Fix the fedora-breaking-changes CI job failures (#900)

I noticed today that the `fedora-breaking-changes` job started
[failing](backport-fedora-breaking-changes-fix):

```
[...]
  In file included from ../common-main.c:1:
  ../git-compat-util.h: In function ‘git_find_last_dir_sep’:
  Error: ../git-compat-util.h:353:16: return discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
    353 |         return strrchr(path, '/');
        |                ^~~~~~~
  cc1: all warnings being treated as errors
```

This is new, I had not seen this before. The reason that this did not
fail earlier is that this CI job used to [use Fedora
43](https://github.com/microsoft/git/actions/runs/24733807372/job/72355187872#step:2:38),
where it succeeded, whereas now it [uses Fedora
44](https://github.com/microsoft/git/actions/runs/25038293016/job/73335043533#step:2:38),
where it fails.

Lucky for us, upstream Git already has fixes for this issue & related
ones, in [the `cf/constness-fixes`
branch](gitgitgadget/git@v2.52.0...cf/constness-fixes),
[the `cf/c23-const-preserving-strchr-updates-0
`
branch](gitgitgadget/git@v2.53.0...cf/c23-const-preserving-strchr-updates-0
), [the `jk/c23-const-preserving-fixes-more`
branch](gitgitgadget/git@270e10a...jk/c23-const-preserving-fixes-more),
[the `jk/c23-const-preserving-fixes`
branch](gitgitgadget/git@41688c1...jk/c23-const-preserving-fixes),
[the `jk/ref-filter-lrstrip-optim`
branch](gitgitgadget/git@v2.53.0...jk/ref-filter-lrstrip-optim)
and [the `ps/history-ergonomics-updates`
branch](gitgitgadget/git@453e7b7...ps/history-ergonomics-updates),
which I hereby backport to the `vfs-2.53.0` branch.

Author: dscho

add-patch.c

@@ -342,7 +342,7 @@ static int parse_hunk_header(struct add_p_state *s, struct hunk *hunk)
 {
 	struct hunk_header *header = &hunk->header;
 	const char *line = s->plain.buf + hunk->start, *p = line;
-	char *eol = memchr(p, '\n', s->plain.len - hunk->start);
+	const char *eol = memchr(p, '\n', s->plain.len - hunk->start);
 
 	if (!eol)
 		eol = s->plain.buf + s->plain.len;

apply.c

@@ -4164,7 +4164,7 @@ static int preimage_oid_in_gitlink_patch(struct patch *p, struct object_id *oid)
 	 */
 	struct fragment *hunk = p->fragments;
 	static const char heading[] = "-Subproject commit ";
-	char *preimage;
+	const char *preimage;
 
 	if (/* does the patch have only one hunk? */
 	    hunk && !hunk->next &&

bloom.c

@@ -501,7 +501,7 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
 		struct hashmap_iter iter;
 
 		for (i = 0; i < diff_queued_diff.nr; i++) {
-			const char *path = diff_queued_diff.queue[i]->two->path;
+			char *path = diff_queued_diff.queue[i]->two->path;
 
 			/*
 			 * Add each leading directory of the changed file, i.e. for
@@ -523,7 +523,7 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
 					free(e);
 
 				if (!last_slash)
-					last_slash = (char*)path;
+					last_slash = path;
 				*last_slash = '\0';
 
 			} while (*path);

builtin/commit.c

@@ -933,7 +933,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 				  logfile);
 		hook_arg1 = "message";
 	} else if (use_message) {
-		char *buffer;
+		const char *buffer;
 		buffer = strstr(use_message_buffer, "\n\n");
 		if (buffer)
 			strbuf_addstr(&sb, skip_blank_lines(buffer + 2));

builtin/config.c

@@ -838,6 +838,7 @@ static int get_urlmatch(const struct config_location_options *opts,
 			const char *var, const char *url)
 {
 	int ret;
+	char *section;
 	char *section_tail;
 	struct config_display_options display_opts = *_display_opts;
 	struct string_list_item *item;
@@ -851,8 +852,8 @@ static int get_urlmatch(const struct config_location_options *opts,
 	if (!url_normalize(url, &config.url))
 		die("%s", config.url.err);
 
-	config.section = xstrdup_tolower(var);
-	section_tail = strchr(config.section, '.');
+	config.section = section = xstrdup_tolower(var);
+	section_tail = strchr(section, '.');
 	if (section_tail) {
 		*section_tail = '\0';
 		config.key = section_tail + 1;
@@ -886,7 +887,7 @@ static int get_urlmatch(const struct config_location_options *opts,
 	string_list_clear(&values, 1);
 	free(config.url.url);
 
-	free((void *)config.section);
+	free(section);
 	return ret;
 }
 

builtin/receive-pack.c

@@ -393,7 +393,7 @@ struct command {
 static void proc_receive_ref_append(const char *prefix)
 {
 	struct proc_receive_ref *ref_pattern;
-	char *p;
+	const char *p;
 	int len;
 
 	CALLOC_ARRAY(ref_pattern, 1);
@@ -989,8 +989,8 @@ static int read_proc_receive_report(struct packet_reader *reader,
 
 	for (;;) {
 		struct object_id old_oid, new_oid;
-		const char *head;
-		const char *refname;
+		char *head;
+		char *refname;
 		char *p;
 		enum packet_read_status status;
 
@@ -1014,7 +1014,8 @@ static int read_proc_receive_report(struct packet_reader *reader,
 		}
 		*p++ = '\0';
 		if (!strcmp(head, "option")) {
-			const char *key, *val;
+			char *key;
+			const char *val;
 
 			if (!hint || !(report || new_report)) {
 				if (!once++)

builtin/remote.c

@@ -332,7 +332,7 @@ static int config_read_branches(const char *key, const char *value,
 		info->remote_name = xstrdup(value);
 		break;
 	case MERGE: {
-		char *space = strchr(value, ' ');
+		const char *space = strchr(value, ' ');
 		value = abbrev_branch(value);
 		while (space) {
 			char *merge;

builtin/rev-parse.c

@@ -267,21 +267,20 @@ static int show_file(const char *arg, int output_prefix)
 
 static int try_difference(const char *arg)
 {
-	char *dotdot;
+	const char *dotdot;
 	struct object_id start_oid;
 	struct object_id end_oid;
 	const char *end;
 	const char *start;
+	char *to_free;
 	int symmetric;
 	static const char head_by_default[] = "HEAD";
 
 	if (!(dotdot = strstr(arg, "..")))
 		return 0;
+	start = to_free = xmemdupz(arg, dotdot - arg);
 	end = dotdot + 2;
-	start = arg;
 	symmetric = (*end == '.');
-
-	*dotdot = 0;
 	end += symmetric;
 
 	if (!*end)
@@ -295,7 +294,7 @@ static int try_difference(const char *arg)
 		 * Just ".."?  That is not a range but the
 		 * pathspec for the parent directory.
 		 */
-		*dotdot = '.';
+		free(to_free);
 		return 0;
 	}
 
@@ -308,7 +307,7 @@ static int try_difference(const char *arg)
 			a = lookup_commit_reference(the_repository, &start_oid);
 			b = lookup_commit_reference(the_repository, &end_oid);
 			if (!a || !b) {
-				*dotdot = '.';
+				free(to_free);
 				return 0;
 			}
 			if (repo_get_merge_bases(the_repository, a, b, &exclude) < 0)
@@ -318,55 +317,56 @@ static int try_difference(const char *arg)
 				show_rev(REVERSED, &commit->object.oid, NULL);
 			}
 		}
-		*dotdot = '.';
+		free(to_free);
 		return 1;
 	}
-	*dotdot = '.';
+	free(to_free);
 	return 0;
 }
 
 static int try_parent_shorthands(const char *arg)
 {
-	char *dotdot;
+	const char *mark;
 	struct object_id oid;
 	struct commit *commit;
 	struct commit_list *parents;
 	int parent_number;
 	int include_rev = 0;
 	int include_parents = 0;
 	int exclude_parent = 0;
+	char *to_free;
 
-	if ((dotdot = strstr(arg, "^!"))) {
+	if ((mark = strstr(arg, "^!"))) {
 		include_rev = 1;
-		if (dotdot[2])
+		if (mark[2])
 			return 0;
-	} else if ((dotdot = strstr(arg, "^@"))) {
+	} else if ((mark = strstr(arg, "^@"))) {
 		include_parents = 1;
-		if (dotdot[2])
+		if (mark[2])
 			return 0;
-	} else if ((dotdot = strstr(arg, "^-"))) {
+	} else if ((mark = strstr(arg, "^-"))) {
 		include_rev = 1;
 		exclude_parent = 1;
 
-		if (dotdot[2]) {
+		if (mark[2]) {
 			char *end;
-			exclude_parent = strtoul(dotdot + 2, &end, 10);
+			exclude_parent = strtoul(mark + 2, &end, 10);
 			if (*end != '\0' || !exclude_parent)
 				return 0;
 		}
 	} else
 		return 0;
 
-	*dotdot = 0;
+	arg = to_free = xmemdupz(arg, mark - arg);
 	if (repo_get_oid_committish(the_repository, arg, &oid) ||
 	    !(commit = lookup_commit_reference(the_repository, &oid))) {
-		*dotdot = '^';
+		free(to_free);
 		return 0;
 	}
 
 	if (exclude_parent &&
 	    exclude_parent > commit_list_count(commit->parents)) {
-		*dotdot = '^';
+		free(to_free);
 		return 0;
 	}
 
@@ -387,7 +387,7 @@ static int try_parent_shorthands(const char *arg)
 		free(name);
 	}
 
-	*dotdot = '^';
+	free(to_free);
 	return 1;
 }
 

builtin/shortlog.c

@@ -76,7 +76,7 @@ static void insert_one_record(struct shortlog *log,
 		if (!eol)
 			eol = oneline + strlen(oneline);
 		if (starts_with(oneline, "[PATCH")) {
-			char *eob = strchr(oneline, ']');
+			const char *eob = strchr(oneline, ']');
 			if (eob && (!eol || eob < eol))
 				oneline = eob + 1;
 		}

config.c

@@ -162,7 +162,7 @@ static int handle_path_include(const struct key_value_info *kvi,
 	 * based on the including config file.
 	 */
 	if (!is_absolute_path(path)) {
-		char *slash;
+		const char *slash;
 
 		if (!kvi || kvi->origin_type != CONFIG_ORIGIN_FILE) {
 			ret = error(_("relative config includes must come from files"));