[RFC PATCH 21/21] usage API: add "core.usageAddSource" config to add <file>:<line>

@@ -101,6 +101,13 @@ core.untrackedCache::
 	`feature.manyFiles` is enabled which sets this setting to
 	`true` by default.
 
+core.usageAddSource::
+	Adds the source "<file>:<line>" numbers to usage messages
+	("usage:", "fatal:", "error:", "warning:"). This setting is
+	primarily intended for those debugging or developing git
+	itself, or to compose a bug report against git itself (see
+	linkgit:git-bugreport[1]).
+
 core.checkStat::
 	When missing or is set to `default`, many fields in the stat
 	structure are checked to detect if a file has been modified

@@ -10,6 +10,15 @@ static void repo_cfg_bool(struct repository *r, const char *key, int *dest,
 		*dest = def;
 }
 
+static void repo_cfg_bool_env(struct repository *r, const char *env,
+			      const char *key, int *dest, int def)
+{
+	*dest = git_env_bool(env, -1);
+	if (*dest != -1)
+		return;
+	repo_cfg_bool(r, key, dest, def);
+}
+
 void prepare_repo_settings(struct repository *r)
 {
 	int experimental;

@@ -45,6 +54,8 @@ void prepare_repo_settings(struct repository *r)
 	repo_cfg_bool(r, "fetch.writecommitgraph", &r->settings.fetch_write_commit_graph, 0);
 	repo_cfg_bool(r, "pack.usesparse", &r->settings.pack_use_sparse, 1);
 	repo_cfg_bool(r, "core.multipackindex", &r->settings.core_multi_pack_index, 1);
+	repo_cfg_bool_env(r, "GIT_TEST_USAGE_ADD_SOURCE", "core.usageaddsource",
+			  &r->settings.usage_add_source, 0);
 	repo_cfg_bool(r, "index.sparse", &r->settings.sparse_index, 0);
 
 	/*

@@ -41,6 +41,8 @@ struct repo_settings {
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
 
 	int core_multi_pack_index;
+
+	int usage_add_source;
 };
 
 struct repository {

@@ -5,6 +5,7 @@
  */
 #include "git-compat-util.h"
 #include "cache.h"
+#include "config.h"
 
 enum usage_kind {
 	USAGE_USAGE,

@@ -14,6 +15,8 @@ enum usage_kind {
 	USAGE_BUG,
 };
 
+static int dying;
+
 static void vreportf(enum usage_kind kind,
 		     const char *file, int line,
 		     const char *err, va_list params)

@@ -23,6 +26,24 @@ static void vreportf(enum usage_kind kind,
 	char msg[4096];
 	char *p, *pend = msg + sizeof(msg);
 	size_t prefix_len;
+	static int addln = -1;
+
+	if (addln < 0 && dying <= 1) {
+		struct repository *r = the_repository;
+		prepare_repo_settings(r);
+		addln = r->settings.usage_add_source;
+	} else if (addln < 0 && dying) {
+		/*
+		 * We're already dying when trying to read our config,
+		 * presumably via prepare_repo_settings(). Do a
+		 * last-ditch effort of trying to get it from the
+		 * environment.
+		 */
+		const char *v = getenv("GIT_TEST_USAGE_ADD_SOURCE");
+		addln = v ? git_parse_maybe_bool(v) : 0;
+		if (addln < 1)
+			addln = 0;
+	}
 
 	switch (kind) {
 	case USAGE_USAGE:

@@ -43,7 +64,7 @@ static void vreportf(enum usage_kind kind,
 	}
 
 	/* truncation via snprintf is OK here */
-	if (kind == USAGE_BUG)
+	if (kind == USAGE_BUG || addln)
 		snprintf(prefix, sizeof(prefix), "%s%s:%d: ", prefix_i18n, file, line);
 	else
 		snprintf(prefix, sizeof(prefix), "%s", prefix_i18n);

@@ -123,7 +144,6 @@ static void warning_builtin(const char *file, int line, const char *warn, va_lis
 
 static int die_is_recursing_builtin(void)
 {
-	static int dying;
 	/*
 	 * Just an arbitrary number X where "a < x < b" where "a" is
 	 * "maximum number of pthreads we'll ever plausibly spawn" and