scanner: fix string interpolation with inner curly braces (fix #12242) (#14553)

vlib/v/scanner/scanner.v

@@ -54,6 +54,7 @@ pub mut:
 	all_tokens                  []token.Token // *only* used in comments_mode: .toplevel_comments, contains all tokens
 	tidx                        int
 	eofs                        int
+	inter_cbr_count             int
 	pref                        &pref.Preferences
 	error_details               []string
 	errors                      []errors.Error
@@ -803,7 +804,11 @@ fn (mut s Scanner) text_scan() token.Token {
 			`{` {
 				// Skip { in `${` in strings
 				if s.is_inside_string {
-					continue
+					if s.text[s.pos - 1] == `$` {
+						continue
+					} else {
+						s.inter_cbr_count++
+					}
 				}
 				return s.new_token(.lcbr, '', 1)
 			}
@@ -817,7 +822,7 @@ fn (mut s Scanner) text_scan() token.Token {
 			`}` {
 				// s = `hello $name !`
 				// s = `hello ${name} !`
-				if s.is_enclosed_inter {
+				if s.is_enclosed_inter && s.inter_cbr_count == 0 {
 					if s.pos < s.text.len - 1 {
 						s.pos++
 					} else {
@@ -832,6 +837,9 @@ fn (mut s Scanner) text_scan() token.Token {
 					ident_string := s.ident_string()
 					return s.new_token(.string, ident_string, ident_string.len + 2) // + two quotes
 				} else {
+					if s.inter_cbr_count > 0 {
+						s.inter_cbr_count--
+					}
 					return s.new_token(.rcbr, '', 1)
 				}
 			}

vlib/v/tests/string_interpolation_inner_cbr_test.v

@@ -0,0 +1,21 @@
+struct St {}
+
+fn foo() ?int {
+	return 22
+}
+
+fn test_string_interpolation_inner_cbr() {
+	s1 := '${foo() or { 11 }}'
+	println(s1)
+	assert s1 == '22'
+
+	s2 := '${St{}}'
+	println(s2)
+	assert s2 == 'St{}'
+
+	s3 := '${{
+		'a': 1
+	}}'
+	println(s3)
+	assert s3 == "{'a': 1}"
+}