func playExample()

in internal/godoc/internal/doc/example.go [153:302]
114 lines of code
33 McCabe index (conditional complexity)

func playExample(fset *token.FileSet, file *ast.File, f *ast.FuncDecl) *ast.File {
	body := f.Body
	tokenFile := fset.File(file.Package)
	if !strings.HasSuffix(file.Name.Name, "_test") {
		// We don't support examples that are part of the
		// greater package (yet).
		return nil
	}

	// Collect top-level declarations in the file.
	topDecls := make(map[*ast.Object]ast.Decl)
	typMethods := make(map[string][]ast.Decl)

	for _, decl := range file.Decls {
		switch d := decl.(type) {
		case *ast.FuncDecl:
			if d.Recv == nil {
				topDecls[d.Name.Obj] = d
			} else {
				if len(d.Recv.List) == 1 {
					t := d.Recv.List[0].Type
					tname, _ := baseTypeName(t)
					typMethods[tname] = append(typMethods[tname], d)
				}
			}
		case *ast.GenDecl:
			for _, spec := range d.Specs {
				switch s := spec.(type) {
				case *ast.TypeSpec:
					topDecls[s.Name.Obj] = d
				case *ast.ValueSpec:
					for _, name := range s.Names {
						topDecls[name.Obj] = d
					}
				}
			}
		}
	}

	// Find unresolved identifiers and uses of top-level declarations.
	depDecls, unresolved := findDeclsAndUnresolved(body, topDecls, typMethods)

	// 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
		}
		if p == "syscall/js" {
			// We don't support examples that import syscall/js,
			// because the package syscall/js is not available in the playground.
			return nil
		}
		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 the "Output:" or "Unordered output:" comment and adjust body
	// end position.
	body, comments = stripOutputComment(body, comments)

	// Include documentation belonging to dependent declarations.
	for _, d := range depDecls {
		switch d := d.(type) {
		case *ast.GenDecl:
			if d.Doc != nil {
				comments = append(comments, d.Doc)
			}
		case *ast.FuncDecl:
			if d.Doc != nil {
				comments = append(comments, d.Doc)
			}
		}
	}

	importDecl := synthesizeImportDecl(namedImports, blankImports, tokenFile)

	// Synthesize main function.
	funcDecl := &ast.FuncDecl{
		Name: ast.NewIdent("main"),
		Type: f.Type,
		Body: body,
	}

	decls := make([]ast.Decl, 0, 2+len(depDecls))
	decls = append(decls, importDecl)
	decls = append(decls, depDecls...)
	decls = append(decls, funcDecl)

	sort.Slice(decls, func(i, j int) bool {
		return decls[i].Pos() < decls[j].Pos()
	})

	sort.Slice(comments, func(i, j int) bool {
		return comments[i].Pos() < comments[j].Pos()
	})

	// Synthesize file.
	return &ast.File{
		Name:     ast.NewIdent("main"),
		Decls:    decls,
		Comments: comments,
	}
}