[AST] Fix crash in 'getOverrideGenericSignature()' when there are no generic params in the GSB

Author: theblixguy

lib/AST/ASTContext.cpp

@@ -4398,6 +4398,7 @@ GenericSignature *
 ASTContext::getOverrideGenericSignature(const ValueDecl *base,
                                         const ValueDecl *derived) {
   auto baseGenericCtx = base->getAsGenericContext();
+  auto derivedGenericCtx = derived->getAsGenericContext();
   auto &ctx = base->getASTContext();
 
   if (!baseGenericCtx) {
@@ -4421,6 +4422,10 @@ ASTContext::getOverrideGenericSignature(const ValueDecl *base,
     return nullptr;
   }
 
+  if (!derivedGenericCtx || !derivedGenericCtx->isGeneric()) {
+    return nullptr;
+  }
+
   if (derivedClass->getGenericSignature() == nullptr &&
       !baseGenericCtx->isGeneric()) {
     return nullptr;
@@ -4449,12 +4454,8 @@ ASTContext::getOverrideGenericSignature(const ValueDecl *base,
   GenericSignatureBuilder builder(ctx);
   builder.addGenericSignature(derivedClass->getGenericSignature());
 
-  if (auto derivedGenericCtx = derived->getAsGenericContext()) {
-    if (derivedGenericCtx->isGeneric()) {
-      for (auto param : *derivedGenericCtx->getGenericParams()) {
-        builder.addGenericParameter(param);
-      }
-    }
+  for (auto param : *derivedGenericCtx->getGenericParams()) {
+    builder.addGenericParameter(param);
   }
 
   auto source =

test/attr/attr_override.swift

@@ -606,6 +606,23 @@ class SR_10198_Base {
 }
 
 class SR_10198_Derived: SR_10198_Base {
-  override func a<T>(_ val: T) -> String { return super.a(val) }
-  override func a<T: Equatable>(_ val: T) -> String { return super.a(val) }
+  override func a<T>(_ val: T) -> String { return super.a(val) } // okay
+  override func a<T: Equatable>(_ val: T) -> String { return super.a(val) } // okay
 }
+
+protocol SR_10198_Base_P {
+  associatedtype Bar
+}
+
+struct SR_10198_Base_S: SR_10198_Base_P {
+  typealias Bar = Int
+}
+
+class SR_10198_Base_1 {
+  init<F: SR_10198_Base_P>(_ arg: F) where F.Bar == Int {}
+}
+
+class SR_10198_Derived_1: SR_10198_Base_1 {
+  init(_ arg1: Int) { super.init(SR_10198_Base_S()) } // okay, doesn't crash
+}
+