fix corner case in collapse_vars (#5026)

fixes #5025

test/compress/collapse_vars.js

@@ -4658,7 +4658,6 @@ replace_all_var_scope: {
     rename = true
     options = {
         collapse_vars: true,
-        reduce_vars: true,
         unused: true,
     }
     mangle = {}
@@ -4677,7 +4676,7 @@ replace_all_var_scope: {
         (function(c, o) {
             switch (~a) {
               case (b += a):
-              case +o:
+              case o++:
             }
         })(--b, a);
         console.log(a, b);

test/compress/functions.js

@@ -6228,3 +6228,33 @@ recursive_collapse: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5025: {
+    options = {
+        collapse_vars: true,
+        inline: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        function f(a) {
+            function g() {
+                b = 42;
+            }
+            g(b = a);
+            var b = this;
+            console.log(typeof b);
+        }
+        f();
+    }
+    expect: {
+        function f(a) {
+            b = a,
+            void (b = 42);
+            var b = this;
+            console.log(typeof b);
+        }
+        f();
+    }
+    expect_stdout: "object"
+}

test/compress/keep_fargs.js

@@ -1151,7 +1151,6 @@ replace_all_var_scope: {
     options = {
         collapse_vars: true,
         keep_fargs: false,
-        reduce_vars: true,
         unused: true,
     }
     mangle = {}
@@ -1170,7 +1169,7 @@ replace_all_var_scope: {
         (function(c) {
             switch (~a) {
               case (b += a):
-              case +c:
+              case c++:
             }
         })((--b, a));
         console.log(a, b);