Revert "Merge pull request #81840 from compnerd/aliases"

This reverts commit 33a324e, reversing
changes made to 0afeafa due to a regression:

```
$ printf "import var Darwin.stderr\n" | /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2025-06-09-a.xctoolchain/usr/bin/swiftc -typecheck - -sdk $(xcrun --show-sdk-path)
<stdin>:1:12: error: ambiguous name 'stderr' in module 'Darwin'
1 | import var Darwin.stderr
  |            `- error: ambiguous name 'stderr' in module 'Darwin'
2 |

_stdio.stderr:2:12: note: found this candidate
1 | @available(macOS 10.9, iOS 7.0, watchOS 2.0, tvOS 9.0, visionOS 1.0, *)
2 | public var stderr: UnsafeMutablePointer<FILE> { get set }
  |            `- note: found this candidate

_stdio.stderr:1:12: note: found this candidate
1 | public var stderr: UnsafeMutablePointer<FILE> { get set }
  |            `- note: found this candidate
```

# Conflicts:
#	test/ClangImporter/Inputs/custom-modules/module.modulemap

Author: MaxDesiatov

lib/ClangImporter/ImportMacro.cpp

@@ -20,7 +20,6 @@
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/DiagnosticsClangImporter.h"
 #include "swift/AST/Expr.h"
-#include "swift/AST/ParameterList.h"
 #include "swift/AST/Stmt.h"
 #include "swift/AST/Types.h"
 #include "swift/Basic/Assertions.h"
@@ -32,7 +31,6 @@
 #include "clang/Lex/MacroInfo.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Sema/DelayedDiagnostic.h"
-#include "clang/Sema/Lookup.h"
 #include "clang/Sema/Sema.h"
 #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
 #include "llvm/ADT/SmallString.h"
@@ -373,104 +371,6 @@ getIntegerConstantForMacroToken(ClangImporter::Implementation &impl,
   return std::nullopt;
 }
 
-namespace {
-ValueDecl *importDeclAlias(ClangImporter::Implementation &clang,
-                           swift::DeclContext *DC, const clang::ValueDecl *D,
-                           Identifier alias) {
-  // Variadic functions cannot be imported into Swift.
-  // FIXME(compnerd) emit a diagnostic for the missing diagnostic.
-  if (const auto *FD = dyn_cast<clang::FunctionDecl>(D))
-    if (FD->isVariadic())
-      return nullptr;
-
-  // Ignore self-referential macros.
-  if (D->getName() == alias.str())
-    return nullptr;
-
-  swift::ValueDecl *VD =
-      dyn_cast_or_null<ValueDecl>(clang.importDecl(D, clang.CurrentVersion));
-  if (VD == nullptr)
-    return nullptr;
-
-  // If the imported decl is named identically, avoid the aliasing.
-  if (VD->getBaseIdentifier().str() == alias.str())
-    return nullptr;
-
-  swift::ASTContext &Ctx = DC->getASTContext();
-  ImportedType Ty =
-      clang.importType(D->getType(), ImportTypeKind::Abstract,
-                       [&clang, &D](Diagnostic &&Diag) {
-                         clang.addImportDiagnostic(D, std::move(Diag),
-                                                   D->getLocation());
-                       }, /*AllowsNSUIntegerAsInt*/true,
-                       Bridgeability::None, { });
-  swift::Type GetterTy = FunctionType::get({}, Ty.getType(), ASTExtInfo{});
-  swift::Type SetterTy =
-      FunctionType::get({AnyFunctionType::Param(Ty.getType())},
-                        Ctx.TheEmptyTupleType, ASTExtInfo{});
-
-  /* Storage */
-  swift::VarDecl *V =
-      new (Ctx) VarDecl(/*IsStatic*/false, VarDecl::Introducer::Var,
-                        SourceLoc(), alias, DC);
-  V->setAccess(swift::AccessLevel::Public);
-  V->setInterfaceType(Ty.getType());
-  V->getAttrs().add(new (Ctx) TransparentAttr(/*Implicit*/true));
-  V->getAttrs().add(new (Ctx) InlineAttr(InlineKind::Always));
-
-  /* Accessor */
-  swift::AccessorDecl *G = nullptr;
-  {
-    G = AccessorDecl::createImplicit(Ctx, AccessorKind::Get, V, false, false,
-                                     TypeLoc(), GetterTy, DC);
-    G->setAccess(swift::AccessLevel::Public);
-    G->setInterfaceType(GetterTy);
-    G->setIsTransparent(true);
-    G->setParameters(ParameterList::createEmpty(Ctx));
-
-    DeclRefExpr *DRE =
-        new (Ctx) DeclRefExpr(ConcreteDeclRef(VD), {}, /*Implicit*/true,
-                              AccessSemantics::Ordinary, Ty.getType());
-    ReturnStmt *RS = ReturnStmt::createImplicit(Ctx, DRE);
-
-    G->setBody(BraceStmt::createImplicit(Ctx, {RS}),
-               AbstractFunctionDecl::BodyKind::TypeChecked);
-  }
-
-  swift::AccessorDecl *S = nullptr;
-  if (isa<clang::VarDecl>(D) &&
-      !cast<clang::VarDecl>(D)->getType().isConstQualified()) {
-    S = AccessorDecl::createImplicit(Ctx, AccessorKind::Set, V, false, false,
-                                     TypeLoc(), Ctx.TheEmptyTupleType, DC);
-    S->setAccess(swift::AccessLevel::Public);
-    S->setInterfaceType(SetterTy);
-    S->setIsTransparent(true);
-    S->setParameters(ParameterList::create(Ctx, {
-      ParamDecl::createImplicit(Ctx, Identifier(), Ctx.getIdentifier("newValue"),
-                                Ty.getType(), DC)
-    }));
-
-    DeclRefExpr *LHS =
-        new (Ctx) DeclRefExpr(ConcreteDeclRef(VD), {}, /*Implicit*/true,
-                              AccessSemantics::Ordinary, Ty.getType());
-    DeclRefExpr *RHS =
-        new (Ctx) DeclRefExpr(S->getParameters()->get(0), {}, /*Implicit*/true,
-                              AccessSemantics::Ordinary, Ty.getType());
-    AssignExpr *AE = new (Ctx) AssignExpr(LHS, SourceLoc(), RHS, true);
-    AE->setType(Ctx.TheEmptyTupleType);
-    S->setBody(BraceStmt::createImplicit(Ctx, {AE}),
-               AbstractFunctionDecl::BodyKind::TypeChecked);
-  }
-
-  /* Bind */
-  V->setImplInfo(S ? StorageImplInfo::getMutableComputed()
-                   : StorageImplInfo::getImmutableComputed());
-  V->setAccessors(SourceLoc(), S ? ArrayRef{G,S} : ArrayRef{G}, SourceLoc());
-
-  return V;
-}
-}
-
 static ValueDecl *importMacro(ClangImporter::Implementation &impl,
                               llvm::SmallSet<StringRef, 4> &visitedMacros,
                               DeclContext *DC, Identifier name,
@@ -609,14 +509,7 @@ static ValueDecl *importMacro(ClangImporter::Implementation &impl,
         }
       }
 
-      /* Create an alias for any Decl */
-      clang::Sema &S = impl.getClangSema();
-      clang::LookupResult R(S, {{tok.getIdentifierInfo()}, {}},
-                            clang::Sema::LookupAnyName);
-      if (S.LookupName(R, S.TUScope))
-        if (R.getResultKind() == clang::LookupResult::LookupResultKind::Found)
-          if (const auto *VD = dyn_cast<clang::ValueDecl>(R.getFoundDecl()))
-            return importDeclAlias(impl, DC, VD, name);
+      // FIXME: If the identifier refers to a declaration, alias it?
     }
 
     // TODO(https://github.com/apple/swift/issues/57735): Seems rare to have a single token that is neither a literal nor an identifier, but add diagnosis.

test/ClangImporter/CoreGraphics_test.swift

@@ -105,7 +105,9 @@ public func testRenames(transform: CGAffineTransform, context: CGContext,
   blackHole(point.applying(transform))
   var rect = rect.applying(transform)
   blackHole(size.applying(transform))
+// CHECK:   %{{.*}} = {{(tail )?}}call { double, double } @CGPointApplyAffineTransform(double %{{.*}}, double %{{.*}}, ptr {{.*}})
 // CHECK:   call void @CGRectApplyAffineTransform(ptr {{.*}}, ptr {{.*}}, ptr {{.*}})
+// CHECK:   %{{.*}} = {{(tail )?}}call { double, double } @CGSizeApplyAffineTransform(double %{{.*}}, double %{{.*}}, ptr {{.*}})
 
   context.concatenate(transform)
   context.rotate(by: CGFloat.pi)

test/ClangImporter/Inputs/custom-modules/Aliases.h

@@ -276,10 +276,6 @@ module "Weird C Module" {
   header "WeirdCModule.h"
 }
 
-module Aliases {
-  header "Aliases.h"
-}
-
 module RetroactiveVersioning {
   header "versioning.h"
 }