From 3b37387e7e436004eb832e995a304fbe5589606d Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Wed, 4 Oct 2017 13:45:49 +0200
Subject: [PATCH 1/2] Bail for binary 'in' expressions - fix #691

---
 .../__tests__/dead-code-elimination-test.js   | 13 ++++++++
 .../src/index.js                              | 33 ++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
index 045305e7d..3c4519e14 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js
@@ -2503,4 +2503,17 @@ describe("dce-plugin", () => {
       plugins: [[deadcode, { tdz: true }]]
     }
   );
+
+  thePlugin(
+    "should bail for binary `in` expressions - fix #691",
+    `
+      function foo(props) {
+        let bar = "width" in props;
+        delete props.width;
+        if (bar) {
+          console.log("foo");
+        }
+      }
+    `
+  );
 });
diff --git a/packages/babel-plugin-minify-dead-code-elimination/src/index.js b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
index e15fae757..7fcb48c04 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/src/index.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
@@ -390,7 +390,9 @@ module.exports = ({ types: t, traverse }) => {
               const isObj = n =>
                 t.isFunction(n) ||
                 t.isObjectExpression(n) ||
-                t.isArrayExpression(n);
+                t.isArrayExpression(n) ||
+                t.isBinaryExpression(n, { operator: "in" });
+
               const isReplacementObj =
                 isObj(replacement) || some(replacement, isObj);
 
@@ -398,6 +400,35 @@ module.exports = ({ types: t, traverse }) => {
                 continue;
               }
 
+              // check if it's safe to replace
+              // To solve https://github.com/babel/minify/issues/691
+              // Here we bail for property checks using the "in" operator
+              // This is because - `in` is a side-effect-free operation but the property
+              // could be deleted between the replacementPath and referencePath
+              // It is expensive to compute the delete operation and we bail for
+              // all the binary "in" operations
+              let inExpression = replacementPath.isBinaryExpression({
+                operator: "in"
+              });
+
+              if (!inExpression) {
+                replacementPath.traverse({
+                  Function(path) {
+                    path.skip();
+                  },
+                  BinaryExpression(path) {
+                    if (path.node.operator === "in") {
+                      inExpression = true;
+                      path.stop();
+                    }
+                  }
+                });
+              }
+
+              if (inExpression) {
+                continue;
+              }
+
               const replaced = replace(binding.referencePaths[0], {
                 binding,
                 scope,

From b710aaf670537bf07aeeedfb3c0a21cb0083763a Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <me@boopathi.in>
Date: Wed, 4 Oct 2017 13:52:39 +0200
Subject: [PATCH 2/2] Remove unnecessary code

---
 .../babel-plugin-minify-dead-code-elimination/src/index.js     | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/babel-plugin-minify-dead-code-elimination/src/index.js b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
index 7fcb48c04..90e7fc998 100644
--- a/packages/babel-plugin-minify-dead-code-elimination/src/index.js
+++ b/packages/babel-plugin-minify-dead-code-elimination/src/index.js
@@ -390,8 +390,7 @@ module.exports = ({ types: t, traverse }) => {
               const isObj = n =>
                 t.isFunction(n) ||
                 t.isObjectExpression(n) ||
-                t.isArrayExpression(n) ||
-                t.isBinaryExpression(n, { operator: "in" });
+                t.isArrayExpression(n);
 
               const isReplacementObj =
                 isObj(replacement) || some(replacement, isObj);