[dev.typeparams] cmd/compile/internal/syntax: type parameters must always be named

Report an error otherwise.

Change-Id: Ia76ea03a3f26b13dd9bca49f7bd42101d1ff1f9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/278475
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

diff --git a/src/cmd/compile/internal/syntax/error_test.go b/src/cmd/compile/internal/syntax/error_test.go
index 72b1ad6333de12157ee8d616554da97e2df2c3ba..919667f1d311d261ee8e68151afc259cfa8ee56a 100644 (file)
--- a/src/cmd/compile/internal/syntax/error_test.go
+++ b/src/cmd/compile/internal/syntax/error_test.go
@@ -128,6 +128,10 @@ func testSyntaxErrors(t *testing.T, filename string) {
        }
        defer f.Close()
 
+       var mode Mode
+       if strings.HasSuffix(filename, ".go2") {
+               mode = AllowGenerics
+       }
        ParseFile(filename, func(err error) {
                e, ok := err.(Error)
                if !ok {
@@ -162,7 +166,7 @@ func testSyntaxErrors(t *testing.T, filename string) {
                } else {
                        t.Errorf("%s: unexpected error: %s", orig, e.Msg)
                }
-       }, nil, 0)
+       }, nil, mode)
 
        if *print {
                fmt.Println()

diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 90b67def0f2037b4cbbe19fc9d1de60c310ce429..e3fb1003a291c8347bcea8fe578505ca4aa1adeb 100644 (file)
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -595,7 +595,7 @@ func (p *parser) typeDecl(group *Group) Decl {
                        p.xnest--
                        if name0, ok := x.(*Name); p.mode&AllowGenerics != 0 && ok && p.tok != _Rbrack {
                                // generic type
-                               d.TParamList = p.paramList(name0, _Rbrack)
+                               d.TParamList = p.paramList(name0, _Rbrack, true)
                                pos := p.pos()
                                if p.gotAssign() {
                                        p.syntaxErrorAt(pos, "generic type cannot be alias")
@@ -664,7 +664,7 @@ func (p *parser) funcDeclOrNil() *FuncDecl {
        f.Pragma = p.takePragma()
 
        if p.got(_Lparen) {
-               rcvr := p.paramList(nil, _Rparen)
+               rcvr := p.paramList(nil, _Rparen, false)
                switch len(rcvr) {
                case 0:
                        p.error("method has no receiver")
@@ -688,7 +688,7 @@ func (p *parser) funcDeclOrNil() *FuncDecl {
                        p.syntaxError("empty type parameter list")
                        p.next()
                } else {
-                       f.TParamList = p.paramList(nil, _Rbrack)
+                       f.TParamList = p.paramList(nil, _Rbrack, true)
                }
        }
        f.Type = p.funcType()
@@ -1313,7 +1313,7 @@ func (p *parser) funcType() *FuncType {
        typ := new(FuncType)
        typ.pos = p.pos()
        p.want(_Lparen)
-       typ.ParamList = p.paramList(nil, _Rparen)
+       typ.ParamList = p.paramList(nil, _Rparen, false)
        typ.ResultList = p.funcResult()
 
        return typ
@@ -1453,7 +1453,7 @@ func (p *parser) funcResult() []*Field {
        }
 
        if p.got(_Lparen) {
-               return p.paramList(nil, _Rparen)
+               return p.paramList(nil, _Rparen, false)
        }
 
        pos := p.pos()
@@ -1677,7 +1677,7 @@ func (p *parser) methodDecl() *Field {
 
                        // A type argument list looks like a parameter list with only
                        // types. Parse a parameter list and decide afterwards.
-                       list := p.paramList(nil, _Rbrack)
+                       list := p.paramList(nil, _Rbrack, false)
                        if len(list) == 0 {
                                // The type parameter list is not [] but we got nothing
                                // due to other errors (reported by paramList). Treat
@@ -1792,7 +1792,8 @@ func (p *parser) paramDeclOrNil(name *Name) *Field {
 // ParameterList = ParameterDecl { "," ParameterDecl } .
 // "(" or "[" has already been consumed.
 // If name != nil, it is the first name after "(" or "[".
-func (p *parser) paramList(name *Name, close token) (list []*Field) {
+// In the result list, either all fields have a name, or no field has a name.
+func (p *parser) paramList(name *Name, close token, requireNames bool) (list []*Field) {
        if trace {
                defer p.trace("paramList")()
        }
@@ -1813,7 +1814,11 @@ func (p *parser) paramList(name *Name, close token) (list []*Field) {
                return false
        })
 
-       // distribute parameter types
+       if len(list) == 0 {
+               return
+       }
+
+       // distribute parameter types (len(list) > 0)
        if named == 0 {
                // all unnamed => found names are named types
                for _, par := range list {
@@ -1822,9 +1827,12 @@ func (p *parser) paramList(name *Name, close token) (list []*Field) {
                                par.Name = nil
                        }
                }
+               if requireNames {
+                       p.syntaxErrorAt(list[0].Type.Pos(), "type parameters must be named")
+               }
        } else if named != len(list) {
                // some named => all must have names and types
-               var pos Pos // error position (or unknown)
+               var pos Pos // left-most error position (or unknown)
                var typ Expr
                for i := len(list) - 1; i >= 0; i-- {
                        if par := list[i]; par.Type != nil {
@@ -1844,7 +1852,13 @@ func (p *parser) paramList(name *Name, close token) (list []*Field) {
                        }
                }
                if pos.IsKnown() {
-                       p.syntaxErrorAt(pos, "mixed named and unnamed parameters")
+                       var msg string
+                       if requireNames {
+                               msg = "type parameters must be named"
+                       } else {
+                               msg = "mixed named and unnamed parameters"
+                       }
+                       p.syntaxErrorAt(pos, msg)
                }
        }
 

diff --git a/src/cmd/compile/internal/syntax/testdata/tparams.go2 b/src/cmd/compile/internal/syntax/testdata/tparams.go2
new file mode 100644 (file)
index 0000000..42031c3
--- /dev/null
+++ b/src/cmd/compile/internal/syntax/testdata/tparams.go2
@@ -0,0 +1,22 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type t[ /* ERROR type parameters must be named */ a, b] struct{}
+type t[a t, b t, /* ERROR type parameters must be named */ c] struct{}
+type t struct {
+       t [n]byte
+       t[a]
+       t[a, b]
+}
+type t interface {
+       t[a]
+       m /* ERROR method cannot have type parameters */ [_ _, /* ERROR mixed */ _]()
+       t[a, b]
+}
+
+func f[ /* ERROR empty type parameter list */ ]()
+func f[ /* ERROR type parameters must be named */ a, b]()
+func f[a t, b t, /* ERROR type parameters must be named */ c]()