Parenthesized expression fix (microsoft#5876)

* Fixes microsoft/pxt-microbit#2399

* Fixes microsoft/pxt-microbit#2345

* Typo fix

* Update to_string_arg.ts

* use charAt instead of startsWith and endsWith

* Fix parentheses check

* Return false directly if last char is not )

Author: FranklinWhale

pxtblocks/blocklycompiler.ts

@@ -1158,7 +1158,7 @@ namespace pxt.blocks {
             }
 
             if (p.shadowOptions && p.shadowOptions.toString && returnType(e, target) !== pString) {
-                return H.mkSimpleCall("+", [H.mkStringLiteral(""), compileExpression(e, target, comments)]);
+                return H.mkSimpleCall("+", [H.mkStringLiteral(""), H.mkParenthesizedExpression(compileExpression(e, target, comments))]);
             }
 
             return compileExpression(e, target, comments)

pxtlib/jsoutput.ts

@@ -219,11 +219,7 @@ namespace pxt.blocks {
         }
 
         export function mkParenthesizedExpression(expression: JsNode): JsNode {
-            return mkGroup([
-                mkText("("),
-                expression,
-                mkText(")")
-            ])
+            return isParenthesized(flattenNode([expression]).output) ? expression : mkGroup([mkText("("), expression, mkText(")")]);
         }
     }
 
@@ -439,4 +435,24 @@ namespace pxt.blocks {
     export function isReservedWord(str: string) {
         return reservedWords.indexOf(str) !== -1;
     }
+
+    export function isParenthesized(fnOutput: string): boolean {
+        if (fnOutput[0] !== "(" || fnOutput[fnOutput.length - 1] !== ")") {
+            return false;
+        }
+        let unclosedParentheses = 1;
+        for (let i = 1; i < fnOutput.length; i++) {
+            const c = fnOutput[i];
+            if (c === "(") {
+                unclosedParentheses++;
+            }
+            else if (c === ")") {
+                unclosedParentheses--;
+                if (unclosedParentheses === 0) {
+                    return i === fnOutput.length - 1;
+                }
+            }
+        }
+        return false;
+    }
 }

tests/blocklycompiler-test/baselines/to_string_arg.ts

@@ -1,5 +1,5 @@
 let item = 0
 console.log("")
-console.log("" + 5)
-console.log("" + item)
+console.log("" + (5))
+console.log("" + (item))
 console.log("" + (0 == 0))