fix corner cases with `delete` (#1796)

`delete Infinity` returns `false` where as `delete (1/0)` returns `true`

2 files changed, 55 insertions, 11 deletions

diff --git a/lib/compress.js b/lib/compress.js
index c199d13f..b001d35c 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -3620,6 +3620,11 @@ merge(Compressor.prototype, {
                 return ref;
             }
         }
+        var parent = compressor.parent();
+        if (parent instanceof AST_UnaryPrefix
+            && parent.operator == "delete"
+            && (parent.expression instanceof AST_SymbolRef
+                || parent.expression.TYPE === self.TYPE)) return self;
         return make_node(AST_UnaryPrefix, self, {
             operator: "void",
             expression: make_node(AST_Number, self, {
@@ -3629,8 +3634,16 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_Infinity, function(self, compressor){
-        var retain = compressor.option("keep_infinity") && !find_variable(compressor, "Infinity");
-        return retain ? self : make_node(AST_Binary, self, {
+        var parent = compressor.parent();
+        if (parent instanceof AST_UnaryPrefix
+            && parent.operator == "delete"
+            && (parent.expression instanceof AST_SymbolRef
+                || parent.expression.TYPE === self.TYPE))
+            return self;
+        if (compressor.option("keep_infinity")
+            && !find_variable(compressor, "Infinity"))
+            return self;
+        return make_node(AST_Binary, self, {
             operator: "/",
             left: make_node(AST_Number, self, {
                 value: 1
@@ -3642,15 +3655,23 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_NaN, function(self, compressor){
-        return find_variable(compressor, "NaN") ? make_node(AST_Binary, self, {
-            operator: "/",
-            left: make_node(AST_Number, self, {
-                value: 0
-            }),
-            right: make_node(AST_Number, self, {
-                value: 0
-            })
-        }) : self;
+        var parent = compressor.parent();
+        if (parent instanceof AST_UnaryPrefix
+                && parent.operator == "delete"
+                && !(parent.expression instanceof AST_SymbolRef
+                    || parent.expression.TYPE === self.TYPE)
+            || find_variable(compressor, "NaN")) {
+            return make_node(AST_Binary, self, {
+                operator: "/",
+                left: make_node(AST_Number, self, {
+                    value: 0
+                }),
+                right: make_node(AST_Number, self, {
+                    value: 0
+                })
+            });
+        }
+        return self;
     });
 
     var ASSIGN_OPS = [ '+', '-', '/', '*', '%', '>>', '<<', '>>>', '|', '^', '&' ];
diff --git a/test/compress/evaluate.js b/test/compress/evaluate.js
index fa432c46..e660071d 100644
--- a/test/compress/evaluate.js
+++ b/test/compress/evaluate.js
@@ -857,3 +857,26 @@ issue_1760_2: {
     }
     expect_stdout: "Infinity"
 }
+
+delete_expr: {
+    options = {
+        evaluate: true,
+    }
+    input: {
+        console.log(delete undefined);
+        console.log(delete void 0);
+        console.log(delete Infinity);
+        console.log(delete (1 / 0));
+        console.log(delete NaN);
+        console.log(delete (0 / 0));
+    }
+    expect: {
+        console.log(delete undefined);
+        console.log(delete void 0);
+        console.log(delete Infinity);
+        console.log(delete (1 / 0));
+        console.log(delete NaN);
+        console.log(delete (0 / 0));
+    }
+    expect_stdout: true
+}