Merge pull request #63849 from ahoppen/ahoppen/equivalent-type-vars

[IDE] Inspect all equivalent type variables to replace a type variable by an archetype

Author: ahoppen

lib/Sema/ConstraintSystem.cpp

@@ -3824,7 +3824,7 @@ Type Solution::simplifyTypeForCodeCompletion(Type Ty) const {
 
   // Replace all type variables (which must come from placeholders) by their
   // generic parameters. Because we call into simplifyTypeImpl
-  Ty = CS.simplifyTypeImpl(Ty, [&CS](TypeVariableType *typeVar) -> Type {
+  Ty = CS.simplifyTypeImpl(Ty, [&CS, this](TypeVariableType *typeVar) -> Type {
     // Code completion depends on generic parameter type being represented in
     // terms of `ArchetypeType` since it's easy to extract protocol requirements
     // from it.
@@ -3841,6 +3841,29 @@ Type Solution::simplifyTypeForCodeCompletion(Type Ty) const {
       return archetype;
     }
 
+    // Sometimes the type variable itself doesn't have have an originator that
+    // can be replaced by an archetype but one of its equivalent type variable
+    // does.
+    // Search thorough all equivalent type variables, looking for one that can
+    // be replaced by a generic parameter.
+    std::vector<std::pair<TypeVariableType *, Type>> bindings(
+        typeBindings.begin(), typeBindings.end());
+    // Make sure we iterate the bindings in a deterministic order.
+    llvm::sort(bindings, [](const std::pair<TypeVariableType *, Type> &lhs,
+                            const std::pair<TypeVariableType *, Type> &rhs) {
+      return lhs.first->getID() < rhs.first->getID();
+    });
+    for (auto binding : bindings) {
+      if (auto placeholder = binding.second->getAs<PlaceholderType>()) {
+        if (placeholder->getOriginator().dyn_cast<TypeVariableType *>() ==
+            typeVar) {
+          if (auto archetype = getTypeVarAsArchetype(binding.first)) {
+            return archetype;
+          }
+        }
+      }
+    }
+
     // When applying the logic below to get contextual types inside result
     // builders, the code completion type variable is connected by a one-way
     // constraint to a type variable in the buildBlock call, but that is not the

test/IDE/complete_subscript.swift

@@ -39,7 +39,7 @@ func test1() {
 
   let _ = MyStruct[#^METATYPE_UNRESOLVED_BRACKET^#
 // METATYPE_UNRESOLVED_BRACKET: Begin completions
-// METATYPE_UNRESOLVED_BRACKET-DAG: Decl[Subscript]/CurrNominal/Flair[ArgLabels]:        ['[']{#(x): Int#}, {#static: _#}[']'][#MyStruct<_>#];
+// METATYPE_UNRESOLVED_BRACKET-DAG: Decl[Subscript]/CurrNominal/Flair[ArgLabels]:        ['[']{#(x): Int#}, {#static: T#}[']'][#MyStruct<T>#];
 // METATYPE_UNRESOLVED_BRACKET: End completions
 
   let _ = MyStruct<Int> #^METATYPE_INT^#