From ddaeac7e1005bf9d3729a0b7a03b005a0b5039e3 Mon Sep 17 00:00:00 2001
From: Devon Govett <devongovett@gmail.com>
Date: Sun, 5 May 2019 21:08:48 -0700
Subject: [PATCH] Shake exports with pure property assignments (#2909)

---
 .../scope-hoisting/es6/pure-assignment/a.js   |  3 ++
 .../scope-hoisting/es6/pure-assignment/b.js   |  4 +++
 packages/shared/scope-hoisting/src/shake.js   | 31 +++++++++----------
 3 files changed, 22 insertions(+), 16 deletions(-)
 create mode 100644 packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/a.js
 create mode 100644 packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/b.js

diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/a.js b/packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/a.js
new file mode 100644
index 00000000000..229761a608f
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/a.js
@@ -0,0 +1,3 @@
+import {foo} from './b';
+
+output = foo;
diff --git a/packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/b.js b/packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/b.js
new file mode 100644
index 00000000000..919f23d1fca
--- /dev/null
+++ b/packages/core/integration-tests/test/integration/scope-hoisting/es6/pure-assignment/b.js
@@ -0,0 +1,4 @@
+export const foo = 2;
+
+export function bar() {}
+bar.displayName = 'hello';
diff --git a/packages/shared/scope-hoisting/src/shake.js b/packages/shared/scope-hoisting/src/shake.js
index fcbdef43ade..b5847fe734a 100644
--- a/packages/shared/scope-hoisting/src/shake.js
+++ b/packages/shared/scope-hoisting/src/shake.js
@@ -1,7 +1,5 @@
 import * as t from '@babel/types';
 
-const EXPORTS_RE = /^\$([^$]+)\$exports$/;
-
 /**
  * This is a small small implementation of dead code removal specialized to handle
  * removing unused exports. All other dead code removal happens in workers on each
@@ -42,31 +40,24 @@ function getUnusedBinding(path, name) {
     return null;
   }
 
-  if (isPure(binding)) {
+  let pure = isPure(binding);
+  if (!binding.referenced && pure) {
     return binding;
   }
 
-  if (!EXPORTS_RE.test(name)) {
-    return null;
-  }
-
   // Is there any references which aren't simple assignments?
   let bailout = binding.referencePaths.some(
     path => !isExportAssignment(path) && !isUnusedWildcard(path)
   );
 
-  if (bailout) {
-    return null;
-  } else {
+  if (!bailout && pure) {
     return binding;
   }
+
+  return null;
 }
 
 function isPure(binding) {
-  if (binding.referenced) {
-    return false;
-  }
-
   if (
     binding.path.isVariableDeclarator() &&
     binding.path.get('id').isIdentifier()
@@ -83,7 +74,8 @@ function isExportAssignment(path) {
     // match "path.any = any;"
     path.parentPath.isMemberExpression() &&
     path.parentPath.parentPath.isAssignmentExpression() &&
-    path.parentPath.parentPath.node.left === path.parentPath.node
+    path.parentPath.parentPath.node.left === path.parentPath.node &&
+    path.parentPath.parentPath.get('right').isPure()
   );
 }
 
@@ -118,6 +110,13 @@ function remove(path) {
   } else if (isUnusedWildcard(path)) {
     remove(path.parentPath);
   } else if (!path.removed) {
-    path.remove();
+    if (
+      path.parentPath.isSequenceExpression() &&
+      path.parent.expressions.length === 1
+    ) {
+      path.parentPath.remove();
+    } else {
+      path.remove();
+    }
   }
 }