Fix "Cannot compile namespaces" error with --isolatedModules and no namespaces

src/compiler/parser.ts

@@ -465,6 +465,10 @@ namespace ts {
         return file.externalModuleIndicator !== undefined;
     }
 
+    export function isInternalModule(file: SourceFile): boolean {
+        return file.internalModuleIndicator !== undefined;
+    }
+
     // Produces a new SourceFile for the 'newText' provided. The 'textChangeRange' parameter
     // indicates what changed between the 'text' that this SourceFile has and the 'newText'.
     // The SourceFile will be created with the compiler attempting to reuse as many nodes from
@@ -677,7 +681,7 @@ namespace ts {
             Debug.assert(token() === SyntaxKind.EndOfFileToken);
             sourceFile.endOfFileToken = <EndOfFileToken>parseTokenNode();
 
-            setExternalModuleIndicator(sourceFile);
+            setInternalExternalModuleIndicators(sourceFile)
 
             sourceFile.nodeCount = nodeCount;
             sourceFile.identifierCount = identifierCount;
@@ -5914,15 +5918,20 @@ namespace ts {
             sourceFile.checkJsDirective = checkJsDirective;
         }
 
-        function setExternalModuleIndicator(sourceFile: SourceFile) {
-            sourceFile.externalModuleIndicator = forEach(sourceFile.statements, node =>
-                hasModifier(node, ModifierFlags.Export)
+        function setInternalExternalModuleIndicators(sourceFile: SourceFile) {
+            forEach(sourceFile.statements, node => {
+                if (hasModifier(node, ModifierFlags.Export)
                     || node.kind === SyntaxKind.ImportEqualsDeclaration && (<ImportEqualsDeclaration>node).moduleReference.kind === SyntaxKind.ExternalModuleReference
                     || node.kind === SyntaxKind.ImportDeclaration
                     || node.kind === SyntaxKind.ExportAssignment
                     || node.kind === SyntaxKind.ExportDeclaration
-                    ? node
-                    : undefined);
+                ) {
+                    sourceFile.externalModuleIndicator = node
+                }
+                else if (node.kind === SyntaxKind.ModuleDeclaration || node.kind === SyntaxKind.NamespaceImport) {
+                    sourceFile.internalModuleIndicator = node
+                }
+            })
         }
 
         const enum ParsingContext {

src/compiler/program.ts

@@ -1849,7 +1849,7 @@ namespace ts {
                     programDiagnostics.add(createCompilerDiagnostic(Diagnostics.Option_isolatedModules_can_only_be_used_when_either_option_module_is_provided_or_option_target_is_ES2015_or_higher));
                 }
 
-                const firstNonExternalModuleSourceFile = forEach(files, f => !isExternalModule(f) && !isDeclarationFile(f) ? f : undefined);
+                const firstNonExternalModuleSourceFile = forEach(files, f => isInternalModule(f) && !isDeclarationFile(f) ? f : undefined);
                 if (firstNonExternalModuleSourceFile) {
                     const span = getErrorSpanForNode(firstNonExternalModuleSourceFile, firstNonExternalModuleSourceFile);
                     programDiagnostics.add(createFileDiagnostic(firstNonExternalModuleSourceFile, span.start, span.length, Diagnostics.Cannot_compile_namespaces_when_the_isolatedModules_flag_is_provided));

src/compiler/types.ts

@@ -2297,6 +2297,8 @@ namespace ts {
 
         // The first node that causes this file to be an external module
         /* @internal */ externalModuleIndicator: Node;
+        // The first node that causes this file to be an internal module
+        /* @internal */ internalModuleIndicator?: Node;
         // The first node that causes this file to be a CommonJS module
         /* @internal */ commonJsModuleIndicator: Node;
 

src/harness/harness.ts

@@ -189,7 +189,7 @@ namespace Utils {
             ts.forEachChild(node, child => { childNodesAndArrays.push(child); }, array => { childNodesAndArrays.push(array); });
 
             for (const childName in node) {
-                if (childName === "parent" || childName === "nextContainer" || childName === "modifiers" || childName === "externalModuleIndicator" ||
+                if (childName === "parent" || childName === "nextContainer" || childName === "modifiers" || childName === "externalModuleIndicator" || childName === "internalModuleIndicator" ||
                     // for now ignore jsdoc comments
                     childName === "jsDocComment" || childName === "checkJsDirective") {
                     continue;