go/doc: propagate types from unexported constants

When constants were declared using unexported constants,
the type information was lost when those constants were filtered out.
This CL propagates the type information of unexported constants
so that it is available for display.

This is a follow-up to CL 144110044, which fixed this problem
specifically for _ constants.

Updates golang#5397.

Change-Id: I3f0c767a4007d88169a5634ab2870deea4e6a740

src/go/doc/exports.go

@@ -26,6 +26,17 @@ func filterIdentList(list []*ast.Ident, blankOk bool) []*ast.Ident {
 	return list[0:j]
 }
 
+// hasExportedOrBlankName reports whether list contains any exported or blank names.
+//
+func hasExportedOrBlankName(list []*ast.Ident) bool {
+	for _, x := range list {
+		if x.IsExported() || x.Name == "_" {
+			return true
+		}
+	}
+	return false
+}
+
 // removeErrorField removes anonymous fields named "error" from an interface.
 // This is called when "error" has been determined to be a local name,
 // not the predeclared type.
@@ -166,6 +177,30 @@ func (r *reader) filterSpec(spec ast.Spec, tok token.Token) bool {
 }
 
 func (r *reader) filterSpecList(list []ast.Spec, tok token.Token) []ast.Spec {
+	if tok == token.CONST {
+		// Propagate any type information that will get lost
+		// when unexported constants are filtered.
+		var prevType ast.Expr
+		for _, spec := range list {
+			spec := spec.(*ast.ValueSpec)
+			if spec.Type == nil && prevType != nil {
+				// copy the type to the current spec
+				name, _ := baseTypeName(prevType)
+				spec.Type = &ast.Ident{
+					NamePos: spec.Pos(),
+					Name:    name,
+				}
+			}
+			if hasExportedOrBlankName(spec.Names) {
+				// both exported and blank names are preserved
+				// so there's no need to propagate the type
+				prevType = nil
+			} else {
+				prevType = spec.Type
+			}
+		}
+	}
+
 	j := 0
 	for _, s := range list {
 		if r.filterSpec(s, tok) {

src/go/doc/testdata/blank.0.golden

@@ -8,6 +8,16 @@ FILENAMES
 	testdata/blank.go
 
 CONSTANTS
+	// T constants counting from unexported constants. 
+	const (
+		C1	T
+		C2
+
+		C3
+
+		C4	int
+	)
+
 	// Package constants. 
 	const (
 		_	int	= iota
@@ -28,7 +38,7 @@ TYPES
 	// 
 	type T int
 
-	// T constants. 
+	// T constants counting from a blank constant. 
 	const (
 		_	T	= iota
 		T1

src/go/doc/testdata/blank.1.golden

@@ -8,6 +8,18 @@ FILENAMES
 	testdata/blank.go
 
 CONSTANTS
+	// T constants counting from unexported constants. 
+	const (
+		tweedledee	T	= iota
+		tweedledum
+		C1
+		C2
+		alice
+		C3
+		redQueen	int	= iota
+		C4
+	)
+
 	// Package constants. 
 	const (
 		_	int	= iota
@@ -37,7 +49,7 @@ TYPES
 	// 
 	type T int
 
-	// T constants. 
+	// T constants counting from a blank constant. 
 	const (
 		_	T	= iota
 		T1

src/go/doc/testdata/blank.2.golden

@@ -8,6 +8,16 @@ FILENAMES
 	testdata/blank.go
 
 CONSTANTS
+	// T constants counting from unexported constants. 
+	const (
+		C1	T
+		C2
+
+		C3
+
+		C4	int
+	)
+
 	// Package constants. 
 	const (
 		_	int	= iota
@@ -28,7 +38,7 @@ TYPES
 	// 
 	type T int
 
-	// T constants. 
+	// T constants counting from a blank constant. 
 	const (
 		_	T	= iota
 		T1

src/go/doc/testdata/blank.go

@@ -8,13 +8,25 @@ package blank
 
 type T int
 
-// T constants.
+// T constants counting from a blank constant.
 const (
 	_ T = iota
 	T1
 	T2
 )
 
+// T constants counting from unexported constants.
+const (
+	tweedledee T = iota
+	tweedledum
+	C1
+	C2
+	alice
+	C3
+	redQueen int = iota
+	C4
+)
+
 // Package constants.
 const (
 	_ int = iota