[PATCH v6 0/7] grep: simplify & delete "init" & "config" code

A simplification and code deletion of the overly complex setup for the grep API, no behavior changes. For v5 see: https://lore.kernel.org/git/cover-v5-0.7-00000000000-20211222T025214Z-avarab@gmail.com

Changes since v4:

 * As Junio pointed out there were behavior changes in the v4. I
   integrated/squashed the change he added to the
   gitster/ab/grep-patterntype branch to add the tests, and a fixed
   7/7 correctly handles the case of a flip-flopping
   grep.extendedRegexp now.

 * Some commit message additions/rewording that I hope will address
   relevant comments from Junio.

Ævar Arnfjörð Bjarmason (7):
  grep.h: remove unused "regex_t regexp" from grep_opt
  log tests: check if grep_config() is called by "log"-like cmds
  grep tests: add missing "grep.patternType" config tests
  built-ins: trust the "prefix" from run_builtin()
  grep.c: don't pass along NULL callback value
  grep API: call grep_config() after grep_init()
  grep: simplify config parsing and option parsing

 builtin/grep.c    |  27 +++++-----
 builtin/log.c     |  13 ++++-
 builtin/ls-tree.c |   2 +-
 git.c             |   1 +
 grep.c            | 126 +++++++++-------------------------------------
 grep.h            |  33 ++++++++----
 revision.c        |   4 +-
 t/t4202-log.sh    |  24 +++++++++
 t/t7810-grep.sh   |  39 ++++++++++++++
 9 files changed, 138 insertions(+), 131 deletions(-)

Range-diff against v5:
1:  b6a3e0e2e08 = 1:  b62e6b6162a grep.h: remove unused "regex_t regexp" from grep_opt
2:  c0d77b2683f = 2:  0edcdb50afd log tests: check if grep_config() is called by "log"-like cmds
3:  f02f246aa23 ! 3:  1b724d5e2e9 grep tests: add missing "grep.patternType" config test
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    grep tests: add missing "grep.patternType" config test
    +    grep tests: add missing "grep.patternType" config tests
     
         Extend the grep tests to assert that setting
         "grep.patternType=extended" followed by "grep.patternType=default"
    @@ Commit message
     
         Let's also test what happens when we have a sequence of "extended"
         followed by "default" and "fixed". In that case the "fixed" should
    -    prevail.
    +    prevail, as well as tests to check that a "grep.extendedRegexp=true"
    +    followed by a "grep.extendedRegexp=false" behaves as though
    +    "grep.extendedRegexp" wasn't provided.
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
    +    Signed-off-by: Junio C Hamano <gitster@pobox.com>
     
      ## t/t7810-grep.sh ##
     @@ t/t7810-grep.sh: do
      		test_cmp expected actual
      	'
      
    ++	test_expect_success "grep $L with grep.extendedRegexp is last-one-wins" '
    ++		echo "${HC}ab:a+bc" >expected &&
    ++		git \
    ++			-c grep.extendedRegexp=true \
    ++			-c grep.patternType=basic \
    ++			-c grep.extendedRegexp=false \
    ++			grep "a+b*c" $H ab >actual &&
    ++		test_cmp expected actual
    ++	'
    ++
    ++	test_expect_success "grep $L with grep.extendedRegexp is last-one-wins & defers to grep.patternType" '
    ++		echo "${HC}ab:abc" >expected &&
    ++		git \
    ++			-c grep.extendedRegexp=true \
    ++			-c grep.patternType=extended \
    ++			-c grep.extendedRegexp=false \
    ++			grep "a+b*c" $H ab >actual &&
    ++		test_cmp expected actual
    ++	'
    ++
     +	test_expect_success "grep $L with grep.patternType=extended and grep.patternType=default" '
     +		echo "${HC}ab:a+bc" >expected &&
     +		git \
4:  a542a352eab = 4:  f4876552771 built-ins: trust the "prefix" from run_builtin()
5:  a33b00a247e = 5:  069b0339146 grep.c: don't pass along NULL callback value
6:  92b1c3958fa = 6:  e38eca56959 grep API: call grep_config() after grep_init()
7:  63de643ebc2 ! 7:  88dfd40bf9e grep: simplify config parsing and option parsing
    @@ Commit message
          1. You can set "grep.patternType", and "[setting it to] 'default'
             will return to the default matching behavior".
     
    +        In that context "the default" meant whatever the configuration
    +        system specified before that change, i.e. via grep.extendedRegexp.
    +
          2. We'd support the existing "grep.extendedRegexp" option, but ignore
             it when the new "grep.patternType" option is set. We said we'd
             only ignore the older "grep.extendedRegexp" option "when the
    @@ Commit message
         grep_init(), which means that much of the complexity here can go
         away.
     
    -    Now as before when we only understand a "grep.extendedRegexp" setting
    -    of "true", and if "grep.patterntype=default" is set we'll interpret it
    -    as "grep.patterntype=basic", except if we previously saw a
    -    "grep.extendedRegexp", then it's interpreted as
    -    "grep.patterntype=extended".
    +    As before "grep.extendedRegexp" is a last-one-wins variable. We need
    +    to maintain state inside parse_pattern_type_arg() to ignore it if a
    +    non-"default" grep.patternType was seen, but otherwise flip between
    +    BRE and ERE for "grep.extendedRegexp=[false|true]".
     
         See my 07a3d411739 (grep: remove regflags from the public grep_opt
         API, 2017-06-29) for addition of the two comments being removed here,
    @@ grep.c: int grep_config(const char *var, const char *value, void *cb)
      		return -1;
      
      	if (!strcmp(var, "grep.extendedregexp")) {
    -+		if (opt->extended_regexp_option)
    ++		if (opt->extended_regexp_option == -1)
     +			return 0;
      		opt->extended_regexp_option = git_config_bool(var, value);
     +		if (opt->extended_regexp_option)
     +			opt->pattern_type_option = GREP_PATTERN_TYPE_ERE;
    ++		else
    ++			opt->pattern_type_option = GREP_PATTERN_TYPE_BRE;
     +		return 0;
     +	}
     +