[Sema] Factor out common code from resolveSingleWitness/ValueWitnesses

No functionality change.

Author: jrose-apple

lib/Sema/TypeCheckProtocol.cpp

@@ -3355,6 +3355,28 @@ CheckTypeWitnessResult swift::checkTypeWitness(TypeChecker &tc, DeclContext *dc,
   return CheckTypeWitnessResult();
 }
 
+ResolveWitnessResult
+ConformanceChecker::resolveWitnessTryingAllStrategies(ValueDecl *requirement) {
+  decltype(&ConformanceChecker::resolveWitnessViaLookup) strategies[] = {
+      &ConformanceChecker::resolveWitnessViaLookup,
+      &ConformanceChecker::resolveWitnessViaDerivation,
+      &ConformanceChecker::resolveWitnessViaDefault};
+
+  for (auto strategy : strategies) {
+    ResolveWitnessResult result = (this->*strategy)(requirement);
+    switch (result) {
+    case ResolveWitnessResult::Success:
+    case ResolveWitnessResult::ExplicitFailed:
+      return result;
+    case ResolveWitnessResult::Missing:
+      // Continue trying.
+      break;
+    }
+  }
+
+  return ResolveWitnessResult::Missing;
+}
+
 /// Attempt to resolve a type witness via member name lookup.
 ResolveWitnessResult ConformanceChecker::resolveTypeWitnessViaLookup(
                        AssociatedTypeDecl *assocType) {
@@ -3784,38 +3806,8 @@ void ConformanceChecker::resolveValueWitnesses() {
     if (isa<AccessorDecl>(requirement))
       continue;
 
-    // Try to resolve the witness via explicit definitions.
-    switch (resolveWitnessViaLookup(requirement)) {
-    case ResolveWitnessResult::Success:
-      finalizeWitness();
-      continue;
-
-    case ResolveWitnessResult::ExplicitFailed:
-      Conformance->setInvalid();
-      continue;
-
-    case ResolveWitnessResult::Missing:
-      // Continue trying below.
-      break;
-    }
-
-    // Try to resolve the witness via derivation.
-    switch (resolveWitnessViaDerivation(requirement)) {
-    case ResolveWitnessResult::Success:
-      finalizeWitness();
-      continue;
-
-    case ResolveWitnessResult::ExplicitFailed:
-      Conformance->setInvalid();
-      continue;
-
-    case ResolveWitnessResult::Missing:
-      // Continue trying below.
-      break;
-    }
-
-    // Try to resolve the witness via defaults.
-    switch (resolveWitnessViaDefault(requirement)) {
+    // Try to resolve the witness.
+    switch (resolveWitnessTryingAllStrategies(requirement)) {
     case ResolveWitnessResult::Success:
       finalizeWitness();
       continue;
@@ -3825,7 +3817,7 @@ void ConformanceChecker::resolveValueWitnesses() {
       continue;
 
     case ResolveWitnessResult::Missing:
-      // Continue trying below.
+      // Let it get diagnosed later.
       break;
     }
   }

lib/Sema/TypeCheckProtocol.h

@@ -629,6 +629,11 @@ class ConformanceChecker : public WitnessChecker {
   /// Resolve a (non-type) witness via default definition or optional.
   ResolveWitnessResult resolveWitnessViaDefault(ValueDecl *requirement);
 
+  /// Resolve a (non-type) witness by trying each standard strategy until one
+  /// of them produces a result.
+  ResolveWitnessResult
+  resolveWitnessTryingAllStrategies(ValueDecl *requirement);
+
   /// Attempt to resolve a type witness via member name lookup.
   ResolveWitnessResult resolveTypeWitnessViaLookup(
                          AssociatedTypeDecl *assocType);

lib/Sema/TypeCheckProtocolInference.cpp

@@ -2083,38 +2083,8 @@ void ConformanceChecker::resolveSingleWitness(ValueDecl *requirement) {
     }
   }
 
-  // Try to resolve the witness via explicit definitions.
-  switch (resolveWitnessViaLookup(requirement)) {
-  case ResolveWitnessResult::Success:
-    return;
-
-  case ResolveWitnessResult::ExplicitFailed:
-    Conformance->setInvalid();
-    recordInvalidWitness(requirement);
-    return;
-
-  case ResolveWitnessResult::Missing:
-    // Continue trying below.
-    break;
-  }
-
-  // Try to resolve the witness via derivation.
-  switch (resolveWitnessViaDerivation(requirement)) {
-  case ResolveWitnessResult::Success:
-    return;
-
-  case ResolveWitnessResult::ExplicitFailed:
-    Conformance->setInvalid();
-    recordInvalidWitness(requirement);
-    return;
-
-  case ResolveWitnessResult::Missing:
-    // Continue trying below.
-    break;
-  }
-
-  // Try to resolve the witness via defaults.
-  switch (resolveWitnessViaDefault(requirement)) {
+  // Try to resolve the witness.
+  switch (resolveWitnessTryingAllStrategies(requirement)) {
   case ResolveWitnessResult::Success:
     return;
 
@@ -2125,6 +2095,5 @@ void ConformanceChecker::resolveSingleWitness(ValueDecl *requirement) {
 
   case ResolveWitnessResult::Missing:
     llvm_unreachable("Should have failed");
-    break;
   }
 }