1611777 - Optional chaining assertions and unreachable code

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[André Bargull [:anba]]

var a, b;
(a + b)?.()

asserts with:

Assertion failure: (kind == ParseNodeKind::ArrayExpr || kind == ParseNodeKind::ObjectExpr || kind == ParseNodeKind::TrueExpr || kind == ParseNodeKind::FalseExpr || kind == ParseNodeKind::StringExpr || kind == ParseNodeKind::NumberExpr || kind == ParseNodeKind::RawUndefinedExpr || kind == ParseNodeKind::NullExpr || kind == ParseNodeKind::Name || kind == ParseNodeKind::Function || kind == ParseNodeKind::ThisExpr || kind == ParseNodeKind::TaggedTemplateExpr || kind == ParseNodeKind::TemplateStringExpr || kind == ParseNodeKind::AwaitExpr || kind == ParseNodeKind::RegExpExpr || kind == ParseNodeKind::ClassDecl || kind == ParseNodeKind::CommaExpr || kind == ParseNodeKind::NewExpr || kind == ParseNodeKind::SetThis || kind == ParseNodeKind::NewTargetExpr) (Unknown ParseNodeKind for OptionalChain), at /home/andre/hg/mozilla-central/js/src/frontend/BytecodeEmitter.cpp:7833

---

({m() { super[0]?.() }}).m()

asserts wth:

Assertion failure: initialDepth_ + 2 == depth, at /home/andre/hg/mozilla-central/js/src/frontend/OptionalEmitter.cpp:58

Comment 1

[Yulia Startsev [:yulia] OOO until July 2026]

anba -- let me know if i can help with this.

Comment 2

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 1: Report syntax error for optional property access in self-hosting code. r=yulia!

We already assert that this case isn't allowed in the bytecode emitter. Also
report a syntax error to match normal property access.

Comment 3

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 2: Merge same blocks in emitDeleteOptionalChain(). r=yulia!

Depends on D61146

Comment 4

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 3: Change emitOptionalCalleeAndThis() parameter to use CallNode. r=yulia!

That way we don't need the explicit cast.

Depends on D61147

Comment 5

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 4: `super` can't occur on the left-hand side of an optional chain. r=yulia!

Moves the isSuper() method from the base class to the (non-optional) derived
classes, because super?.x isn't valid syntax, so it's confusing to be able to
ask if an optional property access is applied on super.

The next part will further simplify BytecodeEmitter::emitDelete{Element,Property}InOptChain().

Depends on D61148

Comment 6

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 5: Remove unnecessary super-handling in optional delete. r=yulia!

The child node of a DeleteOptionalChainExpr node can't be a super-property
accessor, so we can remove this code.

Drive-by: Reindent some stack comments.

Depends on D61151

Comment 7

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 6: Crash for unexpected super-base in optional call. r=yulia!

super?.() isn't valid code, so we don't need to handle this case.

Depends on D61152

Comment 8

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 7: Add missing entries to list of valid optional chain start expressions. r=yulia!

The previous list contained some invalid entries (await and comma-expression)
and was missing some possible parse node kinds.

Depends on D61153

Comment 9

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 8: Add missing emitGet in emitOptionalElemExpression. r=yulia!

Aligns emitOptionalElemExpression() with emitOptionalDotExpression(), so it's
easier to compare both methods against each other.

Depends on D61154

Comment 10

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 9: Replace an if-statement with an assertion. r=yulia!

nextMember is never nullptr, so we don't need to test for it.

Depends on D61155

Comment 11

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 10: Remove unnecessary "allowCallSyntax" parameter from Parser::optionalExpr. r=yulia!

All callers pass allowCallSyntax=true, so we can omit this parameter.

Depends on D61156

Comment 12

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 11: Support optional chaining in class heritage expression. r=yulia!

Depends on D61157

Comment 13

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 12: Use optionalExpr() for update expressions to match spec grammar. r=yulia!

Using optionalExpr matches the spec grammar more closely. This change also
modifies the reported error message. ++a?.b reported before this change
"unexpected token: '?.'", but now reports "invalid increment/decrement operand".

Depends on D61158

Comment 14

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 13: Remove unused default arguments from parser methods. r=yulia!

Depends on D61159

Comment 15

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 14: Simplify two lines in optionalExpr(). r=yulia!

• We don't need to test for tt == TokenKind::Eof when we return for
  tt != TokenKind::OptionalChain anyway.
• Omit local variable for the result value and instead use a tail-call. This
  matches the local style in the parser more closely.

Depends on D61160

Comment 16

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 15: Support FunCall/FunApply optimisations for optional chaining. r=yulia!

This change allows the bytecode emitter to use JSOp::FunCall resp. JSOp::FunApply
for calls in optional chain expressions.

Depends on D61161

Comment 17

[André Bargull [:anba]]

Attachment: Bug 1611777 - Part 16: Pass through ValueUsage in optional chains. r=yulia!

This allows us to emit JSOp::CallIgnoresRv in optional chains.

Depends on D61162

Comment 18

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bdb8620ff7f5
Part 1: Report syntax error for optional property access in self-hosting code. r=yulia
https://hg.mozilla.org/integration/autoland/rev/45f7fa06cc3c
Part 2: Merge same blocks in emitDeleteOptionalChain(). r=yulia
https://hg.mozilla.org/integration/autoland/rev/9615eaa325ed
Part 3: Change emitOptionalCalleeAndThis() parameter to use CallNode. r=yulia
https://hg.mozilla.org/integration/autoland/rev/95890e60c691
Part 4: `super` can't occur on the left-hand side of an optional chain. r=yulia
https://hg.mozilla.org/integration/autoland/rev/9dba40e8b408
Part 5: Remove unnecessary super-handling in optional delete. r=yulia
https://hg.mozilla.org/integration/autoland/rev/4a8a350bba27
Part 6: Crash for unexpected super-base in optional call. r=yulia
https://hg.mozilla.org/integration/autoland/rev/5c9241e7ce20
Part 7: Add missing entries to list of valid optional chain start expressions. r=yulia
https://hg.mozilla.org/integration/autoland/rev/958adec63532
Part 8: Add missing emitGet in emitOptionalElemExpression. r=yulia
https://hg.mozilla.org/integration/autoland/rev/fa5be03a588c
Part 9: Replace an if-statement with an assertion. r=yulia
https://hg.mozilla.org/integration/autoland/rev/e82fbc9dee63
Part 10: Remove unnecessary "allowCallSyntax" parameter from Parser::optionalExpr. r=yulia
https://hg.mozilla.org/integration/autoland/rev/468ff3d2cf8e
Part 11: Support optional chaining in class heritage expression. r=yulia
https://hg.mozilla.org/integration/autoland/rev/849b4d84f743
Part 12: Use optionalExpr() for update expressions to match spec grammar. r=yulia
https://hg.mozilla.org/integration/autoland/rev/9c5786b1bccb
Part 13: Remove unused default arguments from parser methods. r=yulia
https://hg.mozilla.org/integration/autoland/rev/46d27864b908
Part 14: Simplify two lines in optionalExpr(). r=yulia
https://hg.mozilla.org/integration/autoland/rev/075c4404c2c8
Part 15: Support FunCall/FunApply optimisations for optional chaining. r=yulia
https://hg.mozilla.org/integration/autoland/rev/65c1c7d322ed
Part 16: Pass through ValueUsage in optional chains. r=yulia

Comment 19

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/bdb8620ff7f5
https://hg.mozilla.org/mozilla-central/rev/45f7fa06cc3c
https://hg.mozilla.org/mozilla-central/rev/9615eaa325ed
https://hg.mozilla.org/mozilla-central/rev/95890e60c691
https://hg.mozilla.org/mozilla-central/rev/9dba40e8b408
https://hg.mozilla.org/mozilla-central/rev/4a8a350bba27
https://hg.mozilla.org/mozilla-central/rev/5c9241e7ce20
https://hg.mozilla.org/mozilla-central/rev/958adec63532
https://hg.mozilla.org/mozilla-central/rev/fa5be03a588c
https://hg.mozilla.org/mozilla-central/rev/e82fbc9dee63
https://hg.mozilla.org/mozilla-central/rev/468ff3d2cf8e
https://hg.mozilla.org/mozilla-central/rev/849b4d84f743
https://hg.mozilla.org/mozilla-central/rev/9c5786b1bccb
https://hg.mozilla.org/mozilla-central/rev/46d27864b908
https://hg.mozilla.org/mozilla-central/rev/075c4404c2c8
https://hg.mozilla.org/mozilla-central/rev/65c1c7d322ed