Subject: Re: [PATCH 1/1] config: add documentation to config.h

From: Emily Shaffer <[email-masked]>
Date: Fri, 18 Oct 2019 15:51:55 -0700

On Fri, Oct 18, 2019 at 12:06:59AM +0000, Heba Waly via GitGitGadget wrote:
> From: Heba Waly <[email-masked]>

Hi Heba,

Thanks for the patch!

I'd like to highlight to the community that this is an Outreachy
applicant and microproject. Heba, when you send the next version, I
think you can add [Outreachy] manually to the PR subject line - that
should draw the attention of those in the community who are invested in
helping Outreachy applicants.

> 
> This commit is copying and summarizing the documentation from
> documentation/technical/api-config.txt to comments in config.h

I think in the GitGitGadget PR you've got some great comments from Dscho
about how to format your commit message; please take a look at those and
feel free to reach out to me if you're still not sure what's missing or
not.

> Signed-off-by: Heba Waly <[email-masked]>

One thing I miss in this change is the removal of the contents of
Documentation/technical/api-config.txt (or maybe the removal of the file
itself). I'd prefer to see at least for api-config.txt to say something
like "Please refer to comments in 'config.h'"; or, more drastically, for
api-config.txt to be removed entirely.

Having both pieces of documentation standing independently means that
someone who's trying to add new information about the config API won't
know where to add it; eventually they'll add something to config.h but
not api-config.txt, or vice versa, and the two documents will go out of
sync. So we want to move the documentation, rather than copy it.

Plus, having the removed doc as part of this change means I can more
easily look at where the lines of content are coming from and see if you
made any significant changes from the old contents of api-config.txt.
Having a smaller amount of change to review means your review will be
quicker - I don't feel as strong a need to check the grammar, spelling,
etc, because that text has already been reviewed before, and can just
make sure that the placement of each piece of documentation makes sense.

> ---
>  config.h | 327 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 327 insertions(+)
> 
> diff --git a/config.h b/config.h
> index f0ed464004..fa999a2ba0 100644
> --- a/config.h
> +++ b/config.h
> @@ -4,6 +4,40 @@
>  #include "hashmap.h"
>  #include "string-list.h"
>  
> +
> +/**
> + * The config API gives callers a way to access Git configuration files
> + * (and files which have the same syntax). See linkgit:git-config[1] for a
> + * discussion of the config file syntax.
> + *
> + * General Usage
> + * -------------
> + *
> + * Config files are parsed linearly, and each variable found is passed to a
> + * caller-provided callback function. The callback function is responsible
> + * for any actions to be taken on the config option, and is free to ignore
> + * some options. It is not uncommon for the configuration to be parsed
> + * several times during the run of a Git program, with different callbacks
> + * picking out different variables useful to themselves.
> + *
> + * A config callback function takes three parameters:
> + *
> + * - the name of the parsed variable. This is in canonical "flat" form: the
> + *   section, subsection, and variable segments will be separated by dots,
> + *   and the section and variable segments will be all lowercase. E.g.,
> + *   `core.ignorecase`, `diff.SomeType.textconv`.
> + *
> + * - the value of the found variable, as a string. If the variable had no
> + *   value specified, the value will be NULL (typically this means it
> + *   should be interpreted as boolean true).
> + *
> + * - a void pointer passed in by the caller of the config API; this can
> + *   contain callback-specific data
> + *
> + * A config callback should return 0 for success, or -1 if the variable
> + * could not be parsed properly.
> + */
> +
>  struct object_id;
>  
>  /* git_config_parse_key() returns these negated: */
> @@ -73,6 +107,11 @@ struct config_options {
>  
>  typedef int (*config_fn_t)(const char *, const char *, void *);
>  int git_default_config(const char *, const char *, void *);
> +
> +/**
> + * Read a specific file in git-config format.
> + * This function takes the same callback and data parameters as `git_config`.
> + */
>  int git_config_from_file(config_fn_t fn, const char *, void *);
>  int git_config_from_file_with_options(config_fn_t fn, const char *,
>  				      void *,
> @@ -88,33 +127,152 @@ void git_config_push_parameter(const char *text);
>  int git_config_from_parameters(config_fn_t fn, void *data);
>  void read_early_config(config_fn_t cb, void *data);
>  void read_very_early_config(config_fn_t cb, void *data);
> +
> +/**
> + * Most programs will simply want to look up variables in all config files
> + * that Git knows about, using the normal precedence rules. To do this,
> + * call `git_config` with a callback function and void data pointer.
> + *
> + * `git_config` will read all config sources in order of increasing
> + * priority. Thus a callback should typically overwrite previously-seen
> + * entries with new ones (e.g., if both the user-wide `~/.gitconfig` and
> + * repo-specific `.git/config` contain `color.ui`, the config machinery
> + * will first feed the user-wide one to the callback, and then the
> + * repo-specific one; by overwriting, the higher-priority repo-specific
> + * value is left at the end).
> + */
>  void git_config(config_fn_t fn, void *);
> +
> +/**
> + * Lets the caller examine config while adjusting some of the default
> + * behavior of `git_config`. It should almost never be used by "regular"
> + * Git code that is looking up configuration variables.
> + * It is intended for advanced callers like `git-config`, which are
> + * intentionally tweaking the normal config-lookup process.
> + * It takes two extra parameters:
> + *
> + * `config_source`::

I think the wonky trailing "::" is for generating manpages/HTML out of
the asciidoc from the original api-config.txt. I expect it's OK to
remove them throughout this change and format this in a way that makes more
sense for comments which won't be converted into anything else.

> + * If this parameter is non-NULL, it specifies the source to parse for
> + * configuration, rather than looking in the usual files. See `struct
> + * git_config_source` in `config.h` for details. Regular `git_config` defaults
> + * to `NULL`.
> + *
> + * `opts`::
> + * Specify options to adjust the behavior of parsing config files. See `struct
> + * config_options` in `config.h` for details. As an example: regular `git_config`
> + * sets `opts.respect_includes` to `1` by default.
> + */
>  int config_with_options(config_fn_t fn, void *,
>  			struct git_config_source *config_source,
>  			const struct config_options *opts);
> +
> +/**
> + * Value Parsing Helpers
> + * ---------------------

It may not make sense to have the header here in the middle of the doc.

I wonder whether we need the headers at all anymore; or, whether it
makes more sense to put this header in the long comment at the top with
just the list of function names (so someone knows where to look), and
leave the per-function explanations inline with the function they
describe?

> + *
> + * To aid in parsing string values, the config API provides callbacks with
> + * a number of helper functions

In the copy paste, this lost some ending punctuation. I'd advocate
ending this with ":" to indicate "we are about to give the list of those
functions". Although, I wonder whether it makes more sense to rephrase
this into something like "The following helper functions aid in parsing
string values:"? Not sure.

> + */
> +
>  int git_parse_ssize_t(const char *, ssize_t *);
>  int git_parse_ulong(const char *, unsigned long *);
> +
> +/**
> + * Same as `git_config_bool`, except that it returns -1 on error rather
> + * than dying.
> + */
>  int git_parse_maybe_bool(const char *);
> +
> +/**
> + * Parse the string to an integer, including unit factors. Dies on error;
> + * otherwise, returns the parsed result.
> + */
>  int git_config_int(const char *, const char *);
>  int64_t git_config_int64(const char *, const char *);
> +
> +/**
> + * Identical to `git_config_int`, but for unsigned longs.
> + */
>  unsigned long git_config_ulong(const char *, const char *);
>  ssize_t git_config_ssize_t(const char *, const char *);
> +
> +/**
> + * Same as `git_config_bool`, except that integers are returned as-is, and
> + * an `is_bool` flag is unset.
> + */
>  int git_config_bool_or_int(const char *, const char *, int *);
> +
> +/**
> + * Parse a string into a boolean value, respecting keywords like "true" and
> + * "false". Integer values are converted into true/false values (when they
> + * are non-zero or zero, respectively). Other values cause a die(). If
> + * parsing is successful, the return value is the result.
> + */
>  int git_config_bool(const char *, const char *);
> +
> +/**
> + * Allocates and copies the value string into the `dest` parameter; if no
> + * string is given, prints an error message and returns -1.
> + */
>  int git_config_string(const char **, const char *, const char *);
> +
> +/**
> + * Similar to `git_config_string`, but expands `~` or `~user` into the
> + * user's home directory when found at the beginning of the path.
> + */
>  int git_config_pathname(const char **, const char *, const char *);

I might like to see another space under this function so it's clear
that the description isn't talking about expiry, color, or
set_in_file_gently. There are other places where this comment applies,
too.

>  int git_config_expiry_date(timestamp_t *, const char *, const char *);
>  int git_config_color(char *, const char *, const char *);
>  int git_config_set_in_file_gently(const char *, const char *, const char *);
> +
> +/**
> + * write config values to a specific config file
> + * takes a key/value pair as parameter.
> + */

You could reflow this comment and some others so that they extend closer
to the end of the 80c line width; in some cases you can condense the
comment to a single line this way :)

>  void git_config_set_in_file(const char *, const char *, const char *);
>  int git_config_set_gently(const char *, const char *);
> +
> +/**
> + * write config values to `.git/config`
> + * takes a key/value pair as parameter.
> + */
>  void git_config_set(const char *, const char *);
>  int git_config_parse_key(const char *, char **, int *);
>  int git_config_key_is_valid(const char *key);
>  int git_config_set_multivar_gently(const char *, const char *, const char *, int);
>  void git_config_set_multivar(const char *, const char *, const char *, int);
>  int git_config_set_multivar_in_file_gently(const char *, const char *, const char *, const char *, int);
> +
> +/**
> + * takes four parameters:
> + *
> + * - the name of the file, as a string, to which key/value pairs will be written.
> + *
> + * - the name of key, as a string. This is in canonical "flat" form: the section,
> + *   subsection, and variable segments will be separated by dots, and the section
> + *   and variable segments will be all lowercase.
> + *   E.g., `core.ignorecase`, `diff.SomeType.textconv`.
> + *
> + * - the value of the variable, as a string. If value is equal to NULL, it will
> + *   remove the matching key from the config file.
> + *
> + * - the value regex, as a string. It will disregard key/value pairs where value
> + *   does not match.
> + *
> + * - a multi_replace value, as an int. If value is equal to zero, nothing or only
> + *   one matching key/value is replaced, else all matching key/values (regardless
> + *   how many) are removed, before the new pair is written.
> + *
> + * It returns 0 on success.
> + */
>  void git_config_set_multivar_in_file(const char *, const char *, const char *, const char *, int);
> +
> +/**
> + * rename or remove sections in the config file
> + * parameters `old_name` and `new_name`
> + * If NULL is passed through `new_name` parameter,
> + * the section will be removed from the config file.
> + */
>  int git_config_rename_section(const char *, const char *);
>  int git_config_rename_section_in_file(const char *, const char *, const char *);
>  int git_config_copy_section(const char *, const char *);
> @@ -142,6 +300,30 @@ enum config_scope current_config_scope(void);
>  const char *current_config_origin_type(void);
>  const char *current_config_name(void);
>  
> +/**
> + * Include Directives
> + * ------------------
> + *
> + * By default, the config parser does not respect include directives.
> + * However, a caller can use the special `git_config_include` wrapper
> + * callback to support them. To do so, you simply wrap your "real" callback
> + * function and data pointer in a `struct config_include_data`, and pass
> + * the wrapper to the regular config-reading functions. For example:
> + *
> + * -------------------------------------------
> + * int read_file_with_include(const char *file, config_fn_t fn, void *data)
> + * {
> + * struct config_include_data inc = CONFIG_INCLUDE_INIT;
> + * inc.fn = fn;
> + * inc.data = data;
> + * return git_config_from_file(git_config_include, file, &inc);
> + * }
> + * -------------------------------------------
> + *
> + * `git_config` respects includes automatically. The lower-level
> + * `git_config_from_file` does not.
> + *
> + */
>  struct config_include_data {
>  	int depth;
>  	config_fn_t fn;
> @@ -169,6 +351,33 @@ int parse_config_key(const char *var,
>  		     const char **subsection, int *subsection_len,
>  		     const char **key);
>  
> +/**
> + * Custom Configsets
> + * -----------------
> + *
> + * A `config_set` can be used to construct an in-memory cache for
> + * config-like files that the caller specifies (i.e., files like `.gitmodules`,
> + * `~/.gitconfig` etc.). For example,
> + *
> + * ----------------------------------------
> + * struct config_set gm_config;
> + * git_configset_init(&gm_config);
> + * int b;
> + * //we add config files to the config_set
> + * git_configset_add_file(&gm_config, ".gitmodules");
> + * git_configset_add_file(&gm_config, ".gitmodules_alt");
> + *
> + * if (!git_configset_get_bool(gm_config, "submodule.frotz.ignore", &b)) {
> + * //hack hack hack
> + * }
> + *
> + * when we are done with the configset:
> + * git_configset_clear(&gm_config);
> + * ----------------------------------------
> + *
> + * Configset API provides functions for the above mentioned work flow
> + */
> +
>  struct config_set_element {
>  	struct hashmap_entry ent;
>  	char *key;
> @@ -197,15 +406,45 @@ struct config_set {
>  	struct configset_list list;
>  };
>  
> +/**
> + * Initializes the config_set `cs`.
> + */
>  void git_configset_init(struct config_set *cs);
> +
> +/**
> + * Parses the file and adds the variable-value pairs to the `config_set`,
> + * dies if there is an error in parsing the file. Returns 0 on success, or
> + * -1 if the file does not exist or is inaccessible. The user has to decide
> + * if he wants to free the incomplete configset or continue using it when
> + * the function returns -1.
> + */
>  int git_configset_add_file(struct config_set *cs, const char *filename);
> +
> +/**
> + * Finds and returns the value list, sorted in order of increasing priority
> + * for the configuration variable `key` and config set `cs`. When the
> + * configuration variable `key` is not found, returns NULL. The caller
> + * should not free or modify the returned pointer, as it is owned by the cache.
> + */
>  const struct string_list *git_configset_get_value_multi(struct config_set *cs, const char *key);
> +
> +/**
> + * Clears `config_set` structure, removes all saved variable-value pairs.
> + */
>  void git_configset_clear(struct config_set *cs);
>  
>  /*
>   * These functions return 1 if not found, and 0 if found, leaving the found
>   * value in the 'dest' pointer.
>   */
> +
> +/*
> + * Finds the highest-priority value for the configuration variable `key`
> + * and config set `cs`, stores the pointer to it in `value` and returns 0.
> + * When the configuration variable `key` is not found, returns 1 without
> + * touching `value`. The caller should not free or modify `value`, as it
> + * is owned by the cache.
> + */
>  int git_configset_get_value(struct config_set *cs, const char *key, const char **dest);
>  int git_configset_get_string_const(struct config_set *cs, const char *key, const char **dest);
>  int git_configset_get_string(struct config_set *cs, const char *key, char **dest);
> @@ -240,16 +479,92 @@ int repo_config_get_maybe_bool(struct repository *repo,
>  int repo_config_get_pathname(struct repository *repo,
>  			     const char *key, const char **dest);
>  
> +/**
> + * Querying For Specific Variables
> + * -------------------------------
> + *
> + * For programs wanting to query for specific variables in a non-callback
> + * manner, the config API provides two functions `git_config_get_value`
> + * and `git_config_get_value_multi`. They both read values from an internal
> + * cache generated previously from reading the config files.
> + */
> +
> +/**
> + * Finds the highest-priority value for the configuration variable `key`,
> + * stores the pointer to it in `value` and returns 0. When the
> + * configuration variable `key` is not found, returns 1 without touching
> + * `value`. The caller should not free or modify `value`, as it is owned
> + * by the cache.
> + */
>  int git_config_get_value(const char *key, const char **value);
> +
> +/**
> + * Finds and returns the value list, sorted in order of increasing priority
> + * for the configuration variable `key`. When the configuration variable
> + * `key` is not found, returns NULL. The caller should not free or modify
> + * the returned pointer, as it is owned by the cache.
> + */
>  const struct string_list *git_config_get_value_multi(const char *key);
> +
> +/**
> + * Resets and invalidates the config cache.
> + */
>  void git_config_clear(void);
> +
> +/**
> + * Allocates and copies the retrieved string into the `dest` parameter for
> + * the configuration variable `key`; if NULL string is given, prints an
> + * error message and returns -1. When the configuration variable `key` is
> + * not found, returns 1 without touching `dest`.
> + */
>  int git_config_get_string_const(const char *key, const char **dest);
> +
> +/**
> + * Similar to `git_config_get_string_const`, except that retrieved value
> + * copied into the `dest` parameter is a mutable string.
> + */
>  int git_config_get_string(const char *key, char **dest);
> +
> +/**
> + * Finds and parses the value to an integer for the configuration variable
> + * `key`. Dies on error; otherwise, stores the value of the parsed integer in
> + * `dest` and returns 0. When the configuration variable `key` is not found,
> + * returns 1 without touching `dest`.
> + */
>  int git_config_get_int(const char *key, int *dest);
> +
> +/**
> + * Similar to `git_config_get_int` but for unsigned longs.
> + */
>  int git_config_get_ulong(const char *key, unsigned long *dest);
> +
> +/**
> + * Finds and parses the value into a boolean value, for the configuration
> + * variable `key` respecting keywords like "true" and "false". Integer
> + * values are converted into true/false values (when they are non-zero or
> + * zero, respectively). Other values cause a die(). If parsing is successful,
> + * stores the value of the parsed result in `dest` and returns 0. When the
> + * configuration variable `key` is not found, returns 1 without touching
> + * `dest`.
> + */
>  int git_config_get_bool(const char *key, int *dest);
> +
> +/**
> + * Similar to `git_config_get_bool`, except that integers are copied as-is,
> + * and `is_bool` flag is unset.
> + */
>  int git_config_get_bool_or_int(const char *key, int *is_bool, int *dest);
> +
> +/**
> + * Similar to `git_config_get_bool`, except that it returns -1 on error
> + * rather than dying.
> + */
>  int git_config_get_maybe_bool(const char *key, int *dest);
> +
> +/**
> + * Similar to `git_config_get_string`, but expands `~` or `~user` into
> + * the user's home directory when found at the beginning of the path.
> + */
>  int git_config_get_pathname(const char *key, const char **dest);
>  int git_config_get_index_threads(int *dest);
>  int git_config_get_untracked_cache(void);
> @@ -270,7 +585,19 @@ struct key_value_info {
>  	enum config_scope scope;
>  };
>  
> +/**
> + * First prints the error message specified by the caller in `err` and then
> + * dies printing the line number and the file name of the highest priority
> + * value for the configuration variable `key`.
> + */
>  NORETURN void git_die_config(const char *key, const char *err, ...) __attribute__((format(printf, 2, 3)));
> +
> +/**
> + * Helper function which formats the die error message according to the
> + * parameters entered. Used by `git_die_config()`. It can be used by callers
> + * handling `git_config_get_value_multi()` to print the correct error message
> + * for the desired value.
> + */
>  NORETURN void git_die_config_linenr(const char *key, const char *filename, int linenr);
>  
>  #define LOOKUP_CONFIG(mapping, var) \
> -- 
> gitgitgadget

I made a couple of smallish comments about general formatting, but I'm
also interested to know whether you were able to move the entire
contents of api-config.txt across to here. Was there anything that you
couldn't find a place for?

Thanks a lot for this change, and congrats on getting your first review
out! Welcome! :)

 - Emily