[PATCH v2] maintenance --unregister: fix uninit'd data use & -Wdeclaration-after-statement

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Since (maintenance: add option to register in a specific config,
2022-11-09) we've been unable to build with "DEVELOPER=1" without
"DEVOPTS=no-error", as the added code triggers a
"-Wdeclaration-after-statement" warning.

And worse than that, the data handed to git_configset_clear() is
uninitialized, as can be spotted with e.g.:

	./t7900-maintenance.sh -vixd --run=23 --valgrind
	[...]
	+ git maintenance unregister --force
	Conditional jump or move depends on uninitialised value(s)
	   at 0x6B5F1E: git_configset_clear (config.c:2367)
	   by 0x4BA64E: maintenance_unregister (gc.c:1619)
	   by 0x4BD278: cmd_maintenance (gc.c:2650)
	   by 0x409905: run_builtin (git.c:466)
	   by 0x40A21C: handle_builtin (git.c:721)
	   by 0x40A58E: run_argv (git.c:788)
	   by 0x40AF68: cmd_main (git.c:926)
	   by 0x5D39FE: main (common-main.c:57)
	 Uninitialised value was created by a stack allocation
	   at 0x4BA22C: maintenance_unregister (gc.c:1557)

Let's fix both of these issues, and also move the scope of the
variable to the "if" statement it's used in, to make it obvious where
it's used.

Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
Range-diff against v1:
1:  54d405f15f1 ! 1:  f37e99c9d59 builtin/gc.c: fix -Wdeclaration-after-statement
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    builtin/gc.c: fix -Wdeclaration-after-statement
    +    maintenance --unregister: fix uninit'd data use & -Wdeclaration-after-statement
     
    -    In 1f80129d61b (maintenance: add option to register in a specific
    -    config, 2022-11-09) code was added which triggers a
    -    "-Wdeclaration-after-statement" warning, which is on by default with
    -    DEVELOPER=1.
    +    Since (maintenance: add option to register in a specific config,
    +    2022-11-09) we've been unable to build with "DEVELOPER=1" without
    +    "DEVOPTS=no-error", as the added code triggers a
    +    "-Wdeclaration-after-statement" warning.
     
    +    And worse than that, the data handed to git_configset_clear() is
    +    uninitialized, as can be spotted with e.g.:
    +
    +            ./t7900-maintenance.sh -vixd --run=23 --valgrind
    +            [...]
    +            + git maintenance unregister --force
    +            Conditional jump or move depends on uninitialised value(s)
    +               at 0x6B5F1E: git_configset_clear (config.c:2367)
    +               by 0x4BA64E: maintenance_unregister (gc.c:1619)
    +               by 0x4BD278: cmd_maintenance (gc.c:2650)
    +               by 0x409905: run_builtin (git.c:466)
    +               by 0x40A21C: handle_builtin (git.c:721)
    +               by 0x40A58E: run_argv (git.c:788)
    +               by 0x40AF68: cmd_main (git.c:926)
    +               by 0x5D39FE: main (common-main.c:57)
    +             Uninitialised value was created by a stack allocation
    +               at 0x4BA22C: maintenance_unregister (gc.c:1557)
    +
    +    Let's fix both of these issues, and also move the scope of the
    +    variable to the "if" statement it's used in, to make it obvious where
    +    it's used.
    +
    +    Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## builtin/gc.c ##
    -@@ builtin/gc.c: static int maintenance_unregister(int argc, const char **argv, const char *prefi
    - 	int found = 0;
    - 	struct string_list_item *item;
    - 	const struct string_list *list;
    -+	struct config_set cs;
    - 
    - 	argc = parse_options(argc, argv, prefix, options,
    - 			     builtin_maintenance_unregister_usage, 0);
     @@ builtin/gc.c: static int maintenance_unregister(int argc, const char **argv, const char *prefi
      		usage_with_options(builtin_maintenance_unregister_usage,
      				   options);
      
     -	struct config_set cs;
      	if (config_file) {
    ++		struct config_set cs;
    ++
      		git_configset_init(&cs);
      		git_configset_add_file(&cs, config_file);
    + 		list = git_configset_get_value_multi(&cs, key);
    ++		git_configset_clear(&cs);
    + 	} else {
    + 		list = git_config_get_value_multi(key);
    + 	}
    +@@ builtin/gc.c: static int maintenance_unregister(int argc, const char **argv, const char *prefi
    + 		die(_("repository '%s' is not registered"), maintpath);
    + 	}
    + 
    +-	git_configset_clear(&cs);
    + 	free(maintpath);
    + 	return 0;
    + }

 builtin/gc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 56b107e7f0b..d87cf84041f 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1550,11 +1550,13 @@ static int maintenance_unregister(int argc, const char **argv, const char *prefi
 		usage_with_options(builtin_maintenance_unregister_usage,
 				   options);
 
-	struct config_set cs;
 	if (config_file) {
+		struct config_set cs;
+
 		git_configset_init(&cs);
 		git_configset_add_file(&cs, config_file);
 		list = git_configset_get_value_multi(&cs, key);
+		git_configset_clear(&cs);
 	} else {
 		list = git_config_get_value_multi(key);
 	}
@@ -1590,7 +1592,6 @@ static int maintenance_unregister(int argc, const char **argv, const char *prefi
 		die(_("repository '%s' is not registered"), maintpath);
 	}
 
-	git_configset_clear(&cs);
 	free(maintpath);
 	return 0;
 }
-- 
2.38.0.1473.g172bcc0511c