Warn on redundant semicolon after else

Author: someoneigna

src/quick-lint-js/error.h

@@ -1139,6 +1139,12 @@
       { source_code_span continue_statement; },                                \
       .error(QLJS_TRANSLATABLE("continue can only be used inside of a loop"),  \
              continue_statement))                                              \
+                                                                               \
+  QLJS_ERROR_TYPE(                                                             \
+      error_redundant_semicolon_after_else, "E202",                            \
+      { source_code_span semicolon; },                                         \
+      .warning(QLJS_TRANSLATABLE("redundant semicolon after else"),            \
+              semicolon))                                                      \
   /* END */
 
 namespace quick_lint_js {

src/quick-lint-js/parse.h

@@ -2515,6 +2515,13 @@ class parser {
 
     if (this->peek().type == token_type::kw_else) {
       this->skip();
+      if (this->peek().type == token_type::semicolon) {
+        source_code_span semicolon = this->peek().span();
+        this->error_reporter_->report(error_redundant_semicolon_after_else{
+          .semicolon = source_code_span(
+            semicolon.begin(), semicolon.end()),
+        });
+      }
       parse_and_visit_body();
     }
   }

test/test-parse-statement.cpp

@@ -578,6 +578,22 @@ TEST(test_parse, else_without_if) {
   }
 }
 
+TEST(test_parse, else_redundant_semicolon) {
+  {
+    spy_visitor v;
+    padded_string code(u8"if (cond) { body; } else; { body; }"_sv);
+    parser p(&code, &v);
+    EXPECT_TRUE(p.parse_and_visit_statement(v));
+    EXPECT_THAT(v.visits, ElementsAre("visit_variable_use",      // cond
+                                      "visit_enter_block_scope",  // (if)
+                                      "visit_variable_use",       // body
+                                      "visit_exit_block_scope")); // (else)
+    EXPECT_THAT(v.errors, ElementsAre(ERROR_TYPE_FIELD(
+                              error_redundant_semicolon_after_else, semicolon,
+                              offsets_matcher(&code, strlen(u8"if (cond) { body; } else"), u8";"))));
+  }
+}
+
 TEST(test_parse, block_statement) {
   {
     spy_visitor v = parse_and_visit_statement(u8"{ }"_sv);