compiler: correctly generate code for local named types

It is possible to create function-local named types:

    func foo() any {
        type named int
        return named(0)
    }

This patch makes sure they don't alias with named types declared at the
package scope.

Bug originally found by Damian Gryski while working on reflect support.

compiler/interface.go

@@ -118,8 +118,23 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 	if _, ok := typ.Underlying().(*types.Interface); ok {
 		hasMethodSet = false
 	}
-	globalName := "reflect/types.type:" + getTypeCodeName(typ)
-	global := c.mod.NamedGlobal(globalName)
+	typeCodeName, isLocal := getTypeCodeName(typ)
+	globalName := "reflect/types.type:" + typeCodeName
+	var global llvm.Value
+	if isLocal {
+		// This type is a named type inside a function, like this:
+		//
+		//     func foo() any {
+		//         type named int
+		//         return named(0)
+		//     }
+		if obj := c.interfaceTypes.At(typ); obj != nil {
+			global = obj.(llvm.Value)
+		}
+	} else {
+		// Regular type (named or otherwise).
+		global = c.mod.NamedGlobal(globalName)
+	}
 	if global.IsNil() {
 		var typeFields []llvm.Value
 		// Define the type fields. These must match the structs in
@@ -203,6 +218,9 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 		}
 		globalType := types.NewStruct(typeFieldTypes, nil)
 		global = llvm.AddGlobal(c.mod, c.getLLVMType(globalType), globalName)
+		if isLocal {
+			c.interfaceTypes.Set(typ, global)
+		}
 		metabyte := getTypeKind(typ)
 		switch typ := typ.(type) {
 		case *types.Basic:
@@ -330,7 +348,11 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 		alignment := c.targetData.TypeAllocSize(c.i8ptrType)
 		globalValue := c.ctx.ConstStruct(typeFields, false)
 		global.SetInitializer(globalValue)
-		global.SetLinkage(llvm.LinkOnceODRLinkage)
+		if isLocal {
+			global.SetLinkage(llvm.InternalLinkage)
+		} else {
+			global.SetLinkage(llvm.LinkOnceODRLinkage)
+		}
 		global.SetGlobalConstant(true)
 		global.SetAlignment(int(alignment))
 		if c.Debug {
@@ -411,57 +433,84 @@ var basicTypeNames = [...]string{
 // getTypeCodeName returns a name for this type that can be used in the
 // interface lowering pass to assign type codes as expected by the reflect
 // package. See getTypeCodeNum.
-func getTypeCodeName(t types.Type) string {
+func getTypeCodeName(t types.Type) (string, bool) {
 	switch t := t.(type) {
 	case *types.Named:
-		return "named:" + t.String()
+		// Note: check for `t.Obj().Pkg() != nil` for Go 1.18 only.
+		if t.Obj().Pkg() != nil && t.Obj().Parent() != t.Obj().Pkg().Scope() {
+			return "named:" + t.String() + "$local", true
+		}
+		return "named:" + t.String(), false
 	case *types.Array:
-		return "array:" + strconv.FormatInt(t.Len(), 10) + ":" + getTypeCodeName(t.Elem())
+		s, isLocal := getTypeCodeName(t.Elem())
+		return "array:" + strconv.FormatInt(t.Len(), 10) + ":" + s, isLocal
 	case *types.Basic:
-		return "basic:" + basicTypeNames[t.Kind()]
+		return "basic:" + basicTypeNames[t.Kind()], false
 	case *types.Chan:
-		return "chan:" + getTypeCodeName(t.Elem())
+		s, isLocal := getTypeCodeName(t.Elem())
+		return "chan:" + s, isLocal
 	case *types.Interface:
+		isLocal := false
 		methods := make([]string, t.NumMethods())
 		for i := 0; i < t.NumMethods(); i++ {
 			name := t.Method(i).Name()
 			if !token.IsExported(name) {
 				name = t.Method(i).Pkg().Path() + "." + name
 			}
-			methods[i] = name + ":" + getTypeCodeName(t.Method(i).Type())
+			s, local := getTypeCodeName(t.Method(i).Type())
+			if local {
+				isLocal = true
+			}
+			methods[i] = name + ":" + s
 		}
-		return "interface:" + "{" + strings.Join(methods, ",") + "}"
+		return "interface:" + "{" + strings.Join(methods, ",") + "}", isLocal
 	case *types.Map:
-		keyType := getTypeCodeName(t.Key())
-		elemType := getTypeCodeName(t.Elem())
-		return "map:" + "{" + keyType + "," + elemType + "}"
+		keyType, keyLocal := getTypeCodeName(t.Key())
+		elemType, elemLocal := getTypeCodeName(t.Elem())
+		return "map:" + "{" + keyType + "," + elemType + "}", keyLocal || elemLocal
 	case *types.Pointer:
-		return "pointer:" + getTypeCodeName(t.Elem())
+		s, isLocal := getTypeCodeName(t.Elem())
+		return "pointer:" + s, isLocal
 	case *types.Signature:
+		isLocal := false
 		params := make([]string, t.Params().Len())
 		for i := 0; i < t.Params().Len(); i++ {
-			params[i] = getTypeCodeName(t.Params().At(i).Type())
+			s, local := getTypeCodeName(t.Params().At(i).Type())
+			if local {
+				isLocal = true
+			}
+			params[i] = s
 		}
 		results := make([]string, t.Results().Len())
 		for i := 0; i < t.Results().Len(); i++ {
-			results[i] = getTypeCodeName(t.Results().At(i).Type())
+			s, local := getTypeCodeName(t.Results().At(i).Type())
+			if local {
+				isLocal = true
+			}
+			results[i] = s
 		}
-		return "func:" + "{" + strings.Join(params, ",") + "}{" + strings.Join(results, ",") + "}"
+		return "func:" + "{" + strings.Join(params, ",") + "}{" + strings.Join(results, ",") + "}", isLocal
 	case *types.Slice:
-		return "slice:" + getTypeCodeName(t.Elem())
+		s, isLocal := getTypeCodeName(t.Elem())
+		return "slice:" + s, isLocal
 	case *types.Struct:
 		elems := make([]string, t.NumFields())
+		isLocal := false
 		for i := 0; i < t.NumFields(); i++ {
 			embedded := ""
 			if t.Field(i).Embedded() {
 				embedded = "#"
 			}
-			elems[i] = embedded + t.Field(i).Name() + ":" + getTypeCodeName(t.Field(i).Type())
+			s, local := getTypeCodeName(t.Field(i).Type())
+			if local {
+				isLocal = true
+			}
+			elems[i] = embedded + t.Field(i).Name() + ":" + s
 			if t.Tag(i) != "" {
 				elems[i] += "`" + t.Tag(i) + "`"
 			}
 		}
-		return "struct:" + "{" + strings.Join(elems, ",") + "}"
+		return "struct:" + "{" + strings.Join(elems, ",") + "}", isLocal
 	default:
 		panic("unknown type: " + t.String())
 	}
@@ -564,7 +613,11 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 		commaOk = b.CreateCall(fn.GlobalValueType(), fn, []llvm.Value{actualTypeNum}, "")
 
 	} else {
-		globalName := "reflect/types.typeid:" + getTypeCodeName(expr.AssertedType)
+		assertedTypeGlobal := b.getTypeCode(expr.AssertedType)
+		if !assertedTypeGlobal.IsAConstantExpr().IsNil() {
+			assertedTypeGlobal = assertedTypeGlobal.Operand(0) // resolve the GEP operation
+		}
+		globalName := "reflect/types.typeid:" + strings.TrimPrefix(assertedTypeGlobal.Name(), "reflect/types.type:")
 		assertedTypeCodeGlobal := b.mod.NamedGlobal(globalName)
 		if assertedTypeCodeGlobal.IsNil() {
 			// Create a new typecode global.
@@ -640,7 +693,8 @@ func (c *compilerContext) getMethodsString(itf *types.Interface) string {
 // getInterfaceImplementsfunc returns a declared function that works as a type
 // switch. The interface lowering pass will define this function.
 func (c *compilerContext) getInterfaceImplementsFunc(assertedType types.Type) llvm.Value {
-	fnName := getTypeCodeName(assertedType.Underlying()) + ".$typeassert"
+	s, _ := getTypeCodeName(assertedType.Underlying())
+	fnName := s + ".$typeassert"
 	llvmFn := c.mod.NamedFunction(fnName)
 	if llvmFn.IsNil() {
 		llvmFnType := llvm.FunctionType(c.ctx.Int1Type(), []llvm.Type{c.i8ptrType}, false)
@@ -656,7 +710,8 @@ func (c *compilerContext) getInterfaceImplementsFunc(assertedType types.Type) ll
 // thunk is declared, not defined: it will be defined by the interface lowering
 // pass.
 func (c *compilerContext) getInvokeFunction(instr *ssa.CallCommon) llvm.Value {
-	fnName := getTypeCodeName(instr.Value.Type().Underlying()) + "." + instr.Method.Name() + "$invoke"
+	s, _ := getTypeCodeName(instr.Value.Type().Underlying())
+	fnName := s + "." + instr.Method.Name() + "$invoke"
 	llvmFn := c.mod.NamedFunction(fnName)
 	if llvmFn.IsNil() {
 		sig := instr.Method.Type().(*types.Signature)