cmd/compile/internal/syntax: accept "~" and "|" interface elements

Type lists continue to be accepted as before.

While at it, print missing filenames in error tests
(which uses an ad-hoc position representation).

Change-Id: I933b3acbc9cf1985ad8f70f6b206e3a1dbd64d1e
Reviewed-on: https://go-review.googlesource.com/c/go/+/307371
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

4 files changed, 125 insertions, 16 deletions

diff --git a/src/cmd/compile/internal/syntax/error_test.go b/src/cmd/compile/internal/syntax/error_test.go
index 919667f1d3..e4bedf54fd 100644
--- a/src/cmd/compile/internal/syntax/error_test.go
+++ b/src/cmd/compile/internal/syntax/error_test.go
@@ -164,7 +164,7 @@ func testSyntaxErrors(t *testing.T, filename string) {
 			// we have a match - eliminate this error
 			delete(declared, pos)
 		} else {
-			t.Errorf("%s: unexpected error: %s", orig, e.Msg)
+			t.Errorf("%s:%s: unexpected error: %s", filename, orig, e.Msg)
 		}
 	}, nil, mode)
 
@@ -175,7 +175,7 @@ func testSyntaxErrors(t *testing.T, filename string) {
 
 	// report expected but not reported errors
 	for pos, pattern := range declared {
-		t.Errorf("%s: missing error: %s", pos, pattern)
+		t.Errorf("%s:%s: missing error: %s", filename, pos, pattern)
 	}
 }
 
diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index c4ccbb82cb..026297432d 100644
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -735,9 +735,9 @@ func (p *parser) binaryExpr(prec int) Expr {
 		t := new(Operation)
 		t.pos = p.pos()
 		t.Op = p.op
-		t.X = x
 		tprec := p.prec
 		p.next()
+		t.X = x
 		t.Y = p.binaryExpr(tprec)
 		x = t
 	}
@@ -1381,7 +1381,9 @@ func (p *parser) structType() *StructType {
 	return typ
 }
 
-// InterfaceType = "interface" "{" { MethodSpec ";" } "}" .
+// InterfaceType = "interface" "{" { ( MethodDecl | EmbeddedElem | TypeList ) ";" } "}" .
+// TypeList      = "type" Type { "," Type } .
+// TODO(gri) remove TypeList syntax if we accept #45346
 func (p *parser) interfaceType() *InterfaceType {
 	if trace {
 		defer p.trace("interfaceType")()
@@ -1395,9 +1397,15 @@ func (p *parser) interfaceType() *InterfaceType {
 	p.list(_Semi, _Rbrace, func() bool {
 		switch p.tok {
 		case _Name:
-			typ.MethodList = append(typ.MethodList, p.methodDecl())
+			f := p.methodDecl()
+			if f.Name == nil && p.mode&AllowGenerics != 0 {
+				f = p.embeddedElem(f)
+			}
+			typ.MethodList = append(typ.MethodList, f)
+			return false
 
 		case _Lparen:
+			// TODO(gri) Need to decide how to adjust this restriction.
 			p.syntaxError("cannot parenthesize embedded type")
 			f := new(Field)
 			f.pos = p.pos()
@@ -1405,10 +1413,17 @@ func (p *parser) interfaceType() *InterfaceType {
 			f.Type = p.qualifiedName(nil)
 			p.want(_Rparen)
 			typ.MethodList = append(typ.MethodList, f)
+			return false
+
+		case _Operator:
+			if p.op == Tilde && p.mode&AllowGenerics != 0 {
+				typ.MethodList = append(typ.MethodList, p.embeddedElem(nil))
+				return false
+			}
 
 		case _Type:
+			// TODO(gri) remove TypeList syntax if we accept #45346
 			if p.mode&AllowGenerics != 0 {
-				// TODO(gri) factor this better
 				type_ := NewName(p.pos(), "type") // cannot have a method named "type"
 				p.next()
 				if p.tok != _Semi && p.tok != _Rbrace {
@@ -1427,19 +1442,18 @@ func (p *parser) interfaceType() *InterfaceType {
 				} else {
 					p.syntaxError("expecting type")
 				}
-				break
+				return false
 			}
-			fallthrough
+		}
 
-		default:
-			if p.mode&AllowGenerics != 0 {
-				p.syntaxError("expecting method, interface name, or type list")
-				p.advance(_Semi, _Rbrace, _Type)
-			} else {
-				p.syntaxError("expecting method or interface name")
-				p.advance(_Semi, _Rbrace)
-			}
+		if p.mode&AllowGenerics != 0 {
+			p.syntaxError("expecting method, type list, or embedded element")
+			p.advance(_Semi, _Rbrace, _Type) // TODO(gri) remove _Type if we don't accept it anymore
+			return false
 		}
+
+		p.syntaxError("expecting method or interface name")
+		p.advance(_Semi, _Rbrace)
 		return false
 	})
 
@@ -1732,6 +1746,56 @@ func (p *parser) methodDecl() *Field {
 	return f
 }
 
+// EmbeddedElem = MethodSpec | EmbeddedTerm { "|" EmbeddedTerm } .
+func (p *parser) embeddedElem(f *Field) *Field {
+	if trace {
+		defer p.trace("embeddedElem")()
+	}
+
+	if f == nil {
+		f = new(Field)
+		f.pos = p.pos()
+		f.Type = p.embeddedTerm()
+	}
+
+	for p.tok == _Operator && p.op == Or {
+		t := new(Operation)
+		t.pos = p.pos()
+		t.Op = Or
+		p.next()
+		t.X = f.Type
+		t.Y = p.embeddedTerm()
+		f.Type = t
+	}
+
+	return f
+}
+
+// EmbeddedTerm = [ "~" ] Type .
+func (p *parser) embeddedTerm() Expr {
+	if trace {
+		defer p.trace("embeddedTerm")()
+	}
+
+	if p.tok == _Operator && p.op == Tilde {
+		t := new(Operation)
+		t.pos = p.pos()
+		t.Op = Tilde
+		p.next()
+		t.X = p.type_()
+		return t
+	}
+
+	t := p.typeOrNil()
+	if t == nil {
+		t = p.badExpr()
+		p.syntaxError("expecting ~ term or type")
+		p.advance(_Operator, _Semi, _Rparen, _Rbrack, _Rbrace)
+	}
+
+	return t
+}
+
 // ParameterDecl = [ IdentifierList ] [ "..." ] Type .
 func (p *parser) paramDeclOrNil(name *Name) *Field {
 	if trace {
diff --git a/src/cmd/compile/internal/syntax/printer_test.go b/src/cmd/compile/internal/syntax/printer_test.go
index 4890327595..ec4b1de573 100644
--- a/src/cmd/compile/internal/syntax/printer_test.go
+++ b/src/cmd/compile/internal/syntax/printer_test.go
@@ -149,6 +149,15 @@ var exprTests = [][2]string{
 	dup("<-chan E"),
 	dup("chan<- E"),
 
+	// new interfaces
+	dup("interface{int}"),
+	dup("interface{~int}"),
+	dup("interface{~int}"),
+	dup("interface{int | string}"),
+	dup("interface{~int | ~string; float64; m()}"),
+	dup("interface{type a, b, c; ~int | ~string; float64; m()}"),
+	dup("interface{~T[int, string] | string}"),
+
 	// non-type expressions
 	dup("(x)"),
 	dup("x.f"),
diff --git a/src/cmd/compile/internal/syntax/testdata/interface.go2 b/src/cmd/compile/internal/syntax/testdata/interface.go2
new file mode 100644
index 0000000000..a817327a43
--- /dev/null
+++ b/src/cmd/compile/internal/syntax/testdata/interface.go2
@@ -0,0 +1,36 @@
+// Copyright 2021 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.
+
+// This file contains test cases for interfaces containing
+// constraint elements.
+//
+// For now, we accept both ordinary type lists and the
+// more complex constraint elements.
+
+package p
+
+type _ interface {
+	m()
+	type int
+	type int, string
+	E
+}
+
+type _ interface {
+	m()
+	~int
+	int | string
+	int | ~string
+	~int | ~string
+}
+
+
+type _ interface {
+	m()
+	~int
+	T[int, string] | string
+	int | ~T[string, struct{}]
+	~int | ~string
+	type bool, int, float64
+}