Support import completion for merged declaration exports

Author: dfreeman

src/services/codefixes/importFixes.ts

@@ -111,7 +111,7 @@ namespace ts.codefix {
             }
 
             for (const exported of checker.getExportsOfModule(moduleSymbol)) {
-                if ((exported.escapedName === InternalSymbolName.Default || exported.name === symbolName) && skipAlias(exported, checker) === exportedSymbol) {
+                if ((exported.escapedName === InternalSymbolName.Default || exported.name === symbolName) && exported.declarations.some(decl => skipAlias(decl.symbol, checker) === exportedSymbol)) {
                     const isDefaultExport = checker.tryGetMemberInModuleExports(InternalSymbolName.Default, moduleSymbol) === exported;
                     result.push({ moduleSymbol, importKind: isDefaultExport ? ImportKind.Default : ImportKind.Named });
                 }

tests/cases/fourslash/completionsImport_default_fromMergedDeclarations.ts

@@ -0,0 +1,31 @@
+/// <reference path="fourslash.ts" />
+
+// @module: esnext
+
+// @Filename: /a.ts
+////declare module "m" {
+////    export default class M {}
+////}
+
+// @Filename: /b.ts
+////declare module "m" {
+////    export default interface M {}
+////}
+
+// @Filename: /c.ts
+/////**/
+
+goTo.marker("");
+verify.completionListContains({ name: "M", source: "m" }, "class M", "", "class", /*spanIndex*/ undefined, /*hasAction*/ true, {
+    includeCompletionsForModuleExports: true,
+    sourceDisplay: "m",
+});
+
+verify.applyCodeActionFromCompletion("", {
+    name: "M",
+    source: "m",
+    description: `Import 'M' from module "m"`,
+    newFileContent: `import M from "m";
+
+`,
+});