[PATCH v3] pathspec: advice: long and short forms are incompatible

[Stavros Ntentos <stdedos@gmail.com>]

It can be a "reasonable" mistake to mix short and long forms,
e.g. `:!(glob)`, instead of the (correct) `:(exclude,glob)`.

Teach git to issue an advice when such a pathspec is given.
        i.e.: While in short form parsing:
        * if the string contains an open parenthesis [`(`], and
        * without having explicitly terminated magic parsing (`:`)
        issue an advice hinting to that fact.

Based on "Junio C Hamano <gitster@pobox.com>"'s code suggestions:
* https://lore.kernel.org/git/xmqqa6qoqw9n.fsf@gitster.g/
* https://lore.kernel.org/git/xmqqo8f0cr9z.fsf@gitster.g/

Signed-off-by: Stavros Ntentos <133706+stdedos@users.noreply.github.com>
---
 Documentation/config/advice.txt |  3 +++
 advice.c                        |  3 +++
 advice.h                        |  2 ++
 pathspec.c                      | 33 ++++++++++++++++++++++++++++
 t/t6132-pathspec-exclude.sh     | 38 +++++++++++++++++++++++++++++++++
 5 files changed, 79 insertions(+)

diff --git a/Documentation/config/advice.txt b/Documentation/config/advice.txt
index acbd0c09aa..05a3cbc164 100644
--- a/Documentation/config/advice.txt
+++ b/Documentation/config/advice.txt
@@ -119,4 +119,7 @@ advice.*::
 	addEmptyPathspec::
 		Advice shown if a user runs the add command without providing
 		the pathspec parameter.
+	mixedPathspecMagic::
+		Advice shown if a user tries to mix short- and
+		longform pathspec magic.
 --
diff --git a/advice.c b/advice.c
index 164742305f..f94505e0d6 100644
--- a/advice.c
+++ b/advice.c
@@ -33,6 +33,7 @@ int advice_checkout_ambiguous_remote_branch_name = 1;
 int advice_submodule_alternate_error_strategy_die = 1;
 int advice_add_ignored_file = 1;
 int advice_add_empty_pathspec = 1;
+int advice_mixed_pathspec_magic = 1;
 
 static int advice_use_color = -1;
 static char advice_colors[][COLOR_MAXLEN] = {
@@ -95,6 +96,7 @@ static struct {
 	{ "submoduleAlternateErrorStrategyDie", &advice_submodule_alternate_error_strategy_die },
 	{ "addIgnoredFile", &advice_add_ignored_file },
 	{ "addEmptyPathspec", &advice_add_empty_pathspec },
+	{ "mixedPathspecMagic", &advice_mixed_pathspec_magic },
 
 	/* make this an alias for backward compatibility */
 	{ "pushNonFastForward", &advice_push_update_rejected }
@@ -137,6 +139,7 @@ static struct {
 	[ADVICE_STATUS_U_OPTION]			= { "statusUoption", 1 },
 	[ADVICE_SUBMODULE_ALTERNATE_ERROR_STRATEGY_DIE] = { "submoduleAlternateErrorStrategyDie", 1 },
 	[ADVICE_WAITING_FOR_EDITOR]			= { "waitingForEditor", 1 },
+	[ADVICE_MIXED_PATHSPEC_MAGIC]	= { "mixedPathspecMagic", 1 },
 };
 
 static const char turn_off_instructions[] =
diff --git a/advice.h b/advice.h
index bc2432980a..aa229fded8 100644
--- a/advice.h
+++ b/advice.h
@@ -33,6 +33,7 @@ extern int advice_checkout_ambiguous_remote_branch_name;
 extern int advice_submodule_alternate_error_strategy_die;
 extern int advice_add_ignored_file;
 extern int advice_add_empty_pathspec;
+extern int advice_mixed_pathspec_magic;
 
 /*
  * To add a new advice, you need to:
@@ -72,6 +73,7 @@ extern int advice_add_empty_pathspec;
 	ADVICE_STATUS_U_OPTION,
 	ADVICE_SUBMODULE_ALTERNATE_ERROR_STRATEGY_DIE,
 	ADVICE_WAITING_FOR_EDITOR,
+	ADVICE_MIXED_PATHSPEC_MAGIC,
 };
 
 int git_default_advice_config(const char *var, const char *value);
diff --git a/pathspec.c b/pathspec.c
index 18b3be362a..5f77e2e8d8 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -336,6 +336,36 @@ static const char *parse_long_magic(unsigned *magic, int *prefix_len,
 	return pos;
 }
 
+
+/*
+ * Give hint for a common mistake of mixing short and long
+ * form of pathspec magic, as well as possible corrections
+ */
+static void warn_mixed_magic(unsigned magic, const char *elem, const char *pos)
+{
+	struct strbuf longform = STRBUF_INIT;
+	int i;
+
+	if (!advice_enabled(ADVICE_MIXED_PATHSPEC_MAGIC))
+		return;
+
+	for (i = 0; i < ARRAY_SIZE(pathspec_magic); i++) {
+		if (pathspec_magic[i].bit & magic) {
+			if (longform.len)
+				strbuf_addch(&longform, ',');
+			strbuf_addstr(&longform, pathspec_magic[i].name);
+		}
+	}
+	advise_if_enabled(ADVICE_MIXED_PATHSPEC_MAGIC,
+	                  _("'%.*s(...': cannot mix short- and longform pathspec magic!\n"
+	                    "Either spell the shortform magic '%.*s' as ':(%s,...'\n"
+	                    "or end magic pathspec matching with '%.*s:'."),
+	                  (int)(pos - elem), elem,
+	                  (int)(pos - (elem + 1)), elem + 1,
+	                  longform.buf,
+	                  (int)(pos - elem), elem);
+}
+
 /*
  * Parse the pathspec element looking for short magic
  *
@@ -356,6 +386,9 @@ static const char *parse_short_magic(unsigned *magic, const char *elem)
 			continue;
 		}
 
+		if (ch == '(')
+			warn_mixed_magic(*magic, elem, pos);
+
 		if (!is_pathspec_magic(ch))
 			break;
 
diff --git a/t/t6132-pathspec-exclude.sh b/t/t6132-pathspec-exclude.sh
index 30328b87f0..8b9d543e1e 100755
--- a/t/t6132-pathspec-exclude.sh
+++ b/t/t6132-pathspec-exclude.sh
@@ -244,4 +244,42 @@ test_expect_success 'grep --untracked PATTERN :(exclude)*FILE' '
 	test_cmp expect-grep actual-grep
 '
 
+cat > expected_warn <<"EOF"
+hint: ':!(...': cannot mix short- and longform pathspec magic!
+hint: Either spell the shortform magic '!' as ':(exclude,...'
+hint: or end magic pathspec matching with ':!:'.
+hint: Disable this message with "git config advice.mixedPathspecMagic false"
+EOF
+test_expect_success 'warn pathspec not matching longform magic in :!(...)' '
+	git log --oneline --format=%s -- '"'"':!(glob)**/file'"'"' >actual 2>warn &&
+	cat <<EOF >expect &&
+sub2/file
+sub/sub/sub/file
+sub/file2
+sub/sub/file
+sub/file
+file
+EOF
+	cat actual &&
+	cat warn &&
+	test_cmp expect actual &&
+	test_cmp expected_warn warn
+'
+
+test_expect_success 'do not warn pathspec not matching longform magic in :!:(...) (i.e. if magic parsing is explicitly stopped)' '
+	git log --oneline --format=%s -- '"'"':!:(glob)**/file'"'"' >actual 2>warn &&
+	cat <<EOF >expect &&
+sub2/file
+sub/sub/sub/file
+sub/file2
+sub/sub/file
+sub/file
+file
+EOF
+	cat actual &&
+	cat warn &&
+	test_cmp expect actual &&
+	! test_cmp expected_warn warn
+'
+
 test_done
-- 
2.31.1