bugreport: summarize contents of alternates file

In some cases, it could be that the user is having a problem with an
object which isn't present in their normal object directory. We can get
a hint that that might be the case by examining the list of alternates
where their object may be stored instead. Since paths to alternates may
be sensitive, we'll instead count how many alternates have been
specified and note how many of them exist or are broken.

While object-cache.h describes a function "foreach_alt_odb()", this
function does not provide information on broken alternates, which are
skipped over in "link_alt_odb_entry()". Since the goal is to identify
missing alternates, we can gather the contents of
.git/objects/info/alternates manually.

Signed-off-by: Emily Shaffer <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: nasamuffin

Documentation/git-bugreport.txt

@@ -35,6 +35,7 @@ The following information is captured automatically:
  - The number of loose objects in the repository
  - The number of packs and packed objects in the repository
  - A list of the contents of .git/objects/info (or equivalent)
+ - The number of valid and invalid alternates
 
 This tool is invoked via the typical Git setup process, which means that in some
 cases, it might not be able to launch - for example, if a relevant config file

bugreport.c

@@ -255,6 +255,48 @@ static void get_object_info_summary(struct strbuf *obj_info, int nongit)
 	strbuf_release(&dirpath);
 }
 
+static void get_alternates_summary(struct strbuf *alternates_info, int nongit)
+{
+	struct strbuf alternates_path = STRBUF_INIT;
+	struct strbuf alternate = STRBUF_INIT;
+	FILE *file;
+	size_t exists = 0, broken = 0;
+
+	if (nongit) {
+		strbuf_addstr(alternates_info,
+			"not run from a git repository - alternates unavailable\n");
+		return;
+	}
+
+	strbuf_addstr(&alternates_path, get_object_directory());
+	strbuf_complete(&alternates_path, '/');
+	strbuf_addstr(&alternates_path, "info/alternates");
+
+	file = fopen(alternates_path.buf, "r");
+	if (!file) {
+		strbuf_addstr(alternates_info, "No alternates file found.\n");
+		strbuf_release(&alternates_path);
+		return;
+	}
+
+	while (strbuf_getline(&alternate, file) != EOF) {
+		if (!access(alternate.buf, F_OK))
+			exists++;
+		else
+			broken++;
+	}
+
+	strbuf_addf(alternates_info,
+		    "%zd alternates found (%zd working, %zd broken)\n",
+		    exists + broken,
+		    exists,
+		    broken);
+
+	fclose(file);
+	strbuf_release(&alternate);
+	strbuf_release(&alternates_path);
+}
+
 static const char * const bugreport_usage[] = {
 	N_("git bugreport [-o|--output-directory <file>] [-s|--suffix <format>]"),
 	NULL
@@ -355,6 +397,9 @@ int cmd_main(int argc, const char **argv)
 	get_header(&buffer, "Object Info Summary");
 	get_object_info_summary(&buffer, nongit_ok);
 
+	get_header(&buffer, "Alternates");
+	get_alternates_summary(&buffer, nongit_ok);
+
 	report = fopen_for_writing(report_path.buf);
 
 	if (report == NULL) {