From 415144a7f448b9450233d915740c72ed254728bd Mon Sep 17 00:00:00 2001
From: Samuel Reed <samuel.trace.reed@gmail.com>
Date: Sat, 5 Nov 2016 11:15:57 -0500
Subject: [PATCH] feature: Support pure expressions in
 transform-react-constant-elements

---
 .../src/index.js                              | 28 +++++++++++++++++--
 .../constant-elements/pure-deopt/actual.js    |  5 ++++
 .../constant-elements/pure-deopt/expected.js  |  5 ++++
 .../pure-expression-2/actual.js               |  5 ++++
 .../pure-expression-2/expected.js             |  8 ++++++
 .../pure-expression-3/actual.js               | 10 +++++++
 .../pure-expression-3/expected.js             | 10 +++++++
 .../pure-expression/actual.js                 | 11 ++++++++
 .../pure-expression/expected.js               |  8 ++++++
 9 files changed, 88 insertions(+), 2 deletions(-)
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js
 create mode 100644 packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js

diff --git a/packages/babel-plugin-transform-react-constant-elements/src/index.js b/packages/babel-plugin-transform-react-constant-elements/src/index.js
index a25fb67e6c6d..e9ff6950ec70 100644
--- a/packages/babel-plugin-transform-react-constant-elements/src/index.js
+++ b/packages/babel-plugin-transform-react-constant-elements/src/index.js
@@ -1,4 +1,4 @@
-export default function () {
+export default function ({ types: t }) {
   const immutabilityVisitor = {
     enter(path, state) {
       const stop = () => {
@@ -11,15 +11,39 @@ export default function () {
         return;
       }
 
+      // Elements with refs are not safe to hoist.
       if (path.isJSXIdentifier({ name: "ref" }) && path.parentPath.isJSXAttribute({ name: path.node })) {
         return stop();
       }
 
+      // Ignore identifiers & JSX expressions.
       if (path.isJSXIdentifier() || path.isIdentifier() || path.isJSXMemberExpression()) {
         return;
       }
 
-      if (!path.isImmutable()) stop();
+      if (!path.isImmutable()) {
+        // If it's not immutable, it may still be a pure expression.
+        if (path.isPure()) {
+          // If it's statically evaluatable, then evaluate it.
+          const expressionResult = path.evaluate();
+          if (expressionResult.confident) {
+            const resultNode = t.valueToNode(expressionResult.value);
+            // If it evaluated to an immutable value, we can use it.
+            // If not, it is not safe to replace as mutable values could
+            // be mutated after render.
+            // https://github.com/facebook/react/issues/3226
+            if (t.isImmutable(resultNode)) {
+              path.replaceWith(resultNode);
+              path.skip();
+              return;
+            }
+          } else if (t.isIdentifier(expressionResult.deopt)) {
+            // It's safe to stop here if the deopt reason is an identifier.
+            return;
+          }
+        }
+        stop();
+      }
     }
   };
 
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js
new file mode 100644
index 000000000000..4df51832c7ce
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/actual.js
@@ -0,0 +1,5 @@
+// https://github.com/facebook/react/issues/3226
+// Not safe to reuse because it is mutable
+function render() {
+  return <div style={{ width: 100 }} />;
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js
new file mode 100644
index 000000000000..4df51832c7ce
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-deopt/expected.js
@@ -0,0 +1,5 @@
+// https://github.com/facebook/react/issues/3226
+// Not safe to reuse because it is mutable
+function render() {
+  return <div style={{ width: 100 }} />;
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js
new file mode 100644
index 000000000000..0acb75cfaf6a
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/actual.js
@@ -0,0 +1,5 @@
+function render(offset) {
+  return function () {
+    return <div tabIndex={offset + 1} />;
+  };
+}
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js
new file mode 100644
index 000000000000..65df627806b2
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-2/expected.js
@@ -0,0 +1,8 @@
+function render(offset) {
+  var _ref = <div tabIndex={offset + 1} />;
+
+  return function () {
+    return _ref;
+  };
+}
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js
new file mode 100644
index 000000000000..c6b89c77fd1a
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/actual.js
@@ -0,0 +1,10 @@
+const OFFSET = 3;
+
+var Foo = React.createClass({
+  render: function () {
+    return (
+      <div tabIndex={OFFSET + 1} />
+    );
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js
new file mode 100644
index 000000000000..a494d251dc48
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression-3/expected.js
@@ -0,0 +1,10 @@
+const OFFSET = 3;
+
+var _ref = <div tabIndex={4} />;
+
+var Foo = React.createClass({
+  render: function () {
+    return _ref;
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js
new file mode 100644
index 000000000000..5131c839899b
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/actual.js
@@ -0,0 +1,11 @@
+var Foo = React.createClass({
+  render: function () {
+    return (
+      <div data-text={
+        "Some text, " +
+        "and some more too."
+      } />
+    );
+  }
+});
+
diff --git a/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js
new file mode 100644
index 000000000000..4d5e06872e1b
--- /dev/null
+++ b/packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/pure-expression/expected.js
@@ -0,0 +1,8 @@
+var _ref = <div data-text={"Some text, and some more too."} />;
+
+var Foo = React.createClass({
+  render: function () {
+    return _ref;
+  }
+});
+