IRGen: Mangle DWARF types with the right generic signature

The symptom here was a crash in getConformanceAccessPath(), but the root
cause was that the ASTMangler used an incorrect generic signature when
looking up the conformance path for a type parameter.

The mangler requires a generic signature to be set to properly mangle types
containing retroactive conformances. However, DebugInfo just used the
IRGenModule's current signature, which wasn't always the same as the
signature describing the archetypes found inside the SILFunction.

Fixes rdar://problem/81683650 / https://bugs.swift.org/browse/SR-15046.

Author: slavapestov

lib/IRGen/IRGenDebugInfo.cpp

@@ -21,6 +21,7 @@
 #include "GenType.h"
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/Expr.h"
+#include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/IRGenOptions.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/ModuleLoader.h"
@@ -825,9 +826,29 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
       return MetadataTypeDeclCache.find(DbgTy.getDecl()->getName().str())
           ->getKey();
 
+    // This is a bit of a hack. We need a generic signature to use for mangling.
+    // If we started with an interface type, just use IGM.getCurGenericContext(),
+    // since callers that use interface types typically push a signature that way.
+    //
+    // Otherwise, if we have a contextual type, find an archetype and ask it for
+    // it's generic signature. The context generic signature from the IRGenModule
+    // is unlikely to be useful here.
+    GenericSignature Sig;
     Type Ty = DbgTy.getType();
-    if (Ty->hasArchetype())
+    if (Ty->hasArchetype()) {
+      Ty.findIf([&](Type t) -> bool {
+        if (auto *archetypeTy = t->getAs<PrimaryArchetypeType>()) {
+          Sig = archetypeTy->getGenericEnvironment()->getGenericSignature();
+          return true;
+        }
+
+        return false;
+      });
+
       Ty = Ty->mapTypeOutOfContext();
+    } else {
+      Sig = IGM.getCurGenericContext();
+    }
 
     // Strip off top level of type sugar (except for type aliases).
     // We don't want Optional<T> and T? to get different debug types.
@@ -852,7 +873,6 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
         IGM.getSILModule());
 
     Mangle::ASTMangler Mangler;
-    GenericSignature Sig = IGM.getCurGenericContext();
     std::string Result = Mangler.mangleTypeForDebugger(Ty, Sig);
 
     if (!Opts.DisableRoundTripDebugTypes) {

test/IRGen/retroactive_conformance_path.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t) 
-// RUN: %target-build-swift -module-name=test %s -o %t/a.out
+// RUN: %target-build-swift -module-name=test %s -o %t/a.out -requirement-machine=verify
 // RUN: %target-run %t/a.out | %FileCheck %s
 // REQUIRES: executable_test
 // REQUIRES: CPU=arm64 || CPU=x86_64

test/IRGen/retroactive_conformance_path_2.swift

@@ -0,0 +1,9 @@
+// RUN: %target-swift-frontend -emit-ir -g -primary-file %s -requirement-machine=verify
+
+public struct TestType<T: Error> { }
+
+extension Array: Error where Element: Error { }
+
+public struct GenericType<G> {
+    public func test<T>(_ value: TestType<[T]>) { }
+}