fix(semantic): report redeclaration error for import bindings conflicting with value declarations

crates/oxc_semantic/src/checker/javascript.rs

@@ -37,6 +37,34 @@ pub fn check_unresolved_exports(program: &Program<'_>, ctx: &SemanticBuilder<'_>
     }
 }
 
+/// It is a Syntax Error if any element of the BoundNames of ImportDeclaration
+/// also occurs in the VarDeclaredNames or LexicallyDeclaredNames of ModuleItemList.
+/// <https://tc39.es/ecma262/#sec-imports-static-semantics-early-errors>
+pub fn check_import_value_redeclarations(ctx: &SemanticBuilder<'_>) {
+    if !ctx.source_type.is_module() || ctx.source_type.is_typescript() {
+        return;
+    }
+
+    let scope_id = ctx.scoping.root_scope_id();
+    for (_, &symbol_id) in ctx.scoping.get_bindings(scope_id) {
+        let flags = ctx.scoping.symbol_flags(symbol_id);
+        if !flags.contains(SymbolFlags::Import) {
+            continue;
+        }
+        if !flags.intersects(SymbolFlags::Variable | SymbolFlags::Class | SymbolFlags::Function) {
+            continue;
+        }
+        let redeclarations = ctx.scoping.symbol_redeclarations(symbol_id);
+        if redeclarations.len() < 2 {
+            continue;
+        }
+        let name = ctx.scoping.symbol_name(symbol_id);
+        let first = &redeclarations[0];
+        let last = &redeclarations[redeclarations.len() - 1];
+        ctx.error(diagnostics::redeclaration(name, first.span, last.span));
+    }
+}
+
 pub fn check_duplicate_class_elements(ctx: &SemanticBuilder<'_>) {
     let classes = &ctx.class_table_builder.classes;
     classes.iter_enumerated().for_each(|(class_id, _)| {

crates/oxc_semantic/src/checker/mod.rs

@@ -20,6 +20,7 @@ pub fn check<'a>(kind: AstKind<'a>, ctx: &SemanticBuilder<'a>) {
         AstKind::Program(program) => {
             js::check_duplicate_class_elements(ctx);
             js::check_unresolved_exports(program, ctx);
+            js::check_import_value_redeclarations(ctx);
             ts::check_ts_export_assignment_in_program(program, ctx);
         }
         AstKind::BindingIdentifier(ident) => {

crates/oxc_semantic/tests/integration/symbols.rs

@@ -452,3 +452,27 @@ fn test_function_var_redeclaration_in_module() {
     SemanticTester::js("function a() {} var a = ''").has_error("already been declared");
     SemanticTester::js("var a = ''; function a() {}").has_error("already been declared");
 }
+
+// https://github.com/oxc-project/oxc/issues/15961
+#[test]
+fn test_import_value_redeclaration_in_module() {
+    // Import + var
+    SemanticTester::js("import { Foo } from './foo.js'; var Foo;")
+        .has_error("already been declared");
+    SemanticTester::js("var Foo; import { Foo } from './foo.js';")
+        .has_error("already been declared");
+    // Import + let
+    SemanticTester::js("import { Foo } from './foo.js'; let Foo;")
+        .has_error("already been declared");
+    // Import + const
+    SemanticTester::js("import { Foo } from './foo.js'; const Foo = 1;")
+        .has_error("already been declared");
+    // Import + class
+    SemanticTester::js("import { Foo } from './foo.js'; class Foo {}")
+        .has_error("already been declared");
+    // Import + function
+    SemanticTester::js("import { Foo } from './foo.js'; function Foo() {}")
+        .has_error("already been declared");
+    // TypeScript should NOT report this error (declaration merging)
+    SemanticTester::ts("import { Foo } from './foo.js'; var Foo;").has_root_symbol("Foo").test();
+}

tasks/coverage/snapshots/codegen_typescript.snap

@@ -1,5 +1,5 @@
 commit: 95e3aaa9
 
 codegen_typescript Summary:
-AST Parsed     : 9841/9841 (100.00%)
-Positive Passed: 9841/9841 (100.00%)
+AST Parsed     : 9840/9840 (100.00%)
+Positive Passed: 9840/9840 (100.00%)

tasks/coverage/snapshots/estree_typescript.snap

@@ -1,8 +1,8 @@
 commit: 95e3aaa9
 
 estree_typescript Summary:
-AST Parsed     : 9774/9774 (100.00%)
-Positive Passed: 9756/9774 (99.82%)
+AST Parsed     : 9773/9773 (100.00%)
+Positive Passed: 9755/9773 (99.82%)
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/moduleDetectionIsolatedModulesCjsFileScope.ts
 
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/moduleNodeImportRequireEmit.ts

tasks/coverage/snapshots/formatter_typescript.snap

@@ -1,8 +1,8 @@
 commit: 95e3aaa9
 
 formatter_typescript Summary:
-AST Parsed     : 9841/9841 (100.00%)
-Positive Passed: 9789/9841 (99.47%)
+AST Parsed     : 9840/9840 (100.00%)
+Positive Passed: 9788/9840 (99.47%)
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/amdLikeInputDeclarationEmit.ts
 
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/castExpressionParentheses.ts

tasks/coverage/snapshots/parser_typescript.snap

@@ -1,8 +1,8 @@
 commit: 95e3aaa9
 
 parser_typescript Summary:
-AST Parsed     : 9841/9841 (100.00%)
-Positive Passed: 9841/9841 (100.00%)
+AST Parsed     : 9840/9840 (100.00%)
+Positive Passed: 9840/9840 (100.00%)
 Negative Passed: 1530/2558 (59.81%)
 Expect Syntax Error: tasks/coverage/typescript/tests/cases/compiler/FunctionDeclaration3.ts
 

tasks/coverage/snapshots/semantic_typescript.snap

@@ -1,8 +1,8 @@
 commit: 95e3aaa9
 
 semantic_typescript Summary:
-AST Parsed     : 5483/5483 (100.00%)
-Positive Passed: 2951/5483 (53.82%)
+AST Parsed     : 5482/5482 (100.00%)
+Positive Passed: 2950/5482 (53.81%)
 semantic Error: tasks/coverage/typescript/tests/cases/compiler/2dArrays.ts
 Symbol reference IDs mismatch for "Cell":
 after transform: SymbolId(0): [ReferenceId(1)]

tasks/coverage/snapshots/transformer_typescript.snap

@@ -1,8 +1,8 @@
 commit: 95e3aaa9
 
 transformer_typescript Summary:
-AST Parsed     : 9841/9841 (100.00%)
-Positive Passed: 9819/9841 (99.78%)
+AST Parsed     : 9840/9840 (100.00%)
+Positive Passed: 9818/9840 (99.78%)
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/classOverloadForFunction.ts
 
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/exportSpecifierForAGlobal.ts

tasks/coverage/src/typescript/constants.rs

@@ -89,6 +89,9 @@ pub static NOT_SUPPORTED_TEST_PATHS: phf::Set<&'static str> = phf::phf_set![
     // TSC: Does not report errors since `.js` file with `checkJs: false`
     // OXC: Reports errors
     "plainJSRedeclare3.ts",
+    // TSC: Allows import+const redeclaration in `.js` file with `allowJs: true`
+    // OXC: Reports redeclaration error per ES spec
+    "usedImportNotElidedInJs.ts",
     // TSC: Parse without error, they support BOM
     // OXC: We do not ignore or exclude BOM, will be invalid character error
     "bom-utf16be.ts",