NCGenerics: precedence of inverses & reqirements

With the removal of `fromDefault` in StructuralRequirement,
`applyInverses` no longer could distinguish which reqirements came from
`expandDefaults` and which were explicitly written in source. Thus, for
a generic parameter like `<T> where T: Copyable, T: ~Copyable`, the
inverse `~Copyable` was eliminating the explicitly-written requirement,
causing `T` to be noncopyable.

We want to emit an error in such cases, so this swaps things around so
we only ever applyInverses on a requirements list that is from
expandDefaults.

Author: kavon

lib/AST/RequirementMachine/RequirementLowering.cpp

@@ -926,8 +926,11 @@ StructuralRequirementsRequest::evaluate(Evaluator &evaluator,
                       SourceLoc()});
 
     desugarRequirements(result, inverses, errors);
-    InverseRequirement::expandDefaults(ctx, needsDefaultRequirements, result);
-    applyInverses(ctx, needsDefaultRequirements, inverses, result, errors);
+
+    SmallVector<StructuralRequirement, 2> defaults;
+    InverseRequirement::expandDefaults(ctx, needsDefaultRequirements, defaults);
+    applyInverses(ctx, needsDefaultRequirements, inverses, defaults, errors);
+    result.append(defaults);
 
     diagnoseRequirementErrors(ctx, errors,
                               AllowConcreteTypePolicy::NestedAssocTypes);
@@ -994,11 +997,13 @@ StructuralRequirementsRequest::evaluate(Evaluator &evaluator,
 
   desugarRequirements(result, inverses, errors);
 
+  SmallVector<StructuralRequirement, 2> defaults;
   // We do not expand defaults for invertible protocols themselves.
   if (!proto->getInvertibleProtocolKind())
-    InverseRequirement::expandDefaults(ctx, needsDefaultRequirements, result);
+    InverseRequirement::expandDefaults(ctx, needsDefaultRequirements, defaults);
 
-  applyInverses(ctx, needsDefaultRequirements, inverses, result, errors);
+  applyInverses(ctx, needsDefaultRequirements, inverses, defaults, errors);
+  result.append(defaults);
 
   diagnoseRequirementErrors(ctx, errors,
                             AllowConcreteTypePolicy::NestedAssocTypes);

lib/AST/RequirementMachine/RequirementMachineRequests.cpp

@@ -667,8 +667,10 @@ AbstractGenericSignatureRequest::evaluate(
       paramsAsTypes.push_back(gtpt);
   }
 
-  InverseRequirement::expandDefaults(ctx, paramsAsTypes, requirements);
-  applyInverses(ctx, paramsAsTypes, inverses, requirements, errors);
+  SmallVector<StructuralRequirement, 2> defaults;
+  InverseRequirement::expandDefaults(ctx, paramsAsTypes, defaults);
+  applyInverses(ctx, paramsAsTypes, inverses, defaults, errors);
+  requirements.append(defaults);
 
   auto &rewriteCtx = ctx.getRewriteContext();
 
@@ -882,8 +884,10 @@ InferredGenericSignatureRequest::evaluate(
     paramTypes.append(genericParams.begin() + numOuterParams, genericParams.end());
   }
 
-  InverseRequirement::expandDefaults(ctx, paramTypes, requirements);
-  applyInverses(ctx, paramTypes, inverses, requirements, errors);
+  SmallVector<StructuralRequirement, 2> defaults;
+  InverseRequirement::expandDefaults(ctx, paramTypes, defaults);
+  applyInverses(ctx, paramTypes, inverses, defaults, errors);
+  requirements.append(defaults);
 
   auto &rewriteCtx = ctx.getRewriteContext();