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| 1 | +# QLDoc style guide |
| 2 | + |
| 3 | +## Introduction |
| 4 | + |
| 5 | +Valid QL comments are known as QLDoc. This document describes the recommended styles and conventions you should use when writing QLDoc for code contributions in this repository. If there is a conflict between any of the recommendations in this guide and clarity, then clarity should take precedence. |
| 6 | + |
| 7 | +### General requirements |
| 8 | + |
| 9 | +1. Documentation must adhere to the [QLDoc specification](https://help.semmle.com/QL/ql-handbook/qldoc.html). |
| 10 | +1. Documentation comments should be appropriate for users of the code. |
| 11 | +1. Documentation for maintainers of the code must use normal comments. |
| 12 | +1. Use `/** ... */` for documentation, even for single line comments. |
| 13 | + - For single-line documentation, the `/**` and `*/` are written on the same line as the comment. |
| 14 | + - For multi-line documentation, the `/**` and `*/` are written on separate lines. There is a `*` preceding each comment line, aligned on the first `*`. |
| 15 | +1. Use code formatting (`backticks`) within comments for code from the source language, and also for QL code (for example, names of classes, predicates, and variables). |
| 16 | +1. Give explanatory examples of code in the target language, enclosed in ```` ``` ```` or `` ` ``. |
| 17 | + |
| 18 | + |
| 19 | +### Language requirements |
| 20 | + |
| 21 | +1. Use US English. |
| 22 | +1. Use full sentences, with capital letters and full stops, except for the initial sentence of the comment, which may be fragmentary as described below. |
| 23 | +1. Use simple sentence structures and avoid complex or academic language. |
| 24 | +1. Avoid colloquialisms and contractions. |
| 25 | +1. Use words that are in common usage. |
| 26 | + |
| 27 | + |
| 28 | +### Requirements for specific items |
| 29 | + |
| 30 | +1. Public declarations must be documented. |
| 31 | +1. Non-public declarations should be documented. |
| 32 | +1. Declarations in query files should be documented. |
| 33 | +1. Library files (`.qll` files) should be have a documentation comment at the top of the file. |
| 34 | +1. Query files, except for tests, must have a QLDoc query documentation comment at the top of the file. |
| 35 | +1. Where a class denotes a generic concept with subclasses, list those subclasses. |
| 36 | + |
| 37 | +## QLDoc for predicates |
| 38 | + |
| 39 | +1. Refer to all predicate parameters in the predicate documentation. |
| 40 | +1. Reference names, such as types and parameters, using backticks `` ` ``. |
| 41 | +1. Give examples of code in the target language, enclosed in ```` ``` ```` or `` ` ``. |
| 42 | +1. Predicates that override a single predicate don't need QLDoc, as they will inherit it. |
| 43 | + |
| 44 | +### Predicates without result |
| 45 | + |
| 46 | +1. Document predicates that do not have using a third-person verb phrase of the form ``Holds if `arg` has <property>.``. |
| 47 | +1. Avoid: |
| 48 | + - `/**Whether ...*/` |
| 49 | + - `/**"Relates ...*/` |
| 50 | + - Question forms: |
| 51 | + - ``/**Is `x` a foo?*/`` |
| 52 | + - ``/**Does `x` have a bar?*/`` |
| 53 | + |
| 54 | +#### Example |
| 55 | + |
| 56 | +```ql |
| 57 | +/** |
| 58 | + * Holds if the qualifier of this call has type `qualifierType`. |
| 59 | + * `isExactType` indicates whether the type is exact, that is, whether |
| 60 | + * the qualifier is guaranteed not to be a subtype of `qualifierType`. |
| 61 | + */ |
| 62 | +``` |
| 63 | + |
| 64 | +### Predicates with result |
| 65 | + |
| 66 | +1. Document predicates that have a result using a third-person verb phrase of the form `Gets (a|the) <thing>`. |
| 67 | +1. Use "if any" if the item is usually unique, but might be missing. For example |
| 68 | +`Gets the body of this method, if any.`. |
| 69 | +1. If the predicate has more complex behaviour, for example multiple arguments are conceptually "outputs", it can be described like a predicate without a result. For example |
| 70 | +``Holds if `result` is a child of this expression.``. |
| 71 | +1. Avoid: |
| 72 | + - `Get a ...` |
| 73 | + - `The ...` |
| 74 | + - `Results in ...` |
| 75 | + - Any use of `return` |
| 76 | + |
| 77 | +#### Example |
| 78 | +```ql |
| 79 | +/** |
| 80 | + * Gets the expression denoting the super class of this class, |
| 81 | + * or nothing if this is an interface or a class without an `extends` clause. |
| 82 | + */ |
| 83 | +``` |
| 84 | + |
| 85 | +### Deprecated predicates |
| 86 | + |
| 87 | +The documentation for deprecated predicates should be updated to emphasize the deprecation and specify what predicate to use as an alternative. |
| 88 | +Insert a sentence of the form `DEPRECATED: Use <other predicate> instead.` at the start of the QLDoc comment. |
| 89 | + |
| 90 | +#### Example |
| 91 | + |
| 92 | +```ql |
| 93 | +/** DEPRECATED: Use `getAnExpr()` instead. */ |
| 94 | +deprecated Expr getInitializer() |
| 95 | +``` |
| 96 | + |
| 97 | +### Internal predicates |
| 98 | + |
| 99 | +Some predicates are internal-only declarations that cannot be made private. The documentation for internal predicates should begin with `INTERNAL: Do not use.`. |
| 100 | + |
| 101 | +#### Example |
| 102 | + |
| 103 | +```ql |
| 104 | +/** |
| 105 | + * INTERNAL: Do not use. |
| 106 | + */ |
| 107 | +``` |
| 108 | + |
| 109 | +### Special predicates |
| 110 | + |
| 111 | +Certain special predicates should be documented consistently. |
| 112 | + |
| 113 | +- Always document `toString` as |
| 114 | + |
| 115 | + ```ql |
| 116 | + /**Gets a textual representation of this element.*/ |
| 117 | + string toString() { ... } |
| 118 | + ``` |
| 119 | + |
| 120 | +- Always document `hasLocationInfo` be documented like this: |
| 121 | + |
| 122 | + ```ql |
| 123 | + /** |
| 124 | + * Holds if this element is at the specified location. |
| 125 | + * The location spans column `startcolumn` of line `startline` to |
| 126 | + * column `endcolumn` of line `endline` in file `filepath`. |
| 127 | + * For more information, see |
| 128 | + * [Locations](https://help.semmle.com/QL/learn-ql/ql/locations.html). |
| 129 | + */ |
| 130 | +
|
| 131 | + predicate hasLocationInfo(string filepath, int startline, int startcolumn, int endline, int endcolumn) { ... } |
| 132 | + ``` |
| 133 | +## QLDoc for classes |
| 134 | + |
| 135 | +1. Document classes using a noun phrase of the form `A <domain element> that <has property>`. |
| 136 | +1. Use "that", not "which". |
| 137 | +1. Refer to member elements in the singular. |
| 138 | + |
| 139 | +#### Example |
| 140 | + |
| 141 | +```ql |
| 142 | +/** |
| 143 | + * A delegate declaration, for example |
| 144 | + * ``` |
| 145 | + * delegate void Logger(string text); |
| 146 | + * ``` |
| 147 | + */ |
| 148 | +class Delegate extends ... |
| 149 | +``` |
| 150 | + |
| 151 | +```ql |
| 152 | +/** |
| 153 | + * An element that can be called. |
| 154 | + * |
| 155 | + * Either a method (`Method`), a constructor (`Constructor`), a destructor |
| 156 | + * (`Destructor`), an operator (`Operator`), an accessor (`Accessor`), |
| 157 | + * an anonymous function (`AnonymousFunctionExpr`), or a local function |
| 158 | + * (`LocalFunction`). |
| 159 | + */ |
| 160 | +class Callable extends ... |
| 161 | +``` |
| 162 | + |
| 163 | +## QLDoc for modules |
| 164 | + |
| 165 | +Modules should be documented using a third-person verb phrase of the form `Provides <classes and predicates to do something>`. |
| 166 | + |
| 167 | +#### Example |
| 168 | + |
| 169 | +```ql |
| 170 | +/** Provides logic for determining constant expressions. */ |
| 171 | +``` |
| 172 | +```ql |
| 173 | + /** Provides classes representing the control flow graph within functions. */ |
| 174 | + ``` |
| 175 | + |
| 176 | +## Special variables |
| 177 | + |
| 178 | +When referring to `this`, you may either refer to it as `` `this` `` or `this <type>`. For example: |
| 179 | +- ``Holds if `this` is static.`` |
| 180 | +- `Holds if this method is static.` |
| 181 | + |
| 182 | +When referring to `result`, you may either refer to it as `` `result` `` or as `the result`. For example: |
| 183 | +- ``Holds if `result` is a child of this expression.`` |
| 184 | +- `Holds if the result is a child of this expression.` |
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