From e152bb95c588a13ce05b0434572bcad6c54728c9 Mon Sep 17 00:00:00 2001
From: Rich-Harris <richard.a.harris@gmail.com>
Date: Sun, 18 Sep 2016 15:03:20 -0400
Subject: [PATCH] warn on missing unused imports in deshadowing phase, rather
 than throwing - fixes #928

---
 src/ast/scopes/ModuleScope.js                        |  5 +++++
 .../warn-on-unused-missing-imports/_config.js        | 12 ++++++++++++
 test/function/warn-on-unused-missing-imports/foo.js  |  1 +
 test/function/warn-on-unused-missing-imports/main.js |  3 +++
 4 files changed, 21 insertions(+)
 create mode 100644 test/function/warn-on-unused-missing-imports/_config.js
 create mode 100644 test/function/warn-on-unused-missing-imports/foo.js
 create mode 100644 test/function/warn-on-unused-missing-imports/main.js

diff --git a/src/ast/scopes/ModuleScope.js b/src/ast/scopes/ModuleScope.js
index 051fcb4..5a18d6f 100644
--- a/src/ast/scopes/ModuleScope.js
+++ b/src/ast/scopes/ModuleScope.js
@@ -22,8 +22,13 @@ export default class ModuleScope extends Scope {
 			specifier.module.getExports().forEach( name => {
 				names.set(name);
 			});
+
 			if ( specifier.name !== '*' ) {
 				const declaration = specifier.module.traceExport( specifier.name );
+				if ( !declaration ) {
+					this.module.bundle.onwarn( `Non-existent export '${specifier.name}' is imported from ${specifier.module.id} by ${this.module.id}` );
+					return;
+				}
 				const name = declaration.getName( true );
 				if ( name !== specifier.name ) {
 					names.set( declaration.getName( true ) );
diff --git a/test/function/warn-on-unused-missing-imports/_config.js b/test/function/warn-on-unused-missing-imports/_config.js
new file mode 100644
index 0000000..16d69c1
--- /dev/null
+++ b/test/function/warn-on-unused-missing-imports/_config.js
@@ -0,0 +1,12 @@
+const path = require( 'path' );
+const assert = require( 'assert' );
+
+module.exports = {
+	solo: true,
+	description: 'warns on missing (but unused) imports',
+	warnings: warnings => {
+		assert.deepEqual( warnings, [
+			`Non-existent export 'b' is imported from ${path.resolve(__dirname, 'foo.js')} by ${path.resolve(__dirname, 'main.js')}`
+		]);
+	}
+};
diff --git a/test/function/warn-on-unused-missing-imports/foo.js b/test/function/warn-on-unused-missing-imports/foo.js
new file mode 100644
index 0000000..71becd3
--- /dev/null
+++ b/test/function/warn-on-unused-missing-imports/foo.js
@@ -0,0 +1 @@
+export const a = 42;
diff --git a/test/function/warn-on-unused-missing-imports/main.js b/test/function/warn-on-unused-missing-imports/main.js
new file mode 100644
index 0000000..7eaceb9
--- /dev/null
+++ b/test/function/warn-on-unused-missing-imports/main.js
@@ -0,0 +1,3 @@
+import { a, b } from './foo.js';
+
+assert.equal( a, 42 );