compiler: add support for GODEBUG=gotypesalias=1

Since we now require Go 1.22, this became a lot simpler (since we can
now refer to `types.Alias` and `types.Unalias`).

compiler/compiler.go

@@ -389,7 +389,7 @@ func (c *compilerContext) getLLVMType(goType types.Type) llvm.Type {
 // makeLLVMType creates a LLVM type for a Go type. Don't call this, use
 // getLLVMType instead.
 func (c *compilerContext) makeLLVMType(goType types.Type) llvm.Type {
-	switch typ := goType.(type) {
+	switch typ := types.Unalias(goType).(type) {
 	case *types.Array:
 		elemType := c.getLLVMType(typ.Elem())
 		return llvm.ArrayType(elemType, int(typ.Len()))
@@ -497,6 +497,21 @@ func (c *compilerContext) createDIType(typ types.Type) llvm.Metadata {
 	llvmType := c.getLLVMType(typ)
 	sizeInBytes := c.targetData.TypeAllocSize(llvmType)
 	switch typ := typ.(type) {
+	case *types.Alias:
+		// Implement types.Alias just like types.Named: by treating them like a
+		// C typedef.
+		temporaryMDNode := c.dibuilder.CreateReplaceableCompositeType(llvm.Metadata{}, llvm.DIReplaceableCompositeType{
+			Tag:         dwarf.TagTypedef,
+			SizeInBits:  sizeInBytes * 8,
+			AlignInBits: uint32(c.targetData.ABITypeAlignment(llvmType)) * 8,
+		})
+		c.ditypes[typ] = temporaryMDNode
+		md := c.dibuilder.CreateTypedef(llvm.DITypedef{
+			Type: c.getDIType(types.Unalias(typ)), // TODO: use typ.Rhs in Go 1.23
+			Name: typ.String(),
+		})
+		temporaryMDNode.ReplaceAllUsesWith(md)
+		return md
 	case *types.Array:
 		return c.dibuilder.CreateArrayType(llvm.DIArrayType{
 			SizeInBits:  sizeInBytes * 8,
@@ -859,6 +874,11 @@ func (c *compilerContext) createPackage(irbuilder llvm.Builder, pkg *ssa.Package
 				// Interfaces don't have concrete methods.
 				continue
 			}
+			if _, isalias := member.Type().(*types.Alias); isalias {
+				// Aliases don't need to be redefined, since they just refer to
+				// an already existing type whose methods will be defined.
+				continue
+			}
 
 			// Named type. We should make sure all methods are created.
 			// This includes both functions with pointer receivers and those

compiler/interface.go

@@ -122,6 +122,9 @@ func (c *compilerContext) pkgPathPtr(pkgpath string) llvm.Value {
 // This function returns a pointer to the 'kind' field (which might not be the
 // first field in the struct).
 func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
+	// Resolve alias types: alias types are resolved at compile time.
+	typ = types.Unalias(typ)
+
 	ms := c.program.MethodSets.MethodSet(typ)
 	hasMethodSet := ms.Len() != 0
 	_, isInterface := typ.Underlying().(*types.Interface)
@@ -512,7 +515,7 @@ var basicTypeNames = [...]string{
 // interface lowering pass to assign type codes as expected by the reflect
 // package. See getTypeCodeNum.
 func getTypeCodeName(t types.Type) (string, bool) {
-	switch t := t.(type) {
+	switch t := types.Unalias(t).(type) {
 	case *types.Named:
 		if t.Obj().Parent() != t.Obj().Pkg().Scope() {
 			return "named:" + t.String() + "$local", true
@@ -942,7 +945,7 @@ func signature(sig *types.Signature) string {
 // normalization around `byte` vs `uint8` for example.
 func typestring(t types.Type) string {
 	// See: https://github.com/golang/go/blob/master/src/go/types/typestring.go
-	switch t := t.(type) {
+	switch t := types.Unalias(t).(type) {
 	case *types.Array:
 		return "[" + strconv.FormatInt(t.Len(), 10) + "]" + typestring(t.Elem())
 	case *types.Basic:

compiler/map.go

@@ -248,7 +248,7 @@ func (b *builder) createMapIteratorNext(rangeVal ssa.Value, llvmRangeVal, it llv
 // can be compared with runtime.memequal.  Note that padding bytes are undef
 // and can alter two "equal" structs being equal when compared with memequal.
 func hashmapIsBinaryKey(keyType types.Type) bool {
-	switch keyType := keyType.(type) {
+	switch keyType := keyType.Underlying().(type) {
 	case *types.Basic:
 		return keyType.Info()&(types.IsBoolean|types.IsInteger) != 0
 	case *types.Pointer:
@@ -263,8 +263,6 @@ func hashmapIsBinaryKey(keyType types.Type) bool {
 		return true
 	case *types.Array:
 		return hashmapIsBinaryKey(keyType.Elem())
-	case *types.Named:
-		return hashmapIsBinaryKey(keyType.Underlying())
 	default:
 		return false
 	}

flake.nix

@@ -67,9 +67,6 @@
             # has `md5sum`).
             export MD5SUM=md5sum
 
-            # Work around #4819, missing support for generic type aliases.
-            export GODEBUG=gotypesalias=0
-
             # Ugly hack to make the Clang resources directory available.
             export GOFLAGS="\"-ldflags=-X github.com/tinygo-org/tinygo/goenv.clangResourceDir=${llvmPackages_20.clang.cc.lib}/lib/clang/20\" -tags=llvm20"
           '';