util, test: improve inspect escaping

lib/util.js

@@ -90,6 +90,9 @@ let internalDeepEqual;
 /* eslint-disable no-control-regex */
 const strEscapeSequencesRegExp = /[\x00-\x1f\x27\x5c]/;
 const strEscapeSequencesReplacer = /[\x00-\x1f\x27\x5c]/g;
+const strEscapeSequencesRegExpSingle = /[\x00-\x1f\x5c]/;
+const strEscapeSequencesReplacerSingle = /[\x00-\x1f\x5c]/g;
+
 /* eslint-enable no-control-regex */
 
 const keyStrRegExp = /^[a-zA-Z_][a-zA-Z_0-9]*$/;
@@ -116,21 +119,56 @@ const meta = [
   '', '', '', '', '', '', '', '\\\\'
 ];
 
+function addQuotes(str, quotes) {
+  if (quotes === -1) {
+    return `"${str}"`;
+  }
+  if (quotes === -2) {
+    return `\`${str}\``;
+  }
+  return `'${str}'`;
+}
+
 const escapeFn = (str) => meta[str.charCodeAt(0)];
 
 // Escape control characters, single quotes and the backslash.
 // This is similar to JSON stringify escaping.
 function strEscape(str) {
+  let escapeTest = strEscapeSequencesRegExp;
+  let escapeReplace = strEscapeSequencesReplacer;
+  let singleQuote = 39;
+
+  // Check for double quotes. If not present, do not escape single quotes and
+  // instead wrap the text in double quotes. If double quotes exist, check for
+  // backticks. If they do not exist, use those as fallback instead of the
+  // double quotes.
+  if (str.indexOf("'") !== -1) {
+    // This invalidates the charCode and therefore can not be matched for
+    // anymore.
+    if (str.indexOf('"') === -1) {
+      singleQuote = -1;
+    } else if (str.indexOf('`') === -1 && str.indexOf('${') === -1) {
+      singleQuote = -2;
+    }
+    if (singleQuote !== 39) {
+      escapeTest = strEscapeSequencesRegExpSingle;
+      escapeReplace = strEscapeSequencesReplacerSingle;
+    }
+  }
+
   // Some magic numbers that worked out fine while benchmarking with v8 6.0
-  if (str.length < 5000 && !strEscapeSequencesRegExp.test(str))
-    return `'${str}'`;
-  if (str.length > 100)
-    return `'${str.replace(strEscapeSequencesReplacer, escapeFn)}'`;
+  if (str.length < 5000 && !escapeTest.test(str))
+    return addQuotes(str, singleQuote);
+  if (str.length > 100) {
+    str = str.replace(escapeReplace, escapeFn);
+    return addQuotes(str, singleQuote);
+  }
+
   let result = '';
   let last = 0;
   for (var i = 0; i < str.length; i++) {
     const point = str.charCodeAt(i);
-    if (point === 39 || point === 92 || point < 32) {
+    if (point === singleQuote || point === 92 || point < 32) {
       if (last === i) {
         result += meta[point];
       } else {
@@ -144,7 +182,7 @@ function strEscape(str) {
   } else if (last !== i) {
     result += str.slice(last);
   }
-  return `'${result}'`;
+  return addQuotes(result, singleQuote);
 }
 
 function tryStringify(arg) {

test/parallel/test-repl-colors.js

@@ -24,7 +24,7 @@ process.on('exit', function() {
   // https://github.com/nodejs/node/pull/16485#issuecomment-350428638
   // The color setting of the REPL should not have leaked over into
   // the color setting of `util.inspect.defaultOptions`.
-  strictEqual(output.includes(`'\\'string\\''`), true);
+  strictEqual(output.includes(`"'string'"`), true);
   strictEqual(output.includes(`'\u001b[32m\\'string\\'\u001b[39m'`), false);
   strictEqual(inspect.defaultOptions.colors, false);
   strictEqual(repl.writer.options.colors, true);