add hw2

node_modules/sucrase/dist/transformers/OptionalChainingNullishTransformer.js

@@ -0,0 +1,155 @@
+"use strict";Object.defineProperty(exports, "__esModule", {value: true}); function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+var _types = require('../parser/tokenizer/types');
+
+var _Transformer = require('./Transformer'); var _Transformer2 = _interopRequireDefault(_Transformer);
+
+/**
+ * Transformer supporting the optional chaining and nullish coalescing operators.
+ *
+ * Tech plan here:
+ * https://github.com/alangpierce/sucrase/wiki/Sucrase-Optional-Chaining-and-Nullish-Coalescing-Technical-Plan
+ *
+ * The prefix and suffix code snippets are handled by TokenProcessor, and this transformer handles
+ * the operators themselves.
+ */
+ class OptionalChainingNullishTransformer extends _Transformer2.default {
+  constructor( tokens,  nameManager) {
+    super();this.tokens = tokens;this.nameManager = nameManager;;
+  }
+
+  process() {
+    if (this.tokens.matches1(_types.TokenType.nullishCoalescing)) {
+      const token = this.tokens.currentToken();
+      if (this.tokens.tokens[token.nullishStartIndex].isAsyncOperation) {
+        this.tokens.replaceTokenTrimmingLeftWhitespace(", async () => (");
+      } else {
+        this.tokens.replaceTokenTrimmingLeftWhitespace(", () => (");
+      }
+      return true;
+    }
+    if (this.tokens.matches1(_types.TokenType._delete)) {
+      const nextToken = this.tokens.tokenAtRelativeIndex(1);
+      if (nextToken.isOptionalChainStart) {
+        this.tokens.removeInitialToken();
+        return true;
+      }
+    }
+    const token = this.tokens.currentToken();
+    const chainStart = token.subscriptStartIndex;
+    if (
+      chainStart != null &&
+      this.tokens.tokens[chainStart].isOptionalChainStart &&
+      // Super subscripts can't be optional (since super is never null/undefined), and the syntax
+      // relies on the subscript being intact, so leave this token alone.
+      this.tokens.tokenAtRelativeIndex(-1).type !== _types.TokenType._super
+    ) {
+      const param = this.nameManager.claimFreeName("_");
+      let arrowStartSnippet;
+      if (
+        chainStart > 0 &&
+        this.tokens.matches1AtIndex(chainStart - 1, _types.TokenType._delete) &&
+        this.isLastSubscriptInChain()
+      ) {
+        // Delete operations are special: we already removed the delete keyword, and to still
+        // perform a delete, we need to insert a delete in the very last part of the chain, which
+        // in correct code will always be a property access.
+        arrowStartSnippet = `${param} => delete ${param}`;
+      } else {
+        arrowStartSnippet = `${param} => ${param}`;
+      }
+      if (this.tokens.tokens[chainStart].isAsyncOperation) {
+        arrowStartSnippet = `async ${arrowStartSnippet}`;
+      }
+      if (
+        this.tokens.matches2(_types.TokenType.questionDot, _types.TokenType.parenL) ||
+        this.tokens.matches2(_types.TokenType.questionDot, _types.TokenType.lessThan)
+      ) {
+        if (this.justSkippedSuper()) {
+          this.tokens.appendCode(".bind(this)");
+        }
+        this.tokens.replaceTokenTrimmingLeftWhitespace(`, 'optionalCall', ${arrowStartSnippet}`);
+      } else if (this.tokens.matches2(_types.TokenType.questionDot, _types.TokenType.bracketL)) {
+        this.tokens.replaceTokenTrimmingLeftWhitespace(`, 'optionalAccess', ${arrowStartSnippet}`);
+      } else if (this.tokens.matches1(_types.TokenType.questionDot)) {
+        this.tokens.replaceTokenTrimmingLeftWhitespace(`, 'optionalAccess', ${arrowStartSnippet}.`);
+      } else if (this.tokens.matches1(_types.TokenType.dot)) {
+        this.tokens.replaceTokenTrimmingLeftWhitespace(`, 'access', ${arrowStartSnippet}.`);
+      } else if (this.tokens.matches1(_types.TokenType.bracketL)) {
+        this.tokens.replaceTokenTrimmingLeftWhitespace(`, 'access', ${arrowStartSnippet}[`);
+      } else if (this.tokens.matches1(_types.TokenType.parenL)) {
+        if (this.justSkippedSuper()) {
+          this.tokens.appendCode(".bind(this)");
+        }
+        this.tokens.replaceTokenTrimmingLeftWhitespace(`, 'call', ${arrowStartSnippet}(`);
+      } else {
+        throw new Error("Unexpected subscript operator in optional chain.");
+      }
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Determine if the current token is the last of its chain, so that we know whether it's eligible
+   * to have a delete op inserted.
+   *
+   * We can do this by walking forward until we determine one way or another. Each
+   * isOptionalChainStart token must be paired with exactly one isOptionalChainEnd token after it in
+   * a nesting way, so we can track depth and walk to the end of the chain (the point where the
+   * depth goes negative) and see if any other subscript token is after us in the chain.
+   */
+  isLastSubscriptInChain() {
+    let depth = 0;
+    for (let i = this.tokens.currentIndex() + 1; ; i++) {
+      if (i >= this.tokens.tokens.length) {
+        throw new Error("Reached the end of the code while finding the end of the access chain.");
+      }
+      if (this.tokens.tokens[i].isOptionalChainStart) {
+        depth++;
+      } else if (this.tokens.tokens[i].isOptionalChainEnd) {
+        depth--;
+      }
+      if (depth < 0) {
+        return true;
+      }
+
+      // This subscript token is a later one in the same chain.
+      if (depth === 0 && this.tokens.tokens[i].subscriptStartIndex != null) {
+        return false;
+      }
+    }
+  }
+
+  /**
+   * Determine if we are the open-paren in an expression like super.a()?.b.
+   *
+   * We can do this by walking backward to find the previous subscript. If that subscript was
+   * preceded by a super, then we must be the subscript after it, so if this is a call expression,
+   * we'll need to attach the right context.
+   */
+  justSkippedSuper() {
+    let depth = 0;
+    let index = this.tokens.currentIndex() - 1;
+    while (true) {
+      if (index < 0) {
+        throw new Error(
+          "Reached the start of the code while finding the start of the access chain.",
+        );
+      }
+      if (this.tokens.tokens[index].isOptionalChainStart) {
+        depth--;
+      } else if (this.tokens.tokens[index].isOptionalChainEnd) {
+        depth++;
+      }
+      if (depth < 0) {
+        return false;
+      }
+
+      // This subscript token is a later one in the same chain.
+      if (depth === 0 && this.tokens.tokens[index].subscriptStartIndex != null) {
+        return this.tokens.tokens[index - 1].type === _types.TokenType._super;
+      }
+      index--;
+    }
+  }
+} exports.default = OptionalChainingNullishTransformer;