fix(fe): don't emit React-specific diags if Preact was imported

If both React and Preact modules are imported, it's ambiguous whether
JSX references React or Preact. Be conservative and don't report any
React-specific diagnostics in this case.

Author: strager

docs/CHANGELOG.md

@@ -22,7 +22,8 @@ Semantic Versioning.
   setting its thread name on FreeBSD.
 * React-specific JSX diagnostics, such as [E0193][] ("misspelled React
   attribute; write 'className' instead"), are now only reported when 'react' is
-  imported. This fixes false warnings in Preact code. ([#1152][])
+  imported and if 'preact' is not imported. This fixes false warnings in Preact
+  code. ([#1152][])
 
 ## 3.0.0 (2024-01-01)
 

src/quick-lint-js/fe/parse-statement.cpp

@@ -5327,6 +5327,10 @@ void Parser::visited_module_import(const Token &module_name) {
       starts_with(module_name_unescaped, u8"react-dom/"_sv)) {
     this->imported_react_ = true;
   }
+  if (module_name_unescaped == u8"preact"_sv ||
+      starts_with(module_name_unescaped, u8"preact/"_sv)) {
+    this->imported_preact_ = true;
+  }
 }
 
 void Parser::parse_and_visit_variable_declaration_statement(

src/quick-lint-js/fe/parse.cpp

@@ -164,6 +164,10 @@ void Parser::check_all_jsx_attributes() {
     break;
 
   case Parser_JSX_Mode::auto_detect:
+    if (this->imported_react_ + this->imported_preact_ > 1) {
+      // Ambiguous. Don't report any diagnostics.
+      break;
+    }
     if (this->imported_react_) {
       goto react;
     }

src/quick-lint-js/fe/parse.h

@@ -1124,6 +1124,8 @@ class Parser {
 
   // Heuristic. True if React.js was imported.
   bool imported_react_ = false;
+  // Heuristic. True if Preact was imported.
+  bool imported_preact_ = false;
 
   bool in_top_level_ = true;
   bool in_async_function_ = false;

test/test-parse-jsx-react.cpp

@@ -180,5 +180,15 @@ TEST_F(Test_Parse_JSX_React, diagnostic_if_auto_detect_and_react_is_imported) {
       u8"Diag_JSX_Event_Attribute_Should_Be_Camel_Case"_diag,
       u8"Diag_JSX_Attribute_Renamed_By_React"_diag, jsx_auto_detect_options);
 }
+
+TEST_F(Test_Parse_JSX_React,
+       no_diagnostic_if_auto_detect_and_preact_is_imported) {
+  // Preact is incompatible with React.
+  test_parse_and_visit_module(
+      u8"import React from 'react';"_sv
+      u8"c = <div onclick={handler} class=\"c\" />;"_sv
+      u8"import Preact from 'preact';"_sv,
+      no_diags, jsx_auto_detect_options);
+}
 }
 }