Get rid of regexp and handle cursor in trim in doc printer (prettier#…

…13426)

src/document/printer.js

@@ -144,27 +144,43 @@ function generateInd(ind, newPart, options) {
   }
 }
 
-// TODO: Skip cursor placeholder
 // Trim `Tab(U+0009)` and `Space(U+0020)` at the end of line
 function trim(out) {
   let trimCount = 0;
+  let cursorCount = 0;
+  let outIndex = out.length;
 
-  while (out.length > 0) {
-    const last = getLast(out);
-    if (typeof last !== "string") {
-      break;
+  outer: while (outIndex--) {
+    const last = out[outIndex];
+
+    if (last === CURSOR_PLACEHOLDER) {
+      cursorCount++;
+      continue;
     }
 
-    const trimmed = last.replace(/[\t ]*$/, "");
-    trimCount += last.length - trimmed.length;
+    if (process.env.NODE_ENV !== "production" && typeof last !== "string") {
+      throw new Error(`Unexpected value in trim: '${typeof last}'`);
+    }
 
-    if (trimmed !== "") {
-      out[out.length - 1] = trimmed;
-      break;
+    // Not using a regexp here because regexps for trimming off trailing
+    // characters are known to have performance issues.
+    for (let charIndex = last.length - 1; charIndex >= 0; charIndex--) {
+      const char = last[charIndex];
+      if (char === " " || char === "\t") {
+        trimCount++;
+      } else {
+        out[outIndex] = last.slice(0, charIndex + 1);
+        break outer;
+      }
     }
+  }
+
+  if (trimCount > 0 || cursorCount > 0) {
+    out.length = outIndex + 1;
 
-    // All `Tab` or `Space`
-    out.length -= 1;
+    while (cursorCount-- > 0) {
+      out.push(CURSOR_PLACEHOLDER);
+    }
   }
 
   return trimCount;

tests/unit/print-doc-to-string.js

@@ -1,8 +1,29 @@
-import { cursor } from "../../src/document/builders.js";
+import { cursor, hardline } from "../../src/document/builders.js";
 import { printDocToString } from "../../src/document/printer.js";
 
+const options = { printWidth: 80, tabWidth: 2 };
+
 test("Should reject if too many cursor in doc", () => {
   expect(() => {
-    printDocToString([cursor, cursor, cursor], { printWidth: 80, tabWidth: 2 });
+    printDocToString([cursor, cursor, cursor], options);
   }).toThrow({ message: "There are too many 'cursor' in doc." });
 });
+
+test("Should trim blank first line", () => {
+  expect(
+    printDocToString(["   ", hardline, "Prettier", hardline], options).formatted
+  ).toBe("\nPrettier\n");
+});
+
+test("Should properly trim with cursor", () => {
+  expect(
+    printDocToString(
+      [cursor, "Prettier  \t", cursor, "\t \t", hardline],
+      options
+    )
+  ).toEqual({
+    formatted: "Prettier\n",
+    cursorNodeStart: 0,
+    cursorNodeText: "Prettier",
+  });
+});