5 files changed, 44 insertions, 8 deletions

diff --git a/tools/ts_library_builder/README.md b/tools/ts_library_builder/README.md
index de1305dca..e2701f0fb 100644
--- a/tools/ts_library_builder/README.md
+++ b/tools/ts_library_builder/README.md
@@ -72,17 +72,16 @@ like this:
   - This process assumes that all the modules that feed `js/deno.ts` will have a
     public type API that does not have name conflicts.
 - We process the `js/globals.ts` file to generate the global namespace.
-  - Currently we create a `"globals"` module which will contain the type
-    definitions.
   - We create a `Window` interface and a `global` scope augmentation namespace.
   - We iterate over augmentations to the `window` variable declared in the file,
     extract the type information and apply it to both a global variable
     declaration and a property on the `Window` interface.
+  - We identify any type aliases in the module and declare them globally.
 - We take each namespace import to `js/globals.ts`, we resolve the emitted
-  declaration `.d.ts` file and create it as its own namespace withing the
-  `"globals"` module. It is unsafe to just flatten these, because there is a
-  high risk of collisions, but also, it makes authoring the types easier within
-  the generated interface and variable declarations.
+  declaration `.d.ts` file and create it as its own namespace within the global
+  scope. It is unsafe to just flatten these, because there is a high risk of
+  collisions, but also, it makes authoring the types easier within the generated
+  interface and variable declarations.
 - We then validate the resulting definition file and write it out to the
   appropriate build path.
 
diff --git a/tools/ts_library_builder/ast_util.ts b/tools/ts_library_builder/ast_util.ts
index 528036b99..85d0a3480 100644
--- a/tools/ts_library_builder/ast_util.ts
+++ b/tools/ts_library_builder/ast_util.ts
@@ -42,6 +42,22 @@ export function addSourceComment(
   );
 }
 
+/** Add a declaration of a type alias to a node */
+export function addTypeAlias(
+  node: StatementedNode,
+  name: string,
+  type: string,
+  hasDeclareKeyword = false,
+  jsdocs?: JSDoc[]
+) {
+  return node.addTypeAlias({
+    name,
+    type,
+    docs: jsdocs && jsdocs.map(jsdoc => jsdoc.getText()),
+    hasDeclareKeyword
+  });
+}
+
 /** Add a declaration of a variable to a node */
 export function addVariableDeclaration(
   node: StatementedNode,
diff --git a/tools/ts_library_builder/build_library.ts b/tools/ts_library_builder/build_library.ts
index af3fb599d..e1a64215f 100644
--- a/tools/ts_library_builder/build_library.ts
+++ b/tools/ts_library_builder/build_library.ts
@@ -21,7 +21,8 @@ import {
   loadFiles,
   logDiagnostics,
   namespaceSourceFile,
-  normalizeSlashes
+  normalizeSlashes,
+  addTypeAlias
 } from "./ast_util";
 
 export interface BuildLibraryOptions {
@@ -216,6 +217,16 @@ export function mergeGlobal({
     addInterfaceProperty(interfaceDeclaration, property, type);
   }
 
+  // We need to copy over any type aliases
+  for (const typeAlias of sourceFile.getTypeAliases()) {
+    addTypeAlias(
+      targetSourceFile,
+      typeAlias.getName(),
+      typeAlias.getType().getText(sourceFile),
+      true
+    );
+  }
+
   // We need to ensure that we only namespace each source file once, so we
   // will use this map for tracking that.
   const sourceFileMap = new Map<SourceFile, string>();
diff --git a/tools/ts_library_builder/test.ts b/tools/ts_library_builder/test.ts
index 3a18fe29c..71b1d19a0 100644
--- a/tools/ts_library_builder/test.ts
+++ b/tools/ts_library_builder/test.ts
@@ -149,7 +149,15 @@ test(function buildLibraryMerge() {
     variableDeclarations[4].getType().getText(),
     `typeof moduleD.reprocess`
   );
-  assertEqual(variableDeclarations.length, 5);
+  assertEqual(
+    variableDeclarations[5].getType().getText(),
+    `typeof moduleC.Bar`
+  );
+  assertEqual(variableDeclarations.length, 6);
+  const typeAliases = targetSourceFile.getTypeAliases();
+  assertEqual(typeAliases[0].getName(), "Bar");
+  assertEqual(typeAliases[0].getType().getText(), "moduleC.Bar");
+  assertEqual(typeAliases.length, 1);
 });
 
 // TODO author unit tests for `ast_util.ts`
diff --git a/tools/ts_library_builder/testdata/globals.ts b/tools/ts_library_builder/testdata/globals.ts
index e80862025..9d117c794 100644
--- a/tools/ts_library_builder/testdata/globals.ts
+++ b/tools/ts_library_builder/testdata/globals.ts
@@ -8,3 +8,5 @@ foobarbaz.bar = new moduleC.Bar();
 foobarbaz.qat = moduleC.qat;
 foobarbaz.process = moduleE.process;
 foobarbaz.reprocess = moduleD.reprocess;
+foobarbaz.Bar = moduleC.Bar;
+export type Bar = moduleC.Bar;