From ffa73cb4f85cff6607ee385d4b67446df167c2da Mon Sep 17 00:00:00 2001
From: Jordan Rose <jordan_rose@apple.com>
Date: Thu, 8 Nov 2018 15:42:59 -0800
Subject: [PATCH] Verify that a GenericTypeParamDecl's depth and index are
 correct

Re-applied after fixing a bug in Serialization where the DeclContext
wasn't being set correctly for extensions with nested parameters. I
was unable to come up with a reduced test case, but the CoreStore
project in the source compatibility suite was failing without the
Serialization change, and now it isn't.
---
 lib/AST/ASTVerifier.cpp               | 42 +++++++++++++++++++++++++++
 lib/Serialization/Deserialization.cpp |  9 ++++--
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/lib/AST/ASTVerifier.cpp b/lib/AST/ASTVerifier.cpp
index 37155a7f9692a..ac0416ec98f1b 100644
--- a/lib/AST/ASTVerifier.cpp
+++ b/lib/AST/ASTVerifier.cpp
@@ -2738,6 +2738,48 @@ class Verifier : public ASTWalker {
       verifyCheckedBase(nominal);
     }
 
+    void verifyCheckedAlways(GenericTypeParamDecl *GTPD) {
+      PrettyStackTraceDecl debugStack("verifying GenericTypeParamDecl", GTPD);
+
+      const DeclContext *DC = GTPD->getDeclContext();
+      if (!GTPD->getDeclContext()->isInnermostContextGeneric()) {
+        Out << "DeclContext of GenericTypeParamDecl does not have "
+               "generic params\n";
+        abort();
+      }
+
+      GenericParamList *paramList =
+          static_cast<const GenericContext *>(DC)->getGenericParams();
+      if (!paramList) {
+        Out << "DeclContext of GenericTypeParamDecl does not have "
+               "generic params\n";
+        abort();
+      }
+
+      unsigned currentDepth = paramList->getDepth();
+      if (currentDepth < GTPD->getDepth()) {
+        Out << "GenericTypeParamDecl has incorrect depth\n";
+        abort();
+      }
+      while (currentDepth > GTPD->getDepth()) {
+        paramList = paramList->getOuterParameters();
+        --currentDepth;
+      }
+      assert(paramList && "this is guaranteed by the parameter list's depth");
+
+      if (paramList->size() <= GTPD->getIndex() ||
+          paramList->getParams()[GTPD->getIndex()] != GTPD) {
+        if (llvm::is_contained(paramList->getParams(), GTPD))
+          Out << "GenericTypeParamDecl has incorrect index\n";
+        else
+          Out << "GenericTypeParamDecl not found in GenericParamList; "
+                 "incorrect depth or wrong DeclContext\n";
+        abort();
+      }
+
+      verifyCheckedBase(GTPD);
+    }
+
     void verifyChecked(ExtensionDecl *ext) {
       // Make sure that the protocol conformances are complete.
       for (auto conformance : ext->getLocalConformances()) {
diff --git a/lib/Serialization/Deserialization.cpp b/lib/Serialization/Deserialization.cpp
index 74b39c9acbc5e..838d2e36163a2 100644
--- a/lib/Serialization/Deserialization.cpp
+++ b/lib/Serialization/Deserialization.cpp
@@ -2674,7 +2674,7 @@ ModuleFile::getDeclCheckedImpl(DeclID DID) {
                                                         index);
 
     // Always create GenericTypeParamDecls in the associated module;
-    // maybeReadGenericParams() will reparent them.
+    // the real context will reparent them.
     auto DC = getAssociatedModule();
     auto genericParam = createDecl<GenericTypeParamDecl>(DC,
                                                          getIdentifier(nameID),
@@ -3936,9 +3936,12 @@ ModuleFile::getDeclCheckedImpl(DeclID DID) {
     // Generic parameter lists are written from outermost to innermost.
     // Keep reading until we run out of generic parameter lists.
     GenericParamList *outerParams = nullptr;
-    while (auto *genericParams = maybeReadGenericParams(DC, outerParams))
+    while (auto *genericParams = maybeReadGenericParams(DC, outerParams)) {
+      // We do this repeatedly to set up the correct DeclContexts for the
+      // GenericTypeParamDecls in the list.
+      extension->setGenericParams(genericParams);
       outerParams = genericParams;
-    extension->setGenericParams(outerParams);
+    }
 
     configureGenericEnvironment(extension, genericEnvID);