[PATCH v2 0/8] grep: simplify & delete code by changing obscure cfg variable behavior

This series changes the behavior of an obscure interaction between "grep.extendedRegexp=true" and "grep.patternType=default". See 7-8/8. Along the way we can delete a lot of code that was needed to support the previous behavior.

For v1 and a more extensive summary see [1]. Thanks a lot Taylor for the detailed review on v1!

Hopefully this v1 addresses all the feedback on one way or another, it's still 8 patches, but much of the early part of v1 is squashed together & re-done as suggested.

Then there's a mid-series de-duplication of the grep config documentation. I ended up keeping the change to not needlessly pass "cb" around in grep_cmd_config(), but that's now also in its own patch.

1. https://lore.kernel.org/git/cover-0.8-00000000000-20211106T210711Z-avarab@gmail.com/

Ævar Arnfjörð Bjarmason (8):
  grep.h: remove unused "regex_t regexp" from grep_opt
  built-ins: trust the "prefix" from run_builtin()
  log tests: check if grep_config() is called by "log"-like cmds
  grep docs: de-duplicate configuration sections
  grep.c: don't pass along NULL callback value
  grep API: call grep_config() after grep_init()
  grep: simplify config parsing, change grep.<rx config> interaction
  grep: make "extendedRegexp=true" the same as "patternType=extended"

 Documentation/config/grep.txt |  11 ++--
 Documentation/git-grep.txt    |  30 +--------
 builtin/grep.c                |  27 ++++----
 builtin/log.c                 |  13 +++-
 builtin/ls-tree.c             |   9 ++-
 git.c                         |   4 +-
 grep.c                        | 118 ++++------------------------------
 grep.h                        |  35 ++++++----
 revision.c                    |   4 +-
 t/t4202-log.sh                |  16 +++++
 t/t7810-grep.sh               |   4 +-
 11 files changed, 97 insertions(+), 174 deletions(-)

Range-diff against v1:
1:  412b8b65266 = 1:  1435db727ef grep.h: remove unused "regex_t regexp" from grep_opt
2:  244715e3497 < -:  ----------- git.c & grep.c: assert that "prefix" is NULL or non-zero string
3:  3338cc95b81 < -:  ----------- grep: remove unused "prefix_length" member
4:  78298657d69 < -:  ----------- grep.c: move "prefix" out of "struct grep_opt"
-:  ----------- > 2:  63cf2fe266d built-ins: trust the "prefix" from run_builtin()
5:  ba9be0b9283 = 3:  41e38ebb32c log tests: check if grep_config() is called by "log"-like cmds
-:  ----------- > 4:  efe95397d72 grep docs: de-duplicate configuration sections
-:  ----------- > 5:  d0f0ac6c7ae grep.c: don't pass along NULL callback value
6:  933ac853bca ! 6:  917944f79a5 grep API: call grep_config() after grep_init()
    @@ Commit message
         didn't do that, but now that it can't be a concern anymore let's
         remove those comments.
     
    +    This does not change the behavior of any of the configuration
    +    variables or options. That would have been the case if we didn't move
    +    around the grep_config() call in "builtin/log.c". But now that we call
    +    "grep_config" after "git_log_config" and "git_format_config" we'll
    +    need to pass in the already initialized "struct grep_opt *".
    +
         See 6ba9bb76e02 (grep: copy struct in one fell swoop, 2020-11-29) and
         7687a0541e0 (grep: move the configuration parsing logic to grep.[ch],
         2012-10-09) for the commits that added the comments.
     
    +    The memcpy() pattern here will be optimized away and follows the
    +    convention of other *_init() functions. See 5726a6b4012 (*.c *_init():
    +    define in terms of corresponding *_INIT macro, 2021-07-01).
    +
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## builtin/grep.c ##
     @@ builtin/grep.c: static int wait_all(void)
    + 
      static int grep_cmd_config(const char *var, const char *value, void *cb)
      {
    - 	int st = grep_config(var, value, cb);
    --	if (git_color_default_config(var, value, cb) < 0)
    -+	if (git_color_default_config(var, value, NULL) < 0)
    +-	int st = grep_config(var, value, NULL);
    ++	int st = grep_config(var, value, cb);
    + 	if (git_color_default_config(var, value, NULL) < 0)
      		st = -1;
      
    - 	if (!strcmp(var, "grep.threads")) {
     @@ builtin/grep.c: int cmd_grep(int argc, const char **argv, const char *prefix)
    - 		OPT_END()
      	};
    + 	grep_prefix = prefix;
      
     -	git_config(grep_cmd_config, NULL);
      	grep_init(&opt, the_repository);
     +	git_config(grep_cmd_config, &opt);
    - 	opt.caller_priv = &opt_cmd;
      
      	/*
    + 	 * If there is no -- then the paths must exist in the working
     
      ## builtin/log.c ##
     @@ builtin/log.c: static int git_log_config(const char *var, const char *value, void *cb)
    @@ grep.c: int grep_config(const char *var, const char *value, void *cb)
     
      ## grep.h ##
     @@ grep.h: struct grep_opt {
    + 	int show_hunk_mark;
    + 	int file_break;
    + 	int heading;
    ++	void *caller_priv;
    + 	void *priv;
    + 
    + 	void (*output)(struct grep_opt *opt, const void *data, size_t size);
      	void *output_priv;
      };
      
7:  677a8f8520f ! 7:  140a7416223 grep: simplify config parsing, change grep.<rx config> interaction
    @@ Commit message
         but in a way that's consistent with how we parse other
         configuration.
     
    -    Pedantically speaking we're probably breaking past promises here, but
    -    I doubt that this will impact anyone in practice. The reduction in
    -    complexity and resulting consistency with other default config
    -    behavior is worth it.
    +    We are breaking past promises here, but I doubt that this will impact
    +    anyone in practice. The reduction in complexity and resulting
    +    consistency with other default config behavior is worth it.
     
         When "grep.patternType" was introduced in 84befcd0a4a (grep: add a
         grep.patternType configuration setting, 2012-08-03) we made two
    @@ Commit message
             # BRE grep
             git -c grep.extendedRegexp=true -c grep.patternType=basic grep <pattern>
     
    -    But probably not for this to ignore the new "grep.patternType" option
    -    entirely, say if /etc/gitconfig was still setting
    +    But probably not for this to ignore the favored "grep.patternType"
    +    option entirely, say if /etc/gitconfig was still setting
         "grep.extendedRegexp", but "~/.gitconfig" used the new
         "grep.patternType" (and wanted to use the "default" value):
     
    @@ Documentation/config/grep.txt: grep.patternType::
      	If set to true, enable `--extended-regexp` option by default. This
     -	option is ignored when the `grep.patternType` option is set to a value
     -	other than 'default'.
    -+	option is ignored when the `grep.patternType` option is set.
    - 
    - grep.threads::
    - 	Number of grep worker threads to use.
    -
    - ## Documentation/git-grep.txt ##
    -@@ Documentation/git-grep.txt: grep.patternType::
    - 
    - grep.extendedRegexp::
    - 	If set to true, enable `--extended-regexp` option by default. This
    --	option is ignored when the `grep.patternType` option is set to a value
    --	other than 'default'.
     +	option is ignored when the `grep.patternType` option is set.
      
      grep.threads::
8:  dadd5dff77a ! 8:  cc904d93b26 grep: make "extendedRegexp=true" the same as "patternType=extended"
    @@ Documentation/config/grep.txt: grep.patternType::
      grep.extendedRegexp::
     -	If set to true, enable `--extended-regexp` option by default. This
     -	option is ignored when the `grep.patternType` option is set.
    -+	Deprecated synonym for 'grep.patternType=extended`.
    - 
    - grep.threads::
    - 	Number of grep worker threads to use.
    -
    - ## Documentation/git-grep.txt ##
    -@@ Documentation/git-grep.txt: grep.patternType::
    - 	value 'default' will return to the default matching behavior.
    - 
    - grep.extendedRegexp::
    --	If set to true, enable `--extended-regexp` option by default. This
    --	option is ignored when the `grep.patternType` option is set.
     +	Deprecated synonym for 'grep.patternType=extended`.
      
      grep.threads::
    @@ grep.h: struct grep_opt {
      	.colors = { \
      		[GREP_COLOR_CONTEXT] = "", \
      		[GREP_COLOR_FILENAME] = "", \
    -@@ grep.h: struct grep_opt {
    - 		[GREP_COLOR_SELECTED] = "", \
    - 		[GREP_COLOR_SEP] = GIT_COLOR_CYAN, \
    - 	}, \
    --	.only_matching = 0, \
    - 	.color = -1, \
    - 	.output = std_output, \
    - }
     
      ## t/t7810-grep.sh ##
     @@ t/t7810-grep.sh: do