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diff --git a/notes/coding_standard.rst b/notes/coding_standard.rst new file mode 100644 index 0000000..1deed03 --- /dev/null +++ b/notes/coding_standard.rst @@ -0,0 +1,422 @@ +libmaple Coding Standards +========================= + +Author: Marti Bolivar (mbolivar@leaflabs.com) + +LeafLabs team members are required to follow these when producing new +code. Community contributors to libmaple are strongly encouraged to +do so; following these rules will greatly increase the probability +that your patches will be folded in. + +In general, do it like this unless there's a really good reason why +not. You being lazy doesn't count as a good reason. Most, if not +all, of these decisions are entirely arbitrary, but it's important for +readability that we be consistent. + +The file ``.dir-locals.el`` in the libmaple root directory already +ensures that many of these standards are followed by default in Emacs +(but not on Windows, where it would need to be named +``_dir_locals.el``, and no way, man). There's also some elisp +scattered about this file which will provide you additional help. + +Vim customizations to do the same thing would be nice (hint, hint)! + +License +------- + +- Put an MIT license at the beginning of the file (look at any of our + source files for an example). Copyright should go either to you or + to LeafLabs, LLC. + +.. highlight:: scheme + + Emacs: if you don't like seeing the license, you should use + elide-head (which will hide it for you). You can use the following:: + + (require 'elide-head) + (setq programming-mode-hooks '(c-mode-hook c++-mode-hook)) + (add-to-list 'elide-head-headers-to-hide + '("The MIT License" . "DEALINGS IN\n [*] THE SOFTWARE")) + (add-to-list 'elide-head-headers-to-hide + '("The MIT License" . "DEALINGS IN THE\n...SOFTWARE")) + (dolist (hook programming-mode-hooks) + (add-hook hook (lambda () (elide-head)))) + +Whitespace/Indentation +---------------------- + +- 4 space indents. [Set in ``.dir-locals.el``] + +- Unix newlines. [Some exceptions are currently grandfathered in; + these will go away in time.] + +- No tab characters. [Set in ``.dir-locals.el``] + +- No trailing whitespace. For help getting this (and no tab + characters) done automatically in Emacs, you can use this: + + http://github.com/mbolivar/code-fascism + + I hear tell you can get something similar in Vim; ask around, I + guess. + +- Files end in exactly one newline. [The presence of a newline at EOF + is already done by ``c-require-final-newline`` in recent versions of + Emacs.] + +- Exactly two newlines separate source paragraphs (you do separate + your code into paragraphs, don't you?). + +- The first line in a function is non-blank. + +.. highlight:: cpp + +- Exactly one space after ``if``, ``else``, ``for``, and ``while``, + before the following ``{`` or ``(``. One space before ``else``, + after the preceding ``}``. For example:: + + // This is good; we like this: + if (foo) { + while (quux) { + bar(); + } + } else { + baz(); + } + + // THIS IS BAD! DON'T DO THIS: + if(foo){ + while(quux){ + bar(); + } + }else{ + baz(); + } + +- Exactly one space in between binary arithmetic, logical, and + comparison operators and their operands, except for the . and -> + operators. Examples:: + + // This is good: + int x = a + b * (c - d); + if (x != 0 && a > 7) { + SerialUSB.println(x); + } + + // THIS IS BAD! + int x = a+b*(c-d); + if (x!=0 && a>7) { + SerialUSB.println(x); + } + + // This is good: + uint32 adc_data = ADC1_BASE->DR; + SerialUSB.println(adc_data); + + // THIS IS BAD! + uint32 adc_data = ADC1_BASE -> DR; + SerialUSB . println(adc_data); + +- No space between a unary operator and its operand. Examples:: + + // Good: + x++; + + // BAD! + x ++; + + // Good: + y = -x; + + // BAD! + y = - x; + +- If you need to break up a long line: + + * Prefer to break up long expressions after a binary operator. Example:: + + // Good: + if (some_really_long_conditional_wow_this_really_goes_on_forever || + maybe_something_else_could_happen_too) { + ... + } + + // BAD! + if (some_really_long_conditional_wow_this_really_goes_on_forever + || maybe_something_else_could_happen_too) { + ... + } + + * When breaking up a function's arguments over multiple lines, align + the arguments on subsequent lines with the first argument. + Example:: + + // Good: + return_type value_i_got = function_with_a_really_long_name(argument1, + argument2, + argument3); + + // BAD! + return_type value_i_got = function_with_a_really_long_name(argument1, + argument2, + argument3); + + // BAD! + return_type value_i_got = function_with_a_really_long_name(argument1, + argument2, + argument3); + +- In function invocations, no space in between the function name and + the opening parenthesis. Example:: + + // Good: + SerialUSB.println("Hello, world!"); + + // BAD! + SerialUSB.println ("Hello, world!"); + +- Don't indent C code within a conditionally-compiled ``extern "C"`` + block. Example:: + + // Good: + #ifdef __cplusplus + extern "C"{ + #endif + + void some_c_function(void); + + #ifdef __cplusplus + } // extern "C" + #endif + + // BAD! + #ifdef __cplusplus + extern "C"{ + #endif + + void some_c_function(void); + + #ifdef __cplusplus + } // extern "C" + #endif + +.. highlight:: scheme + + Emacs does the "bad" behavior by default, which can be very + annoying. You can turn this off with:: + + (defun c-mode-inextern-lang-hook () + (setcdr (assq 'inextern-lang c-offsets-alist) '-)) + (add-hook 'c-mode-hook c-mode-inextern-lang-hook) + +Comments +-------- + +.. highlight:: c++ + +- Multi-line comments are pretty flexible. Any of these is fine:: + + /* Comment starts here. + * Continued lines have a '*' before them. + * The comment can end after the last line. + */ + + /* Comment starts here. + * The comment can end on the same line. */ + + /* + * You can also place a newline after the opening "/*". + */ + +- Doxygen comments are multi-line comments that begin with ``/**`` + instead. + +- Single-line comments on the same line are ``//`` in C++. (That's OK + in C as well). + +- Single-line comments on their own source line should be ``/* */`` in + C, but can also be ``//`` in C++. (This isn't of great importance). + In Emacs, you can use M-; (comment-dwim), and it'll Do What You + Mean. + +Braces +------ + +- Mostly 1TBS: + + http://en.wikipedia.org/wiki/Indent_style#Variant:_1TBS + + The only difference is that the opening brace of a function's + definition occurs exactly one space character after the closing + parenthesis in that function's parameter list. Example:: + + void func(void) { + ... + } + +Naming conventions +------------------ + +There's always a fight about upper and lower case vs. underscores. +We'll handle this as follows. + +- First, ``Dont_Mix_Like_This``, because ``It_Looks_Really_Ugly``, ok? + [There's been some debate about this, and some exceptions are + already grandfathered in, so in order to settle it, let's call this + a "recommendation" instead of "requirement".] + +- Variables: Use underscores to separate words in C identifiers:: + + int some_example_name; + + User-facing C++ variables should be camel cased + (``thisIsAnExample``, ``boardPWMPins``, etc.), for consistency with + the Arduino style. It's probably a good idea for you to case + non-user facing C++ variables in the C style; this will help + disambiguate what's part of the Wirish API and what's not. + +- Classes: Pascal case. So ``ThisIsAClassName``, but ``thisIsNot``, + ``this_is_not``, and like I said, + ``Dont_You_DareTryANYTHING_STUPID``. + +- Functions: C functions are all lowercase, and words are separated by + underscores. C++ method names are camel cased. + +- Structs: Usually like variables (``adc_dev``, ``adc_reg_map``, + etc.), but it's not crucial. Don't feel obliged to put ``_t`` at + the end of the type name; we don't. + +- Macros and constants: all caps, separated by underscores. C++ + variables with the ``const`` qualifier generally aren't considered + "constants" for the purposes of this rule; i.e., they are cased + according to the rules for variables. We make an exception for + ``PIN_MAP``, because it's the central Wirish data structure. + +- foo.h gets ``#ifdef``\ 'ed to ``_FOO_H_``. + +- Acronyms: The case of letters in an acronym is determined by the + case of the first letter in the acronym, which is determined by + following the above rules. Examples:: + + // Good: + void usb_func() { ... } + void frob_usb_disc() { ... } + class SomethingUSB { + void usbInit(); + void initUSB(); + }; + + // BAD: + class BadUsb { ... }; // say "GoodUSB" instead + void swizzle_USB_disc() { ... } // say "swizzle_usb_disc" instead + +Documentation +------------- + +- You **must** document your code. At a bare minimum, this means + Doxygen comments on every user-facing function and type. + Additionally, you need to individually document the fields and + enumerator values of ``struct``\ s and ``enum``\ s. See any + register map type's definition for an example. + +- For libmaple proper, you don't need comments for each register bit + definition (for now). + +- Doxygen comments generally just belong on types, functions, + etc. that are part of the public user-facing API. This generally + means that if there's ReST documentation for it under docs/source/, + it needs Doxygen comments, and that ReST should use Breathe to pull + that Doxygen comment out. (For more info on this, see docs/README). + + There are some exceptions to this rule since Breathe isn't totally + mature yet and Sphinx's C++ domain is still in flux. In these + cases, document the code "manually" in ReST. + + This should be avoided if at all possible, since it creates a + maintenance burden of documenting things in two places at once, and + makes it easier for documentation to go stale. + + If you do have to document something manually, put a comment in the + source file informing future maintainers about it, so they'll pay + extra attention when making changes. + +- When adding peripheral support, it would be nice if you put + longer-form comments into the /notes/ directory, with a comment in + the corresponding .h file referring to it. See /libmaple/dac.h for + an example. + + This lets us keep the source files relatively free of "introductory" + material, while allowing new readers a convenient starting point. + These longer-form notes also have a habit of turning into + user-facing documentation. + +- For libmaple proper (the pure C library under libmaple/); the + convention is to document any user-facing function at the point where + it is defined. In particular, this means you should document an + externally-linked function defined in a .c file in that .c file, not + in the header file where it is declared to the user. + +General Formatting +------------------ + +- Keep it 80-column clean. That means Emacs says the largest column + number=79. You should turn on column number mode to help you out: + +.. highlight:: scheme + + (column-number-mode 1) + + You can get more help from lineker-mode: + + http://www.helsinki.fi/~sjpaavol/programs/lineker.el + + Just put lineker.el somewhere in your load-path, and: + + (require 'lineker) + (dolist (hook '(c-mode-hook c++-mode-hook)) + (add-hook hook (lambda () (lineker-mode 1)))) + +Language Features and Compiler Extensions +----------------------------------------- + +- In libmaple proper, aim for C99 compatibility. Some GCC extensions + are OK, but let's not go crazy. + +- If you'd like to get code into libmaple which uses a GCC extension + not already in use elsewhere, ask a LeafLabs developer (or another + one, if you are one) what they think about it first. + +- Explicitly approved GCC extensions: + + * asm volatile: + http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html + + * Nested functions: + http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html + +- In wirish, generally be very conservative when using C++ features + that aren't part of C. We are forced to use C++ for Arduino + compatibility (and the general Arduino style of pretending that an + object is a library), but it's an angry beast, and we don't want to + provoke it. The mantra is "C with classes". + +- Explicitly approved C++ features: + + * Initializers that aren't constant; e.g. the ``gpio_dev*`` values + in a ``PIN_MAP``. + + * Default arguments: e.g., the timeout argument defaulting to 0 + (meaning to wait forever) in ``waitForButtonPress()``. + +- Explicitly forbidden C++ features: + + * Templates + +- C++ features that are conditionally allowed, but require explicit + approval from at least two libmaple developers (one of which may be + yourself): + + * Operator overloading: Never allowed when it's just for style. + Potentially allowed when you're implementing a class that models a + mathematical structure, and you'd like to implement + e.g. ``operator+()``. |