Revert "cmd/compile/internal/syntax: support for alias declarations"

This reverts commit 32db3f2756324616b7c856ac9501deccc2491239.

Reason: Decision to back out current alias implementation.

For #16339.

Change-Id: Ib05e3d96041d8347e49cae292f66bec791a1fdc8
Reviewed-on: https://go-review.googlesource.com/32825
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

6 files changed, 38 insertions, 129 deletions

diff --git a/src/cmd/compile/internal/syntax/nodes.go b/src/cmd/compile/internal/syntax/nodes.go
index b88d16e113..bb56df33b1 100644
--- a/src/cmd/compile/internal/syntax/nodes.go
+++ b/src/cmd/compile/internal/syntax/nodes.go
@@ -25,21 +25,14 @@ func (n *node) Line() uint32 {
 	return n.line
 }
 
-// TODO(gri) clean up init/initFrom once we have a good file pos story
 func (n *node) init(p *parser) {
 	n.pos = uint32(p.pos)
 	n.line = uint32(p.line)
 }
 
-func (n *node) initFrom(a *node) {
-	n.pos = a.pos
-	n.line = a.line
-}
-
 // ----------------------------------------------------------------------------
 // Files
 
-// package PkgName; DeclList[0], DeclList[1], ...
 type File struct {
 	PkgName  *Name
 	DeclList []Decl
@@ -56,8 +49,6 @@ type (
 		aDecl()
 	}
 
-	//              Path
-	// LocalPkgName Path
 	ImportDecl struct {
 		LocalPkgName *Name // including "."; nil means no rename present
 		Path         *BasicLit
@@ -65,18 +56,6 @@ type (
 		decl
 	}
 
-	// Name => Orig
-	AliasDecl struct {
-		Tok   token // Const, Type, Var, or Func
-		Name  *Name
-		Orig  Expr
-		Group *Group // nil means not part of a group
-		decl
-	}
-
-	// NameList
-	// NameList      = Values
-	// NameList Type = Values
 	ConstDecl struct {
 		NameList []*Name
 		Type     Expr   // nil means no type
@@ -85,7 +64,6 @@ type (
 		decl
 	}
 
-	// Name Type
 	TypeDecl struct {
 		Name   *Name
 		Type   Expr
@@ -94,9 +72,6 @@ type (
 		decl
 	}
 
-	// NameList Type
-	// NameList Type = Values
-	// NameList      = Values
 	VarDecl struct {
 		NameList []*Name
 		Type     Expr   // nil means no type
@@ -105,10 +80,6 @@ type (
 		decl
 	}
 
-	// func          Name Type { Body }
-	// func          Name Type
-	// func Receiver Name Type { Body }
-	// func Receiver Name Type
 	FuncDecl struct {
 		Attr    map[string]bool // go:attr map
 		Recv    *Field          // nil means regular function
@@ -448,8 +419,6 @@ func (simpleStmt) aSimpleStmt() {}
 // ----------------------------------------------------------------------------
 // Comments
 
-// TODO(gri) Consider renaming to CommentPos, CommentPlacement, etc.
-//           Kind = Above doesn't make much sense.
 type CommentKind uint
 
 const (
diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 1ed20651b1..a959c6cd25 100644
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -317,38 +317,16 @@ func (p *parser) importDecl(group *Group) Decl {
 	return d
 }
 
-// AliasSpec = identifier "=>" [ PackageName "." ] identifier .
-func (p *parser) aliasDecl(tok token, name *Name, group *Group) Decl {
-	// no tracing since this is already called from a const/type/var/funcDecl
-
-	d := new(AliasDecl)
-	d.initFrom(&name.node)
-
-	// lhs identifier and "=>" have been consumed already
-
-	d.Tok = tok
-	d.Name = name
-	d.Orig = p.dotname(p.name())
-	d.Group = group
-
-	return d
-}
-
-// ConstSpec = IdentifierList [ [ Type ] "=" ExpressionList ] | AliasSpec .
+// ConstSpec = IdentifierList [ [ Type ] "=" ExpressionList ] .
 func (p *parser) constDecl(group *Group) Decl {
 	if trace {
 		defer p.trace("constDecl")()
 	}
 
-	name := p.name()
-	if p.got(_Rarrow) {
-		return p.aliasDecl(Const, name, group)
-	}
-
 	d := new(ConstDecl)
-	d.initFrom(&name.node)
+	d.init(p)
 
-	d.NameList = p.nameList(name)
+	d.NameList = p.nameList(p.name())
 	if p.tok != _EOF && p.tok != _Semi && p.tok != _Rparen {
 		d.Type = p.tryType()
 		if p.got(_Assign) {
@@ -360,21 +338,16 @@ func (p *parser) constDecl(group *Group) Decl {
 	return d
 }
 
-// TypeSpec = identifier Type | AliasSpec .
+// TypeSpec = identifier Type .
 func (p *parser) typeDecl(group *Group) Decl {
 	if trace {
 		defer p.trace("typeDecl")()
 	}
 
-	name := p.name()
-	if p.got(_Rarrow) {
-		return p.aliasDecl(Type, name, group)
-	}
-
 	d := new(TypeDecl)
-	d.initFrom(&name.node)
+	d.init(p)
 
-	d.Name = name
+	d.Name = p.name()
 	d.Type = p.tryType()
 	if d.Type == nil {
 		p.syntax_error("in type declaration")
@@ -386,21 +359,16 @@ func (p *parser) typeDecl(group *Group) Decl {
 	return d
 }
 
-// VarSpec = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) | AliasSpec .
+// VarSpec = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .
 func (p *parser) varDecl(group *Group) Decl {
 	if trace {
 		defer p.trace("varDecl")()
 	}
 
-	name := p.name()
-	if p.got(_Rarrow) {
-		return p.aliasDecl(Var, name, group)
-	}
-
 	d := new(VarDecl)
-	d.initFrom(&name.node)
+	d.init(p)
 
-	d.NameList = p.nameList(name)
+	d.NameList = p.nameList(p.name())
 	if p.got(_Assign) {
 		d.Values = p.exprList()
 	} else {
@@ -417,28 +385,31 @@ func (p *parser) varDecl(group *Group) Decl {
 	return d
 }
 
-var badRecv = new(Field) // to signal invalid receiver in funcDecl
-
-// FunctionDecl = "func" FunctionName ( Function | Signature ) | "func" AliasSpec .
+// FunctionDecl = "func" FunctionName ( Function | Signature ) .
 // FunctionName = identifier .
 // Function     = Signature FunctionBody .
 // MethodDecl   = "func" Receiver MethodName ( Function | Signature ) .
 // Receiver     = Parameters .
-func (p *parser) funcDecl() Decl {
+func (p *parser) funcDecl() *FuncDecl {
 	if trace {
 		defer p.trace("funcDecl")()
 	}
 
-	var recv *Field
+	f := new(FuncDecl)
+	f.init(p)
+
+	badRecv := false
 	if p.tok == _Lparen {
-		recv = badRecv
-		switch list := p.paramList(); len(list) {
+		rcvr := p.paramList()
+		switch len(rcvr) {
 		case 0:
 			p.error("method has no receiver")
+			badRecv = true
 		case 1:
-			recv = list[0]
+			f.Recv = rcvr[0]
 		default:
 			p.error("method has multiple receivers")
+			badRecv = true
 		}
 	}
 
@@ -448,11 +419,6 @@ func (p *parser) funcDecl() Decl {
 		return nil
 	}
 
-	name := p.name()
-	if recv == nil && p.got(_Rarrow) {
-		return p.aliasDecl(Func, name, nil)
-	}
-
 	// TODO(gri) check for regular functions only
 	// if name.Sym.Name == "init" {
 	// 	name = renameinit()
@@ -467,11 +433,7 @@ func (p *parser) funcDecl() Decl {
 	// 	}
 	// }
 
-	f := new(FuncDecl)
-	f.initFrom(&name.node) // TODO(gri) is this the correct position for methods?
-
-	f.Recv = recv
-	f.Name = name
+	f.Name = p.name()
 	f.Type = p.funcType()
 	if gcCompat {
 		f.node = f.Type.node
@@ -486,7 +448,7 @@ func (p *parser) funcDecl() Decl {
 	// 	p.error("can only use //go:noescape with external func implementations")
 	// }
 
-	if recv == badRecv {
+	if badRecv {
 		return nil // TODO(gri) better solution
 	}
 	return f
@@ -555,7 +517,7 @@ func (p *parser) unaryExpr() Expr {
 			return x
 		}
 
-	case _Larrow:
+	case _Arrow:
 		// receive op (<-x) or receive-only channel (<-chan E)
 		p.next()
 
@@ -969,7 +931,7 @@ func (p *parser) tryType() Expr {
 		p.next()
 		return indirect(p.type_())
 
-	case _Larrow:
+	case _Arrow:
 		// recvchantype
 		p.next()
 		p.want(_Chan)
@@ -1015,7 +977,7 @@ func (p *parser) tryType() Expr {
 		p.next()
 		t := new(ChanType)
 		t.init(p)
-		if p.got(_Larrow) {
+		if p.got(_Arrow) {
 			t.Dir = SendOnly
 		}
 		t.Elem = p.chanElem()
@@ -1358,7 +1320,7 @@ func (p *parser) paramDecl() *Field {
 	case _Name:
 		f.Name = p.name()
 		switch p.tok {
-		case _Name, _Star, _Larrow, _Func, _Lbrack, _Chan, _Map, _Struct, _Interface, _Lparen:
+		case _Name, _Star, _Arrow, _Func, _Lbrack, _Chan, _Map, _Struct, _Interface, _Lparen:
 			// sym name_or_type
 			f.Type = p.type_()
 
@@ -1373,7 +1335,7 @@ func (p *parser) paramDecl() *Field {
 			f.Name = nil
 		}
 
-	case _Larrow, _Star, _Func, _Lbrack, _Chan, _Map, _Struct, _Interface, _Lparen:
+	case _Arrow, _Star, _Func, _Lbrack, _Chan, _Map, _Struct, _Interface, _Lparen:
 		// name_or_type
 		f.Type = p.type_()
 
@@ -1507,7 +1469,7 @@ func (p *parser) simpleStmt(lhs Expr, rangeOk bool) SimpleStmt {
 			p.next()
 			return p.newAssignStmt(op, lhs, ImplicitOne)
 
-		case _Larrow:
+		case _Arrow:
 			// lhs <- rhs
 			p.next()
 			s := new(SendStmt)
@@ -1860,7 +1822,7 @@ func (p *parser) commClause() *CommClause {
 		p.next()
 		lhs := p.exprList()
 
-		if _, ok := lhs.(*ListExpr); !ok && p.tok == _Larrow {
+		if _, ok := lhs.(*ListExpr); !ok && p.tok == _Arrow {
 			// lhs <- x
 		} else {
 			// lhs
@@ -1940,7 +1902,7 @@ func (p *parser) stmt() Stmt {
 
 	case _Literal, _Func, _Lparen, // operands
 		_Lbrack, _Struct, _Map, _Chan, _Interface, // composite types
-		_Larrow: // receive operator
+		_Arrow: // receive operator
 		return p.simpleStmt(nil, false)
 
 	case _For:
diff --git a/src/cmd/compile/internal/syntax/printer.go b/src/cmd/compile/internal/syntax/printer.go
index 8f12707304..0cacf1e5d4 100644
--- a/src/cmd/compile/internal/syntax/printer.go
+++ b/src/cmd/compile/internal/syntax/printer.go
@@ -473,11 +473,11 @@ func (p *printer) printRawNode(n Node) {
 
 	case *ChanType:
 		if n.Dir == RecvOnly {
-			p.print(_Larrow)
+			p.print(_Arrow)
 		}
 		p.print(_Chan)
 		if n.Dir == SendOnly {
-			p.print(_Larrow)
+			p.print(_Arrow)
 		}
 		p.print(blank, n.Elem)
 
@@ -495,7 +495,7 @@ func (p *printer) printRawNode(n Node) {
 		p.print(n.X)
 
 	case *SendStmt:
-		p.print(n.Chan, blank, _Larrow, blank, n.Value)
+		p.print(n.Chan, blank, _Arrow, blank, n.Value)
 
 	case *AssignStmt:
 		p.print(n.Lhs)
@@ -603,12 +603,6 @@ func (p *printer) printRawNode(n Node) {
 		}
 		p.print(n.Path)
 
-	case *AliasDecl:
-		if n.Group == nil {
-			p.print(n.Tok, blank)
-		}
-		p.print(n.Name, blank, _Rarrow, blank, n.Orig)
-
 	case *ConstDecl:
 		if n.Group == nil {
 			p.print(_Const, blank)
@@ -763,8 +757,6 @@ func groupFor(d Decl) (token, *Group) {
 	switch d := d.(type) {
 	case *ImportDecl:
 		return _Import, d.Group
-	case *AliasDecl:
-		return d.Tok, d.Group
 	case *ConstDecl:
 		return _Const, d.Group
 	case *TypeDecl:
diff --git a/src/cmd/compile/internal/syntax/scanner.go b/src/cmd/compile/internal/syntax/scanner.go
index bd38943c30..b84fcc5fd1 100644
--- a/src/cmd/compile/internal/syntax/scanner.go
+++ b/src/cmd/compile/internal/syntax/scanner.go
@@ -229,7 +229,7 @@ redo:
 			goto assignop
 		}
 		if c == '-' {
-			s.tok = _Larrow
+			s.tok = _Arrow
 			break
 		}
 		s.ungetr()
@@ -253,16 +253,11 @@ redo:
 		s.tok = _Operator
 
 	case '=':
-		c = s.getr()
-		if c == '=' {
+		if s.getr() == '=' {
 			s.op, s.prec = Eql, precCmp
 			s.tok = _Operator
 			break
 		}
-		if c == '>' {
-			s.tok = _Rarrow
-			break
-		}
 		s.ungetr()
 		s.tok = _Assign
 
diff --git a/src/cmd/compile/internal/syntax/scanner_test.go b/src/cmd/compile/internal/syntax/scanner_test.go
index 0e0ff1b172..38a7e0da4c 100644
--- a/src/cmd/compile/internal/syntax/scanner_test.go
+++ b/src/cmd/compile/internal/syntax/scanner_test.go
@@ -210,8 +210,7 @@ var sampleTokens = [...]struct {
 	{_IncOp, "--", Sub, precAdd},
 	{_Assign, "=", 0, 0},
 	{_Define, ":=", 0, 0},
-	{_Larrow, "<-", 0, 0},
-	{_Rarrow, "=>", 0, 0},
+	{_Arrow, "<-", 0, 0},
 
 	// delimiters
 	{_Lparen, "(", 0, 0},
diff --git a/src/cmd/compile/internal/syntax/tokens.go b/src/cmd/compile/internal/syntax/tokens.go
index 4a02c0ce3b..bd0118a141 100644
--- a/src/cmd/compile/internal/syntax/tokens.go
+++ b/src/cmd/compile/internal/syntax/tokens.go
@@ -22,8 +22,7 @@ const (
 	_IncOp
 	_Assign
 	_Define
-	_Larrow
-	_Rarrow
+	_Arrow
 	_Star
 
 	// delimitors
@@ -70,12 +69,6 @@ const (
 )
 
 const (
-	// for AliasDecl
-	Const = _Const
-	Type  = _Type
-	Var   = _Var
-	Func  = _Func
-
 	// for BranchStmt
 	Break       = _Break
 	Continue    = _Continue
@@ -101,8 +94,7 @@ var tokstrings = [...]string{
 	_IncOp:    "opop",
 	_Assign:   "=",
 	_Define:   ":=",
-	_Larrow:   "<-",
-	_Rarrow:   "=>",
+	_Arrow:    "<-",
 	_Star:     "*",
 
 	// delimitors