[Outreachy PATCH] var: refactor to use parse-options API

[kerylefondji7@gmail.com]

From: kerylefondji <kerylefondji7@gmail.com>

Refactor 'git var' command handling to use an existing API (parse-options API)
instead of ad hoc code for argument parsing.

Previously, the ad hoc code lacked proper validation for option
combinations. Specifically, listing all variables (-l) and requesting a
specific variable name are mutually exclusive operations, but the code
did not enforce this restriction, causing test failures.

This change:
- Includes the parse-options.h header and defines builtin_var_options.
- Adds an explicit check to ensure that combining '-l' with additional
  positional arguments correctly triggers a usage error.

All 27 automated tests in t0007-git-var.sh pass successfully.
---
 builtin/var.c | 50 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/builtin/var.c b/builtin/var.c
index cc3a43cde2..20ea4e0489 100644
--- a/builtin/var.c
+++ b/builtin/var.c
@@ -18,8 +18,11 @@
 #include "path.h"
 #include "strbuf.h"
 #include "run-command.h"
-
-static const char var_usage[] = "git var (-l | <variable>)";
+#include "parse-options.h"
+static const char * const var_usage[] = {
+	N_("git var (-l | <variable>)"),
+	NULL
+};
 
 static char *committer(int ident_flag)
 {
@@ -220,22 +223,39 @@ int cmd_var(int argc,
 	    struct repository *repo UNUSED)
 {
 	const struct git_var *git_var;
-	char *val;
+        char *val;
+        int list = 0; /* Flag to track if -l/--list option is used */
 
-	show_usage_if_asked(argc, argv, var_usage);
-	if (argc != 2)
-		usage(var_usage);
+        /* Define the accepted command-line options */
+        struct option builtin_var_options[] = {
+                OPT_BOOL('l', "list", &list, N_("list builtin variables")),
+                OPT_END()
+        };
 
-	if (strcmp(argv[1], "-l") == 0) {
-		repo_config(the_repository, show_config, NULL);
-		list_vars();
-		return 0;
-	}
-	repo_config(the_repository, git_default_config, NULL);
+        /* Parse options using the standard API */
+        argc = parse_options(argc, argv, prefix, builtin_var_options,
+                             var_usage, 0);
+
+        /* If the user requested to list all variables (-l) */
+       
+if (list) {
+    if (argc > 0)
+        usage(var_usage[0]);
+    repo_config(the_repository, show_config, NULL);
+    list_vars();
+    return 0;
+}
+
+        /* Ensure only one positional argument (the variable name) remains */
+        if (argc != 1)
+                usage(var_usage[0]);
+
+        repo_config(the_repository, git_default_config, NULL);
 
-	git_var = get_git_var(argv[1]);
-	if (!git_var)
-		usage(var_usage);
+        /* Retrieve the specific git variable (note: now at argv[0] after parsing) */
+        git_var = get_git_var(argv[0]);
+        if (!git_var)
+                usage(var_usage[0]);
 
 	val = git_var->read(IDENT_STRICT);
 	if (!val)
-- 
2.53.0