From 9117266d4b7ca6dfaf088ede86e83d6b3ee8aa0b Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Wed, 20 Feb 2019 19:52:10 +0000
Subject: [PATCH] Bug 1527671 - Assign the correct start position to arrow
 functions. r=arai,jorendorff

This position ends up being used for source notes in some cases now, meaning that this can
cause breakpoints to be given the wrong position when assigned to a variable. This fixes
that by using the correct token for the position value.

This fix also ensures that `cur->pos.end` is updated when skipping functions because
expression statements set their end based on the end position of the expression, and
if the expression statements end token is the end of a skipped function, we would
otherwise read the wrong position triggering assertion failures.

Differential Revision: https://phabricator.services.mozilla.com/D19714

--HG--
extra : moz-landing-system : lando
---
 js/src/frontend/Parser.cpp                      |  5 +++--
 js/src/frontend/TokenStream.cpp                 |  1 +
 .../debug/Script-getPossibleBreakpoints.js      | 17 ++++++++++++++++-
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index 5bd02f91e025..1a01ca108c7b 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -8024,7 +8024,8 @@ typename ParseHandler::Node GeneralParser<ParseHandler, Unit>::assignExpr(
     if (!tokenStream.getToken(&next, TokenStream::Operand)) {
       return null();
     }
-    uint32_t toStringStart = pos().begin;
+    TokenPos startPos = pos();
+    uint32_t toStringStart = startPos.begin;
     anyChars.ungetToken();
 
     FunctionAsyncKind asyncKind = FunctionAsyncKind::SyncFunction;
@@ -8049,7 +8050,7 @@ typename ParseHandler::Node GeneralParser<ParseHandler, Unit>::assignExpr(
     }
 
     FunctionSyntaxKind syntaxKind = FunctionSyntaxKind::Arrow;
-    FunctionNodeType funNode = handler.newFunction(syntaxKind, pos());
+    FunctionNodeType funNode = handler.newFunction(syntaxKind, startPos);
     if (!funNode) {
       return null();
     }
diff --git a/js/src/frontend/TokenStream.cpp b/js/src/frontend/TokenStream.cpp
index 46960f34d75e..c0a57c1105ae 100644
--- a/js/src/frontend/TokenStream.cpp
+++ b/js/src/frontend/TokenStream.cpp
@@ -1275,6 +1275,7 @@ bool TokenStreamSpecific<Unit, AnyCharsAccess>::advance(size_t position) {
   TokenStreamAnyChars& anyChars = anyCharsAccess();
   Token* cur = const_cast<Token*>(&anyChars.currentToken());
   cur->pos.begin = this->sourceUnits.offset();
+  cur->pos.end = cur->pos.begin;
   MOZ_MAKE_MEM_UNDEFINED(&cur->type, sizeof(cur->type));
   anyChars.lookahead = 0;
   return true;
diff --git a/js/src/jit-test/tests/debug/Script-getPossibleBreakpoints.js b/js/src/jit-test/tests/debug/Script-getPossibleBreakpoints.js
index e374fea241d7..9717bf268211 100644
--- a/js/src/jit-test/tests/debug/Script-getPossibleBreakpoints.js
+++ b/js/src/jit-test/tests/debug/Script-getPossibleBreakpoints.js
@@ -259,7 +259,7 @@ assertBreakpoints(`
   }
 `);
 assertBreakpoints(`
-  var fn /*S*/= () => {
+  var fn = /*S*/() => {
     /*S*/console./*B*/log("fn");
     /*S*/return /*B*/new Proxy({ prop: 42 }, {
       deleteProperty() {
@@ -268,6 +268,21 @@ assertBreakpoints(`
     });
   /*B*/};
 `);
+assertBreakpoints(`
+  var fn = /*S*/async (arg) => {
+    /*S*/console./*B*/log("fn");
+  /*B*/};
+`);
+assertBreakpoints(`
+  var fn = /*S*/arg => {
+    /*S*/console./*B*/log("fn");
+  /*B*/};
+`);
+assertBreakpoints(`
+  var fn = /*S*/async arg => {
+    /*S*/console./*B*/log("fn");
+  /*B*/};
+`);
 assertBreakpoints(`
   if ((/*S*/delete /*B*/fn().prop) + /*B*/b()) {
     /*S*/console./*B*/log("foo");