6 files changed, 45 insertions, 7 deletions
diff --git a/js/globals.ts b/js/globals.ts
index 45a4ccb01..af99ae7e0 100644
--- a/js/globals.ts
+++ b/js/globals.ts
@@ -104,3 +104,10 @@ export type TextDecoder = textEncoding.TextDecoder;
 window.performance = new performanceUtil.Performance();
 
 window.workerMain = workers.workerMain;
+
+// below are interfaces that are available in TypeScript but
+// have different signatures
+export interface ImportMeta {
+  url: string;
+  main: boolean;
+}
diff --git a/js/lib.web_assembly.d.ts b/js/lib.web_assembly.d.ts
index ccefdd077..8c357840a 100644
--- a/js/lib.web_assembly.d.ts
+++ b/js/lib.web_assembly.d.ts
@@ -170,10 +170,4 @@ declare namespace WebAssembly {
   }
 }
 
-// TODO Move ImportMeta intos its own lib.import_meta.d.ts file?
-interface ImportMeta {
-  url: string;
-  main: boolean;
-}
-
 /* eslint-enable @typescript-eslint/no-unused-vars, @typescript-eslint/no-explicit-any */
diff --git a/tools/ts_library_builder/ast_util.ts b/tools/ts_library_builder/ast_util.ts
index f18daa398..b43145e75 100644
--- a/tools/ts_library_builder/ast_util.ts
+++ b/tools/ts_library_builder/ast_util.ts
@@ -73,6 +73,21 @@ export function addTypeAlias(
   });
 }
 
+/** Add a declaration of an interface to a node */
+export function addInterfaceDeclaration(
+  node: StatementedNode,
+  interfaceDeclaration: InterfaceDeclaration
+) {
+  const interfaceStructure = interfaceDeclaration.getStructure();
+
+  return node.addInterface({
+    name: interfaceStructure.name,
+    properties: interfaceStructure.properties,
+    docs: interfaceStructure.docs,
+    hasDeclareKeyword: true
+  });
+}
+
 /** 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 0006a8aa4..c2d0ef109 100644
--- a/tools/ts_library_builder/build_library.ts
+++ b/tools/ts_library_builder/build_library.ts
@@ -2,6 +2,7 @@ import { writeFileSync } from "fs";
 import { join } from "path";
 import * as prettier from "prettier";
 import {
+  InterfaceDeclaration,
   ExpressionStatement,
   NamespaceDeclarationKind,
   Project,
@@ -11,6 +12,7 @@ import {
   TypeGuards
 } from "ts-morph";
 import {
+  addInterfaceDeclaration,
   addInterfaceProperty,
   addSourceComment,
   addTypeAlias,
@@ -219,6 +221,7 @@ export function mergeGlobal({
       node: ExpressionStatement;
     }
   >();
+  const globalInterfaces: InterfaceDeclaration[] = [];
 
   // For every augmentation of the global variable in source file, we want
   // to extract the type and add it to the global variable map
@@ -243,6 +246,8 @@ export function mergeGlobal({
           }
         }
       }
+    } else if (TypeGuards.isInterfaceDeclaration(node) && node.isExported()) {
+      globalInterfaces.push(node);
     }
   });
 
@@ -277,6 +282,11 @@ export function mergeGlobal({
     );
   }
 
+  // We need to copy over any interfaces
+  for (const interfaceDeclaration of globalInterfaces) {
+    addInterfaceDeclaration(targetSourceFile, interfaceDeclaration);
+  }
+
   // 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 b1a4ae344..c4c923490 100644
--- a/tools/ts_library_builder/test.ts
+++ b/tools/ts_library_builder/test.ts
@@ -162,7 +162,7 @@ function buildLibraryMerge() {
   assert(targetSourceFile.getNamespace("moduleF") != null);
   assert.equal(targetSourceFile.getNamespaces().length, 4);
   assert(targetSourceFile.getInterface("FooBar") != null);
-  assert.equal(targetSourceFile.getInterfaces().length, 1);
+  assert.equal(targetSourceFile.getInterfaces().length, 2);
   const variableDeclarations = targetSourceFile.getVariableDeclarations();
   assert.equal(variableDeclarations[0].getType().getText(), `FooBar`);
   assert.equal(variableDeclarations[1].getType().getText(), `FooBar`);
@@ -188,6 +188,14 @@ function buildLibraryMerge() {
   assert.equal(typeAliases[0].getName(), "Bar");
   assert.equal(typeAliases[0].getType().getText(), "moduleC.Bar");
   assert.equal(typeAliases.length, 1);
+  const exportedInterface = targetSourceFile.getInterfaceOrThrow("FizzBuzz");
+  const interfaceProperties = exportedInterface.getStructure().properties;
+  assert(interfaceProperties != null);
+  assert.equal(interfaceProperties!.length, 2);
+  assert.equal(interfaceProperties![0].name, "foo");
+  assert.equal(interfaceProperties![0].type, "string");
+  assert.equal(interfaceProperties![1].name, "bar");
+  assert.equal(interfaceProperties![1].type, "number");
 }
 
 function testInlineFiles() {
diff --git a/tools/ts_library_builder/testdata/globals.ts b/tools/ts_library_builder/testdata/globals.ts
index c6c6f9476..4fff7e8f9 100644
--- a/tools/ts_library_builder/testdata/globals.ts
+++ b/tools/ts_library_builder/testdata/globals.ts
@@ -9,3 +9,7 @@ foobarbaz.process = moduleE.process;
 foobarbaz.reprocess = moduleD.reprocess;
 foobarbaz.Bar = moduleC.Bar;
 export type Bar = moduleC.Bar;
+export interface FizzBuzz {
+  foo: string;
+  bar: number;
+}