diff --git a/Documentation/technical/api-error-handling.txt b/Documentation/technical/api-error-handling.txt
index 8be4f4d0d6..70bf1d3e52 100644
--- a/Documentation/technical/api-error-handling.txt
+++ b/Documentation/technical/api-error-handling.txt
@@ -1,12 +1,34 @@
 Error reporting in git
 ======================
 
-`BUG`, `die`, `usage`, `error`, and `warning` report errors of
+`BUG`, `bug`, `die`, `usage`, `error`, and `warning` report errors of
 various kinds.
 
 - `BUG` is for failed internal assertions that should never happen,
   i.e. a bug in git itself.
 
+- `bug` (lower-case, not `BUG`) is supposed to be used like `BUG` but
+  prints a "BUG" message instead of calling `abort()`.
++
+A call to `bug()` will then result in a "real" call to the `BUG()`
+function, either explicitly by invoking `BUG_if_bug()` after call(s)
+to `bug()`, or implicitly at `exit()` time where we'll check if we
+encountered any outstanding `bug()` invocations.
++
+If there were no prior calls to `bug()` before invoking `BUG_if_bug()`
+the latter is a NOOP. The `BUG_if_bug()` function takes the same
+arguments as `BUG()` itself. Calling `BUG_if_bug()` explicitly isn't
+necessary, but ensures that we die as soon as possible.
++
+If you know you had prior calls to `bug()` then calling `BUG()` itself
+is equivalent to calling `BUG_if_bug()`, the latter being a wrapper
+calling `BUG()` if we've set a flag indicating that we've called
+`bug()`.
++
+This is for the convenience of APIs who'd like to potentially report
+more than one "bug", such as the optbug() validation in
+parse-options.c.
+
 - `die` is for fatal application errors.  It prints a message to
   the user and exits with status 128.
 
diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index f4a8a69087..77a150b30e 100644
--- a/Documentation/technical/api-trace2.txt
+++ b/Documentation/technical/api-trace2.txt
@@ -465,8 +465,8 @@ completed.)
 ------------
 
 `"error"`::
-	This event is emitted when one of the `BUG()`, `error()`, `die()`,
-	`warning()`, or `usage()` functions are called.
+	This event is emitted when one of the `BUG()`, `bug()`, `error()`,
+	`die()`, `warning()`, or `usage()` functions are called.
 +
 ------------
 {
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index e6e1d636f9..31b48e728b 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1810,21 +1810,17 @@ static int should_process_cmd(struct command *cmd)
 	return !cmd->error_string && !cmd->skip_update;
 }
 
-static void warn_if_skipped_connectivity_check(struct command *commands,
+static void BUG_if_skipped_connectivity_check(struct command *commands,
 					       struct shallow_info *si)
 {
 	struct command *cmd;
-	int checked_connectivity = 1;
 
 	for (cmd = commands; cmd; cmd = cmd->next) {
-		if (should_process_cmd(cmd) && si->shallow_ref[cmd->index]) {
-			error("BUG: connectivity check has not been run on ref %s",
-			      cmd->ref_name);
-			checked_connectivity = 0;
-		}
+		if (should_process_cmd(cmd) && si->shallow_ref[cmd->index])
+			bug("connectivity check has not been run on ref %s",
+			    cmd->ref_name);
 	}
-	if (!checked_connectivity)
-		BUG("connectivity check skipped???");
+	BUG_if_bug("connectivity check skipped???");
 }
 
 static void execute_commands_non_atomic(struct command *commands,
@@ -2005,7 +2001,7 @@ static void execute_commands(struct command *commands,
 		execute_commands_non_atomic(commands, si);
 
 	if (shallow_update)
-		warn_if_skipped_connectivity_check(commands, si);
+		BUG_if_skipped_connectivity_check(commands, si);
 }
 
 static struct command **queue_command(struct command **tail,
diff --git a/cache-tree.c b/cache-tree.c
index a92c23eec3..ff794d940f 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -722,14 +722,14 @@ struct tree* write_in_core_index_as_tree(struct repository *repo) {
 	ret = write_index_as_tree_internal(&o, index_state, was_valid, 0, NULL);
 	if (ret == WRITE_TREE_UNMERGED_INDEX) {
 		int i;
-		fprintf(stderr, "BUG: There are unmerged index entries:\n");
+		bug("there are unmerged index entries:");
 		for (i = 0; i < index_state->cache_nr; i++) {
 			const struct cache_entry *ce = index_state->cache[i];
 			if (ce_stage(ce))
-				fprintf(stderr, "BUG: %d %.*s\n", ce_stage(ce),
-					(int)ce_namelen(ce), ce->name);
+				bug("%d %.*s", ce_stage(ce),
+				    (int)ce_namelen(ce), ce->name);
 		}
-		BUG("unmerged index entries when writing inmemory index");
+		BUG("unmerged index entries when writing in-core index");
 	}
 
 	return lookup_tree(repo, &index_state->cache_tree->oid);
diff --git a/common-main.c b/common-main.c
index 29fb7452f8..c531372f3f 100644
--- a/common-main.c
+++ b/common-main.c
@@ -55,10 +55,30 @@ int main(int argc, const char **argv)
 
 	result = cmd_main(argc, argv);
 
-	/*
-	 * We define exit() to call trace2_cmd_exit_fl() in
-	 * git-compat-util.h. Whether we reach this or exit()
-	 * elsewhere we'll always run our trace2 exit handler.
-	 */
+	/* Not exit(3), but a wrapper calling our common_exit() */
 	exit(result);
 }
+
+static void check_bug_if_BUG(void)
+{
+	if (!bug_called_must_BUG)
+		return;
+	BUG("on exit(): had bug() call(s) in this process without explicit BUG_if_bug()");
+}
+
+/* We wrap exit() to call common_exit() in git-compat-util.h */
+int common_exit(const char *file, int line, int code)
+{
+	/*
+	 * For non-POSIX systems: Take the lowest 8 bits of the "code"
+	 * to e.g. turn -1 into 255. On a POSIX system this is
+	 * redundant, see exit(3) and wait(2), but as it doesn't harm
+	 * anything there we don't need to guard this with an "ifdef".
+	 */
+	code &= 0xff;
+
+	check_bug_if_BUG();
+	trace2_cmd_exit_fl(file, line, code);
+
+	return code;
+}
diff --git a/git-compat-util.h b/git-compat-util.h
index d9457b9aae..fd36d3bfdc 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1326,9 +1326,19 @@ static inline int regexec_buf(const regex_t *preg, const char *buf, size_t size,
 /* usage.c: only to be used for testing BUG() implementation (see test-tool) */
 extern int BUG_exit_code;
 
+/* usage.c: if bug() is called we should have a BUG_if_bug() afterwards */
+extern int bug_called_must_BUG;
+
 __attribute__((format (printf, 3, 4))) NORETURN
 void BUG_fl(const char *file, int line, const char *fmt, ...);
 #define BUG(...) BUG_fl(__FILE__, __LINE__, __VA_ARGS__)
+__attribute__((format (printf, 3, 4)))
+void bug_fl(const char *file, int line, const char *fmt, ...);
+#define bug(...) bug_fl(__FILE__, __LINE__, __VA_ARGS__)
+#define BUG_if_bug(...) do { \
+	if (bug_called_must_BUG) \
+		BUG_fl(__FILE__, __LINE__, __VA_ARGS__); \
+} while (0)
 
 #ifndef FSYNC_METHOD_DEFAULT
 #ifdef __APPLE__
@@ -1459,8 +1469,8 @@ int cmd_main(int, const char **);
  * Intercept all calls to exit() and route them to trace2 to
  * optionally emit a message before calling the real exit().
  */
-int trace2_cmd_exit_fl(const char *file, int line, int code);
-#define exit(code) exit(trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
+int common_exit(const char *file, int line, int code);
+#define exit(code) exit(common_exit(__FILE__, __LINE__, (code)))
 
 /*
  * You can mark a stack variable with UNLEAK(var) to avoid it being
diff --git a/parse-options.c b/parse-options.c
index 6e57744fd2..edf55d3ef5 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -14,15 +14,15 @@ enum opt_parsed {
 	OPT_UNSET = 1<<1,
 };
 
-static int optbug(const struct option *opt, const char *reason)
+static void optbug(const struct option *opt, const char *reason)
 {
-	if (opt->long_name) {
-		if (opt->short_name)
-			return error("BUG: switch '%c' (--%s) %s",
-				     opt->short_name, opt->long_name, reason);
-		return error("BUG: option '%s' %s", opt->long_name, reason);
-	}
-	return error("BUG: switch '%c' %s", opt->short_name, reason);
+	if (opt->long_name && opt->short_name)
+		bug("switch '%c' (--%s) %s", opt->short_name,
+		    opt->long_name, reason);
+	else if (opt->long_name)
+		bug("option '%s' %s", opt->long_name, reason);
+	else
+		bug("switch '%c' %s", opt->short_name, reason);
 }
 
 static const char *optname(const struct option *opt, enum opt_parsed flags)
@@ -441,28 +441,27 @@ static void check_typos(const char *arg, const struct option *options)
 
 static void parse_options_check(const struct option *opts)
 {
-	int err = 0;
 	char short_opts[128];
 
 	memset(short_opts, '\0', sizeof(short_opts));
 	for (; opts->type != OPTION_END; opts++) {
 		if ((opts->flags & PARSE_OPT_LASTARG_DEFAULT) &&
 		    (opts->flags & PARSE_OPT_OPTARG))
-			err |= optbug(opts, "uses incompatible flags "
-					"LASTARG_DEFAULT and OPTARG");
+			optbug(opts, "uses incompatible flags "
+			       "LASTARG_DEFAULT and OPTARG");
 		if (opts->short_name) {
 			if (0x7F <= opts->short_name)
-				err |= optbug(opts, "invalid short name");
+				optbug(opts, "invalid short name");
 			else if (short_opts[opts->short_name]++)
-				err |= optbug(opts, "short name already used");
+				optbug(opts, "short name already used");
 		}
 		if (opts->flags & PARSE_OPT_NODASH &&
 		    ((opts->flags & PARSE_OPT_OPTARG) ||
 		     !(opts->flags & PARSE_OPT_NOARG) ||
 		     !(opts->flags & PARSE_OPT_NONEG) ||
 		     opts->long_name))
-			err |= optbug(opts, "uses feature "
-					"not supported for dashless options");
+			optbug(opts, "uses feature "
+			       "not supported for dashless options");
 		switch (opts->type) {
 		case OPTION_COUNTUP:
 		case OPTION_BIT:
@@ -471,33 +470,33 @@ static void parse_options_check(const struct option *opts)
 		case OPTION_NUMBER:
 			if ((opts->flags & PARSE_OPT_OPTARG) ||
 			    !(opts->flags & PARSE_OPT_NOARG))
-				err |= optbug(opts, "should not accept an argument");
+				optbug(opts, "should not accept an argument");
 			break;
 		case OPTION_CALLBACK:
 			if (!opts->callback && !opts->ll_callback)
-				BUG("OPTION_CALLBACK needs one callback");
-			if (opts->callback && opts->ll_callback)
-				BUG("OPTION_CALLBACK can't have two callbacks");
+				optbug(opts, "OPTION_CALLBACK needs one callback");
+			else if (opts->callback && opts->ll_callback)
+				optbug(opts, "OPTION_CALLBACK can't have two callbacks");
 			break;
 		case OPTION_LOWLEVEL_CALLBACK:
 			if (!opts->ll_callback)
-				BUG("OPTION_LOWLEVEL_CALLBACK needs a callback");
+				optbug(opts, "OPTION_LOWLEVEL_CALLBACK needs a callback");
 			if (opts->callback)
-				BUG("OPTION_LOWLEVEL_CALLBACK needs no high level callback");
+				optbug(opts, "OPTION_LOWLEVEL_CALLBACK needs no high level callback");
 			break;
 		case OPTION_ALIAS:
-			BUG("OPT_ALIAS() should not remain at this point. "
-			    "Are you using parse_options_step() directly?\n"
-			    "That case is not supported yet.");
+			optbug(opts, "OPT_ALIAS() should not remain at this point. "
+			       "Are you using parse_options_step() directly?\n"
+			       "That case is not supported yet.");
+			break;
 		default:
 			; /* ok. (usually accepts an argument) */
 		}
 		if (opts->argh &&
 		    strcspn(opts->argh, " _") != strlen(opts->argh))
-			err |= optbug(opts, "multi-word argh should use dash to separate words");
+			optbug(opts, "multi-word argh should use dash to separate words");
 	}
-	if (err)
-		exit(128);
+	BUG_if_bug("invalid 'struct option'");
 }
 
 static void parse_options_start_1(struct parse_opt_ctx_t *ctx,
diff --git a/t/helper/test-trace2.c b/t/helper/test-trace2.c
index 59b124bb5f..180c7f53f3 100644
--- a/t/helper/test-trace2.c
+++ b/t/helper/test-trace2.c
@@ -198,7 +198,7 @@ static int ut_006data(int argc, const char **argv)
 	return 0;
 }
 
-static int ut_007bug(int argc, const char **argv)
+static int ut_007BUG(int argc, const char **argv)
 {
 	/*
 	 * Exercise BUG() to ensure that the message is printed to trace2.
@@ -206,6 +206,28 @@ static int ut_007bug(int argc, const char **argv)
 	BUG("the bug message");
 }
 
+static int ut_008bug(int argc, const char **argv)
+{
+	bug("a bug message");
+	bug("another bug message");
+	BUG_if_bug("an explicit BUG_if_bug() following bug() call(s) is nice, but not required");
+	return 0;
+}
+
+static int ut_009bug_BUG(int argc, const char **argv)
+{
+	bug("a bug message");
+	bug("another bug message");
+	/* The BUG_if_bug(...) isn't here, but we'll spot bug() calls on exit()! */
+	return 0;
+}
+
+static int ut_010bug_BUG(int argc, const char **argv)
+{
+	bug("a bug message");
+	BUG("a BUG message");
+}
+
 /*
  * Usage:
  *     test-tool trace2 <ut_name_1> <ut_usage_1>
@@ -222,7 +244,10 @@ static struct unit_test ut_table[] = {
 	{ ut_004child,    "004child",  "[<child_command_line>]" },
 	{ ut_005exec,     "005exec",   "<git_command_args>" },
 	{ ut_006data,     "006data",   "[<category> <key> <value>]+" },
-	{ ut_007bug,      "007bug",    "" },
+	{ ut_007BUG,      "007bug",    "" },
+	{ ut_008bug,      "008bug",    "" },
+	{ ut_009bug_BUG,  "009bug_BUG","" },
+	{ ut_010bug_BUG,  "010bug_BUG","" },
 };
 /* clang-format on */
 
diff --git a/t/t0210-trace2-normal.sh b/t/t0210-trace2-normal.sh
index 37c359bd5a..80e76a4695 100755
--- a/t/t0210-trace2-normal.sh
+++ b/t/t0210-trace2-normal.sh
@@ -168,6 +168,82 @@ test_expect_success 'BUG messages are written to trace2' '
 	test_cmp expect actual
 '
 
+test_expect_success 'bug messages with BUG_if_bug() are written to trace2' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_expect_code 99 env GIT_TRACE2="$(pwd)/trace.normal" \
+		test-tool trace2 008bug 2>err &&
+	cat >expect <<-\EOF &&
+	a bug message
+	another bug message
+	an explicit BUG_if_bug() following bug() call(s) is nice, but not required
+	EOF
+	sed "s/^.*: //" <err >actual &&
+	test_cmp expect actual &&
+
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 008bug
+		cmd_name trace2 (trace2)
+		error a bug message
+		error another bug message
+		error an explicit BUG_if_bug() following bug() call(s) is nice, but not required
+		exit elapsed:_TIME_ code:99
+		atexit elapsed:_TIME_ code:99
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'bug messages without explicit BUG_if_bug() are written to trace2' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_expect_code 99 env GIT_TRACE2="$(pwd)/trace.normal" \
+		test-tool trace2 009bug_BUG 2>err &&
+	cat >expect <<-\EOF &&
+	a bug message
+	another bug message
+	had bug() call(s) in this process without explicit BUG_if_bug()
+	EOF
+	sed "s/^.*: //" <err >actual &&
+	test_cmp expect actual &&
+
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 009bug_BUG
+		cmd_name trace2 (trace2)
+		error a bug message
+		error another bug message
+		error on exit(): had bug() call(s) in this process without explicit BUG_if_bug()
+		exit elapsed:_TIME_ code:99
+		atexit elapsed:_TIME_ code:99
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'bug messages followed by BUG() are written to trace2' '
+	test_when_finished "rm trace.normal actual expect" &&
+	test_expect_code 99 env GIT_TRACE2="$(pwd)/trace.normal" \
+		test-tool trace2 010bug_BUG 2>err &&
+	cat >expect <<-\EOF &&
+	a bug message
+	a BUG message
+	EOF
+	sed "s/^.*: //" <err >actual &&
+	test_cmp expect actual &&
+
+	perl "$TEST_DIRECTORY/t0210/scrub_normal.perl" <trace.normal >actual &&
+	cat >expect <<-EOF &&
+		version $V
+		start _EXE_ trace2 010bug_BUG
+		cmd_name trace2 (trace2)
+		error a bug message
+		error a BUG message
+		exit elapsed:_TIME_ code:99
+		atexit elapsed:_TIME_ code:99
+	EOF
+	test_cmp expect actual
+'
+
 sane_unset GIT_TRACE2_BRIEF
 
 # Now test without environment variables and get all Trace2 settings
diff --git a/trace2.c b/trace2.c
index e01cf77f1a..0c0a11e07d 100644
--- a/trace2.c
+++ b/trace2.c
@@ -202,17 +202,15 @@ void trace2_cmd_start_fl(const char *file, int line, const char **argv)
 					    argv);
 }
 
-int trace2_cmd_exit_fl(const char *file, int line, int code)
+void trace2_cmd_exit_fl(const char *file, int line, int code)
 {
 	struct tr2_tgt *tgt_j;
 	int j;
 	uint64_t us_now;
 	uint64_t us_elapsed_absolute;
 
-	code &= 0xff;
-
 	if (!trace2_enabled)
-		return code;
+		return;
 
 	trace_git_fsync_stats();
 	trace2_collect_process_info(TRACE2_PROCESS_INFO_EXIT);
@@ -226,8 +224,6 @@ int trace2_cmd_exit_fl(const char *file, int line, int code)
 		if (tgt_j->pfn_exit_fl)
 			tgt_j->pfn_exit_fl(file, line, us_elapsed_absolute,
 					   code);
-
-	return code;
 }
 
 void trace2_cmd_error_va_fl(const char *file, int line, const char *fmt,
diff --git a/trace2.h b/trace2.h
index 1b109f57d0..88d906ea83 100644
--- a/trace2.h
+++ b/trace2.h
@@ -101,14 +101,8 @@ void trace2_cmd_start_fl(const char *file, int line, const char **argv);
 
 /*
  * Emit an 'exit' event.
- *
- * Write the exit-code that will be passed to exit() or returned
- * from main().
- *
- * Use this prior to actually calling exit().
- * See "#define exit()" in git-compat-util.h
  */
-int trace2_cmd_exit_fl(const char *file, int line, int code);
+void trace2_cmd_exit_fl(const char *file, int line, int code);
 
 #define trace2_cmd_exit(code) (trace2_cmd_exit_fl(__FILE__, __LINE__, (code)))
 
diff --git a/usage.c b/usage.c
index b738dd178b..79900d0287 100644
--- a/usage.c
+++ b/usage.c
@@ -290,18 +290,24 @@ void warning(const char *warn, ...)
 /* Only set this, ever, from t/helper/, when verifying that bugs are caught. */
 int BUG_exit_code;
 
-static NORETURN void BUG_vfl(const char *file, int line, const char *fmt, va_list params)
+static void BUG_vfl_common(const char *file, int line, const char *fmt,
+			   va_list params)
 {
 	char prefix[256];
-	va_list params_copy;
-	static int in_bug;
-
-	va_copy(params_copy, params);
 
 	/* truncation via snprintf is OK here */
 	snprintf(prefix, sizeof(prefix), "BUG: %s:%d: ", file, line);
 
 	vreportf(prefix, fmt, params);
+}
+
+static NORETURN void BUG_vfl(const char *file, int line, const char *fmt, va_list params)
+{
+	va_list params_copy;
+	static int in_bug;
+
+	va_copy(params_copy, params);
+	BUG_vfl_common(file, line, fmt, params);
 
 	if (in_bug)
 		abort();
@@ -317,11 +323,28 @@ static NORETURN void BUG_vfl(const char *file, int line, const char *fmt, va_lis
 NORETURN void BUG_fl(const char *file, int line, const char *fmt, ...)
 {
 	va_list ap;
+
+	bug_called_must_BUG = 0;
+
 	va_start(ap, fmt);
 	BUG_vfl(file, line, fmt, ap);
 	va_end(ap);
 }
 
+int bug_called_must_BUG;
+void bug_fl(const char *file, int line, const char *fmt, ...)
+{
+	va_list ap, cp;
+
+	bug_called_must_BUG = 1;
+
+	va_copy(cp, ap);
+	va_start(ap, fmt);
+	BUG_vfl_common(file, line, fmt, ap);
+	va_end(ap);
+	trace2_cmd_error_va(fmt, cp);
+}
+
 #ifdef SUPPRESS_ANNOTATED_LEAKS
 void unleak_memory(const void *ptr, size_t len)
 {