[Type checker] Work around issues with badly broken generic code.

The GenericTypeOrArchetypeResolver changes are effectively porting
some existing hacks from the now-dead
PartialGenericTypeOrArchetypeResolver, which dodges some regressions
in the compiler-crashers suite and fixes 11 new crashers. There is
undoubtedly a more principled approach to fix these problems, most of
which now step from recursively looking for a generic environment that
isn't there, but doing so requires improvements to our name lookup.

Author: DougGregor

lib/Sema/TypeCheckDecl.cpp

@@ -7050,6 +7050,10 @@ void TypeChecker::validateDecl(ValueDecl *D, bool resolveTypeParams) {
       return;
     proto->computeType();
 
+    auto iBTC = proto->isBeingTypeChecked();
+    proto->setIsBeingTypeChecked();
+    SWIFT_DEFER { proto->setIsBeingTypeChecked(iBTC); };
+
     // Resolve the inheritance clauses for each of the associated
     // types.
     for (auto member : proto->getMembers()) {

lib/Sema/TypeCheckGeneric.cpp

@@ -87,13 +87,14 @@ Type GenericTypeToArchetypeResolver::resolveGenericTypeParamType(
 
   // Hack: See parseGenericParameters(). When the issue there is fixed,
   // we won't need the isInvalid() check anymore.
-  if (gpDecl->isInvalid())
+  if (gpDecl->isInvalid() || !GenericEnv)
     return ErrorType::get(gpDecl->getASTContext());
 
-  if (auto *Env = GenericEnv)
-    return Env->mapTypeIntoContext(gp);
+  auto type = GenericEnv->getMappingIfPresent(gp);
+  if (!type)
+    return ErrorType::get(gpDecl->getASTContext());;
 
-  return ErrorType::get(gpDecl->getASTContext());
+  return *type;
 }
 
 Type GenericTypeToArchetypeResolver::resolveDependentMemberType(
@@ -113,6 +114,10 @@ Type GenericTypeToArchetypeResolver::resolveSelfAssociatedType(
 
 Type GenericTypeToArchetypeResolver::resolveTypeOfContext(DeclContext *dc,
                                                           bool wantSelf) {
+  // FIXME: Fallback case.
+  if (dc->isGenericContext() && !dc->isValidGenericContext())
+    return getTypeOfContext(dc, wantSelf);
+
   return ArchetypeBuilder::mapTypeIntoContext(
       dc->getParentModule(), GenericEnv,
       getTypeOfContext(dc, wantSelf));

validation-test/IDE/crashers/032-swift-expr-propagatelvalueaccesskind.swift

@@ -1,3 +1,2 @@
 // RUN: not --crash %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
-// REQUIRES: asserts
 {()=(var a{#^A^#

validation-test/compiler_crashers/28209-swift-protocoldecl-requiresclassslow.swift renamed to validation-test/compiler_crashers_fixed/28209-swift-protocoldecl-requiresclassslow.swift

@@ -1,4 +1,4 @@
-// RUN: not --crash %target-swift-frontend %s -typecheck
+// RUN: not %target-swift-frontend %s -typecheck
 // REQUIRES: asserts
 
 // Distributed under the terms of the MIT license

validation-test/compiler_crashers/28351-swift-functiontype-get.swift renamed to validation-test/compiler_crashers_fixed/28351-swift-functiontype-get.swift

@@ -5,5 +5,5 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -typecheck
+// RUN: not %target-swift-frontend %s -typecheck
 extension A{{}protocol A}protocol A:class{protocol A{}typealias e:A

validation-test/compiler_crashers/28392-swift-dependentgenerictyperesolver-resolveselfassociatedtype.swift renamed to validation-test/compiler_crashers_fixed/28392-swift-dependentgenerictyperesolver-resolveselfassociatedtype.swift

@@ -5,7 +5,7 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -typecheck
+// RUN: not %target-swift-frontend %s -typecheck
 // REQUIRES: asserts
 {
 class A{

validation-test/compiler_crashers/28408-swift-typechecker-checkinheritanceclause.swift renamed to validation-test/compiler_crashers_fixed/28408-swift-typechecker-checkinheritanceclause.swift

@@ -5,7 +5,7 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -typecheck
+// RUN: not %target-swift-frontend %s -typecheck
 // REQUIRES: asserts
 class A{{
 {

validation-test/compiler_crashers/28423-swift-typechecker-validatedecl.swift renamed to validation-test/compiler_crashers_fixed/28423-swift-typechecker-validatedecl.swift

@@ -5,7 +5,7 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -typecheck
+// RUN: not %target-swift-frontend %s -typecheck
 // REQUIRES: asserts
 protocol a
 protocol a{

validation-test/compiler_crashers/28435-swift-genericenvironment-maptypeintocontext.swift renamed to validation-test/compiler_crashers_fixed/28435-swift-genericenvironment-maptypeintocontext.swift

@@ -5,7 +5,7 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -typecheck
+// RUN: not %target-swift-frontend %s -typecheck
 enum ST:d
 protocol a{typealias d:A.B{
 {

validation-test/compiler_crashers/28453-found-interfacetoarchetypemap-end-missing-generic-parameter-failed.swift renamed to validation-test/compiler_crashers_fixed/28453-found-interfacetoarchetypemap-end-missing-generic-parameter-failed.swift

@@ -5,7 +5,7 @@
 // See https://swift.org/LICENSE.txt for license information
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -emit-ir
+// RUN: not %target-swift-frontend %s -emit-ir
 // REQUIRES: asserts
 protocol a{}protocol a{
 typealias e=a