.de/webdocs/c/beginners-guide-away-from-scanf.html>
[2] <http://cvsweb.netbsd.org/bsdweb.cgi/~checkout~/src/share/misc/style>

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Copyright © 2024 DTB <trinity@trinity.moe>
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