cmd/compile: revert user-visible changes related to aliases

Reason: Decision to back out current alias implementation.

Leaving import/export related code in place for now.

For #16339.

TBR=mdempsky

Change-Id: Ib0897cab2c1c3dc8a541f2efb9893271b0b0efe2
Reviewed-on: https://go-review.googlesource.com/32757
Reviewed-by: Robert Griesemer <gri@golang.org>

2 files changed, 1 insertions, 119 deletions

diff --git a/src/cmd/compile/internal/gc/noder.go b/src/cmd/compile/internal/gc/noder.go
index 10bd09e72f..0189242d18 100644
--- a/src/cmd/compile/internal/gc/noder.go
+++ b/src/cmd/compile/internal/gc/noder.go
@@ -61,9 +61,6 @@ func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
 		case *syntax.ImportDecl:
 			p.importDecl(decl)
 
-		case *syntax.AliasDecl:
-			p.aliasDecl(decl)
-
 		case *syntax.VarDecl:
 			l = append(l, p.varDecl(decl)...)
 
@@ -150,100 +147,6 @@ func (p *noder) importDecl(imp *syntax.ImportDecl) {
 	my.Block = 1 // at top level
 }
 
-func (p *noder) aliasDecl(decl *syntax.AliasDecl) {
-	// Because alias declarations must refer to imported entities
-	// which are already set up, we can do all checks right here.
-	// We won't know anything about entities that have not been
-	// declared yet, but since they cannot have been imported, we
-	// know there's an error and we don't care about the details.
-
-	// The original entity must be denoted by a qualified identifier.
-	// (The parser doesn't make this restriction to be more error-
-	// tolerant.)
-	qident, ok := decl.Orig.(*syntax.SelectorExpr)
-	if !ok {
-		// TODO(gri) This prints a dot-imported object with qualification
-		//           (confusing error). Fix this.
-		yyerror("invalid alias: %v is not a package-qualified identifier", p.expr(decl.Orig))
-		return
-	}
-
-	pkg := p.expr(qident.X)
-	if pkg.Op != OPACK {
-		yyerror("invalid alias: %v is not a package", pkg)
-		return
-	}
-	pkg.Used = true
-
-	// Resolve original entity
-	orig := oldname(restrictlookup(qident.Sel.Value, pkg.Name.Pkg))
-	if orig.Sym.Flags&SymAlias != 0 {
-		Fatalf("original %v marked as alias", orig.Sym)
-	}
-
-	// An alias declaration must not refer to package unsafe.
-	if orig.Sym.Pkg == unsafepkg {
-		yyerror("invalid alias: %v refers to package unsafe (%v)", decl.Name.Value, orig)
-		return
-	}
-
-	// The aliased entity must be from a matching constant, type, variable,
-	// or function declaration, respectively.
-	var what string
-	switch decl.Tok {
-	case syntax.Const:
-		if orig.Op != OLITERAL {
-			what = "constant"
-		}
-	case syntax.Type:
-		if orig.Op != OTYPE {
-			what = "type"
-		}
-	case syntax.Var:
-		if orig.Op != ONAME || orig.Class != PEXTERN {
-			what = "variable"
-		}
-	case syntax.Func:
-		if orig.Op != ONAME || orig.Class != PFUNC {
-			what = "function"
-		}
-	default:
-		Fatalf("unexpected token: %s", decl.Tok)
-	}
-	if what != "" {
-		yyerror("invalid alias: %v is not a %s", orig, what)
-		return
-	}
-
-	// handle special cases
-	switch decl.Name.Value {
-	case "_":
-		return // don't declare blank aliases
-	case "init":
-		yyerror("cannot declare init - must be non-alias function declaration")
-		return
-	}
-
-	// declare alias
-	// (this is similar to handling dot imports)
-	asym := p.name(decl.Name)
-	if asym.Def != nil {
-		redeclare(asym, "in alias declaration")
-		return
-	}
-	asym.Flags |= SymAlias
-	asym.Def = orig
-	asym.Block = block
-	asym.Lastlineno = lineno
-
-	if exportname(asym.Name) {
-		// TODO(gri) newname(asym) is only needed to satisfy exportsym
-		// (and indirectly, exportlist). We should be able to just
-		// collect the Syms, eventually.
-		exportsym(newname(asym))
-	}
-}
-
 func (p *noder) varDecl(decl *syntax.VarDecl) []*Node {
 	names := p.declNames(decl.NameList)
 
diff --git a/src/go/internal/gcimporter/testdata/exports.go b/src/go/internal/gcimporter/testdata/exports.go
index 0033f3027b..9a0273ba20 100644
--- a/src/go/internal/gcimporter/testdata/exports.go
+++ b/src/go/internal/gcimporter/testdata/exports.go
@@ -7,11 +7,7 @@
 
 package exports
 
-import (
-	"go/ast"
-	"go/build"
-	"math"
-)
+import "go/ast"
 
 // Issue 3682: Correctly read dotted identifiers from export data.
 const init1 = 0
@@ -29,10 +25,6 @@ const (
 	C7     = `bar\n`
 )
 
-const (
-	C8 => math.Pi
-)
-
 type (
 	T1  int
 	T2  [10]int
@@ -81,21 +73,12 @@ type (
 	T28 func(T28) T28
 )
 
-type (
-	T29 => ast.File
-	T30 => build.Context
-)
-
 var (
 	V0 int
 	V1         = -991.0
 	V2 float32 = 1.2
 )
 
-var (
-	V3 => build.Default
-)
-
 func F1()         {}
 func F2(x int)    {}
 func F3() int     { return 0 }
@@ -103,7 +86,3 @@ func F4() float32 { return 0 }
 func F5(a, b, c int, u, v, w struct{ x, y T1 }, more ...interface{}) (p, q, r chan<- T10)
 
 func (p *T1) M1()
-
-func F6 => math.Sin
-func F7 => ast.IsExported
-func F8 => build.Import