Destructuring in pattern matching

Author: rattrayalex

src/parser/expression.js

@@ -678,6 +678,10 @@ pp.parseExprAtom = function (refShorthandDefaultPos) {
       return this.parseParenAndDistinguishExpression(null, null, canBeArrow);
 
     case tt.bracketL:
+      if (this.hasPlugin("lightscript") && this.state.inMatchCaseTest && !refShorthandDefaultPos) {
+        // re-enter this fn, but with refShorthandDefaultPos and state tracking
+        return this.parseMatchCaseTestPattern();
+      }
       node = this.startNode();
       this.next();
       if (this.hasPlugin("lightscript") && this.match(tt._for)) {
@@ -688,6 +692,10 @@ pp.parseExprAtom = function (refShorthandDefaultPos) {
       return this.finishNode(node, "ArrayExpression");
 
     case tt.braceL:
+      if (this.hasPlugin("lightscript") && this.state.inMatchCaseTest && !refShorthandDefaultPos) {
+        // re-enter this fn, but with refShorthandDefaultPos and state tracking
+        return this.parseMatchCaseTestPattern();
+      }
       return this.parseObj(false, refShorthandDefaultPos);
 
     case tt._function:
@@ -1166,6 +1174,9 @@ pp.parsePropertyName = function (prop) {
 // Initialize empty function node.
 
 pp.initFunction = function (node, isAsync) {
+  if (this.hasPlugin("lightscript") && this.state.inMatchCaseTest) {
+    this.unexpected(node.start, "Cannot match on functions.");
+  }
   node.id = null;
   node.generator = false;
   node.expression = false;

src/plugins/lightscript.js

@@ -559,6 +559,7 @@ pp.parseMatchStatement = function (node) {
 };
 
 pp.parseMatch = function (node, isExpression) {
+  if (this.state.inMatchCaseTest) this.unexpected();
   this.expect(tt._match);
   node.discriminant = this.parseParenExpression();
 
@@ -594,8 +595,12 @@ pp.parseMatchCase = function (isExpression) {
 
   node.test = this.parseMatchCaseTest();
 
-  if (this.eat(tt._with)) {
-    node.binding = this.parseBindingAtom();
+  if (this.isContextual("as")) {
+    if (!this.state.allowMatchCaseTestPattern) {
+      this.unexpected(null, "Cannot rename after destructuring.");
+    }
+    this.next();
+    node.binding = this.parseIdentifier();
   }
 
   if (isExpression) {
@@ -619,6 +624,7 @@ pp.parseMatchCase = function (isExpression) {
 pp.parseMatchCaseTest = function () {
   // can't be nested so no need to read/restore old value
   this.state.inMatchCaseTest = true;
+  this.state.allowMatchCaseTestPattern = true;
 
   this.expect(tt.bitwiseOR);
   if (this.isLineBreak()) this.unexpected(this.state.lastTokEnd, "Illegal newline.");
@@ -633,6 +639,7 @@ pp.parseMatchCaseTest = function () {
   }
 
   this.state.inMatchCaseTest = false;
+  this.state.allowMatchCaseTestPattern = false;
   return test;
 };
 
@@ -649,8 +656,7 @@ pp.isSubscriptTokenForMatchCase = function (tokenType) {
   return (
     tokenType === tt.dot ||
     tokenType === tt.elvis ||
-    tokenType === tt.tilde ||
-    tokenType === tt.bracketL
+    tokenType === tt.tilde
   );
 };
 
@@ -672,6 +678,27 @@ pp.allowMatchCasePlaceholder = function () {
   return false;
 };
 
+pp.parseMatchCaseTestPattern = function () {
+  if (!this.state.allowMatchCaseTestPattern) {
+    this.unexpected(null, "Only one pattern allowed per match case test.");
+  }
+
+  const oldInMatchCaseTestPattern = this.state.inMatchCaseTestPattern;
+  this.state.inMatchCaseTestPattern = true;
+
+  // re-enter parent function, allowing patterns.
+  const refShorthandDefaultPos = { start: 0 };
+  const node = this.parseExprAtom(refShorthandDefaultPos);
+
+  // once we have finished recursing through a pattern, disallow future patterns
+  this.state.inMatchCaseTestPattern = oldInMatchCaseTestPattern;
+  if (this.state.inMatchCaseTestPattern === false) {
+    this.state.allowMatchCaseTestPattern = false;
+  }
+
+  return node;
+};
+
 
 export default function (instance) {
 

src/tokenizer/state.js

@@ -41,6 +41,8 @@ export default class State {
     // for lightscript
     this.indentLevel = 0;
     this.inMatchCaseTest = false;
+    this.inMatchCaseTestPattern = false;
+    this.allowMatchCaseTestPattern = false;
 
     this.type = tt.eof;
     this.value = null;

test/fixtures/lightscript/match/basic-destructuring/actual.js

@@ -1,8 +1,6 @@
 match x:
   | a: 1
   | b: b
-  | c with c: c
-  | d with { d }: d
-  | e with { e = 1 }: e
-  | f with [ f ]: f
-  | g with [ g = 1 ]: g
+  | c as c: c
+  | as as as: as
+  | ~isNumber() as n: n + 1