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[TypeChecker] Don’t crash if a ExplicitCastExpr doesn’t have a cast type #59664

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merged 1 commit into from
Jun 29, 2022
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[TypeChecker] Don’t crash if a ExplicitCastExpr doesn’t have a cast type #59664

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2 changes: 1 addition & 1 deletion lib/Sema/TypeCheckAvailability.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3229,7 +3229,7 @@ class ExprAvailabilityWalker : public ASTWalker {
maybeDiagParameterizedExistentialErasure(EE, Where);
}
if (auto *CC = dyn_cast<ExplicitCastExpr>(E)) {
if (!isa<CoerceExpr>(CC) &&
if (!isa<CoerceExpr>(CC) && CC->getCastType() &&
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@xedin xedin Jun 24, 2022 •
edited by ahoppen
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I took a quick look at this and I might have an idea about what is going on. Based on the stacktrace -diagnoseStmtAvailability walks into an AbstractClosureExpr because ExprAvailabilityWalker always returns true from shouldWalkIntoClosure but:

  1. Result builders currently have multi-statement closure inference disabled due to some ordering issues related to one-way constraints;
  2. In code completion mode we always pass LeaveClosureBodiesUnchecked to the constraint system;

I wonder if something like this might reproduce the crash:

import SwiftUI

struct S<T> {
}

extension S : ExpressibleByIntegerLiteral {
  typealias IntegerLiteralType = Int8

  init(integerLiteral: IntegerLiteralType) {
  }
}

struct MyView : View {
  var body: some View {
    Group {
      EmptyView()

      test {
        let x =  #^COMPLETE^# as S<String>
        print(x)
      }
    }
  }

  func test(_: () -> Void) -> some View {
    return EmptyView()
  }
}

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That example doesn’t reproduce the crash for me. AFAICT closures aren’t walked
https://github.com/apple/swift/blob/ba42be5fcf2d663a589a3f5e4efe0ffcffb101fa/lib/Sema/MiscDiagnostics.cpp#L64-L65

I very much suspect that this issue will be resolved fundamentally when we get rid of LeaveClosureBodiesUnchecked and I’m wondering if it makes sense to hunt for a reproducing test case now since the fix seems pretty straight-forward.

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The check you pointed out would skip walking into some decls in the closures, not the closures themselves though. I think this issue needs to be addressed in a different way by adjusting the check in ExprAvailabilityWalker, otherwise it would just crash in some other place…

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I managed to find a reproducer that’s not code completion specific. With this reproducer at hand, I would argue that the fix is correct because AFAICT it appears correct that a ExplicitCastExpr has no CastType if that type is invalid. So we need to check if the type is valid (i.e. not null) before calling hasParameterizedExistential.

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How did an expression with incorrect cast end up getting past to a syntactic diagnostics?

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AFAICT it appears correct that a ExplicitCastExpr has no CastType if that type is invalid.

I don't know for sure if that makes sense in this case, but some other places I saw where the type was invalid the expected was to have an ErrorType instead of a null type. But again not sure if that is the case here...

CC->getCastType()->hasParameterizedExistential()) {
SourceLoc loc = CC->getCastTypeRepr() ? CC->getCastTypeRepr()->getLoc()
: E->getLoc();
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19 changes: 19 additions & 0 deletions validation-test/compiler_crashers_2_fixed/rdar95629905.swift
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
// RUN: %target-typecheck-verify-swift

@resultBuilder
struct ViewBuilder {
static func buildBlock(_ x: Int) -> Int { x }
}

func test(_: () -> Void) -> Int {
return 42
}

struct MyView {
@ViewBuilder var body: Int {
test {
"ab" is Unknown // expected-error{{cannot find type 'Unknown' in scope}}
print("x")
}
}
}