From d1dcc76a27c2bf5809454f522001d13067f7ba15 Mon Sep 17 00:00:00 2001
From: Vignesh Shanmugam <vignesh.shanmugam22@gmail.com>
Date: Tue, 21 Mar 2017 17:36:22 +0100
Subject: [PATCH] handle default statements with fallthrough properly [fix
 #423]

---
 .../__tests__/simplify-test.js                | 26 +++++++++++++++++++
 .../babel-plugin-minify-simplify/src/index.js | 24 +++++++----------
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/packages/babel-plugin-minify-simplify/__tests__/simplify-test.js b/packages/babel-plugin-minify-simplify/__tests__/simplify-test.js
index f3c35fa84..9a35aedaa 100644
--- a/packages/babel-plugin-minify-simplify/__tests__/simplify-test.js
+++ b/packages/babel-plugin-minify-simplify/__tests__/simplify-test.js
@@ -3098,4 +3098,30 @@ describe("simplify-plugin", () => {
     }
     expect(transform(source)).toBe(expected);
   });
+
+  it("should fix issue#423 with fallthrough in default case", () => {
+    const source = unpad(
+      `
+      function foo(bar) {
+        switch (bar) {
+          case 'a':
+            return 1;
+          case 'b':
+          default:
+            return 4;
+          case 'c':
+            return 3;
+        }
+      }
+    `
+    );
+    const expected = unpad(
+      `
+      function foo(bar) {
+        return bar === 'a' ? 1 : bar === 'c' ? 3 : 4;
+      }
+    `
+    );
+    expect(transform(source)).toBe(expected);
+  });
 });
diff --git a/packages/babel-plugin-minify-simplify/src/index.js b/packages/babel-plugin-minify-simplify/src/index.js
index d4960e4bc..9a0c1d8d9 100644
--- a/packages/babel-plugin-minify-simplify/src/index.js
+++ b/packages/babel-plugin-minify-simplify/src/index.js
@@ -1263,7 +1263,7 @@ module.exports = ({ types: t }) => {
               return;
             }
 
-            const consTestPairs = [];
+            let consTestPairs = [];
             let fallThru = [];
             let defaultRet;
             for (const switchCase of node.cases) {
@@ -1273,6 +1273,7 @@ module.exports = ({ types: t }) => {
 
               const cons = switchCase.consequent[0];
 
+              // default case
               if (!switchCase.test) {
                 if (!t.isReturnStatement(cons)) {
                   return;
@@ -1282,11 +1283,7 @@ module.exports = ({ types: t }) => {
               }
 
               if (!switchCase.consequent.length) {
-                if (fallThru.length) {
-                  fallThru.push(switchCase.test);
-                } else {
-                  fallThru = [switchCase.test];
-                }
+                fallThru.push(switchCase.test);
                 continue;
               }
 
@@ -1300,7 +1297,8 @@ module.exports = ({ types: t }) => {
                 node.discriminant,
                 switchCase.test
               );
-              if (fallThru.length) {
+
+              if (fallThru.length && !defaultRet) {
                 test = fallThru.reduceRight(
                   (right, test) =>
                     t.logicalExpression(
@@ -1310,8 +1308,8 @@ module.exports = ({ types: t }) => {
                     ),
                   test
                 );
-                fallThru = [];
               }
+              fallThru = [];
 
               consTestPairs.push([test, cons.argument || VOID_0]);
             }
@@ -1387,11 +1385,7 @@ module.exports = ({ types: t }) => {
               }
 
               if (!switchCase.consequent.length) {
-                if (fallThru.length) {
-                  fallThru.push(switchCase.test);
-                } else {
-                  fallThru = [switchCase.test];
-                }
+                fallThru.push(switchCase.test);
                 continue;
               }
 
@@ -1416,7 +1410,7 @@ module.exports = ({ types: t }) => {
                 node.discriminant,
                 switchCase.test
               );
-              if (fallThru.length) {
+              if (fallThru.length && !defaultExpr) {
                 test = fallThru.reduceRight(
                   (right, test) =>
                     t.logicalExpression(
@@ -1426,8 +1420,8 @@ module.exports = ({ types: t }) => {
                     ),
                   test
                 );
-                fallThru = [];
               }
+              fallThru = [];
 
               exprTestPairs.push([test, cons.expression]);
             }