go/printer: support for printing alias declarations

For #16339.

Change-Id: Ie2e3338b87e84f45cda0868213bbcd2dae9ab6e3
Reviewed-on: https://go-review.googlesource.com/30212
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/go/printer/nodes.go b/src/go/printer/nodes.go
index 11f26d45ea39429afb6eed2f4ee03588812dbaf5..4e5cd1e20bf38b5388fcb399fd2a5b6d895e6653 100644 (file)
--- a/src/go/printer/nodes.go
+++ b/src/go/printer/nodes.go
@@ -1309,13 +1309,26 @@ 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
+       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)
        for i, s := range specs {
-               t := s.(*ast.ValueSpec)
-               if t.Values != nil {
+               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 {
                        if i0 < 0 {
-                               // start of a run of ValueSpecs with non-nil Values
+                               // start of a run with values
                                i0 = i
                                keepType = false
                        }
@@ -1326,7 +1339,7 @@ func keepTypeColumn(specs []ast.Spec) []bool {
                                i0 = -1
                        }
                }
-               if t.Type != nil {
+               if hasType {
                        keepType = true
                }
        }
@@ -1338,6 +1351,25 @@ 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
@@ -1421,6 +1453,17 @@ 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)
@@ -1472,7 +1515,16 @@ func (p *printer) genDecl(d *ast.GenDecl) {
                                                p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
                                        }
                                        p.recordLine(&line)
-                                       p.valueSpec(s.(*ast.ValueSpec), keepType[i])
+                                       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)
+                                       }
                                }
                        } else {
                                var line int

diff --git a/src/go/printer/testdata/declarations.golden b/src/go/printer/testdata/declarations.golden
index 82f5e0f9147be69128d1a0183bfb058d65443b55..4d888cc8a495fd9510d8d3ff5a6037076198d821 100644 (file)
--- a/src/go/printer/testdata/declarations.golden
+++ b/src/go/printer/testdata/declarations.golden
@@ -985,3 +985,49 @@ 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
+       b       => A
+       c       => foo
+       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

diff --git a/src/go/printer/testdata/declarations.input b/src/go/printer/testdata/declarations.input
index a0a3783b846fbed661713caee409bdc41ec1afef..c3a76858b7a147df46ea90142a20a9734b06770d 100644 (file)
--- a/src/go/printer/testdata/declarations.input
+++ b/src/go/printer/testdata/declarations.input
@@ -999,3 +999,49 @@ 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
+       b = A
+       c = foo
+       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