Improve string print perfomance (#16763)

changelog_unreleased/javascript/16563.md

@@ -1,4 +1,4 @@
-#### Don't remove useless `\` in string literals (#16563 by @sosukesuzuki)
+#### Don't remove useless `\` in string literals (#16563 by @sosukesuzuki, #16763 by @fisker)
 
 Previously, Prettier would remove useless escape characters (`\`) from string literals. However, this behavior was inconsistent as it did not apply to template literals, which was reported in [issue #16542](https://github.com/prettier/prettier/issues/16542).
 
@@ -8,7 +8,7 @@ After discussing this internally, the Prettier team concluded that removing usel
 
 This change disables the removal of useless escape characters in string literals across all languages supported by Prettier. To keep the previous behavior, we recommend using ESLint rules like [`no-useless-escape`](https://eslint.org/docs/latest/rules/no-useless-escape).
 
-Escaping quotes within string literals (e.g. `"\"\'"`) works the same as before. This is explained on the [Rationale](https://prettier.io/docs/en/rationale.html#strings) page of the official documentation.
+Escaped quotes (e.g. `"\"\'"`) may get unescaped when changing between different quotes. This is explained on the [Rationale](https://prettier.io/docs/en/rationale.html#strings) page of the official documentation.
 
 <!-- prettier-ignore -->
 ```jsx

src/utils/print-string.js

@@ -1,9 +1,12 @@
+import assert from "node:assert";
 import getPreferredQuote from "./get-preferred-quote.js";
 import makeString from "./make-string.js";
 
 /** @import {Quote} from "./get-preferred-quote.js" */
 
 function printString(raw, options) {
+  assert(/^(?<quote>["']).*\k<quote>$/su.test(raw));
+
   // `rawContent` is the string exactly like it appeared in the input source
   // code, without its enclosing quotes.
   const rawContent = raw.slice(1, -1);
@@ -26,6 +29,12 @@ function printString(raw, options) {
         ? "'"
         : getPreferredQuote(rawContent, options.singleQuote);
 
+  const originalQuote = raw.charAt(0);
+
+  if (originalQuote === enclosingQuote) {
+    return raw;
+  }
+
   // It might sound unnecessary to use `makeString` even if the string already
   // is enclosed with `enclosingQuote`, but it isn't. The string could contain
   // unnecessary escapes (such as in `"\'"`). Always using `makeString` makes

tests/format/css/quotes/__snapshots__/format.test.js.snap

@@ -137,7 +137,7 @@ one 'two' three {}
 
     /* One of each with unnecessary escapes. */
     content: '"\\'';
-    content: '"\\'';
+    content: '\\"\\'';
 
     /* More double quotes than single quotes. */
     content: '"\\'"';
@@ -156,8 +156,8 @@ one 'two' three {}
     content: '\\\\';
 
     /* Backslases. */
-    content: "\\"\\\\\\"\\\\\\\\\\" ''\\\\'\\\\'\\\\\\\\'";
-    content: '\\'\\\\\\'\\\\\\\\\\' ""\\\\"\\\\"\\\\\\\\"';
+    content: "\\"\\\\\\"\\\\\\\\\\" '\\'\\\\'\\\\\\'\\\\\\\\'";
+    content: '\\'\\\\\\'\\\\\\\\\\' "\\"\\\\"\\\\\\"\\\\\\\\"';
 
     /* Somewhat more real-word example. */
     content: "He's sayin': \\"How's it goin'?\\" Don't ask me why.";
@@ -332,7 +332,7 @@ one 'two' three {}
     content: "\\"'";
 
     /* One of each with unnecessary escapes. */
-    content: "\\"'";
+    content: "\\"\\'";
     content: "\\"'";
 
     /* More double quotes than single quotes. */
@@ -352,8 +352,8 @@ one 'two' three {}
     content: "\\\\";
 
     /* Backslases. */
-    content: "\\"\\\\\\"\\\\\\\\\\" ''\\\\'\\\\'\\\\\\\\'";
-    content: '\\'\\\\\\'\\\\\\\\\\' ""\\\\"\\\\"\\\\\\\\"';
+    content: "\\"\\\\\\"\\\\\\\\\\" '\\'\\\\'\\\\\\'\\\\\\\\'";
+    content: '\\'\\\\\\'\\\\\\\\\\' "\\"\\\\"\\\\\\"\\\\\\\\"';
 
     /* Somewhat more real-word example. */
     content: "He's sayin': \\"How's it goin'?\\" Don't ask me why.";

tests/format/js/quotes/__snapshots__/format.test.js.snap

@@ -234,8 +234,8 @@ singleQuote: true
 ("'");
 
 // Unnecessary escapes.
-("'");
-('"');
+("\\'");
+('\\"');
 ('\\a');
 ('\\a');
 ('hol\\a');
@@ -270,7 +270,7 @@ singleQuote: true
 
 // One of each with unnecessary escapes.
 ('"\\'');
-('"\\'');
+('\\"\\'');
 
 // More double quotes than single quotes.
 ('"\\'"');
@@ -289,8 +289,8 @@ singleQuote: true
 ('\\\\');
 
 // Backslases.
-("\\"\\\\\\"\\\\\\\\\\" ''\\\\'\\\\'\\\\\\\\'");
-('\\'\\\\\\'\\\\\\\\\\' ""\\\\"\\\\"\\\\\\\\"');
+("\\"\\\\\\"\\\\\\\\\\" '\\'\\\\'\\\\\\'\\\\\\\\'");
+('\\'\\\\\\'\\\\\\\\\\' "\\"\\\\"\\\\\\"\\\\\\\\"');
 
 // Somewhat more real-word example.
 ("He's sayin': \\"How's it goin'?\\" Don't ask me why.");
@@ -446,8 +446,8 @@ printWidth: 80
 ("'");
 
 // Unnecessary escapes.
-("'");
-('"');
+("\\'");
+('\\"');
 ("\\a");
 ("\\a");
 ("hol\\a");
@@ -481,7 +481,7 @@ printWidth: 80
 ("\\"'");
 
 // One of each with unnecessary escapes.
-("\\"'");
+("\\"\\'");
 ("\\"'");
 
 // More double quotes than single quotes.
@@ -501,8 +501,8 @@ printWidth: 80
 ("\\\\");
 
 // Backslases.
-("\\"\\\\\\"\\\\\\\\\\" ''\\\\'\\\\'\\\\\\\\'");
-('\\'\\\\\\'\\\\\\\\\\' ""\\\\"\\\\"\\\\\\\\"');
+("\\"\\\\\\"\\\\\\\\\\" '\\'\\\\'\\\\\\'\\\\\\\\'");
+('\\'\\\\\\'\\\\\\\\\\' "\\"\\\\"\\\\\\"\\\\\\\\"');
 
 // Somewhat more real-word example.
 ("He's sayin': \\"How's it goin'?\\" Don't ask me why.");

tests/format/js/strings/__snapshots__/format.test.js.snap

@@ -11,6 +11,9 @@ export const MSG_GENERIC_OPERATION_FAILURE_BODY_1 =
   goog.getMsg("That's all we know");
 
 export const MSG_GENERIC_OPERATION_FAILURE_BODY_2 =
+  goog.getMsg('That\\'s all we know');
+
+export const MSG_GENERIC_OPERATION_FAILURE_BODY_3 =
   goog.getMsg("That\\'s all we know");
 
 =====================================output=====================================
@@ -20,6 +23,10 @@ export const MSG_GENERIC_OPERATION_FAILURE_BODY_1 =
 export const MSG_GENERIC_OPERATION_FAILURE_BODY_2 =
   goog.getMsg("That's all we know");
 
+export const MSG_GENERIC_OPERATION_FAILURE_BODY_3 = goog.getMsg(
+  "That\\'s all we know",
+);
+
 ================================================================================
 `;
 
@@ -34,6 +41,9 @@ export const MSG_GENERIC_OPERATION_FAILURE_BODY_1 =
   goog.getMsg("That's all we know");
 
 export const MSG_GENERIC_OPERATION_FAILURE_BODY_2 =
+  goog.getMsg('That\\'s all we know');
+
+export const MSG_GENERIC_OPERATION_FAILURE_BODY_3 =
   goog.getMsg("That\\'s all we know");
 
 =====================================output=====================================
@@ -43,6 +53,10 @@ export const MSG_GENERIC_OPERATION_FAILURE_BODY_1 =
 export const MSG_GENERIC_OPERATION_FAILURE_BODY_2 =
   goog.getMsg("That's all we know");
 
+export const MSG_GENERIC_OPERATION_FAILURE_BODY_3 = goog.getMsg(
+  "That\\'s all we know"
+);
+
 ================================================================================
 `;
 
@@ -279,11 +293,11 @@ trailingComma: "all"
   "'",
 
   '"',
-  '"',
+  '\\"',
   '\\\\"',
 
   "'",
-  "'",
+  "\\'",
   "\\\\'",
 
   "'\\"",
@@ -342,11 +356,11 @@ trailingComma: "es5"
   "'",
 
   '"',
-  '"',
+  '\\"',
   '\\\\"',
 
   "'",
-  "'",
+  "\\'",
   "\\\\'",
 
   "'\\"",

tests/format/js/strings/escaped.js

@@ -2,4 +2,7 @@ export const MSG_GENERIC_OPERATION_FAILURE_BODY_1 =
   goog.getMsg("That's all we know");
 
 export const MSG_GENERIC_OPERATION_FAILURE_BODY_2 =
+  goog.getMsg('That\'s all we know');
+
+export const MSG_GENERIC_OPERATION_FAILURE_BODY_3 =
   goog.getMsg("That\'s all we know");