[SE-0491] Parse and ASTGen module selectors #84362

beccadax · 2025-09-17T23:33:32Z

This PR adds support for module selectors to the legacy parser and also updates ASTGen to lower the module selector-related syntax nodes introduced by swiftlang/swift-syntax#3091. Although the compiler parses module selectors with this PR, they don't have any actual effect on name lookup or other compiler behavior.

Makes progress on rdar://problem/19481048. Extracted from #34556. Currently under review as SE-0491.

beccadax · 2025-10-07T18:04:22Z

@swift-ci smoke test

rintaro · 2025-10-10T15:36:46Z

lib/ASTGen/Sources/ASTGen/ASTGen.swift

  @inline(__always)
  func generateSourceLoc(_ node: some SyntaxProtocol) -> SourceLoc {
-    SourceLoc(at: node.positionAfterSkippingLeadingTrivia, in: self.base)
+    precondition(node.positionAfterSkippingLeadingTrivia.utf8Offset < 0x0000000100000000)


What is this for?

I think this was something I added to chase down a bug caused by missing tokens having very large, invalid offsets that turned into out-of-bounds SourceLocs. It probably doesn't belong in this PR; the constant here is a fairly arbitrary "big enough" value.

rintaro · 2025-10-10T15:44:43Z

lib/ASTGen/Sources/ASTGen/ASTGen.swift

+    arguments: (
+      leftParen: TokenSyntax,
+      labels: some Collection<TokenSyntax>,
+      rightParen: TokenSyntax
+    )? = Optional<(leftParen: TokenSyntax, labels: [TokenSyntax], rightParen: TokenSyntax)>.none


Can't this be just DeclNameArgumentsSyntax ?

Suggested change

arguments: (

leftParen: TokenSyntax,

labels: some Collection<TokenSyntax>,

rightParen: TokenSyntax

)? = Optional<(leftParen: TokenSyntax, labels: [TokenSyntax], rightParen: TokenSyntax)>.none

arguments: DeclNameArgumentsSyntax? = nil

Looks like it can be. Good catch!

lib/ASTGen/Sources/ASTGen/Decls.swift

lib/Parse/ParseDecl.cpp

rintaro · 2025-10-10T17:31:54Z

lib/Parse/ParseDecl.cpp

+      diagnose(Tok, diag::replace_module_selector_with_member_lookup)
+        .fixItReplace(Tok.getLoc(), ".");
+    }
+    HasNext = consumeIf(tok::period) || consumeIf(tok::colon_colon);


Could you align the implementation with SwiftParser?

rintaro · 2025-10-10T17:45:24Z

lib/Parse/ParseExpr.cpp

+  DeclNameRef nameRef =
+      parseDeclNameRef(nameLoc, diag::impossible_parse,
+                       DeclNameFlag::AllowAnonymousParamNames |
+                       DeclNameFlag::ModuleSelectorUnsupported);


Is this needed? I believe this is only called when Tok is tok::dollarident so there's no chance to have a module selector here.

Yeah, I could roll this back. It was more important back when parseDeclNameRef() always parsed a module selector and just diagnosed it when you passed ModuleSelectorUnsupported.

rintaro · 2025-10-10T17:51:54Z

lib/Parse/ParseExpr.cpp

+  if (P.Tok.is(tok::identifier) && P.peekToken().is(tok::colon_colon)) {
+    return P.lookahead(2, [&](auto &scope) {


How about making isAtModuleSelector() returning number of module selector tokens and

Suggested change

if (P.Tok.is(tok::identifier) && P.peekToken().is(tok::colon_colon)) {

return P.lookahead(2, [&](auto &scope) {

if (auto numTokens = P.isAtModuleSelector()) {

return P.lookahead(*numTokens, [&](auto &scope) {

lib/Parse/ParseStmt.cpp

rintaro · 2025-10-10T17:56:44Z

lib/Parse/ParseType.cpp

    break;
  case tok::kw_protocol:
-    if (startsWithLess(peekToken())) {
+    if (Tok.is(tok::kw_protocol) && startsWithLess(peekToken())) {


I don't think this is needed.

You're right; I think it was briefly needed until I factored out diagnoseAndRecover() into a helper lambda.

beccadax · 2025-10-15T22:22:15Z

I've also updated the ASTGen work to reflect the fact that SwiftSyntax no longer considers this to be experimental syntax.

beccadax · 2025-10-15T22:22:20Z

@swift-ci smoke test

beccadax · 2025-10-15T23:24:03Z

@swift-ci smoke test

rintaro

Other than these small comments, this looks good to me!

rintaro · 2025-10-16T17:03:34Z

include/swift/AST/DiagnosticsParse.def

 ERROR(experimental_using_decl_disabled,PointsToFirstBadToken,
      "'using' is an experimental feature that is currently disabled", ())

+ERROR(impossible_parse,none,


Not used? (I'm fine with having this, but just to make sure I don't miss anything)

Removing it.

rintaro · 2025-10-16T17:06:32Z

lib/AST/ASTDumper.cpp

      printFlag(!ABIRoleInfo(D).providesAPI(), "abi_only");

-      printSourceRange(D->getSourceRange(), &D->getASTContext());
+      if (D->getStartLoc().isValid() && D->getEndLoc().isValid())


Suggested change

if (D->getStartLoc().isValid() && D->getEndLoc().isValid())

if (D->getSourceRange().isValid())

If you did this because there's a case D->getStartLoc().isValid() != D->getEndLoc().isValid(), we should fix that.

I already did (we talked about it in the first review round), but if something like that ever happens again, it'll be helpful to have ASTDumper not crash trying to dump the invalid range.

Decl::getStartLoc()/Decl::getEndLoc() are implemented as:

swift/include/swift/AST/Decl.h

Lines 1139 to 1143 in d030c8f

/// Returns the starting location of the entire declaration.

SourceLoc getStartLoc() const { return getSourceRange().Start; }

/// Returns the end location of the entire declaration.

SourceLoc getEndLoc() const { return getSourceRange().End; }

If there was a invalid mismatch, it'd already crashed at this point.

Okay, I can drop that change.

When closing paren is missing, point at the location where it should be found, not the opening paren.

A PatternBindingEntry formed from a MissingPatternSyntax has no valid SourceLocs in it, and a PatternBindingDecl containing only PatternBindingEntries with no valid SourceLocs trips an assertion during availability checking. (Generating dummy SourceLocs can cause invalid overlaps between AvailabilityScopes, so that’s not a workable solution.) The fix is to: • Refuse to generate a PatternBindingEntry from a PatternBindingSyntax with a MissingPatternSyntax (MissingPatternSyntaxes at nested positions don’t have this problem) • Refuse to generate a PatternBindingDecl with no PatternBindingEntries This ensures that the invalid AST nodes are never formed. No current test cases hit this problem, but certain invalid module selector tests can run into this situation when run with ASTGen.

beccadax · 2025-10-16T20:31:46Z

@swift-ci please test

beccadax · 2025-10-17T04:14:48Z

@swift-ci test macOS platform

beccadax · 2025-10-17T21:19:05Z

@swift-ci test macOS platform

beccadax requested review from CodaFi, DougGregor, bnbarham, hamishknight, hborla, rintaro, slavapestov and xedin as code owners September 17, 2025 23:33

beccadax requested a review from tshortli September 18, 2025 21:21

rintaro reviewed Oct 10, 2025

View reviewed changes

beccadax force-pushed the mod-squad-parse branch from fe22d37 to f7df829 Compare October 15, 2025 22:21

beccadax requested a review from rintaro October 15, 2025 22:22

beccadax force-pushed the mod-squad-parse branch 2 times, most recently from 65464e8 to 6f72d14 Compare October 15, 2025 23:23

rintaro reviewed Oct 16, 2025

View reviewed changes

beccadax added 10 commits October 16, 2025 13:30

Use parseDeclNameRef in a few more places

cab38af

[NFC] Add DeclNameLoc to specialize/dynamicReplacement

c9bb85a

[NFC] Tweak source loc of @_implements error

0ae6154

When closing paren is missing, point at the location where it should be found, not the opening paren.

[NFC] Make pattern type checking more defensive

e28601e

[NFC-ish] Do lookahead without llvm::function_ref

5895473

[NFC] Add tok::colon_colon to parser

f1db5d3

Parse module selectors in permitted locations

f82881c

Allow :: as an alias for . in scoped imports

b6e22cb

Update and test ASTGen for module selectors

683ce9d

beccadax force-pushed the mod-squad-parse branch from 6f72d14 to 683ce9d Compare October 16, 2025 20:31

beccadax enabled auto-merge October 16, 2025 20:32

beccadax mentioned this pull request Oct 18, 2025

[SE-0491] Fix malformed arg label error with module selector #84994

Merged

beccadax merged commit d8d226c into swiftlang:main Oct 18, 2025
5 checks passed

beccadax mentioned this pull request Oct 21, 2025

[SE-0491] Implement lookup and diagnostics for module selectors (MyMod::someName) #34556

Merged

		if (P.Tok.is(tok::identifier) && P.peekToken().is(tok::colon_colon)) {
		return P.lookahead(2, [&](auto &scope) {

	if (D->getStartLoc().isValid() && D->getEndLoc().isValid())
	if (D->getSourceRange().isValid())

	/// Returns the starting location of the entire declaration.
	SourceLoc getStartLoc() const { return getSourceRange().Start; }

	/// Returns the end location of the entire declaration.
	SourceLoc getEndLoc() const { return getSourceRange().End; }

[SE-0491] Parse and ASTGen module selectors #84362

[SE-0491] Parse and ASTGen module selectors #84362

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beccadax commented Sep 17, 2025

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beccadax commented Oct 15, 2025

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beccadax Oct 16, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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beccadax commented Oct 16, 2025

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beccadax Oct 16, 2025 •

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