fix corner case in reduce_vars (#5891)

fixes #5890

Author: alexlamsl

lib/compress.js

@@ -1397,15 +1397,24 @@ Compressor.prototype.compress = function(node) {
                     first = false;
                     push(tw, true);
                 }
-            })
+            });
             if (!first) pop(tw);
-            walk_body(node, tw);
+            var defined_ids = tw.defined_ids;
+            var safe_ids = tw.safe_ids;
+            node.body.forEach(function(branch) {
+                push(tw, true);
+                branch.walk(tw);
+                if (aborts(branch)) {
+                    tw.defined_ids = defined_ids;
+                    tw.safe_ids = safe_ids;
+                }
+            });
+            tw.defined_ids = defined_ids;
+            tw.safe_ids = safe_ids;
             return true;
         });
         def(AST_SwitchBranch, function(tw) {
-            push(tw, true);
             walk_body(this, tw);
-            pop(tw);
             return true;
         });
         def(AST_SymbolCatch, function() {
@@ -1501,7 +1510,7 @@ Compressor.prototype.compress = function(node) {
             }
             mark_fn_def(tw, d, value);
         });
-        def(AST_Template, function(tw, descend) {
+        def(AST_Template, function(tw) {
             var node = this;
             var tag = node.tag;
             if (!tag) return;
@@ -1549,7 +1558,7 @@ Compressor.prototype.compress = function(node) {
             if (node.bfinally) node.bfinally.walk(tw);
             return true;
         });
-        def(AST_Unary, function(tw, descend) {
+        def(AST_Unary, function(tw) {
             var node = this;
             if (!UNARY_POSTFIX[node.operator]) return;
             var exp = node.expression;

test/compress/functions.js

@@ -5720,9 +5720,9 @@ issue_3929: {
             var abc = function f() {
                 (function() {
                     switch (f) {
-                    default:
+                      default:
                         var abc = 0;
-                    case 0:
+                      case 0:
                         abc.p;
                     }
                     console.log(typeof f);
@@ -5736,10 +5736,9 @@ issue_3929: {
             var abc = function f() {
                 (function() {
                     switch (f) {
-                    default:
-                        var abc = 0;
-                    case 0:
-                        abc.p;
+                      default:
+                      case 0:
+                        0..p;
                     }
                     console.log(typeof f);
                 })();

test/compress/switches.js

@@ -1688,3 +1688,42 @@ issue_5543_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5890: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = {};
+        a.p;
+        try {
+            switch (42) {
+              default:
+                a = null;
+              case false:
+                a.q;
+            }
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = {};
+        a.p;
+        try {
+            switch (42) {
+              default:
+                a = null;
+              case false:
+                a.q;
+            }
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}