// lastComment returns the last comment inside the provided block.
func lastComment(b *ast.BlockStmt, c []*ast.CommentGroup) (i int, last *ast.CommentGroup) {
pos, end := b.Pos(), b.End()
for j, cg := range c {
if cg.Pos() < pos {
continue
}
if cg.End() > end {
break
}
i, last = j, cg
}
return
}
// playExample synthesizes a new *ast.File based on the provided
// file with the provided function body as the body of main.
func playExample(file *ast.File, body *ast.BlockStmt) *ast.File {
if !strings.HasSuffix(file.Name.Name, "_test") {
// We don't support examples that are part of the
// greater package (yet).
return nil
}
// Find top-level declarations in the file.
topDecls := make(map[*ast.Object]bool)
for _, decl := range file.Decls {
switch d := decl.(type) {
case *ast.FuncDecl:
topDecls[d.Name.Obj] = true
case *ast.GenDecl:
for _, spec := range d.Specs {
switch s := spec.(type) {
case *ast.TypeSpec:
topDecls[s.Name.Obj] = true
case *ast.ValueSpec:
for _, id := range s.Names {
topDecls[id.Obj] = true
}
}
}
}
}
// Find unresolved identifiers and uses of top-level declarations.
unresolved := make(map[string]bool)
usesTopDecl := false
var inspectFunc func(ast.Node) bool
inspectFunc = func(n ast.Node) bool {
// For selector expressions, only inspect the left hand side.
// (For an expression like fmt.Println, only add "fmt" to the
// set of unresolved names, not "Println".)
if e, ok := n.(*ast.SelectorExpr); ok {
ast.Inspect(e.X, inspectFunc)
return false
}
// For key value expressions, only inspect the value
// as the key should be resolved by the type of the
// composite literal.
if e, ok := n.(*ast.KeyValueExpr); ok {
ast.Inspect(e.Value, inspectFunc)
return false
}
if id, ok := n.(*ast.Ident); ok {
if id.Obj == nil {
unresolved[id.Name] = true
} else if topDecls[id.Obj] {
usesTopDecl = true
}
}
return true
}
ast.Inspect(body, inspectFunc)
if usesTopDecl {
// We don't support examples that are not self-contained (yet).
return nil
}
// Remove predeclared identifiers from unresolved list.
for n := range unresolved {
if predeclaredTypes[n] || predeclaredConstants[n] || predeclaredFuncs[n] {
delete(unresolved, n)
}
}
// Use unresolved identifiers to determine the imports used by this
// example. The heuristic assumes package names match base import
// paths for imports w/o renames (should be good enough most of the time).
namedImports := make(map[string]string) // [name]path
var blankImports []ast.Spec // _ imports
for _, s := range file.Imports {
p, err := strconv.Unquote(s.Path.Value)
if err != nil {
continue
}
n := path.Base(p)
if s.Name != nil {
n = s.Name.Name
switch n {
case "_":
blankImports = append(blankImports, s)
continue
case ".":
// We can't resolve dot imports (yet).
return nil
}
}
if unresolved[n] {
namedImports[n] = p
delete(unresolved, n)
}
}
// If there are other unresolved identifiers, give up because this
// synthesized file is not going to build.
if len(unresolved) > 0 {
return nil
}
// Include documentation belonging to blank imports.
var comments []*ast.CommentGroup
for _, s := range blankImports {
if c := s.(*ast.ImportSpec).Doc; c != nil {
comments = append(comments, c)
}
}
// Include comments that are inside the function body.
for _, c := range file.Comments {
if body.Pos() <= c.Pos() && c.End() <= body.End() {
comments = append(comments, c)
}
}
// Strip "Output:" comment and adjust body end position.
body, comments = stripOutputComment(body, comments)
// Synthesize import declaration.
importDecl := &ast.GenDecl{
Tok: token.IMPORT,
Lparen: 1, // Need non-zero Lparen and Rparen so that printer
Rparen: 1, // treats this as a factored import.
}
for n, p := range namedImports {
s := &ast.ImportSpec{Path: &ast.BasicLit{Value: strconv.Quote(p)}}
if path.Base(p) != n {
s.Name = ast.NewIdent(n)
}
importDecl.Specs = append(importDecl.Specs, s)
}
importDecl.Specs = append(importDecl.Specs, blankImports...)
// Synthesize main function.
funcDecl := &ast.FuncDecl{
Name: ast.NewIdent("main"),
Type: &ast.FuncType{Params: &ast.FieldList{}}, // FuncType.Params must be non-nil
Body: body,
}
// Synthesize file.
return &ast.File{
Name: ast.NewIdent("main"),
Decls: []ast.Decl{importDecl, funcDecl},
Comments: comments,
}
}