[Sema] Reject tuple extensions early when feature is disabled

Tuple extensions are still an experimental feature, but we have a
number of crashers in the repo for them because we still use their
type-checker machinery even when disabled. Change the logic here such
that we reject them early in extension binding when the feature is
disabled. This will ensure we address the crashers before productizing.

Author: hamishknight

lib/AST/NameLookup.cpp

@@ -3630,7 +3630,17 @@ NominalTypeDecl *ExtensionDecl::computeExtendedNominal(
   if (nominalTypes.empty())
     return nullptr;
 
-  return nominalTypes[0];
+  auto *result = nominalTypes[0];
+
+  // Tuple extensions are experimental, if the feature isn't enabled let's not
+  // bind this extension at all. This fixes a bunch of crashers that we don't
+  // yet properly handle with the feature enabled.
+  if (isa<BuiltinTupleDecl>(result) &&
+      !ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
+    return nullptr;
+  }
+
+  return result;
 }
 
 NominalTypeDecl *

lib/Sema/TypeCheckDecl.cpp

@@ -3089,6 +3089,13 @@ ExtendedTypeRequest::evaluate(Evaluator &eval, ExtensionDecl *ext) const {
     return error();
   }
 
+  // Tuple extensions are experimental.
+  if (extendedType->is<TupleType>() &&
+      !ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
+    diags.diagnose(ext, diag::experimental_tuple_extension);
+    return error();
+  }
+
   // Cannot extend function types, metatypes, existentials, etc.
   if (!extendedType->is<TupleType>() &&
       !extendedType->getAnyNominal() &&

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -3652,10 +3652,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       return;
 
     auto &ctx = ED->getASTContext();
-
-    if (!ctx.LangOpts.hasFeature(Feature::TupleConformances)) {
-      ED->diagnose(diag::experimental_tuple_extension);
-    }
+    ASSERT(ctx.LangOpts.hasFeature(Feature::TupleConformances) &&
+           "Extension binding should not have permitted this");
 
     if (!isValidExtendedTypeForTupleExtension(ED)) {
       ED->diagnose(diag::tuple_extension_wrong_type,

validation-test/IDE/crashers/38a36bbe0fc496da.swift renamed to validation-test/IDE/crashers_fixed/38a36bbe0fc496da.swift

@@ -1,5 +1,5 @@
 // {"kind":"complete","original":"61e9155a","signature":"swift::ide::CodeCompletionResultBuilder::takeResult()"}
-// RUN: not --crash %target-swift-ide-test -code-completion -batch-code-completion -skip-filecheck -code-completion-diagnostics -source-filename %s
+// RUN: %target-swift-ide-test -code-completion -batch-code-completion -skip-filecheck -code-completion-diagnostics -source-filename %s
 extension ()
 where
   #^^# == <#type#>

validation-test/compiler_crashers_2/0217ed2d301f5d7b.swift renamed to validation-test/compiler_crashers_2_fixed/0217ed2d301f5d7b.swift

@@ -1,5 +1,5 @@
 // {"kind":"typecheck","original":"679d3d53","signature":"(anonymous namespace)::PrintAST::visit(swift::Decl*)"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension () {
   class let a
 }

validation-test/compiler_crashers_2/4e921915ae337fb5.swift renamed to validation-test/compiler_crashers_2_fixed/4e921915ae337fb5.swift

@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"swift::ConditionalRequirementsRequest::evaluate(swift::Evaluator&, swift::NormalProtocolConformance*) const","signatureAssert":"Assertion failed: (typeSig.getCanonicalSignature().getGenericParams() == extensionSig.getCanonicalSignature().getGenericParams()), function evaluate"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 protocol a typealias b<c> = () extension b : a

validation-test/compiler_crashers_2/548b48b935d4153a.swift renamed to validation-test/compiler_crashers_2_fixed/548b48b935d4153a.swift

@@ -1,4 +1,4 @@
 // {"kind":"typecheck","signature":"swift::NominalType::get(swift::NominalTypeDecl*, swift::Type, swift::ASTContext const&)","signatureAssert":"Assertion failed: ((!Parent || Parent->is<NominalType>() || Parent->is<BoundGenericType>() || Parent->is<UnboundGenericType>()) && \"parent must be a nominal type\"), function get"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension() {
   struct a extension a

validation-test/compiler_crashers_2/662d871271047482.swift renamed to validation-test/compiler_crashers_2_fixed/662d871271047482.swift

@@ -1,5 +1,5 @@
 // {"kind":"typecheck","original":"2e2249a5","signature":"swift::TypeBase::computeCanonicalType()","signatureAssert":"Assertion failed: (Result->isCanonical()), function computeCanonicalType"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 typealias a<b> = (
 >extension a where b ==  {
 c

validation-test/compiler_crashers_2/666bd08556187ed3.swift renamed to validation-test/compiler_crashers_2_fixed/666bd08556187ed3.swift

@@ -1,3 +1,3 @@
 // {"kind":"typecheck","signature":"(anonymous namespace)::DeclChecker::visit(swift::Decl*)","signatureAssert":"Assertion failed: (false && \"Huh?\"), function isValidExtendedTypeForTupleExtension"}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 extension repeat (

validation-test/compiler_crashers_2_fixed/966aa8f86a7565d3.swift

@@ -0,0 +1,12 @@
+// {"kind":"typecheck","original":"71a26232","signature":"swift::Decl::getDescriptiveKind() const"}
+// RUN: not %target-swift-frontend -typecheck %s
+typealias a = ()
+extension a {
+  func
+    < (b: Self, c: Self)
+  {
+    for (d, e) in repeat (each b    each c) {
+      d < &e
+    }
+  }
+}