From fac0aa2b8aca8605835e604afe8b39903cc89b75 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L." <alexlamsl@gmail.com>
Date: Fri, 26 Jul 2024 04:10:29 +0300
Subject: [PATCH] fix corner case in `reduce_vars` (#5893)

fixes #5892
---
 lib/compress.js              | 27 ++++++--------
 test/compress/functions.js   |  3 +-
 test/compress/reduce_vars.js | 33 +++++++++++++++++
 test/compress/switches.js    | 71 ++++++++++++++++++++++++++++++++++++
 4 files changed, 117 insertions(+), 17 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 725ef91fc07..8e135e2df7e 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -641,7 +641,7 @@ Compressor.prototype.compress = function(node) {
             var defined_ids = Object.create(tw.defined_ids);
             var safe_ids = Object.create(tw.safe_ids);
             if (!sequential) {
-                defined_ids.seq = {};
+                defined_ids.seq = Object.create(null);
                 safe_ids.seq = {};
             }
             tw.defined_ids = defined_ids;
@@ -654,18 +654,22 @@ Compressor.prototype.compress = function(node) {
         }
 
         function access(tw, def) {
-            tw.defined_ids[def.id] = tw.defined_ids.seq;
+            var seq = tw.defined_ids.seq;
+            tw.defined_ids[def.id] = seq;
+            seq[def.id] = true;
         }
 
         function assign(tw, def) {
-            tw.assigned_ids[def.id] = tw.defined_ids.seq;
-            tw.defined_ids[def.id] = false;
+            var seq = tw.defined_ids.seq;
+            tw.assigned_ids[def.id] = seq;
+            seq[def.id] = false;
         }
 
         function safe_to_access(tw, def) {
             var seq = tw.defined_ids.seq;
             var defined = tw.defined_ids[def.id];
             if (defined !== seq) return false;
+            if (!defined[def.id]) return false;
             var assigned = tw.assigned_ids[def.id];
             return !assigned || assigned === seq;
         }
@@ -1399,22 +1403,13 @@ Compressor.prototype.compress = function(node) {
                 }
             });
             if (!first) pop(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;
+            walk_body(node, tw);
             return true;
         });
         def(AST_SwitchBranch, function(tw) {
+            push(tw, true);
             walk_body(this, tw);
+            pop(tw);
             return true;
         });
         def(AST_SymbolCatch, function() {
diff --git a/test/compress/functions.js b/test/compress/functions.js
index be9ede3d3fe..3d8fc477a1b 100644
--- a/test/compress/functions.js
+++ b/test/compress/functions.js
@@ -5737,8 +5737,9 @@ issue_3929: {
                 (function() {
                     switch (f) {
                       default:
+                        var abc = 0;
                       case 0:
-                        0..p;
+                        abc.p;
                     }
                     console.log(typeof f);
                 })();
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 36deccf0bcb..edd95bd009e 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -8460,3 +8460,36 @@ issue_5872_3: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5892: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        try {
+            var a = 42;
+            a.p;
+            if (console)
+                a = null;
+            a.q;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            var a = 42;
+            a.p;
+            if (console)
+                a = null;
+            a.q;
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/switches.js b/test/compress/switches.js
index 2e23f3e3b55..681a919925e 100644
--- a/test/compress/switches.js
+++ b/test/compress/switches.js
@@ -1727,3 +1727,74 @@ issue_5890: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5892_1: {
+    options = {
+        reduce_vars: true,
+        unused: true,
+        toplevel: true,
+    }
+    input: {
+        try {
+            switch (42) {
+              case null:
+                var a = "foo";
+              default:
+                a.p;
+            }
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            switch (42) {
+              case null:
+                var a = "foo";
+              default:
+                a.p;
+            }
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5892_2: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        try {
+            switch (42) {
+              case null:
+                var a = "foo";
+              default:
+                a.p;
+            }
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            switch (42) {
+              case null:
+                var a = "foo";
+              default:
+                a.p;
+            }
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}