From a31f559d0a63c6373f4496f7553197342869a434 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 15 Apr 2026 00:33:27 +0300
Subject: [PATCH] parser: fix assert without comma but with message confusion
 with vfmt (fixes #25005)

---
 cmd/tools/vfmt.v                              | 13 ++++++++--
 cmd/tools/vfmt_test.v                         | 25 +++++++++++++++++++
 vlib/v/parser/parser.v                        |  8 ++++++
 .../assert_missing_comma_message_err.out      |  5 ++++
 .../tests/assert_missing_comma_message_err.vv |  3 +++
 5 files changed, 52 insertions(+), 2 deletions(-)
 create mode 100644 cmd/tools/vfmt_test.v
 create mode 100644 vlib/v/parser/tests/assert_missing_comma_message_err.out
 create mode 100644 vlib/v/parser/tests/assert_missing_comma_message_err.vv

diff --git a/cmd/tools/vfmt.v b/cmd/tools/vfmt.v
index 769436b4f..498cd7741 100644
--- a/cmd/tools/vfmt.v
+++ b/cmd/tools/vfmt.v
@@ -166,7 +166,7 @@ fn main() {
 }
 
 fn (foptions &FormatOptions) verify_file(prefs &pref.Preferences, fpath string) bool {
-	fcontent := foptions.formated_content_from_file(prefs, fpath)
+	fcontent := foptions.formated_content_from_file(prefs, fpath) or { return false }
 	content := os.read_file(fpath) or { return false }
 	return fcontent == content
 }
@@ -188,9 +188,12 @@ fn (foptions &FormatOptions) vlog(msg string) {
 	}
 }
 
-fn (foptions &FormatOptions) formated_content_from_file(prefs &pref.Preferences, file string) string {
+fn (foptions &FormatOptions) formated_content_from_file(prefs &pref.Preferences, file string) !string {
 	mut table := ast.new_table()
 	file_ast := parser.parse_file(file, mut table, .parse_comments, prefs)
+	if file_ast.errors.len > 0 {
+		return error('the file contains parser errors')
+	}
 	table.new_int = foptions.is_new_int
 	formated_content := fmt.fmt(file_ast, mut table, prefs, foptions.is_debug)
 	return formated_content
@@ -209,6 +212,9 @@ fn (foptions &FormatOptions) format_file(file string) {
 	foptions.vlog('vfmt2 running fmt.fmt over file: ${file}')
 	prefs, mut table := setup_preferences_and_table()
 	file_ast := parser.parse_file(file, mut table, .parse_comments, prefs)
+	if file_ast.errors.len > 0 {
+		exit(2)
+	}
 	// checker.new_checker(table, prefs).check(file_ast)
 	table.new_int = foptions.is_new_int
 	formatted_content := fmt.fmt(file_ast, mut table, prefs, foptions.is_debug)
@@ -222,6 +228,9 @@ fn (foptions &FormatOptions) format_pipe() {
 	prefs, mut table := setup_preferences_and_table()
 	input_text := os.get_raw_lines_joined()
 	file_ast := parser.parse_text(input_text, '', mut table, .parse_comments, prefs)
+	if file_ast.errors.len > 0 {
+		exit(1)
+	}
 	// checker.new_checker(table, prefs).check(file_ast)
 	table.new_int = foptions.is_new_int
 	formatted_content := fmt.fmt(file_ast, mut table, prefs, foptions.is_debug,
diff --git a/cmd/tools/vfmt_test.v b/cmd/tools/vfmt_test.v
new file mode 100644
index 000000000..872cbd6cb
--- /dev/null
+++ b/cmd/tools/vfmt_test.v
@@ -0,0 +1,25 @@
+import os
+
+const vexe = @VEXE
+const vfmt_test_tdir = os.join_path(os.vtmp_dir(), 'vfmt_test_25005')
+
+fn testsuite_begin() {
+	os.rmdir_all(vfmt_test_tdir) or {}
+	os.mkdir_all(vfmt_test_tdir)!
+}
+
+fn testsuite_end() {
+	os.rmdir_all(vfmt_test_tdir) or {}
+}
+
+fn test_fmt_keeps_invalid_assert_source_unchanged() {
+	source_path := os.join_path(vfmt_test_tdir, 'invalid_assert_message.v')
+	original := "fn main() {\n\tassert false 'bye'\n}\n"
+	os.write_file(source_path, original)!
+
+	res := os.execute('${os.quoted_path(vexe)} fmt -w ${os.quoted_path(source_path)}')
+
+	assert res.exit_code != 0, res.output
+	assert res.output.contains('unexpected string `bye`, expecting `,`'), res.output
+	assert os.read_file(source_path)! == original
+}
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 51f5fc13e..65bae2e4a 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -1217,6 +1217,14 @@ fn (mut p Parser) stmt(is_top_level bool) ast.Stmt {
 				extra = p.expr(0)
 				// dump(extra)
 				extra_pos = extra_pos.extend(p.tok.pos())
+			} else if p.tok.line_nr == p.prev_tok.line_nr + p.prev_tok.lit.count('\n')
+				&& p.tok.kind !in [.comment, .semicolon, .rcbr, .eof] {
+				line_nr := p.tok.line_nr
+				err := p.unexpected(got: p.tok.str(), expecting: '`,`')
+				for p.tok.kind != .eof && p.tok.line_nr == line_nr {
+					p.next()
+				}
+				return err
 			}
 			return ast.AssertStmt{
 				expr:      expr
diff --git a/vlib/v/parser/tests/assert_missing_comma_message_err.out b/vlib/v/parser/tests/assert_missing_comma_message_err.out
new file mode 100644
index 000000000..3eea19faa
--- /dev/null
+++ b/vlib/v/parser/tests/assert_missing_comma_message_err.out
@@ -0,0 +1,5 @@
+vlib/v/parser/tests/assert_missing_comma_message_err.vv:2:15: error: unexpected string `bye`, expecting `,`
+    1 | fn main() {
+    2 |     assert false 'bye'
+      |                  ~~~~~
+    3 | }
diff --git a/vlib/v/parser/tests/assert_missing_comma_message_err.vv b/vlib/v/parser/tests/assert_missing_comma_message_err.vv
new file mode 100644
index 000000000..e925ad52b
--- /dev/null
+++ b/vlib/v/parser/tests/assert_missing_comma_message_err.vv
@@ -0,0 +1,3 @@
+fn main() {
+	assert false 'bye'
+}
-- 
2.39.5