feat(eslint-plugin): Begin rewrite of indent rule

.eslintrc.json

@@ -9,6 +9,7 @@
   "rules": {
     "comma-dangle": ["error", "always-multiline"],
     "curly": ["error", "all"],
+    "no-dupe-class-members": "off",
     "no-mixed-operators": "error",
     "no-console": "off",
     "no-undef": "off",

packages/eslint-plugin/src/rules/indent-new-do-not-use/BinarySearchTree.ts

@@ -0,0 +1,60 @@
+// The following code is adapted from the the code in eslint.
+// License: https://github.com/eslint/eslint/blob/48700fc8408f394887cdedd071b22b757700fdcb/LICENSE
+
+import { TSESTree } from '@typescript-eslint/typescript-estree';
+import createTree = require('functional-red-black-tree');
+
+export type TokenOrComment = TSESTree.Token | TSESTree.Comment;
+export interface TreeValue {
+  offset: number;
+  from: TokenOrComment | null;
+  force: boolean;
+}
+
+/**
+ * A mutable balanced binary search tree that stores (key, value) pairs. The keys are numeric, and must be unique.
+ * This is intended to be a generic wrapper around a balanced binary search tree library, so that the underlying implementation
+ * can easily be swapped out.
+ */
+export class BinarySearchTree {
+  private rbTree = createTree<TreeValue, number>();
+
+  /**
+   * Inserts an entry into the tree.
+   */
+  public insert(key: number, value: TreeValue): void {
+    const iterator = this.rbTree.find(key);
+
+    if (iterator.valid) {
+      this.rbTree = iterator.update(value);
+    } else {
+      this.rbTree = this.rbTree.insert(key, value);
+    }
+  }
+
+  /**
+   * Finds the entry with the largest key less than or equal to the provided key
+   * @returns The found entry, or null if no such entry exists.
+   */
+  public findLe(key: number): { key: number; value: TreeValue } {
+    const iterator = this.rbTree.le(key);
+
+    return { key: iterator.key, value: iterator.value };
+  }
+
+  /**
+   * Deletes all of the keys in the interval [start, end)
+   */
+  public deleteRange(start: number, end: number): void {
+    // Exit without traversing the tree if the range has zero size.
+    if (start === end) {
+      return;
+    }
+    const iterator = this.rbTree.ge(start);
+
+    while (iterator.valid && iterator.key < end) {
+      this.rbTree = this.rbTree.remove(iterator.key);
+      iterator.next();
+    }
+  }
+}

packages/eslint-plugin/src/rules/indent-new-do-not-use/OffsetStorage.ts

@@ -0,0 +1,277 @@
+// The following code is adapted from the the code in eslint.
+// License: https://github.com/eslint/eslint/blob/48700fc8408f394887cdedd071b22b757700fdcb/LICENSE
+
+import { TokenInfo } from './TokenInfo';
+import { BinarySearchTree, TokenOrComment } from './BinarySearchTree';
+import { TSESTree } from '@typescript-eslint/typescript-estree';
+
+/**
+ * A class to store information on desired offsets of tokens from each other
+ */
+export class OffsetStorage {
+  private tokenInfo: TokenInfo;
+  private indentSize: number;
+  private indentType: string;
+  private tree: BinarySearchTree;
+  private lockedFirstTokens: WeakMap<TokenOrComment, TokenOrComment>;
+  private desiredIndentCache: WeakMap<TokenOrComment, string>;
+  private ignoredTokens: WeakSet<TokenOrComment>;
+  /**
+   * @param tokenInfo a TokenInfo instance
+   * @param indentSize The desired size of each indentation level
+   * @param indentType The indentation character
+   */
+  constructor(tokenInfo: TokenInfo, indentSize: number, indentType: string) {
+    this.tokenInfo = tokenInfo;
+    this.indentSize = indentSize;
+    this.indentType = indentType;
+
+    this.tree = new BinarySearchTree();
+    this.tree.insert(0, { offset: 0, from: null, force: false });
+
+    this.lockedFirstTokens = new WeakMap();
+    this.desiredIndentCache = new WeakMap();
+    this.ignoredTokens = new WeakSet();
+  }
+
+  private getOffsetDescriptor(token: TokenOrComment) {
+    return this.tree.findLe(token.range[0]).value;
+  }
+
+  /**
+   * Sets the offset column of token B to match the offset column of token A.
+   * **WARNING**: This matches a *column*, even if baseToken is not the first token on its line. In
+   * most cases, `setDesiredOffset` should be used instead.
+   * @param baseToken The first token
+   * @param offsetToken The second token, whose offset should be matched to the first token
+   */
+  public matchOffsetOf(
+    baseToken: TokenOrComment,
+    offsetToken: TokenOrComment,
+  ): void {
+    /*
+     * lockedFirstTokens is a map from a token whose indentation is controlled by the "first" option to
+     * the token that it depends on. For example, with the `ArrayExpression: first` option, the first
+     * token of each element in the array after the first will be mapped to the first token of the first
+     * element. The desired indentation of each of these tokens is computed based on the desired indentation
+     * of the "first" element, rather than through the normal offset mechanism.
+     */
+    this.lockedFirstTokens.set(offsetToken, baseToken);
+  }
+
+  /**
+   * Sets the desired offset of a token.
+   *
+   * This uses a line-based offset collapsing behavior to handle tokens on the same line.
+   * For example, consider the following two cases:
+   *
+   * (
+   *     [
+   *         bar
+   *     ]
+   * )
+   *
+   * ([
+   *     bar
+   * ])
+   *
+   * Based on the first case, it's clear that the `bar` token needs to have an offset of 1 indent level (4 spaces) from
+   * the `[` token, and the `[` token has to have an offset of 1 indent level from the `(` token. Since the `(` token is
+   * the first on its line (with an indent of 0 spaces), the `bar` token needs to be offset by 2 indent levels (8 spaces)
+   * from the start of its line.
+   *
+   * However, in the second case `bar` should only be indented by 4 spaces. This is because the offset of 1 indent level
+   * between the `(` and the `[` tokens gets "collapsed" because the two tokens are on the same line. As a result, the
+   * `(` token is mapped to the `[` token with an offset of 0, and the rule correctly decides that `bar` should be indented
+   * by 1 indent level from the start of the line.
+   *
+   * This is useful because rule listeners can usually just call `setDesiredOffset` for all the tokens in the node,
+   * without needing to check which lines those tokens are on.
+   *
+   * Note that since collapsing only occurs when two tokens are on the same line, there are a few cases where non-intuitive
+   * behavior can occur. For example, consider the following cases:
+   *
+   * foo(
+   * ).
+   *     bar(
+   *         baz
+   *     )
+   *
+   * foo(
+   * ).bar(
+   *     baz
+   * )
+   *
+   * Based on the first example, it would seem that `bar` should be offset by 1 indent level from `foo`, and `baz`
+   * should be offset by 1 indent level from `bar`. However, this is not correct, because it would result in `baz`
+   * being indented by 2 indent levels in the second case (since `foo`, `bar`, and `baz` are all on separate lines, no
+   * collapsing would occur).
+   *
+   * Instead, the correct way would be to offset `baz` by 1 level from `bar`, offset `bar` by 1 level from the `)`, and
+   * offset the `)` by 0 levels from `foo`. This ensures that the offset between `bar` and the `)` are correctly collapsed
+   * in the second case.
+   *
+   * @param token The token
+   * @param fromToken The token that `token` should be offset from
+   * @param offset The desired indent level
+   */
+  public setDesiredOffset(
+    token: TokenOrComment,
+    fromToken: TokenOrComment | null,
+    offset: number,
+  ): void {
+    this.setDesiredOffsets(token.range, fromToken, offset);
+  }
+
+  /**
+   * Sets the desired offset of all tokens in a range
+   * It's common for node listeners in this file to need to apply the same offset to a large, contiguous range of tokens.
+   * Moreover, the offset of any given token is usually updated multiple times (roughly once for each node that contains
+   * it). This means that the offset of each token is updated O(AST depth) times.
+   * It would not be performant to store and update the offsets for each token independently, because the rule would end
+   * up having a time complexity of O(number of tokens * AST depth), which is quite slow for large files.
+   *
+   * Instead, the offset tree is represented as a collection of contiguous offset ranges in a file. For example, the following
+   * list could represent the state of the offset tree at a given point:
+   *
+   * * Tokens starting in the interval [0, 15) are aligned with the beginning of the file
+   * * Tokens starting in the interval [15, 30) are offset by 1 indent level from the `bar` token
+   * * Tokens starting in the interval [30, 43) are offset by 1 indent level from the `foo` token
+   * * Tokens starting in the interval [43, 820) are offset by 2 indent levels from the `bar` token
+   * * Tokens starting in the interval [820, ∞) are offset by 1 indent level from the `baz` token
+   *
+   * The `setDesiredOffsets` methods inserts ranges like the ones above. The third line above would be inserted by using:
+   * `setDesiredOffsets([30, 43], fooToken, 1);`
+   *
+   * @param range A [start, end] pair. All tokens with range[0] <= token.start < range[1] will have the offset applied.
+   * @param fromToken The token that this is offset from
+   * @param offset The desired indent level
+   * @param force `true` if this offset should not use the normal collapsing behavior. This should almost always be false.
+   */
+  public setDesiredOffsets(
+    range: [number, number],
+    fromToken: TokenOrComment | null,
+    offset: number = 0,
+    force: boolean = false,
+  ): void {
+    /*
+     * Offset ranges are stored as a collection of nodes, where each node maps a numeric key to an offset
+     * descriptor. The tree for the example above would have the following nodes:
+     *
+     * * key: 0, value: { offset: 0, from: null }
+     * * key: 15, value: { offset: 1, from: barToken }
+     * * key: 30, value: { offset: 1, from: fooToken }
+     * * key: 43, value: { offset: 2, from: barToken }
+     * * key: 820, value: { offset: 1, from: bazToken }
+     *
+     * To find the offset descriptor for any given token, one needs to find the node with the largest key
+     * which is <= token.start. To make this operation fast, the nodes are stored in a balanced binary
+     * search tree indexed by key.
+     */
+
+    const descriptorToInsert = { offset, from: fromToken, force };
+
+    const descriptorAfterRange = this.tree.findLe(range[1]).value;
+
+    const fromTokenIsInRange =
+      fromToken &&
+      fromToken.range[0] >= range[0] &&
+      fromToken.range[1] <= range[1];
+    // this has to be before the delete + insert below or else you'll get into a cycle
+    const fromTokenDescriptor = fromTokenIsInRange
+      ? this.getOffsetDescriptor(fromToken!)
+      : null;
+
+    // First, remove any existing nodes in the range from the tree.
+    this.tree.deleteRange(range[0] + 1, range[1]);
+
+    // Insert a new node into the tree for this range
+    this.tree.insert(range[0], descriptorToInsert);
+
+    /*
+     * To avoid circular offset dependencies, keep the `fromToken` token mapped to whatever it was mapped to previously,
+     * even if it's in the current range.
+     */
+    if (fromTokenIsInRange) {
+      this.tree.insert(fromToken!.range[0], fromTokenDescriptor!);
+      this.tree.insert(fromToken!.range[1], descriptorToInsert);
+    }
+
+    /*
+     * To avoid modifying the offset of tokens after the range, insert another node to keep the offset of the following
+     * tokens the same as it was before.
+     */
+    this.tree.insert(range[1], descriptorAfterRange);
+  }
+
+  /**
+   * Gets the desired indent of a token
+   * @returns The desired indent of the token
+   */
+  public getDesiredIndent(token: TokenOrComment): string {
+    if (!this.desiredIndentCache.has(token)) {
+      if (this.ignoredTokens.has(token)) {
+        /*
+         * If the token is ignored, use the actual indent of the token as the desired indent.
+         * This ensures that no errors are reported for this token.
+         */
+        this.desiredIndentCache.set(
+          token,
+          this.tokenInfo.getTokenIndent(token),
+        );
+      } else if (this.lockedFirstTokens.has(token)) {
+        const firstToken = this.lockedFirstTokens.get(token)!;
+
+        this.desiredIndentCache.set(
+          token,
+
+          // (indentation for the first element's line)
+          this.getDesiredIndent(
+            this.tokenInfo.getFirstTokenOfLine(firstToken),
+          ) +
+            // (space between the start of the first element's line and the first element)
+            this.indentType.repeat(
+              firstToken.loc.start.column -
+                this.tokenInfo.getFirstTokenOfLine(firstToken).loc.start.column,
+            ),
+        );
+      } else {
+        const offsetInfo = this.getOffsetDescriptor(token);
+        const offset =
+          offsetInfo.from &&
+          offsetInfo.from.loc.start.line === token.loc.start.line &&
+          !/^\s*?\n/u.test(token.value) &&
+          !offsetInfo.force
+            ? 0
+            : offsetInfo.offset * this.indentSize;
+
+        this.desiredIndentCache.set(
+          token,
+          (offsetInfo.from ? this.getDesiredIndent(offsetInfo.from) : '') +
+            this.indentType.repeat(offset),
+        );
+      }
+    }
+
+    return this.desiredIndentCache.get(token)!;
+  }
+
+  /**
+   * Ignores a token, preventing it from being reported.
+   */
+  ignoreToken(token: TokenOrComment): void {
+    if (this.tokenInfo.isFirstTokenOfLine(token)) {
+      this.ignoredTokens.add(token);
+    }
+  }
+
+  /**
+   * Gets the first token that the given token's indentation is dependent on
+   * @returns The token that the given token depends on, or `null` if the given token is at the top level
+   */
+  getFirstDependency(token: TSESTree.Token): TSESTree.Token | null;
+  getFirstDependency(token: TokenOrComment): TokenOrComment | null;
+  getFirstDependency(token: TokenOrComment): TokenOrComment | null {
+    return this.getOffsetDescriptor(token).from;
+  }
+}