Promote applyFix and applyFixes helpers into core library.

lib/markdownlint.js

@@ -1204,6 +1204,119 @@ function readConfigSync(file, parsers, fs) {
   return config;
 }
 
+/**
+ * Normalizes the fields of a RuleOnErrorFixInfo instance.
+ *
+ * @param {RuleOnErrorFixInfo} fixInfo RuleOnErrorFixInfo instance.
+ * @param {number} [lineNumber] Line number.
+ * @returns {RuleOnErrorFixInfoNormalized} Normalized RuleOnErrorFixInfo instance.
+ */
+function normalizeFixInfo(fixInfo, lineNumber = 0) {
+  return {
+    "lineNumber": fixInfo.lineNumber || lineNumber,
+    "editColumn": fixInfo.editColumn || 1,
+    "deleteCount": fixInfo.deleteCount || 0,
+    "insertText": fixInfo.insertText || ""
+  };
+}
+
+/**
+ * Applies the specified fix to a Markdown content line.
+ *
+ * @param {string} line Line of Markdown content.
+ * @param {RuleOnErrorFixInfo} fixInfo RuleOnErrorFixInfo instance.
+ * @param {string} [lineEnding] Line ending to use.
+ * @returns {string | null} Fixed content or null if deleted.
+ */
+function applyFix(line, fixInfo, lineEnding = "\n") {
+  const { editColumn, deleteCount, insertText } = normalizeFixInfo(fixInfo);
+  const editIndex = editColumn - 1;
+  return (deleteCount === -1) ?
+    null :
+    line.slice(0, editIndex) + insertText.replace(/\n/g, lineEnding) + line.slice(editIndex + deleteCount);
+}
+
+/**
+ * Applies as many of the specified fixes as possible to Markdown content.
+ *
+ * @param {string} input Lines of Markdown content.
+ * @param {RuleOnErrorInfo[]} errors RuleOnErrorInfo instances.
+ * @returns {string} Fixed content.
+ */
+function applyFixes(input, errors) {
+  const lineEnding = helpers.getPreferredLineEnding(input, require("node:os"));
+  const lines = input.split(helpers.newLineRe);
+  // Normalize fixInfo objects
+  let fixInfos = errors
+    .filter((error) => error.fixInfo)
+    // @ts-ignore
+    .map((error) => normalizeFixInfo(error.fixInfo, error.lineNumber));
+  // Sort bottom-to-top, line-deletes last, right-to-left, long-to-short
+  fixInfos.sort((a, b) => {
+    const aDeletingLine = (a.deleteCount === -1);
+    const bDeletingLine = (b.deleteCount === -1);
+    return (
+      (b.lineNumber - a.lineNumber) ||
+      (aDeletingLine ? 1 : (bDeletingLine ? -1 : 0)) ||
+      (b.editColumn - a.editColumn) ||
+      (b.insertText.length - a.insertText.length)
+    );
+  });
+  // Remove duplicate entries (needed for following collapse step)
+  // eslint-disable-next-line jsdoc/valid-types
+  /** @type RuleOnErrorFixInfo */
+  let lastFixInfo = {};
+  fixInfos = fixInfos.filter((fixInfo) => {
+    const unique = (
+      (fixInfo.lineNumber !== lastFixInfo.lineNumber) ||
+      (fixInfo.editColumn !== lastFixInfo.editColumn) ||
+      (fixInfo.deleteCount !== lastFixInfo.deleteCount) ||
+      (fixInfo.insertText !== lastFixInfo.insertText)
+    );
+    lastFixInfo = fixInfo;
+    return unique;
+  });
+  // Collapse insert/no-delete and no-insert/delete for same line/column
+  lastFixInfo = {
+    "lineNumber": -1
+  };
+  for (const fixInfo of fixInfos) {
+    if (
+      (fixInfo.lineNumber === lastFixInfo.lineNumber) &&
+      (fixInfo.editColumn === lastFixInfo.editColumn) &&
+      !fixInfo.insertText &&
+      (fixInfo.deleteCount > 0) &&
+      lastFixInfo.insertText &&
+      !lastFixInfo.deleteCount) {
+      fixInfo.insertText = lastFixInfo.insertText;
+      lastFixInfo.lineNumber = 0;
+    }
+    lastFixInfo = fixInfo;
+  }
+  fixInfos = fixInfos.filter((fixInfo) => fixInfo.lineNumber);
+  // Apply all (remaining/updated) fixes
+  let lastLineIndex = -1;
+  let lastEditIndex = -1;
+  for (const fixInfo of fixInfos) {
+    const { lineNumber, editColumn, deleteCount } = fixInfo;
+    const lineIndex = lineNumber - 1;
+    const editIndex = editColumn - 1;
+    if (
+      (lineIndex !== lastLineIndex) ||
+      (deleteCount === -1) ||
+      ((editIndex + deleteCount) <=
+        (lastEditIndex - ((deleteCount > 0) ? 0 : 1)))
+    ) {
+      // @ts-ignore
+      lines[lineIndex] = applyFix(lines[lineIndex], fixInfo, lineEnding);
+    }
+    lastLineIndex = lineIndex;
+    lastEditIndex = editIndex;
+  }
+  // Return corrected input
+  return lines.filter((line) => line !== null).join(lineEnding);
+}
+
 /**
  * Gets the (semantic) version of the library.
  *
@@ -1223,6 +1336,8 @@ markdownlint.promises = {
   "extendConfig": extendConfigPromise,
   "readConfig": readConfigPromise
 };
+markdownlint.applyFix = applyFix;
+markdownlint.applyFixes = applyFixes;
 module.exports = markdownlint;
 
 // Type declarations
@@ -1341,6 +1456,16 @@ module.exports = markdownlint;
  * @property {string} [insertText] Text to insert (after deleting).
  */
 
+/**
+ * RuleOnErrorInfo with all optional properties present.
+ *
+ * @typedef {Object} RuleOnErrorFixInfoNormalized
+ * @property {number} lineNumber Line number (1-based).
+ * @property {number} editColumn Column of the fix (1-based).
+ * @property {number} deleteCount Count of characters to delete.
+ * @property {string} insertText Text to insert (after deleting).
+ */
+
 /**
  * Rule definition.
  *