fix(typescript): fix false positive with import and var with same name

The following is valid TypeScript if the imported x is a type-only
declaration (e.g. an interface):

    import {x} from './mod';
    x = 42;
    var x;

quick-lint-js incorrectly emits a warning for this code. Fix it.

Unfortunately, this fix introduces another bug where we do not
diagnose the following code:

    import {x} from './mod';
    x = 42;

I prefer the new bug because it does not reject valid code.

Author: strager

docs/CHANGELOG.md

@@ -6,6 +6,14 @@ based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 quick-lint-js' version numbers are arbitrary. quick-lint-js does *not* adhere to
 Semantic Versioning.
 
+## Unreleased
+
+### Fixed
+
+* TypeScript support (still experimental):
+  * Assigning to a variable with the same name as an `import`ed type no longer
+    falsely reports [E0185][] ("assignment to imported variable").
+
 ## 2.19.0 (2023-12-30)
 
 [Downloads](https://c.quick-lint-js.com/releases/2.19.0/)

src/quick-lint-js/fe/variable-analyzer.cpp

@@ -876,11 +876,15 @@ void Variable_Analyzer::report_error_if_assignment_is_illegal(
     QLJS_WARNING_PUSH
     QLJS_WARNING_IGNORE_GCC("-Wnull-dereference")
 
-    this->diag_reporter_->report(Diag_Assignment_To_Imported_Variable{
-        .declaration = declaration->span(),
-        .assignment = assignment.span(),
-        .var_kind = kind,
-    });
+    // HACK(#1141): Avoid false positives in TypeScript by disabling this
+    // diagnostic for now.
+    if (!this->options_.import_variable_can_be_runtime_or_type) {
+      this->diag_reporter_->report(Diag_Assignment_To_Imported_Variable{
+          .declaration = declaration->span(),
+          .assignment = assignment.span(),
+          .var_kind = kind,
+      });
+    }
 
     QLJS_WARNING_POP
     break;

test/test-variable-analyzer-module.cpp

@@ -36,6 +36,8 @@ TEST(Test_Variable_Analyzer_Module, assign_to_immutable_imported_variable) {
       u8"^ .assignment"_diag
       u8"{.var_kind=Variable_Kind::_import}"_diag,
       javascript_analyze_options, default_globals);
+
+  // TODO(#1141): Report Diag_Assignment_To_Imported_Variable in TypeScript.
 }
 
 TEST(Test_Variable_Analyzer_Module, export_use_after_declaration_is_okay) {

test/test-variable-analyzer-multiple-declarations.cpp

@@ -290,6 +290,23 @@ TEST(Test_Variable_Analyzer_Multiple_Declarations,
   }
 }
 
+TEST(
+    Test_Variable_Analyzer_Multiple_Declarations,
+    using_implicit_type_import_and_runtime_variable_with_same_name_is_not_an_error) {
+  test_parse_and_analyze(u8"import x from ''; let x; x;"_sv, no_diags,
+                         typescript_analyze_options, default_globals);
+  test_parse_and_analyze(u8"let x; import x from ''; x;"_sv, no_diags,
+                         typescript_analyze_options, default_globals);
+  test_parse_and_analyze(u8"import x from ''; x; var x;"_sv, no_diags,
+                         typescript_analyze_options, default_globals);
+  test_parse_and_analyze(u8"import x from ''; let x; x = null;"_sv, no_diags,
+                         typescript_analyze_options, default_globals);
+  test_parse_and_analyze(u8"import x from ''; let x; x = null;"_sv, no_diags,
+                         typescript_analyze_options, default_globals);
+  test_parse_and_analyze(u8"import x from ''; x = null; var x;"_sv, no_diags,
+                         typescript_analyze_options, default_globals);
+}
+
 TEST(Test_Variable_Analyzer_Multiple_Declarations,
      typescript_import_does_not_conflict_with_type_only_variables) {
   for (String8_View other_thing : {