godoc: don't show directories w/o packages in flat dir mode

The main change is simple: Both the Directory and DirEntry
struct have an extra field 'HasPkg' indicating whether the
directory contains any package files. The remaining changes
are more comments and adjustments to the template files.

Fixes #3121.

R=golang-dev, bradfitz, sameer
CC=golang-dev
https://golang.org/cl/5699072

lib/godoc/package.html

@@ -167,21 +167,27 @@
 	<th>&nbsp;&nbsp;&nbsp;&nbsp;</th>
 	<th style="text-align: left; width: auto">Synopsis</th>
 	</tr>
+	{{if not $.DirFlat}}
 		<tr>
 		<td><a href="..">..</a></td>
 		</tr>
+	{{end}}
 	{{range .List}}
-	<tr>
-		<td>
 		{{if $.DirFlat}}
-			<a href="{{html .Path}}">{{html .Path}}</a>
-		{{else}}
-			{{repeat `&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;` .Depth}}<a href="{{html .Path}}">{{html .Name}}</a>
+			{{if .HasPkg}}
+				<tr>
+				<td><a href="{{html .Path}}">{{html .Path}}</a></td>
+				<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
+				<td style="width: auto">{{html .Synopsis}}</td>
+				</tr>
 			{{end}}
-		</td>
+		{{else}}
+			<tr>
+			<td>{{repeat `&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;` .Depth}}<a href="{{html .Path}}">{{html .Name}}</a></td>
 			<td>&nbsp;&nbsp;&nbsp;&nbsp;</td>
 			<td style="width: auto">{{html .Synopsis}}</td>
 			</tr>
 		{{end}}
+	{{end}}
 	</table>
 {{end}}

lib/godoc/package.txt

@@ -76,8 +76,8 @@ OTHER PACKAGES
 
 */}}{{with .Dirs}}
 SUBDIRECTORIES
-{{if $.DirFlat}}{{range .List}}
-	{{.Path}}{{end}}
+{{if $.DirFlat}}{{range .List}}{{if .HasPkg}}
+	{{.Path}}{{end}}{{end}}
 {{else}}{{range .List}}
 	{{repeat `. ` .Depth}}{{.Name}}{{end}}
 {{end}}{{end}}

src/cmd/godoc/dirtrees.go

@@ -24,9 +24,10 @@ const testdataDirName = "testdata"
 
 type Directory struct {
 	Depth    int
-	Path  string // includes Name
-	Name  string
-	Text  string       // package documentation, if any
+	Path     string       // directory path; includes Name
+	Name     string       // directory name
+	HasPkg   bool         // true if the directory contains at least one package
+	Synopsis string       // package documentation, if any
 	Dirs     []*Directory // subdirectories
 }
 
@@ -62,7 +63,11 @@ func (b *treeBuilder) newDirTree(fset *token.FileSet, path, name string, depth i
 		// return a dummy directory so that the parent directory
 		// doesn't get discarded just because we reached the max
 		// directory depth
-		return &Directory{depth, path, name, "", nil}
+		return &Directory{
+			Depth: depth,
+			Path:  path,
+			Name:  name,
+		}
 	}
 
 	list, err := fs.ReadDir(path)
@@ -145,7 +150,14 @@ func (b *treeBuilder) newDirTree(fset *token.FileSet, path, name string, depth i
 		}
 	}
 
-	return &Directory{depth, path, name, synopsis, dirs}
+	return &Directory{
+		Depth:    depth,
+		Path:     path,
+		Name:     name,
+		HasPkg:   hasPkgFiles,
+		Synopsis: synopsis,
+		Dirs:     dirs,
+	}
 }
 
 // newDirectory creates a new package directory tree with at most maxDepth
@@ -247,9 +259,10 @@ func (dir *Directory) lookup(path string) *Directory {
 type DirEntry struct {
 	Depth    int    // >= 0
 	Height   int    // = DirList.MaxHeight - Depth, > 0
-	Path     string // includes Name, relative to DirList root
-	Name     string
-	Synopsis string
+	Path     string // directory path; includes Name, relative to DirList root
+	Name     string // directory name
+	HasPkg   bool   // true if the directory contains at least one package 
+	Synopsis string // package documentation, if any
 }
 
 type DirList struct {
@@ -304,7 +317,8 @@ func (root *Directory) listing(skipRoot bool) *DirList {
 		}
 		p.Path = path
 		p.Name = d.Name
-		p.Synopsis = d.Text
+		p.HasPkg = d.HasPkg
+		p.Synopsis = d.Synopsis
 		i++
 	}