add nullish coalescing

Author: mysticatea

acorn-loose/src/expression.js

@@ -102,7 +102,7 @@ lp.parseExprOp = function(left, start, minPrec, noIn, indent, line) {
         let rightStart = this.storeCurrentPos()
         node.right = this.parseExprOp(this.parseMaybeUnary(false), rightStart, prec, noIn, indent, line)
       }
-      this.finishNode(node, /&&|\|\|/.test(node.operator) ? "LogicalExpression" : "BinaryExpression")
+      this.finishNode(node, /&&|\|\||\?\?/.test(node.operator) ? "LogicalExpression" : "BinaryExpression")
       return this.parseExprOp(node, start, minPrec, noIn, indent, line)
     }
   }

acorn/src/expression.js

@@ -169,7 +169,7 @@ pp.parseExprOps = function(noIn, refDestructuringErrors) {
   let startPos = this.start, startLoc = this.startLoc
   let expr = this.parseMaybeUnary(refDestructuringErrors, false)
   if (this.checkExpressionErrors(refDestructuringErrors)) return expr
-  return expr.start === startPos && expr.type === "ArrowFunctionExpression" ? expr : this.parseExprOp(expr, startPos, startLoc, -1, noIn)
+  return expr.start === startPos && expr.type === "ArrowFunctionExpression" ? expr : this.parseExprOp(expr, startPos, startLoc, -1, noIn, 0)
 }
 
 // Parse binary operators with the operator precedence parsing
@@ -178,17 +178,28 @@ pp.parseExprOps = function(noIn, refDestructuringErrors) {
 // defer further parser to one of its callers when it encounters an
 // operator that has a lower precedence than the set it is parsing.
 
-pp.parseExprOp = function(left, leftStartPos, leftStartLoc, minPrec, noIn) {
+// shortCircuitOps:
+// * 1 = only `||` and `&&` are allowed
+// * 2 = only `??` is allowed
+// * others = all
+
+pp.parseExprOp = function(left, leftStartPos, leftStartLoc, minPrec, noIn, shortCircuitOps) {
   let prec = this.type.binop
   if (prec != null && (!noIn || this.type !== tt._in)) {
+    let logical = this.type === tt.logicalOR || this.type === tt.logicalAND
+    let coalesce = this.type === tt.coalesce
+    if (shortCircuitOps === 1 && coalesce || shortCircuitOps === 2 && logical) {
+      this.raiseRecoverable(this.start, "Logical expressions and coalesce expressions cannot be mixed. Wrap either by parentheses")
+    }
+    shortCircuitOps = shortCircuitOps || (logical ? 1 : coalesce ? 2 : 0)
+
     if (prec > minPrec) {
-      let logical = this.type === tt.logicalOR || this.type === tt.logicalAND
       let op = this.value
       this.next()
       let startPos = this.start, startLoc = this.startLoc
-      let right = this.parseExprOp(this.parseMaybeUnary(null, false), startPos, startLoc, prec, noIn)
-      let node = this.buildBinary(leftStartPos, leftStartLoc, left, right, op, logical)
-      return this.parseExprOp(node, leftStartPos, leftStartLoc, minPrec, noIn)
+      let right = this.parseExprOp(this.parseMaybeUnary(null, false), startPos, startLoc, prec, noIn, shortCircuitOps)
+      let node = this.buildBinary(leftStartPos, leftStartLoc, left, right, op, logical || coalesce)
+      return this.parseExprOp(node, leftStartPos, leftStartLoc, minPrec, noIn, shortCircuitOps)
     }
   }
   return left

acorn/src/tokenize.js

@@ -287,6 +287,14 @@ pp.readToken_eq_excl = function(code) { // '=!'
   return this.finishOp(code === 61 ? tt.eq : tt.prefix, 1)
 }
 
+pp.readToken_question = function() { // '?'
+  if (this.options.ecmaVersion >= 11) {
+    let next = this.input.charCodeAt(this.pos + 1)
+    if (next === 63) return this.finishOp(tt.coalesce, 2)
+  }
+  return this.finishOp(tt.question, 1)
+}
+
 pp.getTokenFromCode = function(code) {
   switch (code) {
   // The interpretation of a dot depends on whether it is followed
@@ -304,7 +312,6 @@ pp.getTokenFromCode = function(code) {
   case 123: ++this.pos; return this.finishToken(tt.braceL)
   case 125: ++this.pos; return this.finishToken(tt.braceR)
   case 58: ++this.pos; return this.finishToken(tt.colon)
-  case 63: ++this.pos; return this.finishToken(tt.question)
 
   case 96: // '`'
     if (this.options.ecmaVersion < 6) break
@@ -354,6 +361,9 @@ pp.getTokenFromCode = function(code) {
   case 61: case 33: // '=!'
     return this.readToken_eq_excl(code)
 
+  case 63: // '?'
+    return this.readToken_question()
+
   case 126: // '~'
     return this.finishOp(tt.prefix, 1)
   }

acorn/src/tokentype.js

@@ -108,6 +108,7 @@ export const types = {
   star: binop("*", 10),
   slash: binop("/", 10),
   starstar: new TokenType("**", {beforeExpr: true}),
+  coalesce: binop("??", 1),
 
   // Keyword token types.
   _break: kw("break"),

test/run.js

@@ -16,6 +16,7 @@
   require("./tests-optional-catch-binding.js");
   require("./tests-bigint.js");
   require("./tests-dynamic-import.js");
+  require("./tests-nullish-coalescing.js");
   var acorn = require("../acorn")
   var acorn_loose = require("../acorn-loose")