From df09db7518019c13c939805895501f6e390f9ece Mon Sep 17 00:00:00 2001
From: Alan Pierce <alangpierce@gmail.com>
Date: Mon, 14 Aug 2017 08:33:00 -0700
Subject: [PATCH] fix: don't convert `var` to `let` or `const` in a switch case
 (#136)

Fixes https://github.com/decaffeinate/decaffeinate/issues/1171

Potentially add-variable-declarations and esnext could be smarter in this case,
e.g. by declaring the variable outside the switch or even creating a block
scope, but the easy thing is to just keep the declaration as `var`. Since `var`
doesn't have a temporal dead zone, a declaration in any switch case will work
for all switch cases.
---
 .../mostRestrictiveKindForDeclaration.js      |  4 +
 .../var-in-switch/_expected/main.js           | 10 +++
 .../var-in-switch/_expected/metadata.json     |  5 ++
 .../var-in-switch/_expected/warnings.json     | 76 +++++++++++++++++++
 .../var-in-switch/config.json                 |  3 +
 .../var-in-switch/main.js                     | 10 +++
 6 files changed, 108 insertions(+)
 create mode 100644 test/form/declarations.block-scope/var-in-switch/_expected/main.js
 create mode 100644 test/form/declarations.block-scope/var-in-switch/_expected/metadata.json
 create mode 100644 test/form/declarations.block-scope/var-in-switch/_expected/warnings.json
 create mode 100644 test/form/declarations.block-scope/var-in-switch/config.json
 create mode 100644 test/form/declarations.block-scope/var-in-switch/main.js

diff --git a/src/utils/mostRestrictiveKindForDeclaration.js b/src/utils/mostRestrictiveKindForDeclaration.js
index c1fac537..3f8788ab 100644
--- a/src/utils/mostRestrictiveKindForDeclaration.js
+++ b/src/utils/mostRestrictiveKindForDeclaration.js
@@ -13,6 +13,10 @@ export default function mostRestrictiveKindForDeclaration(path: Path): Declarati
   let { scope } = path;
   let isConst = path.node.declarations.every(declaration => declaration.init);
 
+  if (t.isSwitchCase(path.parent)) {
+    return 'var';
+  }
+
   for (let id in ids) {
     let binding = scope.getBinding(id);
 
diff --git a/test/form/declarations.block-scope/var-in-switch/_expected/main.js b/test/form/declarations.block-scope/var-in-switch/_expected/main.js
new file mode 100644
index 00000000..1cd3ad0a
--- /dev/null
+++ b/test/form/declarations.block-scope/var-in-switch/_expected/main.js
@@ -0,0 +1,10 @@
+switch (a) {
+  case 1:
+    var x = 1;
+    console.log(x);
+    break;
+  case 2:
+    x = 2;
+    console.log(x);
+    break;
+}
diff --git a/test/form/declarations.block-scope/var-in-switch/_expected/metadata.json b/test/form/declarations.block-scope/var-in-switch/_expected/metadata.json
new file mode 100644
index 00000000..eb7dd968
--- /dev/null
+++ b/test/form/declarations.block-scope/var-in-switch/_expected/metadata.json
@@ -0,0 +1,5 @@
+{
+  "declarations.block-scope": {
+    "declarations": []
+  }
+}
\ No newline at end of file
diff --git a/test/form/declarations.block-scope/var-in-switch/_expected/warnings.json b/test/form/declarations.block-scope/var-in-switch/_expected/warnings.json
new file mode 100644
index 00000000..2f13f771
--- /dev/null
+++ b/test/form/declarations.block-scope/var-in-switch/_expected/warnings.json
@@ -0,0 +1,76 @@
+[
+  {
+    "node": {
+      "type": "VariableDeclaration",
+      "start": 27,
+      "end": 37,
+      "loc": {
+        "start": {
+          "line": 3,
+          "column": 4
+        },
+        "end": {
+          "line": 3,
+          "column": 14
+        }
+      },
+      "declarations": [
+        {
+          "type": "VariableDeclarator",
+          "start": 31,
+          "end": 36,
+          "loc": {
+            "start": {
+              "line": 3,
+              "column": 8
+            },
+            "end": {
+              "line": 3,
+              "column": 13
+            }
+          },
+          "id": {
+            "type": "Identifier",
+            "start": 31,
+            "end": 32,
+            "loc": {
+              "start": {
+                "line": 3,
+                "column": 8
+              },
+              "end": {
+                "line": 3,
+                "column": 9
+              },
+              "identifierName": "x"
+            },
+            "name": "x"
+          },
+          "init": {
+            "type": "NumericLiteral",
+            "start": 35,
+            "end": 36,
+            "loc": {
+              "start": {
+                "line": 3,
+                "column": 12
+              },
+              "end": {
+                "line": 3,
+                "column": 13
+              }
+            },
+            "extra": {
+              "rawValue": 1,
+              "raw": "1"
+            },
+            "value": 1
+          }
+        }
+      ],
+      "kind": "var"
+    },
+    "type": "unsupported-declaration",
+    "message": "'var' declaration cannot be converted to block scope"
+  }
+]
\ No newline at end of file
diff --git a/test/form/declarations.block-scope/var-in-switch/config.json b/test/form/declarations.block-scope/var-in-switch/config.json
new file mode 100644
index 00000000..065dfd4a
--- /dev/null
+++ b/test/form/declarations.block-scope/var-in-switch/config.json
@@ -0,0 +1,3 @@
+{
+  "description": "does not convert `var` declarations within switch cases"
+}
diff --git a/test/form/declarations.block-scope/var-in-switch/main.js b/test/form/declarations.block-scope/var-in-switch/main.js
new file mode 100644
index 00000000..1cd3ad0a
--- /dev/null
+++ b/test/form/declarations.block-scope/var-in-switch/main.js
@@ -0,0 +1,10 @@
+switch (a) {
+  case 1:
+    var x = 1;
+    console.log(x);
+    break;
+  case 2:
+    x = 2;
+    console.log(x);
+    break;
+}