Revert "go/printer: support for printing alias declarations"

This reverts commit 59c63c71.

Reason: Decision to back out current alias implementation.

For #16339.

Change-Id: Idd135fe84b7ce4814cb3632f717736fc6985634c
Reviewed-on: https://go-review.googlesource.com/32822Reviewed-by: Chris Manghane <cmang@golang.org>

src/go/printer/nodes.go

@@ -1309,26 +1309,13 @@ func keepTypeColumn(specs []ast.Spec) []bool {
 		}
 	}
 
-	i0 := -1          // if i0 >= 0 we are in a run and i0 is the start of the run
-	var keepType bool // valid if we are in a run (i0 >= 0)
+	i0 := -1 // if i0 >= 0 we are in a run and i0 is the start of the run
+	var keepType bool
 	for i, s := range specs {
-		var hasValues, hasType bool
-		switch t := s.(type) {
-		case *ast.AliasSpec:
-			// like a ValueSpec with values (alias origin), but no type
-			hasValues = true
-
-		case *ast.ValueSpec:
-			hasValues = len(t.Values) > 0
-			hasType = t.Type != nil
-
-		default:
-			panic("internal error: unexpected ast.Spec")
-		}
-
-		if hasValues {
+		t := s.(*ast.ValueSpec)
+		if t.Values != nil {
 			if i0 < 0 {
-				// start of a run with values
+				// start of a run of ValueSpecs with non-nil Values
 				i0 = i
 				keepType = false
 			}
@@ -1339,7 +1326,7 @@ func keepTypeColumn(specs []ast.Spec) []bool {
 				i0 = -1
 			}
 		}
-		if hasType {
+		if t.Type != nil {
 			keepType = true
 		}
 	}
@@ -1351,25 +1338,6 @@ func keepTypeColumn(specs []ast.Spec) []bool {
 	return m
 }
 
-func (p *printer) aliasSpec(s *ast.AliasSpec, keepTypeCol bool) {
-	p.setComment(s.Doc)
-	p.expr(s.Name)
-	extraTabs := 3
-	if keepTypeCol {
-		p.print(vtab)
-		extraTabs--
-	}
-	p.print(vtab, token.ALIAS, blank)
-	p.expr(s.Orig)
-	extraTabs--
-	if s.Comment != nil {
-		for ; extraTabs > 0; extraTabs-- {
-			p.print(vtab)
-		}
-		p.setComment(s.Comment)
-	}
-}
-
 func (p *printer) valueSpec(s *ast.ValueSpec, keepType bool) {
 	p.setComment(s.Doc)
 	p.identList(s.Names, false) // always present
@@ -1453,17 +1421,6 @@ func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
 		p.setComment(s.Comment)
 		p.print(s.EndPos)
 
-	case *ast.AliasSpec:
-		p.setComment(s.Doc)
-		p.expr(s.Name)
-		if n == 1 {
-			p.print(blank)
-		} else {
-			p.print(vtab)
-		}
-		p.print(token.ALIAS, blank)
-		p.expr(s.Orig)
-
 	case *ast.ValueSpec:
 		if n != 1 {
 			p.internalError("expected n = 1; got", n)
@@ -1515,16 +1472,7 @@ func (p *printer) genDecl(d *ast.GenDecl) {
 						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
 					}
 					p.recordLine(&line)
-					switch t := s.(type) {
-					case *ast.AliasSpec:
-						p.aliasSpec(t, keepType[i])
-
-					case *ast.ValueSpec:
-						p.valueSpec(t, keepType[i])
-
-					default:
-						p.internalError("unknown ast.Spec type: %T", t)
-					}
+					p.valueSpec(s.(*ast.ValueSpec), keepType[i])
 				}
 			} else {
 				var line int

src/go/printer/testdata/declarations.golden

@@ -985,47 +985,3 @@ func _(struct {
 	x	int
 	y	int
 })	// no extra comma between } and )
-
-// alias declarations
-const c => C
-const c => p.C
-const (
-	a		= 123
-	b	int	= 456
-	c		=> foo
-	ddd		=> p.Foo
-)
-
-// TODO(gri) Currently = and => line up in the formatted output,
-//           but because = and => have different lengths, the
-//           text following doesn't line up. Consider putting that
-//           text into its own column.
-const (
-	a	int	= iota	// a comment
-	b		=> p.B	// b comment
-	c			// c comment
-	d	=> p.C		// d comment
-	e	=> p.E
-	f
-	g	float32	= 9.8
-)
-
-type c => C
-type c => p.C
-type (
-	s	struct{}
-	a	=> A
-	ddd	=> p.Foo
-)
-
-var c => C
-var c => p.C
-var (
-	a		= 123
-	b	int	= 456
-	c		=> foo
-	ddd		=> p.Foo
-)
-
-func f => F
-func f_long => p.F

src/go/printer/testdata/declarations.input

@@ -999,47 +999,3 @@ func _(struct {
 	x int
 	y int
 }) // no extra comma between } and )
-
-// alias declarations
-const c => C
-const c => p.C
-const (
-	a = 123
-	b int = 456
-	c => foo
-	ddd => p.Foo
-)
-
-// TODO(gri) Currently = and => line up in the formatted output,
-//           but because = and => have different lengths, the
-//           text following doesn't line up. Consider putting that
-//           text into its own column.
-const (
-	a int = iota // a comment
-	b => p.B // b comment
-	c // c comment
-	d => p.C // d comment
-	e => p.E
-	f
-	g float32 = 9.8
-)
-
-type c => C
-type c => p.C
-type (
-	s struct{}
-	a => A
-	ddd => p.Foo
-)
-
-var c => C
-var c => p.C
-var (
-	a = 123
-	b int = 456
-	c => foo
-	ddd => p.Foo
-)
-
-func f => F
-func f_long => p.F
\ No newline at end of file