[NFC][RequirementMachine] Rename some of the RequirementError::Kind cases,

add documentation for each case, and move RequirementError to
lib/AST/RequirementMachine/Diagnostics.h.

Author: hborla

include/swift/AST/Requirement.h

@@ -124,55 +124,6 @@ struct StructuralRequirement {
   bool inferred = false;
 };
 
-/// Represents an invalid requirement, such as `T: Int`.
-///
-/// Invalid requirements are recorded while computing the
-/// generic signature of a declaration, and diagnosed via
-/// \c diagnoseRequirementErrors .
-struct RequirementError {
-  /// The kind of requirement error.
-  enum class Kind {
-    InvalidConformance,
-    ConcreteTypeMismatch,
-    NonTypeParameter,
-    RedundantRequirement,
-  } kind;
-
-  /// The invalid requirement.
-  Requirement requirement;
-
-  SourceLoc loc;
-
-private:
-  RequirementError(Kind kind, Requirement requirement, SourceLoc loc)
-    : kind(kind), requirement(requirement), loc(loc) {}
-
-public:
-  static RequirementError forInvalidConformance(Type subjectType,
-                                                Type constraint,
-                                                SourceLoc loc) {
-    Requirement requirement(RequirementKind::Conformance, subjectType, constraint);
-    return {Kind::InvalidConformance, requirement, loc};
-  }
-
-  static RequirementError forConcreteTypeMismatch(Type type1,
-                                                  Type type2,
-                                                  SourceLoc loc) {
-    Requirement requirement(RequirementKind::SameType, type1, type2);
-    return {Kind::ConcreteTypeMismatch, requirement, loc};
-  }
-
-  static RequirementError forNonTypeParameter(Requirement req,
-                                              SourceLoc loc) {
-    return {Kind::NonTypeParameter, req, loc};
-  }
-
-  static RequirementError forRedundantRequirement(Requirement req,
-                                                  SourceLoc loc) {
-    return {Kind::RedundantRequirement, req, loc};
-  }
-};
-
 } // end namespace swift
 
 #endif

lib/AST/RequirementMachine/Diagnostics.h

@@ -0,0 +1,80 @@
+//===--- Diagnostics.h - Requirement machine diagnostics --------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_REQUIREMENT_DIAGNOSTICS_H
+#define SWIFT_REQUIREMENT_DIAGNOSTICS_H
+
+#include "swift/AST/Requirement.h"
+#include "swift/AST/Type.h"
+
+namespace swift {
+
+namespace rewriting {
+
+/// Represents an invalid requirement, such as `T: Int`.
+///
+/// Invalid requirements are recorded while computing the
+/// generic signature of a declaration, and diagnosed via
+/// \c diagnoseRequirementErrors .
+struct RequirementError {
+  /// The kind of requirement error.
+  enum class Kind {
+    /// A constraint to a non-protocol, non-class type, e.g. T: Int.
+    InvalidTypeRequirement,
+    /// A type mismatch, e.g. Int == String.
+    ConcreteTypeMismatch,
+    /// A requirement proven to be false, e.g. Bool: Collection
+    ConflictingRequirement,
+    /// A redundant requirement, e.g. T == T.
+    RedundantRequirement,
+  } kind;
+
+  /// The invalid requirement.
+  Requirement requirement;
+
+  SourceLoc loc;
+
+private:
+  RequirementError(Kind kind, Requirement requirement, SourceLoc loc)
+    : kind(kind), requirement(requirement), loc(loc) {}
+
+public:
+  static RequirementError forInvalidTypeRequirement(Type subjectType,
+                                                    Type constraint,
+                                                    SourceLoc loc) {
+    Requirement requirement(RequirementKind::Conformance, subjectType, constraint);
+    return {Kind::InvalidTypeRequirement, requirement, loc};
+  }
+
+  static RequirementError forConcreteTypeMismatch(Type type1,
+                                                  Type type2,
+                                                  SourceLoc loc) {
+    Requirement requirement(RequirementKind::SameType, type1, type2);
+    return {Kind::ConcreteTypeMismatch, requirement, loc};
+  }
+
+  static RequirementError forConflictingRequirement(Requirement req,
+                                                    SourceLoc loc) {
+    return {Kind::ConflictingRequirement, req, loc};
+  }
+
+  static RequirementError forRedundantRequirement(Requirement req,
+                                                  SourceLoc loc) {
+    return {Kind::RedundantRequirement, req, loc};
+  }
+};
+
+} // end namespace rewriting
+
+} // end namespace swift
+
+#endif

lib/AST/RequirementMachine/RequirementLowering.cpp

@@ -135,7 +135,7 @@ static void desugarSuperclassRequirement(Type subjectType,
           RequirementError::forRedundantRequirement(requirement, loc));
     } else {
       errors.push_back(
-          RequirementError::forNonTypeParameter(requirement, loc));
+          RequirementError::forConflictingRequirement(requirement, loc));
     }
 
     return;
@@ -157,7 +157,7 @@ static void desugarLayoutRequirement(Type subjectType,
           RequirementError::forRedundantRequirement(requirement, loc));
     } else {
       errors.push_back(
-          RequirementError::forNonTypeParameter(requirement, loc));
+          RequirementError::forConflictingRequirement(requirement, loc));
     }
 
     return;
@@ -193,7 +193,7 @@ static void desugarConformanceRequirement(Type subjectType, Type constraintType,
       auto *module = protoDecl->getParentModule();
       auto conformance = module->lookupConformance(subjectType, protoDecl);
       if (conformance.isInvalid()) {
-        errors.push_back(RequirementError::forNonTypeParameter(
+        errors.push_back(RequirementError::forConflictingRequirement(
             {RequirementKind::Conformance, subjectType, constraintType}, loc));
         return;
       }
@@ -303,9 +303,9 @@ static void realizeTypeRequirement(Type subjectType, Type constraintType,
     desugarSuperclassRequirement(subjectType, constraintType, loc, reqs, errors);
   } else {
     errors.push_back(
-        RequirementError::forInvalidConformance(subjectType,
-                                                constraintType,
-                                                loc));
+        RequirementError::forInvalidTypeRequirement(subjectType,
+                                                    constraintType,
+                                                    loc));
     return;
   }
 
@@ -557,7 +557,7 @@ bool swift::rewriting::diagnoseRequirementErrors(
       continue;
 
     switch (error.kind) {
-    case RequirementError::Kind::InvalidConformance: {
+    case RequirementError::Kind::InvalidTypeRequirement: {
       Type subjectType = error.requirement.getFirstType();
       Type constraint = error.requirement.getSecondType();
 
@@ -607,7 +607,7 @@ bool swift::rewriting::diagnoseRequirementErrors(
       break;
     }
 
-    case RequirementError::Kind::NonTypeParameter: {
+    case RequirementError::Kind::ConflictingRequirement: {
       ctx.Diags.diagnose(loc, diag::requires_not_suitable_archetype,
                          error.requirement.getFirstType());
       diagnosedError = true;

lib/AST/RequirementMachine/RequirementLowering.h

@@ -18,6 +18,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
 #include <vector>
+#include "Diagnostics.h"
 #include "RewriteContext.h"
 #include "Symbol.h"
 #include "Term.h"