docs: add API and naming

.pymarkdown.json

@@ -4,6 +4,10 @@
             "//": "Does not work with GitHub issue templates",
             "enabled": false
         },
+        "line-length": {
+            "//": "Disabled because necessary for tables, and no option to disable for them as of 0.9.6",
+            "enabled": false
+        },
         "no-inline-html": {
             "//": "https://github.com/jackdewinter/pymarkdown/issues/22",
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CONTRIBUTING.md

@@ -42,6 +42,9 @@ that. Don't be disappointed if it does or doesn't happen instantly.
 
 Also, please bear the following coding guidelines in mind:
 
+- See the [API and naming](doc/api-and-naming.md) document for information
+  about conventions to follow related to those topics.
+
 - Do not use Perl, Ruby, Python etc. to do text processing unless the
   command for which you are writing the completion code implies the
   presence of one of those languages.

doc/api-and-naming.md

@@ -0,0 +1,95 @@
+# API and naming
+
+## General API conventions
+
+Most of the functions in bash-completion generate completions and directly
+inject them to the `COMPREPLY` array variable, as required for completions to
+work.
+
+Most other functions make use of "output" variables, i.e. assign values to
+them. The most common one of these is named `ret`. Consult the commentary
+before each function in the source to find out the specific names.
+`local`izing output variables before invoking a function that populates them
+is the caller's responsibility.
+Note that if calling multiple functions that assign output to the same variable
+during one completion function run, each result should be copied to another
+variable between the calls to avoid it possibly being overwritten and lost on
+the next call. Also, the variables should also be ensured to be clear before
+each call that references the value, variable name, or their existence,
+typically by `unset -v`ing them when multiple such calls are used,
+to avoid them interfering with each other.
+
+## Naming
+
+Due to its nature, bash-completion adds a number of functions and variables in
+the shell's environment.
+
+|                                     | `bash_completion`   | `completions/*`                                                            |
+|:------------------------------------|:--------------------|:---------------------------------------------------------------------------|
+| public configuration variables      | `BASH_COMPLETION_*` | `BASH_COMPLETION_CMD_${Command^^}_${Config^^}`                             |
+| private non-local variables         | `_comp__*`          | `_comp_cmd_${Command}__${Data}`                                            |
+| private non-local mutable variables | `_comp__*_mut_*`    | `_comp_cmd_${Command}__mut_${Data}`                                        |
+| exporter function local variables   | `_*` (not `_comp*`) | `_*` (not `_comp*`)                                                        |
+| public/exported functions           | `_comp_*`           | `_comp_cmd_${Command}` (functions for `complete -F`)                       |
+|                                     |                     | `_comp_xfunc_${Command}_${Utility}` (functions for use with `_comp_xfunc`) |
+| private/internal functions          | `_comp__*`          | `_comp_cmd_${Command}__${Utility}` (utility functions)                     |
+
+`${Command}` refers to a command name (with characters not allowed in POSIX
+function or variable names replaced by an underscore), `${Config}` the name of
+a configurable thing, `^^` means uppercase, `${Data}` is an identifier for the
+data contained in the variable, and `${Utility}` describes the typical usage of
+the function.
+
+Variables and functions affecting multiple completions are usually defined
+in the main `bash_completion` file and do not require any additional files to
+be sourced. Variables and functions in command specific completion files in
+`completions/*` follow a slightly different naming scheme; they include
+`cmd` in their name as well as the name of the command.
+
+Public configuration variables are shell ones that affect the runtime behavior
+of various completions. As a rule of thumb, we lean towards not providing
+customizability but rather strive to provide great completion behavior out of
+the box. But there are some, see [configuration](configuration.md).
+
+Variables and functions whose name contains a double underscore (`__`) anywhere
+in their name are private implementation details, not part of the stable API,
+and not intended to be used outside of their defining context. Internally, the
+double underscores serve as privacy scope delimiters; there can be more than one
+pair of them in a name, and functions and variables are intended to reference
+and call other functions and variables within that scope, one level deep,
+sharing a common prefix. For example, a function named `_comp_foo` is "allowed"
+to access `_comp_foo__*` where `*` does not contain any double underscores,
+i.e. it should not access `_comp_foo__something__*` despite the common prefix.
+
+Private non-local variables are considered readonly by default.  When a
+completion function needs to change variables for e.g. caching purposes, the
+variables should contain the infix `*_mut_*` anywhere in their names.  This is
+needed to tell the test framework to allow these variables changing.
+Nevertheless, the completion results should be consistent among different calls
+and unaffected by the state of the cache variables when it is called.
+
+Internal local variables of functions that "export" their results using a
+variable name that is passed in start with an underscore and do not start with
+`_comp`. The variable names that are passed in for this purpose must not start
+with an underscore.
+
+Functions with names prefixed with `_comp_xfunc_` are intended to be used
+through the `_comp_xfunc` function from files other than the one they are
+defined in. From the same file they can be used directly using their complete
+name.
+
+Function names start with an underscore in order to avoid them being
+included in completions of command names. (Except naturally when a command
+starting with an underscore is being completed.) The underscore prefix does
+not have anything to do with whether the thing is considered public or
+private in the API, nor anything else really.
+
+The `BASH_COMPLETION_` prefix provides a namespace and makes it clear what
+these variables relate to. The `_comp` in other names serves a similar purpose,
+but because these are used a lot in the code (unlike the public configuration
+variables), using something shorter is beneficial. We hope and believe this is
+distinctive and clash free enough.
+
+It is known that a lot of functions and variables in the tree do not follow
+these naming rules yet. Things introduced after version 2.11 should, and we are
+evaluating our options for handling older ones.

doc/styleguide.md

@@ -111,19 +111,6 @@ over actual values. If an index or value is to be accessed later on instead of
 being just locally for looping, use a more descriptive and specific name for
 it.
 
-## Function names
+## Function and variable names
 
-Use the `_comp_` prefix for all function names, and `_comp_cmd_` for functions
-defined in per command completion files and not anywhere else. Prefixing with
-an underscore helps keep the functions out of the way for most command name
-completions (except obviously ones starting with an underscore or ones that have
-nothing typed in yet), and having a consistent prefix helps avoid some clashes
-and gives a hint where a function originates from.
-
-It is known that a lot of functions in the tree do not follow this practice.
-This is due to backwards compatibility reasons, but all functions introduced
-after version 2.11 should follow this name prefix rule.
-
-## Variable naming
-
-To be written.
+See [API and naming](api-and-naming.md).