snippet generator for godoc search results

R=rsc
http://go/go-review/1013014

src/cmd/godoc/snippet.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains the infrastructure to create a code
+// snippet for search results.
+//
+// Note: At the moment, this only creates HTML snippets.
+
+package main
+
+import (
+	"bytes";
+	"go/ast";
+	"go/printer";
+	"fmt";
+	"strings";
+)
+
+
+type Snippet struct {
+	Line	int;
+	Text	string;
+}
+
+
+type snippetStyler struct {
+	Styler;				// defined in godoc.go
+	highlight	*ast.Ident;	// identifier to highlight
+}
+
+
+func (s *snippetStyler) LineTag(line int) (text []uint8, tag printer.HtmlTag) {
+	return;	// no LineTag for snippets
+}
+
+
+func (s *snippetStyler) Ident(id *ast.Ident) (text []byte, tag printer.HtmlTag) {
+	text = strings.Bytes(id.Value);
+	if s.highlight == id {
+		tag = printer.HtmlTag{"<span class=highlight>", "</span>"};
+	}
+	return;
+}
+
+
+func newSnippet(decl ast.Decl, id *ast.Ident) *Snippet {
+	var buf bytes.Buffer;
+	writeNode(&buf, decl, true, &snippetStyler{highlight: id});
+	return &Snippet{id.Pos().Line, buf.String()};
+}
+
+
+func findSpec(list []ast.Spec, id *ast.Ident) ast.Spec {
+	for _, spec := range list {
+		switch s := spec.(type) {
+		case *ast.ImportSpec:
+			if s.Name == id {
+				return s;
+			}
+		case *ast.ValueSpec:
+			for _, n := range s.Names {
+				if n == id {
+					return s;
+				}
+			}
+		case *ast.TypeSpec:
+			if s.Name == id {
+				return s;
+			}
+		}
+	}
+	return nil;
+}
+
+
+func genSnippet(d *ast.GenDecl, id *ast.Ident) *Snippet {
+	s := findSpec(d.Specs, id);
+	if s == nil {
+		return nil;	//  declaration doesn't contain id - exit gracefully
+	}
+
+	// only use the spec containing the id for the snippet
+	dd := &ast.GenDecl{d.Doc, d.Position, d.Tok, d.Lparen, []ast.Spec{s}, d.Rparen};
+
+	return newSnippet(dd, id);
+}
+
+
+func funcSnippet(d *ast.FuncDecl, id *ast.Ident) *Snippet {
+	if d.Name != id {
+		return nil;	//  declaration doesn't contain id - exit gracefully
+	}
+
+	// only use the function signature for the snippet
+	dd := &ast.FuncDecl{d.Doc, d.Recv, d.Name, d.Type, nil};
+
+	return newSnippet(dd, id);
+}
+
+
+// NewSnippet creates a text snippet from a declaration decl containing an
+// identifier id. Parts of the declaration not containing the identifier
+// may be removed for a more compact snippet.
+//
+func NewSnippet(decl ast.Decl, id *ast.Ident) (s *Snippet) {
+	switch d := decl.(type) {
+	case *ast.GenDecl:
+		s = genSnippet(d, id);
+	case *ast.FuncDecl:
+		s = funcSnippet(d, id);
+	}
+
+	// handle failure gracefully
+	if s == nil {
+		s = &Snippet{
+			id.Pos().Line,
+			fmt.Sprintf(`could not generate a snippet for <span class="highlight">%s</span>`, id.Value),
+		};
+	}
+	return;
+}