Syntactic placeholders

commit d5d4e74 Author: William C. Johnson <[email protected]> Date: Sun Jul 16 20:41:48 2017 -0400 Allow placeholder to be changed via config commit 32e43a0 Author: William C. Johnson <[email protected]> Date: Sun Jul 16 20:24:59 2017 -0400 Spread placeholder tests commit 73b9d32 Author: William C. Johnson <[email protected]> Date: Sun Jul 16 15:31:50 2017 -0400 Initial implementation of syntactic placeholders
wcjohnson · Jul 17, 2017 · 70ee2c8 · 70ee2c8
1 parent 7701096
commit 70ee2c8
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Showing 19 changed files with 599 additions and 6 deletions.
diff --git a/src/options.js b/src/options.js
@@ -9,7 +9,8 @@ export const defaultOptions: {
   allowImportExportEverywhere: boolean,
   allowSuperOutsideMethod: boolean,
   plugins: Array<string>,
-  strictMode: any
+  strictMode: any,
+  placeholder: string
 } = {
   // Source type ("script" or "module") for different semantics
   sourceType: "script",
@@ -30,6 +31,8 @@ export const defaultOptions: {
   plugins: [],
   // TODO
   strictMode: null,
+  // Default placeholder for use with syntacticPlaceholder plugin
+  placeholder: "_"
 };
 
 // Interpret and default an options object

diff --git a/src/parser/expression.js b/src/parser/expression.js
@@ -412,7 +412,7 @@ pp.parseSubscripts = function (base, startPos, startLoc, noCalls) {
         node.property = this.parseExprAtom();
         node.computed = true;
       } else {
-        node.property = this.parseIdentifier(true);
+        node.property = this.parseIdentifierOrPlaceholder(true);
         node.computed = false;
       }
       base = this.finishNode(node, "MemberExpression");
@@ -431,7 +431,7 @@ pp.parseSubscripts = function (base, startPos, startLoc, noCalls) {
           node.property = this.parseLiteral(this.state.value, "NumericLiteral");
           node.computed = true;
         } else {
-          node.property = this.parseIdentifier(true);
+          node.property = this.parseIdentifierOrPlaceholder(true);
           node.computed = false;
         }
       } else if (op === "?[") {
@@ -651,7 +651,7 @@ pp.parseExprAtom = function (refShorthandDefaultPos) {
       node = this.startNode();
       const allowAwait = this.state.value === "await" && this.state.inAsync;
       const allowYield = this.shouldAllowYieldIdentifier();
-      const id = this.parseIdentifier(allowAwait || allowYield);
+      const id = this.parseIdentifierOrPlaceholder(allowAwait || allowYield);
 
       if (id.name === "await") {
         if (this.state.inAsync || this.inModule) {
@@ -661,7 +661,7 @@ pp.parseExprAtom = function (refShorthandDefaultPos) {
         this.next();
         return this.parseFunction(node, false, false, true);
       } else if (canBeArrow && id.name === "async" && this.match(tt.name)) {
-        const params = [this.parseIdentifier()];
+        const params = [this.parseIdentifierOrPlaceholder()];
         this.check(tt.arrow);
         // let foo = bar => {};
         return this.parseArrowExpression(node, params, true);
@@ -1134,6 +1134,7 @@ pp.parseObj = function (isPattern, refShorthandDefaultPos) {
     if (!isPattern && this.isContextual("async")) {
       if (isGenerator) this.unexpected();
 
+      // TODO: syntacticPlaceholder: is a placeholder legal here?
       const asyncId = this.parseIdentifier();
       if (this.match(tt.colon) || this.match(tt.parenL) || this.match(tt.braceR) || this.match(tt.eq) || this.match(tt.comma) || (this.hasPlugin("lightscript") && this.isLineBreak())) {
         prop.key = asyncId;
@@ -1262,6 +1263,7 @@ pp.parsePropertyName = function (prop) {
     prop.computed = false;
     const oldInPropertyName = this.state.inPropertyName;
     this.state.inPropertyName = true;
+    // TODO: syntacticPlaceholder: is a placeholder legal here?
     prop.key = (this.match(tt.num) || this.match(tt.string)) ? this.parseExprAtom() : this.parseIdentifier(true);
     this.state.inPropertyName = oldInPropertyName;
   }
@@ -1465,6 +1467,15 @@ pp.parseIdentifier = function (liberal) {
   return this.finishNode(node, "Identifier");
 };
 
+// Syntactic placeholders: shunt based on plugin status
+pp.parseIdentifierOrPlaceholder = function(liberal) {
+  if (this.hasPlugin("syntacticPlaceholder")) {
+    return this._parseIdentifierOrPlaceholder(liberal);
+  } else {
+    return this.parseIdentifier(liberal);
+  }
+};
+
 pp.checkReservedWord = function (word, startLoc, checkKeywords, isBinding) {
   if (this.isReservedWord(word) || (checkKeywords && this.isKeyword(word))) {
     this.raise(startLoc, word + " is a reserved word");

diff --git a/src/plugins/syntacticPlaceholder.js b/src/plugins/syntacticPlaceholder.js
@@ -0,0 +1,51 @@
+import Parser from "../parser";
+import { types as tt } from "../tokenizer/types";
+const pp = Parser.prototype;
+
+export default function(parser) {
+  if (parser.__syntacticPlaceholderPluginInstalled) return;
+  parser.__syntacticPlaceholderPluginInstalled = true;
+
+  const ph = parser.options.placeholder || "_";
+  const quotedPh = (ph + "").replace(/[.?*+^$[\]\\(){}|-]/g, "\\$&");
+  const phRegex = new RegExp("^" + quotedPh + "([0-9]*)$");
+
+  pp.isPlaceholderName = function(name) {
+    return phRegex.test(name);
+  };
+
+  // c/p parseIdentifier
+  pp._parseIdentifierOrPlaceholder = function(liberal) {
+    const node = this.startNode();
+    if (!liberal) {
+      this.checkReservedWord(this.state.value, this.state.start, !!this.state.type.keyword, false);
+    }
+
+    let name;
+    if (this.match(tt.name)) {
+      name = this.state.value;
+    } else if (this.state.type.keyword) {
+      name = this.state.type.keyword;
+    } else {
+      this.unexpected();
+    }
+
+    const matches = phRegex.exec(name);
+    if (matches) {
+      if (matches[1]) node.index = parseInt(matches[1]);
+      this.next();
+      return this.finishNode(node, "PlaceholderExpression");
+    }
+
+    node.name = name;
+
+    if (!liberal && node.name === "await" && this.state.inAsync) {
+      this.raise(node.start, "invalid use of await inside of an async function");
+    }
+
+    node.loc.identifierName = node.name;
+
+    this.next();
+    return this.finishNode(node, "Identifier");
+  };
+}
diff --git a/src/plugins/tildeCall.js b/src/plugins/tildeCall.js
@@ -13,7 +13,7 @@ export default function(parser) {
     node.left = left;
 
     // allow `this`, Identifier or MemberExpression, but not calls
-    const right = this.match(tt._this) ? this.parseExprAtom() : this.parseIdentifier();
+    const right = this.match(tt._this) ? this.parseExprAtom() : this.parseIdentifierOrPlaceholder();
     node.right = this.parseSubscripts(right, this.state.start, this.state.startLoc, true);
 
     // Allow safe tilde calls (a~b?(c))

diff --git a/src/registerPlugins.js b/src/registerPlugins.js
@@ -7,6 +7,7 @@ import safeCallExistentialPlugin from "./plugins/safeCallExistential";
 import bangCallPlugin from "./plugins/bangCall";
 import significantWhitespacePlugin from "./plugins/significantWhitespace";
 import enhancedComprehensionPlugin from "./plugins/enhancedComprehension";
+import syntacticPlaceholderPlugin from "./plugins/syntacticPlaceholder";
 import { matchCoreSyntax, match } from "./plugins/match";
 
 function noncePlugin() {}
@@ -79,4 +80,8 @@ export default function registerPlugins(plugins, metadata) {
   registerPlugin("objectBlockAmbiguity_preferObject", noncePlugin, {
     dependencies: ["lightscript"]
   });
+
+  // Parse identifiers beginning with `_` or another user-chosen symbol
+  // as PlaceholderExpressions.
+  registerPlugin("syntacticPlaceholder", syntacticPlaceholderPlugin);
 }
diff --git a/test/fixtures/syntactic-placeholder/basic/basic/actual.js b/test/fixtures/syntactic-placeholder/basic/basic/actual.js
@@ -0,0 +1 @@
+_
diff --git a/test/fixtures/syntactic-placeholder/basic/basic/expected.json b/test/fixtures/syntactic-placeholder/basic/basic/expected.json
@@ -0,0 +1,64 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 1,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 1
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 1,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 1
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 1,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 1
+          }
+        },
+        "expression": {
+          "type": "PlaceholderExpression",
+          "start": 0,
+          "end": 1,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 1
+            }
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}
diff --git a/test/fixtures/syntactic-placeholder/basic/indexed/actual.js b/test/fixtures/syntactic-placeholder/basic/indexed/actual.js
@@ -0,0 +1 @@
+_1
diff --git a/test/fixtures/syntactic-placeholder/basic/indexed/expected.json b/test/fixtures/syntactic-placeholder/basic/indexed/expected.json
@@ -0,0 +1,65 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 2,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 2
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 2,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 2
+      }
+    },
+    "sourceType": "script",
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 2,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 2
+          }
+        },
+        "expression": {
+          "type": "PlaceholderExpression",
+          "start": 0,
+          "end": 2,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 2
+            }
+          },
+          "index": 1
+        }
+      }
+    ],
+    "directives": []
+  }
+}
diff --git a/test/fixtures/syntactic-placeholder/basic/spread-indexed/actual.js b/test/fixtures/syntactic-placeholder/basic/spread-indexed/actual.js
@@ -0,0 +1 @@
+-> [..._1]