Fix incorrect function hoisting in some case statements (#16363)

packages/babel-core/src/transformation/block-hoist-plugin.ts

@@ -23,29 +23,40 @@ const blockHoistPlugin: PluginObject = {
   visitor: {
     Block: {
       exit({ node }) {
-        const { body } = node;
-
-        // Largest SMI
-        let max = 2 ** 30 - 1;
-        let hasChange = false;
-        for (let i = 0; i < body.length; i++) {
-          const n = body[i];
-          const p = priority(n);
-          if (p > max) {
-            hasChange = true;
-            break;
-          }
-          max = p;
-        }
-        if (!hasChange) return;
-
-        // My kingdom for a stable sort!
-        node.body = stableSort(body.slice());
+        node.body = performHoisting(node.body);
+      },
+    },
+    SwitchCase: {
+      exit({ node }) {
+        // In case statements, hoisting is difficult to perform correctly due to
+        // functions that are declared and referenced in different blocks.
+        // Nevertheless, hoisting the statements *inside* of each case should at
+        // least mitigate the failure cases.
+        node.consequent = performHoisting(node.consequent);
       },
     },
   },
 };
 
+function performHoisting(body: Statement[]): Statement[] {
+  // Largest SMI
+  let max = 2 ** 30 - 1;
+  let hasChange = false;
+  for (let i = 0; i < body.length; i++) {
+    const n = body[i];
+    const p = priority(n);
+    if (p > max) {
+      hasChange = true;
+      break;
+    }
+    max = p;
+  }
+  if (!hasChange) return body;
+
+  // My kingdom for a stable sort!
+  return stableSort(body.slice());
+}
+
 export default function loadBlockHoistPlugin(): Plugin {
   if (!LOADED_PLUGIN) {
     // cache the loaded blockHoist plugin plugin

packages/babel-plugin-transform-block-scoped-functions/test/fixtures/block-scoped-functions/issue-14960/input.js

@@ -0,0 +1,9 @@
+{
+  switch (1) {
+    case 1:
+      expect(f()).toBe(1);
+      function f() {
+        return 1;
+      }
+  }
+}

packages/babel-plugin-transform-block-scoped-functions/test/fixtures/block-scoped-functions/issue-14960/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["transform-block-scoped-functions"]
+}

packages/babel-plugin-transform-block-scoped-functions/test/fixtures/block-scoped-functions/issue-14960/output.js

@@ -0,0 +1,9 @@
+{
+  switch (1) {
+    case 1:
+      let f = function () {
+        return 1;
+      };
+      expect(f()).toBe(1);
+  }
+}

packages/babel-plugin-transform-block-scoping/test/fixtures/general/switch/output.js

@@ -19,6 +19,6 @@ switch (true) {
     var _c = 4;
     var _d = 5;
   case false:
-    class _e {}
     var _f = function () {};
+    class _e {}
 }