[CodeCompletion] Call into simplifyTypeImpl when simplifying a type for code completion

This makes sure we e.g. resolve dependent member types after we perform type variable to generic parameter substitutions for code completion

Author: ahoppen

include/swift/Sema/ConstraintSystem.h

@@ -1288,6 +1288,24 @@ class Solution {
   /// type variables for their fixed types.
   Type simplifyType(Type type) const;
 
+  // To aid code completion, we need to attempt to convert type placeholders
+  // back into underlying generic parameters if possible, since type
+  // of the code completion expression is used as "expected" (or contextual)
+  // type so it's helpful to know what requirements it has to filter
+  // the list of possible member candidates e.g.
+  //
+  // \code
+  // func test<T: P>(_: [T]) {}
+  //
+  // test(42.#^MEMBERS^#)
+  // \code
+  //
+  // It's impossible to resolve `T` in this case but code completion
+  // expression should still have a type of `[T]` instead of `[<<hole>>]`
+  // because it helps to produce correct contextual member list based on
+  // a conformance requirement associated with generic parameter `T`.
+  Type simplifyTypeForCodeCompletion(Type type) const;
+
   /// Coerce the given expression to the given type.
   ///
   /// This operation cannot fail.

lib/IDE/ArgumentCompletion.cpp

@@ -115,7 +115,7 @@ void ArgumentTypeCheckCompletionCallback::sawSolutionImpl(const Solution &S) {
   }
 
   ValueDecl *FuncD = SelectedOverload->choice.getDeclOrNull();
-  Type FuncTy = S.simplifyType(SelectedOverload->openedType)->getRValueType();
+  Type FuncTy = S.simplifyTypeForCodeCompletion(SelectedOverload->openedType);
 
   // For completion as the arg in a call to the implicit [keypath: _] subscript
   // the solver can't know what kind of keypath is expected without an actual

lib/IDE/TypeCheckCompletionCallback.cpp

@@ -51,47 +51,8 @@ Type swift::ide::getTypeForCompletion(const constraints::Solution &S,
 
   Type Result;
 
-  // To aid code completion, we need to attempt to convert type placeholders
-  // back into underlying generic parameters if possible, since type
-  // of the code completion expression is used as "expected" (or contextual)
-  // type so it's helpful to know what requirements it has to filter
-  // the list of possible member candidates e.g.
-  //
-  // \code
-  // func test<T: P>(_: [T]) {}
-  //
-  // test(42.#^MEMBERS^#)
-  // \code
-  //
-  // It's impossible to resolve `T` in this case but code completion
-  // expression should still have a type of `[T]` instead of `[<<hole>>]`
-  // because it helps to produce correct contextual member list based on
-  // a conformance requirement associated with generic parameter `T`.
   if (isExpr<CodeCompletionExpr>(Node)) {
-    auto completionTy = S.getType(Node).transform([&](Type type) -> Type {
-      if (auto *typeVar = type->getAs<TypeVariableType>())
-        return S.getFixedType(typeVar);
-      return type;
-    });
-
-    Result = S.simplifyType(completionTy.transform([&](Type type) {
-      if (auto *placeholder = type->getAs<PlaceholderType>()) {
-        if (auto *typeVar =
-                placeholder->getOriginator().dyn_cast<TypeVariableType *>()) {
-          if (auto *GP = typeVar->getImpl().getGenericParameter()) {
-            // Code completion depends on generic parameter type being
-            // represented in terms of `ArchetypeType` since it's easy
-            // to extract protocol requirements from it.
-            if (auto *GPD = GP->getDecl())
-              return GPD->getInnermostDeclContext()->mapTypeIntoContext(GP);
-          }
-        }
-
-        return Type(CS.getASTContext().TheUnresolvedType);
-      }
-
-      return type;
-    }));
+    Result = S.simplifyTypeForCodeCompletion(S.getType(Node));
   } else {
     Result = S.getResolvedType(Node);
   }

lib/Sema/ConstraintSystem.cpp

@@ -3496,6 +3496,48 @@ Type Solution::simplifyType(Type type) const {
   return resolvedType;
 }
 
+Type Solution::simplifyTypeForCodeCompletion(Type Ty) const {
+  auto &CS = getConstraintSystem();
+
+  // First, instantiate all type variables that we know, but don't replace
+  // placeholders by unresolved types.
+  Ty = CS.simplifyTypeImpl(Ty, [this](TypeVariableType *typeVar) -> Type {
+    return getFixedType(typeVar);
+  });
+
+  // Next, replace all placeholders by type variables. We know that all type
+  // variables now in the type originate from placeholders.
+  Ty = Ty.transform([](Type type) -> Type {
+    if (auto *placeholder = type->getAs<PlaceholderType>()) {
+      if (auto *typeVar =
+              placeholder->getOriginator().dyn_cast<TypeVariableType *>()) {
+        return typeVar;
+      }
+    }
+
+    return type;
+  });
+
+  // Replace all type variables (which must come from placeholders) by their
+  // generic parameters. Because we call into simplifyTypeImpl
+  Ty = CS.simplifyTypeImpl(Ty, [](TypeVariableType *typeVar) -> Type {
+    if (auto *GP = typeVar->getImpl().getGenericParameter()) {
+      // Code completion depends on generic parameter type being
+      // represented in terms of `ArchetypeType` since it's easy
+      // to extract protocol requirements from it.
+      if (auto *GPD = GP->getDecl()) {
+        return GPD->getInnermostDeclContext()->mapTypeIntoContext(GP);
+      }
+    }
+    return typeVar;
+  });
+
+  // Remove any remaining type variables and placeholders
+  Ty = simplifyType(Ty);
+
+  return Ty->getRValueType();
+}
+
 size_t Solution::getTotalMemory() const {
   return sizeof(*this) + typeBindings.getMemorySize() +
          overloadChoices.getMemorySize() +

test/IDE/complete_call_arg.swift

@@ -1317,7 +1317,7 @@ func testPlaceholderNoBetterThanArchetype() {
   }
 // PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_1:     Begin completions, 2 items
 // PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_1-DAG: Pattern/Local/Flair[ArgLabels]:     {#footer: String#}[#String#];
-// PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_1-DAG: Pattern/Local/Flair[ArgLabels]:     {#content: () -> _##() -> _#}[#() -> _#];
+// PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_1-DAG: Pattern/Local/Flair[ArgLabels]:     {#content: () -> Content##() -> Content#}[#() -> Content#];
 // PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_1:     End completions
 
   Section(header: TectionHeaderView(text: "abc"), #^PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_2?check=PLACEHOLDER_NO_BETTER_THAN_ARCHETYPE_1^#)