object spread: also drop non-nullish constants (e.g. { ...true }) (#…

…1141)

This is a follow-up to 6f04338 (#1004)

lib/compress/index.js

@@ -3758,7 +3758,7 @@ def_optimize(AST_Array, function(self, compressor) {
     return self;
 });
 
-function inline_object_prop_spread(props, compressor) {
+function inline_object_prop_spread(props) {
     for (var i = 0; i < props.length; i++) {
         var prop = props[i];
         if (prop instanceof AST_Expansion) {
@@ -3770,15 +3770,14 @@ function inline_object_prop_spread(props, compressor) {
                 props.splice(i, 1, ...expr.properties);
                 // Step back one, as the property at i is now new.
                 i--;
-            } else if (expr instanceof AST_Constant
-                && !(expr instanceof AST_String)) {
+            } else if ((
+                    // `expr.is_constant()` returns `false` for `AST_RegExp`, so need both.
+                    expr instanceof AST_Constant
+                    || expr.is_constant()
+                ) && !(expr instanceof AST_String)) {
                 // Unlike array-like spread, in object spread, spreading a
                 // non-iterable value silently does nothing; it is thus safe
-                // to remove. AST_String is the only iterable AST_Constant.
-                props.splice(i, 1);
-                i--;
-            } else if (is_nullish(expr, compressor)) {
-                // Likewise, null and undefined can be silently removed.
+                // to remove. AST_String is the only iterable constant.
                 props.splice(i, 1);
                 i--;
             }
@@ -3791,7 +3790,7 @@ def_optimize(AST_Object, function(self, compressor) {
     if (optimized !== self) {
         return optimized;
     }
-    inline_object_prop_spread(self.properties, compressor);
+    inline_object_prop_spread(self.properties);
     return self;
 });
 

test/compress/expansions.js

@@ -103,7 +103,31 @@ object_spread: {
     ]
 }
 
-object_spread_nullish_undefined: {
+object_spread_constant: {
+    input: {
+        id({
+            ...null,
+            ...undefined,
+            ...true,
+            ...void 0,
+            ...!0,
+            ...~"foo",
+            .../baz/,
+            ...-/baz2/,
+
+            ..."bar",
+        });
+    }
+
+    expect: {
+        id({
+            ..."bar"
+        })
+    }
+}
+
+// https://github.com/terser/terser/pull/1071
+object_spread_inline_after_dropping_undefined: {
     input: {
         let o = { ...undefined, ...{a: true} }
         id(o);
@@ -114,8 +138,7 @@ object_spread_nullish_undefined: {
         id(o)
     }
 }
-
-object_spread_nullish_null: {
+object_spread_inline_after_dropping_null: {
     input: {
         let o = { ...null, ...{a: true} }
         id(o);