Method getLocFromIndex

packages/plugin-kit/src/source-code.js:423–476

* Converts a source text index into a `{ line: number, column: number }` pair. * @param {number} index The index of a character in a file. * @throws {TypeError|RangeError} If non-numeric index or index out of range. * @returns {{line: number, column: number}} A `{ line: number, column: number

(index)

	 * @public
	 */
	getLocFromIndex(index) {
		if (typeof index !== "number") {
			throw new TypeError("Expected `index` to be a number.");
		}

		if (index < 0 || index > this.text.length) {
			throw new RangeError(
				`Index out of range (requested index ${index}, but source text has length ${this.text.length}).`,
			);
		}

		const {
			start: { line: lineStart, column: columnStart },
			end: { line: lineEnd, column: columnEnd },
		} = this.getLoc(this.ast);

		// If the index is at the start, return the start location of the root node.
		if (index === 0) {
			return {
				line: lineStart,
				column: columnStart,
			};
		}

		// If the index is `this.text.length`, return the location one "spot" past the last character of the file.
		if (index === this.text.length) {
			return {
				line: lineEnd,
				column: columnEnd,
			};
		}

		// Ensure `#lineStartIndices` are lazily calculated.
		this.#ensureLineStartIndicesFromIndex(index);

		/*
		 * To figure out which line `index` is on, determine the last place at which index could
		 * be inserted into `#lineStartIndices` to keep the list sorted.
		 */
		const lineNumber =
			(index >= (this.#lineStartIndices.at(-1) ?? 0)
				? this.#lineStartIndices.length
				: findLineNumberBinarySearch(this.#lineStartIndices, index)) -
			1 +
			lineStart;

		return {
			line: lineNumber,
			column:
				index -
				this.#lineStartIndices[lineNumber - lineStart] +
				columnStart,
		};
	}

	/**
	 * Converts a `{ line: number, column: number }` pair into a source text index.