From b0d6b3f578927b720cbe691cc488e427b6dc4b0f Mon Sep 17 00:00:00 2001
From: William Taylor <git@will.au>
Date: Fri, 14 Aug 2026 15:47:36 +1000
Subject: [PATCH] BridgeJS: Emit diagnostics from extensions properly

---
 .../BridgeJSCore/SwiftToSkeleton.swift        | 38 ++++++++++++++++---
 .../BridgeJSToolTests/DiagnosticsTests.swift  | 38 +++++++++++++++++++
 2 files changed, 71 insertions(+), 5 deletions(-)

diff --git a/Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift b/Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift
index f37bfb822..937ec5c41 100644
--- a/Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift
+++ b/Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift
@@ -222,15 +222,14 @@ public final class SwiftToSkeleton {
                 validatedJavaScriptModulePaths.insert(path)
             }
 
-            let exportErrors = exportCollector.errors.filter { $0.severity == .error }
             let importErrorsFatal = importCollector.errors.filter {
                 $0.severity == .error && !$0.message.contains("Unsupported type '")
             }
-            let fileWarnings = (exportCollector.errors + importCollector.errors).filter { $0.severity == .warning }
+            let fileWarnings = importCollector.errors.filter { $0.severity == .warning }
             warnings.append(contentsOf: fileWarnings.map { (file: inputFilePath, diagnostic: $0) })
-            if !exportErrors.isEmpty || !importErrorsFatal.isEmpty {
+            if !importErrorsFatal.isEmpty {
                 perSourceErrors.append(
-                    (inputFilePath: inputFilePath, errors: exportErrors + importErrorsFatal)
+                    (inputFilePath: inputFilePath, errors: importErrorsFatal)
                 )
             }
 
@@ -249,6 +248,18 @@ public final class SwiftToSkeleton {
             source.resolveDeferredExtensions(against: exportCollectors)
         }
 
+        // We have to collect diagnostics after all deferred extensions are resolved, since they could generate some.
+        for ((_, inputFilePath), exportCollector) in zip(sourceFiles, exportCollectors) {
+            let exportErrors = exportCollector.errors.filter { $0.severity == .error }
+            let fileWarnings = exportCollector.errors.filter { $0.severity == .warning }
+            warnings.append(contentsOf: fileWarnings.map { (file: inputFilePath, diagnostic: $0) })
+            if !exportErrors.isEmpty {
+                perSourceErrors.append(
+                    (inputFilePath: inputFilePath, errors: exportErrors)
+                )
+            }
+        }
+
         for collector in exportCollectors {
             collector.finalize(&exported)
         }
@@ -858,6 +869,17 @@ extension AttributeListSyntax {
     }
 }
 
+private final class JSAttributeFinder: SyntaxVisitor {
+    private(set) var found = false
+
+    override func visit(_ node: AttributeSyntax) -> SyntaxVisitorContinueKind {
+        if node.attributeNameText == "JS" {
+            found = true
+        }
+        return .skipChildren
+    }
+}
+
 private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
     var exportedFunctions: [ExportedFunction] = []
     /// The names of the exported classes, in the order they were written in the source file
@@ -1910,7 +1932,7 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
                     break
                 }
             }
-            if !resolved {
+            if !resolved, containsJSAnnotatedDeclaration(ext.memberBlock.members) {
                 diagnose(
                     node: ext.extendedType,
                     message: "Unsupported type '\(ext.extendedType.trimmedDescription)'.",
@@ -1920,6 +1942,12 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
         }
     }
 
+    private func containsJSAnnotatedDeclaration(_ members: MemberBlockItemListSyntax) -> Bool {
+        let finder = JSAttributeFinder(viewMode: .sourceAccurate)
+        finder.walk(members)
+        return finder.found
+    }
+
     /// Walks extension members under the matching type’s state, returning whether the type was found.
     ///
     /// Note: The lookup scans dictionaries keyed by `makeKey(name:namespace:)`, matching only by
diff --git a/Plugins/BridgeJS/Tests/BridgeJSToolTests/DiagnosticsTests.swift b/Plugins/BridgeJS/Tests/BridgeJSToolTests/DiagnosticsTests.swift
index 5abdf8fb2..4f45a9880 100644
--- a/Plugins/BridgeJS/Tests/BridgeJSToolTests/DiagnosticsTests.swift
+++ b/Plugins/BridgeJS/Tests/BridgeJSToolTests/DiagnosticsTests.swift
@@ -26,6 +26,44 @@ import Testing
         }
     }
 
+    @Test
+    func extensionOfUnknownTypeWithJSMemberProducesDiagnostic() throws {
+        let source = """
+            extension Unknown {
+                @JS func bridged() -> Int { 42 }
+            }
+            """
+        let diagnostics = try #require(moduleDiagnostics(source: source))
+        #expect(diagnostics.description.contains("Unsupported type 'Unknown'"))
+    }
+
+    @Test
+    func extensionWithoutJSMembersIsIgnored() throws {
+        let source = """
+            extension String {
+                func helper() -> Int { 42 }
+            }
+            """
+        #expect(moduleDiagnostics(source: source) == nil)
+    }
+
+    @Test
+    func invalidJSMemberInsideExtensionProducesDiagnostic() throws {
+        let source = """
+            @JS class Host {
+                @JS init() {}
+            }
+
+            extension Host {
+                @JS struct Bad {
+                    var field = 1
+                }
+            }
+            """
+        let diagnostics = try #require(moduleDiagnostics(source: source))
+        #expect(diagnostics.description.contains("Struct field must have explicit type annotation"))
+    }
+
     @Test
     func missingJavaScriptModuleProducesDiagnostic() throws {
         let source = """