// Render with Asciidoctor = LTTng-tools C API documentation guidelines Philippe Proulx 25 August 2021 :toc: left This document explains how to write documentation for the LTTng-tools C{nbsp}API. == General rules * Use four spaces to indent Doxygen text and two spaces to indent HTML. * Try to stay behind the 72^th^ column mark when possible. * Use https://en.wikipedia.org/wiki/Non-breaking_space[`+ +`] wherever needed. * Refer to a function with the `func()` form and to an enumerator/structure/variable or type with the `#name` syntax. + You don't need any `struct`/`enum` prefix with Doxygen. * When you refer to any keyword or definition, use the `+\c+` command if it's a single word, otherwise surround the words with `` and ``: + -- ---- @returns Event rule on success, or \c NULL on error. ---- -- * Use the `$$\$$__command__` style in text (paragraphs, list items, definition terms, and the rest) and the `@__command__` style for other locations (for example, `@brief`, `@param`, `@sa`, `@file`). * Use a `@code{.unparsed}` block for a plain text block (shell input, for example): + ---- @code{.unparsed} $ lttng enable-event --all --kernel --syscall @endcode ---- * In the text, use custom aliases when applicable. + See `Doxyfile.in` for the list of available aliases. == Function documentation Full example: ---- /*! @brief Does something (third person singular, simple present) with some parameter \lt_p{param} unless some other parameter \lt_p{other_param} has some value. Full documentation goes here and adds any relevant information that's not in the brief description. @code /* If needed, put any C code in a code block. */ @endcode Crucifix scenester vegan organic neutra palo santo glossier occupy truffaut. Meh fixie taiyaki single-origin coffee wayfarers. Thundercats farm-to-table shoreditch vinyl. @remarks This is where you would put some remarks. Occupy flexitarian neutra, edison bulb bespoke sriracha post-ironic. Mlkshk plaid pop-up polaroid chillwave, ennui neutra. See this image: @image html mein-illustration.png "Caption goes here." @note @parblock This is a multiparagraph note. Tote bag sartorial distillery, try-hard succulents wayfarers DIY YOLO four loko jianbing farm-to-table unicorn vice. Mumblecore semiotics raw denim palo santo chartreuse helvetica shabby chic, distillery pabst poke swag copper mug blue bottle. @endpar @attention Use an attention command if this message is really important. @attention @parblock An attention block with more than one paragraph: @code some_code(23) @endcode Elit dolore pariatur ex anim officia cupidatat adipisicing mollit incididunt irure anim nostrud. @endparblock @param[in] param Description of this parameter. @param[in] other_param @parblock Description of this other parameter. Nulla consequat tempus libero, sed finibus velit. Offal actually vinyl taiyaki kickstarter etsy. @endparblock @param[out] out_param On success, \lt_p{*out_param} contains to something useful. @retval #LTTNG_SOME_STATUS_OK Success. @retval #LTTNG_SOME_STATUS_MEMORY_ERROR Out of memory. @retval #LTTNG_SOME_STATUS_ERROR @parblock Longer description for this specific status. Organic locavore sartorial 3 wolf moon brooklyn, VHS pug distillery schlitz tofu banjo chambray you probably haven't heard of them hot chicken copper mug. Neutra kale chips kombucha, salvia green juice live-edge swag biodiesel scenester austin yuccie dreamcatcher cronut small batch. @endparblock @lt_pre_not_null{param} @lt_pre_not_null{other_param} @pre \lt_p{param} is like this or like that. @post \lt_p{other_param} is still in some state, and woke jean waistcoat. @sa lttng_some_other_function() -- Does something else with some parameter. @sa lttng_another_function() -- Cardigan celiac palo santo, tacos chicharrones pitchfork chambray photo booth subway tile 90's street. */ ---- Parts: . **Opening Doxygen comment**. + Use `+/*!+`. . **Brief description**. + Use third person singular in the simple present tense: you're documenting what the function does. Assume that the sentence implicitly starts with "`This function`". + Try to mention, briefly, all the parameters (with `\lt_p`) and what the function returns. + End the sentence with a period. . **Detailed description**. + Write complete sentences. + Refer to parameters (with `\lt_p`) as much as possible. + In general, keep paragraphs short: often, a single sentence is enough. + Refer to the documented function with "`this function`". + Write notes (`@note` command), remarks (`@remark` command), or attentions (`@attention` command) when needed. Most notes and remarks, however, can be simple paragraphs. Use `@parblock` end `@endparblock` to have more than one note/remark/warning paragraph. . **Parameter descriptions** (if any). + Use the `@param[in]`, `@param[out]`, and `@param[in,out]` commands depending on the parameter direction. + Document parameters in the declaration order. + Refer to other parameters (with `\lt_p`) when useful for the reader. + End each description with a period. + Use `@parblock` end `@endparblock` to have more than one paragraph for a given parameter description. + Make sure there's no blank line, except within a `@parblock` block, within the parameter description block so that Doxygen puts all the descriptions in the same section. For example, _don't_ write this: + ---- @param[in] hexagon Ugh literally +1 aesthetic, fashion axe try-hard mixtape pork belly four loko. @param[in] selfies Brooklyn ethical migas, viral edison bulb meggings butcher flexitarian letterpress humblebrag kombucha pour-over etsy sriracha blog. ---- . **Return value** (if any). + If the function returns a status code:: Use the `@retval` command multiple times to document each relevant status: + ---- @retval #LTTNG_SOME_STATUS_OK Success. @retval #LTTNG_SOME_STATUS_SOME_ERROR Some error. ---- + End each description with a period. + Use `@parblock` and `@endparblock` to have more than one paragraph for a given return value description. + Make sure there's no blank line, except within a `@parblock` block, within the return value description block so that Doxygen puts all the descriptions in the same section. For example, _don't_ write this: + ---- @retval #LTTNG_SOME_STATUS_OK Success. @retval #LTTNG_SOME_STATUS_SOME_ERROR Some error. ---- If the function returns a simple value:: Use the `@returns` command to document it. + Refer to parameters (with `\lt_p`) when useful for the reader. + End the description with a period. . **Preconditions** (if any). + List all the function's preconditions with the `@pre` command or any alias which starts with `@lt_pre` (see `Doxyfile.in`). + Use the simple present tense. + Do not write the word "`must`" as a precondition is already a requirement. + End the description with a period. + Make sure there's no blank line within the precondition description block so that Doxygen puts all the descriptions in the same section. For example, _don't_ write this: + ---- @lt_pre_not_null{param} @pre \lt_p{param} is like this or like that. ---- . **Postconditions** (if any). + List all the function's _relevant_ postconditions with the `@post` command or any alias which starts with `@lt_post` (see `Doxyfile.in`). + Anything that the body of the function documentation describes and which forms the nature of the function doesn't need to be written as an explicit postcondition. For example, if a function adds some object{nbsp}A to some object{nbsp}B, don't write the postcondition "`B{nbsp}contains{nbsp}A`". + Use the simple present tense. + End the description with a period. + Make sure there's no blank line within the postcondition description block so that Doxygen puts all the descriptions in the same section. For example, _don't_ write this: + ---- @post The returned pointer is blue. @post \lt_p{other_param} is still in some state, and woke jean waistcoat. ---- . **Items to see also** (if any). + Use the `@sa` command, multiple times if needed, to refer to related functions or types. + This is a way for you to inform the reader about other existing, related items. Keep in mind that the reader doesn't always know where to look for things. + In the brief description of the referred item, _don't_ mention its parameters, if any. + End each brief description with a period. + Make sure there's no blank line within the item description block so that Doxygen puts all the descriptions in the same section. For example, _don't_ write this: + ---- @sa lttng_some_other_function() -- Does something else with a parameter. @sa lttng_another_function() -- Cardigan celiac palo santo, tacos chicharrones pitchfork chambray photo booth subway tile 90's street. ---- == Writing style The ultimate goal of the LTTng-tools C{nbsp}API documentation is to make the layman write code using this API as fast and correct as possible without having to ask for help. For this purpose, the documentation must be as clear as possible, just like the function and type names try to be. Don't hesitate to repeat technical terms, even in the same sentence, if needed. For example, if you document an "`event rule`", then always use the term "`event rule`" in the documentation, not "`event`", nor "`rule`", since they are ambiguous. You can use light emphasis to show the importance of a part of the text with the `\em` command (one word) or by surrounding the text to emphasize with `` and ``. Likewise, you can use strong emphasis when needed with the `\b` command (one word) or with `` and ``. In general, prefer light emphasis to strong emphasis, and use it economically. Links to other parts of the documentation are very important. Consider that the reader never knows that other functions exist other than the one she's reading. Use as many internal links as possible. Use the following forms of links: `__func__()`:: Automatic link to the function or macro named `__func__`. `#__name__`:: Automatic link to the type or enumerator named `__name__`. `\ref __ref__`:: Link to `__ref__` (page name, group name, function or macro name, type name, variable name, etc.) using its default text. `\ref __ref__ "__some text__"`:: Link to `__ref__` (page name, group name, function or macro name, type name, variable name, etc.) using the text `__some text__`. See Doxygen's "`http://www.doxygen.nl/manual/autolink.html[Automatic link generation]`" page for other ways to create automatic links. Follow, as much as possible, the https://docs.microsoft.com/en-ca/style-guide/welcome/[Microsoft Style Guide] when you document the API. This includes: * Use an active voice. * Use a gender-neutral language. * Use the present tense (you almost never need the future tense). * Address your reader directly (use "`you`"). * Use contractions ("`it's`", "`you're`", "`don't`", and the rest). * Avoid anthropomorphism. * Ensure parallelism in lists, procedures, and sentences. * Terminate list items with a period, except when the list only contains very short items. * Do not use Latin abbreviations. * Use "`and`" or "`or`" instead of a slash. * Avoid using negatives. * Avoid using "`should`": most of the time, you mean "`must`", and that's very clear for the reader.