[SR-14545] Assertion failure "Generic parameter index mismatch" when returning nil for optional generic return type

[ahoppen]

Previous ID	SR-14545
Radar	rdar://problem/77259607
Original Reporter	@ahoppen
Type	Bug
Status	Closed
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Source Tooling
Labels	Bug, FoundByStressTester
Assignee	@hamishknight
Priority	Medium

md5: 235cbf9debc811ffaaf45fd8deb5c80d

Issue Description:

The following new test case causes an assertion failure:

protocol MyView {}

extension MyView {
  func foo<Content>() -> Content? {
// RUN: %sourcekitd-test -req=conformingmethods -pos=%(line + 1):15 %s -- %s
    return nil
  }
}

Assertion failed: (param->getIndex() == count && "Generic parameter index mismatch"), function GenericSignatureImpl, file /Users/alex/swift-src/swift/lib/AST/GenericSignature.cpp, line 67.
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
0.  While performing new completion
1.  While evaluating request CodeCompletionSecondPassRequest(source_file "/Users/alex/swift-src/swift/test/SourceKit/ConformingMethods/test.swift", )
2.  While evaluating request AbstractGenericSignatureRequest(NULL, {Content, U}, {})
/Users/alex/swift-src/nbuild/Release+Asserts/tools/swift/test-macosx-x86_64/SourceKit/ConformingMethods/Output/test.swift.script: line 1: 30719 Abort trap: 6           /Users/alex/swift-src/nbuild/Release+Asserts/bin/sourcekitd-test -module-cache-path '/Users/alex/swift-src/nbuild/Release+Asserts/swift-test-results/x86_64-apple-macosx10.9/clang-module-cache' -req=conformingmethods -pos=6:15 /Users/alex/swift-src/swift/test/SourceKit/ConformingMethods/test.swift -- /Users/alex/swift-src/swift/test/SourceKit/ConformingMethods/test.swift

[ahoppen]

@swift-ci create

[ahoppen]

Fixed in #38503