workaround Safari quirks (#5033)

closes #5032

lib/compress.js

@@ -108,6 +108,7 @@ function Compressor(options, false_by_default) {
         unsafe_undefined: false,
         unused          : !false_by_default,
         varify          : !false_by_default,
+        webkit          : false,
         yields          : !false_by_default,
     }, true);
     var evaluate = this.options["evaluate"];
@@ -5857,6 +5858,7 @@ merge(Compressor.prototype, {
                 if (head_refs.start.block !== tail_refs.start.block
                     || !mergeable(head_refs, tail_refs)
                     || (head_refs.start.loop || !same_scope(def)) && !mergeable(tail_refs, head_refs)
+                    || compressor.option("webkit") && is_funarg(def) !== is_funarg(tail.definition)
                     || !all(tail_refs, function(sym) {
                         return sym.scope.find_variable(def.name) === def;
                     })) {

lib/minify.js

@@ -100,7 +100,7 @@ function minify(files, options) {
         if (options.keep_fnames) set_shorthand("keep_fnames", options, [ "compress", "mangle" ]);
         if (options.toplevel) set_shorthand("toplevel", options, [ "compress", "mangle" ]);
         if (options.v8) set_shorthand("v8", options, [ "mangle", "output" ]);
-        if (options.webkit) set_shorthand("webkit", options, [ "mangle", "output" ]);
+        if (options.webkit) set_shorthand("webkit", options, [ "compress", "mangle", "output" ]);
         var quoted_props;
         if (options.mangle) {
             options.mangle = defaults(options.mangle, {

test/compress/awaits.js

@@ -1915,3 +1915,77 @@ issue_5023_2: {
     expect_stdout: "PASS"
     node_version: ">=8"
 }
+
+issue_5032_normal: {
+    options = {
+        merge_vars: true,
+        webkit: false,
+    }
+    input: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        async function f(a) {
+            var b = log(a), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS");
+    }
+    expect: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        async function f(c) {
+            var b = log(c), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS");
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+    node_version: ">=8"
+}
+
+issue_5032_webkit: {
+    options = {
+        merge_vars: true,
+        webkit: true,
+    }
+    input: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        async function f(a) {
+            var b = log(a), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS");
+    }
+    expect: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        async function f(a) {
+            var b = log(a), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS");
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+    node_version: ">=8"
+}

test/compress/yields.js

@@ -1142,3 +1142,77 @@ issue_5019_2: {
     ]
     node_version: ">=4"
 }
+
+issue_5032_normal: {
+    options = {
+        merge_vars: true,
+        webkit: false,
+    }
+    input: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        function *f(a) {
+            var b = log(a), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS").next();
+    }
+    expect: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        function *f(c) {
+            var b = log(c), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS").next();
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+    node_version: ">=4"
+}
+
+issue_5032_webkit: {
+    options = {
+        merge_vars: true,
+        webkit: true,
+    }
+    input: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        function *f(a) {
+            var b = log(a), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS").next();
+    }
+    expect: {
+        function log(value) {
+            console.log(value);
+            return value;
+        }
+        function *f(a) {
+            var b = log(a), c = b;
+            log(b);
+            log(c);
+        }
+        f("PASS").next();
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+        "PASS",
+    ]
+    node_version: ">=4"
+}