Yield explicit errors when encountering typeparams.

Even though the compiler was usually able to compile them into
_something_, the code was likely incorrect in all cases. To prevent
users from tripping up on that the compiler will return an error if it
encounters type params until
gopherjs#1013 is resolved.

Author: nevkontakte

build/build.go

@@ -279,6 +279,8 @@ func parseAndAugment(xctx XContext, pkg *PackageData, isTest bool, fileSet *toke
 						s := spec.(*ast.TypeSpec)
 						if replacedDeclNames[s.Name.Name] {
 							s.Name = ast.NewIdent("_")
+							s.Type = &ast.StructType{Struct: s.Pos(), Fields: &ast.FieldList{}}
+							s.TypeParams = nil
 						}
 					}
 				case token.VAR, token.CONST:

compiler/natives/src/go/doc/doc_test.go

@@ -0,0 +1,37 @@
+//go:build js
+
+package doc
+
+import (
+	"fmt"
+	"testing"
+)
+
+func compareSlices(t *testing.T, name string, got, want interface{}, compareElem interface{}) {
+	// TODO(nevkontakte): Remove this override after generics are supported.
+	// https://github.com/gopherjs/gopherjs/issues/1013.
+	switch got.(type) {
+	case []*Func:
+		got := got.([]*Func)
+		want := want.([]*Func)
+		compareElem := compareElem.(func(t *testing.T, msg string, got, want *Func))
+		if len(got) != len(want) {
+			t.Errorf("%s: got %d, want %d", name, len(got), len(want))
+		}
+		for i := 0; i < len(got) && i < len(want); i++ {
+			compareElem(t, fmt.Sprintf("%s[%d]", name, i), got[i], want[i])
+		}
+	case []*Type:
+		got := got.([]*Type)
+		want := want.([]*Type)
+		compareElem := compareElem.(func(t *testing.T, msg string, got, want *Type))
+		if len(got) != len(want) {
+			t.Errorf("%s: got %d, want %d", name, len(got), len(want))
+		}
+		for i := 0; i < len(got) && i < len(want); i++ {
+			compareElem(t, fmt.Sprintf("%s[%d]", name, i), got[i], want[i])
+		}
+	default:
+		t.Errorf("unexpected argument type %T", got)
+	}
+}

compiler/natives/src/reflect/reflect_test.go

@@ -285,6 +285,9 @@ func TestMethodCallValueCodePtr(t *testing.T) {
 	t.Skip("methodValueCallCodePtr() is not applicable in GopherJS")
 }
 
+type B struct{}
+
+//gopherjs:prune-original
 func TestIssue50208(t *testing.T) {
 	t.Skip("This test required generics, which are not yet supported: https://github.com/gopherjs/gopherjs/issues/1013")
 }

compiler/package.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"go/ast"
 	"go/constant"
+	"go/scanner"
 	"go/token"
 	"go/types"
 	"sort"
@@ -398,6 +399,13 @@ func Compile(importPath string, files []*ast.File, fileSet *token.FileSet, impor
 	var mainFunc *types.Func
 	for _, fun := range functions {
 		o := funcCtx.pkgCtx.Defs[fun.Name].(*types.Func)
+
+		if fun.Type.TypeParams.NumFields() > 0 {
+			return nil, scanner.Error{
+				Pos: fileSet.Position(fun.Type.TypeParams.Pos()),
+				Msg: fmt.Sprintf("function %s: type parameters are not supported by GopherJS: https://github.com/gopherjs/gopherjs/issues/1013", o.Name()),
+			}
+		}
 		funcInfo := funcCtx.pkgCtx.FuncDeclInfos[o]
 		d := Decl{
 			FullName: o.FullName(),
@@ -480,6 +488,14 @@ func Compile(importPath string, files []*ast.File, fileSet *token.FileSet, impor
 			continue
 		}
 		typeName := funcCtx.objectName(o)
+
+		if named, ok := o.Type().(*types.Named); ok && named.TypeParams().Len() > 0 {
+			return nil, scanner.Error{
+				Pos: fileSet.Position(o.Pos()),
+				Msg: fmt.Sprintf("type %s: type parameters are not supported by GopherJS: https://github.com/gopherjs/gopherjs/issues/1013", o.Name()),
+			}
+		}
+
 		d := Decl{
 			Vars:            []string{typeName},
 			DceObjectFilter: o.Name(),