have parser trap const declaration without value (#2756)

fixes #2751

lib/parse.js

@@ -1862,7 +1862,7 @@ function parse($TEXT, options) {
                     name  : as_symbol(sym_type),
                     value : is("operator", "=")
                         ? (next(), expression(false, no_in))
-                        : !no_in && kind === "const" && S.input.has_directive("use strict")
+                        : !no_in && kind === "const"
                             ? croak("Missing initializer in const declaration") : null,
                     end   : prev()
                 });

test/compress/block-scope.js

@@ -41,7 +41,7 @@ do_not_remove_anon_blocks_if_they_have_decls: {
                 var x;
             }
             {
-                const y;
+                const y = 1;
                 class Zee {};
             }
         }
@@ -59,7 +59,7 @@ do_not_remove_anon_blocks_if_they_have_decls: {
             }
             var x;
             {
-                const y;
+                const y = 1;
                 class Zee {}
             }
         }
@@ -77,12 +77,12 @@ remove_unused_in_global_block: {
     input: {
         {
             let x;
-            const y;
+            const y = 1;
             class Zee {};
             var w;
         }
         let ex;
-        const why;
+        const why = 2;
         class Zed {};
         var wut;
         console.log(x, y, Zee);
@@ -90,7 +90,7 @@ remove_unused_in_global_block: {
     expect: {
         var w;
         let ex;
-        const why;
+        const why = 2;
         class Zed {};
         var wut;
         console.log(x, y, Zee);

test/compress/drop-unused.js

@@ -215,7 +215,7 @@ unused_block_decls: {
     input: {
         function foo() {
             {
-                const x;
+                const x = 1;
             }
             {
                 let y;

test/input/invalid/const.js

@@ -1,8 +1,3 @@
 function f() {
     const a;
 }
-
-function g() {
-    "use strict";
-    const a;
-}

test/mocha/cli.js

@@ -408,7 +408,7 @@ describe("bin/uglifyjs", function () {
             assert.ok(err);
             assert.strictEqual(stdout, "");
             assert.strictEqual(stderr.split(/\n/).slice(0, 4).join("\n"), [
-                "Parse error at test/input/invalid/const.js:7,11",
+                "Parse error at test/input/invalid/const.js:2,11",
                 "    const a;",
                 "           ^",
                 "ERROR: Missing initializer in const declaration"