fix dead_code on block-scoped function under "use strict" (#2006)

Technically not part of ES5, but commonly used code exists in the wild.

lib/compress.js

@@ -1222,7 +1222,7 @@ merge(Compressor.prototype, {
                 target.push(node);
                 return true;
             }
-            if (node instanceof AST_Defun) {
+            if (node instanceof AST_Defun && (node === stat || !compressor.has_directive("use strict"))) {
                 target.push(node);
                 return true;
             }

test/compress/dead-code.js

@@ -31,7 +31,7 @@ dead_code_2_should_warn: {
         function f() {
             g();
             x = 10;
-            throw "foo";
+            throw new Error("foo");
             // completely discarding the `if` would introduce some
             // bugs.  UglifyJS v1 doesn't deal with this issue; in v2
             // we copy any declarations to the upper scope.
@@ -46,16 +46,60 @@ dead_code_2_should_warn: {
                 })();
             }
         }
+        f();
     }
     expect: {
         function f() {
             g();
             x = 10;
-            throw "foo";
+            throw new Error("foo");
             var x;
             function g(){};
         }
+        f();
     }
+    expect_stdout: true
+    node_version: "<=4"
+}
+
+dead_code_2_should_warn_strict: {
+    options = {
+        dead_code: true
+    };
+    input: {
+        "use strict";
+        function f() {
+            g();
+            x = 10;
+            throw new Error("foo");
+            // completely discarding the `if` would introduce some
+            // bugs.  UglifyJS v1 doesn't deal with this issue; in v2
+            // we copy any declarations to the upper scope.
+            if (x) {
+                y();
+                var x;
+                function g(){};
+                // but nested declarations should not be kept.
+                (function(){
+                    var q;
+                    function y(){};
+                })();
+            }
+        }
+        f();
+    }
+    expect: {
+        "use strict";
+        function f() {
+            g();
+            x = 10;
+            throw new Error("foo");
+            var x;
+        }
+        f();
+    }
+    expect_stdout: true
+    node_version: "=4"
 }
 
 dead_code_constant_boolean_should_warn_more: {
@@ -78,6 +122,7 @@ dead_code_constant_boolean_should_warn_more: {
             foo();
             var moo;
         }
+        bar();
     }
     expect: {
         var foo;
@@ -86,8 +131,46 @@ dead_code_constant_boolean_should_warn_more: {
         // as for the for, it should keep:
         var x = 10, y;
         var moo;
+        bar();
     }
     expect_stdout: true
+    node_version: "<=4"
+}
+
+dead_code_constant_boolean_should_warn_more_strict: {
+    options = {
+        dead_code    : true,
+        loops        : true,
+        booleans     : true,
+        conditionals : true,
+        evaluate     : true,
+        side_effects : true,
+    };
+    input: {
+        "use strict";
+        while (!((foo && bar) || (x + "0"))) {
+            console.log("unreachable");
+            var foo;
+            function bar() {}
+        }
+        for (var x = 10, y; x && (y || x) && (!typeof x); ++x) {
+            asdf();
+            foo();
+            var moo;
+        }
+        bar();
+    }
+    expect: {
+        "use strict";
+        var foo;
+        // nothing for the while
+        // as for the for, it should keep:
+        var x = 10, y;
+        var moo;
+        bar();
+    }
+    expect_stdout: true
+    node_version: ">=4"
 }
 
 try_catch_finally: {

test/compress/issue-1034.js

@@ -116,3 +116,137 @@ non_hoisted_function_after_return_2b: {
         "WARN: Dropping unreachable code [test/compress/issue-1034.js:101,12]",
     ]
 }
+
+non_hoisted_function_after_return_strict: {
+    options = {
+        hoist_funs: false, dead_code: true, conditionals: true, comparisons: true,
+        evaluate: true, booleans: true, loops: true, unused: true, keep_fargs: true,
+        if_return: true, join_vars: true, cascade: true, side_effects: true
+    }
+    input: {
+        "use strict";
+        function foo(x) {
+            if (x) {
+                return bar();
+                not_called1();
+            } else {
+                return baz();
+                not_called2();
+            }
+            function bar() { return 7; }
+            return not_reached;
+            function UnusedFunction() {}
+            function baz() { return 8; }
+        }
+        console.log(foo(0), foo(1));
+    }
+    expect: {
+        "use strict";
+        function foo(x) {
+            return x ? bar() : baz();
+            function bar() { return 7 }
+            function baz() { return 8 }
+        }
+        console.log(foo(0), foo(1));
+    }
+    expect_stdout: "8 7"
+    expect_warnings: [
+        'WARN: Dropping unreachable code [test/compress/issue-1034.js:131,16]',
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:134,16]",
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:137,12]",
+        "WARN: Dropping unused function UnusedFunction [test/compress/issue-1034.js:138,21]"
+    ]
+}
+
+non_hoisted_function_after_return_2a_strict: {
+    options = {
+        hoist_funs: false, dead_code: true, conditionals: true, comparisons: true,
+        evaluate: true, booleans: true, loops: true, unused: true, keep_fargs: true,
+        if_return: true, join_vars: true, cascade: true, side_effects: true,
+        collapse_vars: false, passes: 2, warnings: "verbose"
+    }
+    input: {
+        "use strict";
+        function foo(x) {
+            if (x) {
+                return bar(1);
+                var a = not_called(1);
+            } else {
+                return bar(2);
+                var b = not_called(2);
+            }
+            var c = bar(3);
+            function bar(x) { return 7 - x; }
+            function nope() {}
+            return b || c;
+        }
+        console.log(foo(0), foo(1));
+    }
+    expect: {
+        "use strict";
+        function foo(x) {
+            return bar(x ? 1 : 2);
+            function bar(x) {
+                return 7 - x;
+            }
+        }
+        console.log(foo(0), foo(1));
+    }
+    expect_stdout: "5 6"
+    expect_warnings: [
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:173,16]",
+        "WARN: Declarations in unreachable code! [test/compress/issue-1034.js:173,16]",
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:176,16]",
+        "WARN: Declarations in unreachable code! [test/compress/issue-1034.js:176,16]",
+        "WARN: Dropping unused variable a [test/compress/issue-1034.js:173,20]",
+        "WARN: Dropping unused function nope [test/compress/issue-1034.js:180,21]",
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:178,12]",
+        "WARN: Declarations in unreachable code! [test/compress/issue-1034.js:178,12]",
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:181,12]",
+        "WARN: Dropping unused variable b [test/compress/issue-1034.js:176,20]",
+        "WARN: Dropping unused variable c [test/compress/issue-1034.js:178,16]",
+    ]
+}
+
+non_hoisted_function_after_return_2b_strict: {
+    options = {
+        hoist_funs: false, dead_code: true, conditionals: true, comparisons: true,
+        evaluate: true, booleans: true, loops: true, unused: true, keep_fargs: true,
+        if_return: true, join_vars: true, cascade: true, side_effects: true,
+        collapse_vars: false
+    }
+    input: {
+        "use strict";
+        function foo(x) {
+            if (x) {
+                return bar(1);
+            } else {
+                return bar(2);
+                var b;
+            }
+            var c = bar(3);
+            function bar(x) {
+                return 7 - x;
+            }
+            return b || c;
+        }
+        console.log(foo(0), foo(1));
+    }
+    expect: {
+        "use strict";
+        function foo(x) {
+            return bar(x ? 1 : 2);
+            function bar(x) { return 7 - x; }
+        }
+        console.log(foo(0), foo(1));
+    }
+    expect_stdout: "5 6"
+    expect_warnings: [
+        // duplicate warnings no longer emitted
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:225,16]",
+        "WARN: Declarations in unreachable code! [test/compress/issue-1034.js:225,16]",
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:227,12]",
+        "WARN: Declarations in unreachable code! [test/compress/issue-1034.js:227,12]",
+        "WARN: Dropping unreachable code [test/compress/issue-1034.js:231,12]",
+    ]
+}