feat(linter/plugins): add SourceCode#lineStartIndices getter (#16510)

Add a getter `lineStartIndices` to `SourceCode`. ESLint has this property, but it's undocumented. Possible that some ESLint plugins rely on it (if it's there, people will use it!).

Author: overlookmotel

apps/oxlint/src-js/plugins/location.ts

@@ -57,7 +57,7 @@ const LINE_BREAK_PATTERN = /\r\n|[\r\n\u2028\u2029]/gu;
 // Lazily populated when `SOURCE_CODE.lines` is accessed.
 // `lineStartIndices` starts as `[0]`, and `resetLines` doesn't remove that initial element, so it's never empty.
 export const lines: string[] = [];
-const lineStartIndices: number[] = [0];
+export const lineStartIndices: number[] = [0];
 
 /**
  * Split source text into lines.

apps/oxlint/src-js/plugins/source_code.ts

@@ -14,6 +14,7 @@ import {
   getOffsetFromLineColumn,
   initLines,
   lines,
+  lineStartIndices,
   resetLines,
 } from "./location.ts";
 import { resetScopeManager, SCOPE_MANAGER } from "./scope.ts";
@@ -180,6 +181,15 @@ export const SOURCE_CODE = Object.freeze({
     return lines;
   },
 
+  /**
+   * Character offset of the first character of each line in source text,
+   * split according to specification's definition of line breaks.
+   */
+  get lineStartIndices(): number[] {
+    if (lines.length === 0) initLines();
+    return lineStartIndices;
+  },
+
   /**
    * Array of all tokens and comments in the file, in source order.
    */

apps/oxlint/test/fixtures/sourceCode/output.snap.md

@@ -7,6 +7,7 @@
   | text: "let foo, bar;\n\n// x\n// y\n"
   | getText(): "let foo, bar;\n\n// x\n// y\n"
   | lines: ["let foo, bar;","","// x","// y",""]
+  | lineStartIndices: [0,14,15,20,25]
   | locs:
   |   0 => { line: 1, column: 0 }("l")
   |   1 => { line: 1, column: 1 }("e")
@@ -55,6 +56,7 @@
   | text: "let foo, bar;\n\n// x\n// y\n"
   | getText(): "let foo, bar;\n\n// x\n// y\n"
   | lines: ["let foo, bar;","","// x","// y",""]
+  | lineStartIndices: [0,14,15,20,25]
   | locs:
   |   0 => { line: 1, column: 0 }("l")
   |   1 => { line: 1, column: 1 }("e")
@@ -163,6 +165,7 @@
   | text: "let qux;\n"
   | getText(): "let qux;\n"
   | lines: ["let qux;",""]
+  | lineStartIndices: [0,9]
   | locs:
   |   0 => { line: 1, column: 0 }("l")
   |   1 => { line: 1, column: 1 }("e")
@@ -193,6 +196,7 @@
   | text: "let qux;\n"
   | getText(): "let qux;\n"
   | lines: ["let qux;",""]
+  | lineStartIndices: [0,9]
   | locs:
   |   0 => { line: 1, column: 0 }("l")
   |   1 => { line: 1, column: 1 }("e")

apps/oxlint/test/fixtures/sourceCode/plugin.ts

@@ -16,8 +16,11 @@ const SPAN: Node = {
 
 const createRule: Rule = {
   create(context) {
-    const { sourceCode } = context,
-      { ast, lines, text } = sourceCode;
+    const { sourceCode } = context;
+
+    // Get these first to check they work before `sourceText` or `ast` are accessed
+    const { lineStartIndices, lines } = sourceCode;
+    const { ast, text } = sourceCode;
 
     assert(context.getSourceCode() === sourceCode);
 
@@ -36,6 +39,7 @@ const createRule: Rule = {
         `text: ${JSON.stringify(text)}\n` +
         `getText(): ${JSON.stringify(sourceCode.getText())}\n` +
         `lines: ${JSON.stringify(lines)}\n` +
+        `lineStartIndices: ${JSON.stringify(lineStartIndices)}\n` +
         `locs:${locs}\n` +
         // @ts-ignore
         `ast: "${ast.body[0].declarations[0].id.name}"\n` +
@@ -83,8 +87,11 @@ const createOnceRule: Rule = {
     return {
       before() {
         const { sourceCode } = context;
+
+        // Get these first to check they work before `sourceText` or `ast` are accessed
+        const { lineStartIndices, lines } = sourceCode;
         ast = sourceCode.ast;
-        const { lines, text } = sourceCode;
+        const { text } = sourceCode;
 
         let locs = "";
         for (let offset = 0; offset <= text.length; offset++) {
@@ -101,6 +108,7 @@ const createOnceRule: Rule = {
             `text: ${JSON.stringify(text)}\n` +
             `getText(): ${JSON.stringify(sourceCode.getText())}\n` +
             `lines: ${JSON.stringify(lines)}\n` +
+            `lineStartIndices: ${JSON.stringify(lineStartIndices)}\n` +
             `locs:${locs}\n` +
             // @ts-ignore
             `ast: "${ast.body[0].declarations[0].id.name}"\n` +