playground: Add ability to fix imports via goimports.

playground/index.html

@@ -12,6 +12,9 @@
       <span id="controls">
         <input type="button" value="Run" ng-click="run(false)" />
         <input type="button" value="Format" ng-click="format()" />
+        <label title="Rewrite imports on Format">
+          <input ng-model="imports" type="checkbox" />Imports
+        </label>
         <input type="button" value="Share" ng-click="share()" />
         <input type="text" class="show-share-url-{{showShareUrl}}" id="share-url" value="{{shareUrl}}" onfocus="select()" />
       </span>

playground/internal/imports/fix.go

@@ -0,0 +1,179 @@
+// Copyright 2013 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.
+
+package imports
+
+import (
+	"go/ast"
+	"go/token"
+	"path"
+	"strings"
+
+	"golang.org/x/tools/go/ast/astutil"
+)
+
+// importToGroup is a list of functions which map from an import path to
+// a group number.
+var importToGroup = []func(importPath string) (num int, ok bool){
+	func(importPath string) (num int, ok bool) {
+		if strings.HasPrefix(importPath, "appengine") {
+			return 2, true
+		}
+		return
+	},
+	func(importPath string) (num int, ok bool) {
+		if strings.Contains(importPath, ".") {
+			return 1, true
+		}
+		return
+	},
+}
+
+func importGroup(importPath string) int {
+	for _, fn := range importToGroup {
+		if n, ok := fn(importPath); ok {
+			return n
+		}
+	}
+	return 0
+}
+
+func fixImports(fset *token.FileSet, f *ast.File) (added []string, err error) {
+	// refs are a set of possible package references currently unsatisfied by imports.
+	// first key: either base package (e.g. "fmt") or renamed package
+	// second key: referenced package symbol (e.g. "Println")
+	refs := make(map[string]map[string]bool)
+
+	// decls are the current package imports. key is base package or renamed package.
+	decls := make(map[string]*ast.ImportSpec)
+
+	// collect potential uses of packages.
+	var visitor visitFn
+	visitor = visitFn(func(node ast.Node) ast.Visitor {
+		if node == nil {
+			return visitor
+		}
+		switch v := node.(type) {
+		case *ast.ImportSpec:
+			if v.Name != nil {
+				decls[v.Name.Name] = v
+			} else {
+				local := importPathToName(strings.Trim(v.Path.Value, `\"`))
+				decls[local] = v
+			}
+		case *ast.SelectorExpr:
+			xident, ok := v.X.(*ast.Ident)
+			if !ok {
+				break
+			}
+			if xident.Obj != nil {
+				// if the parser can resolve it, it's not a package ref
+				break
+			}
+			pkgName := xident.Name
+			if refs[pkgName] == nil {
+				refs[pkgName] = make(map[string]bool)
+			}
+			if decls[pkgName] == nil {
+				refs[pkgName][v.Sel.Name] = true
+			}
+		}
+		return visitor
+	})
+	ast.Walk(visitor, f)
+
+	// Nil out any unused ImportSpecs, to be removed in following passes
+	unusedImport := map[string]bool{}
+	for pkg, is := range decls {
+		if refs[pkg] == nil && pkg != "_" && pkg != "." {
+			unusedImport[strings.Trim(is.Path.Value, `"`)] = true
+		}
+	}
+	for ipath := range unusedImport {
+		if ipath == "C" {
+			// Don't remove cgo stuff.
+			continue
+		}
+		astutil.DeleteImport(fset, f, ipath)
+	}
+
+	// Search for imports matching potential package references.
+	searches := 0
+	type result struct {
+		ipath string
+		name  string
+		err   error
+	}
+	results := make(chan result)
+	for pkgName, symbols := range refs {
+		if len(symbols) == 0 {
+			continue // skip over packages already imported
+		}
+		go func(pkgName string, symbols map[string]bool) {
+			ipath, rename, err := findImport(pkgName, symbols)
+			r := result{ipath: ipath, err: err}
+			if rename {
+				r.name = pkgName
+			}
+			results <- r
+		}(pkgName, symbols)
+		searches++
+	}
+	for i := 0; i < searches; i++ {
+		result := <-results
+		if result.err != nil {
+			return nil, result.err
+		}
+		if result.ipath != "" {
+			if result.name != "" {
+				astutil.AddNamedImport(fset, f, result.name, result.ipath)
+			} else {
+				astutil.AddImport(fset, f, result.ipath)
+			}
+			added = append(added, result.ipath)
+		}
+	}
+
+	return added, nil
+}
+
+// importPathToName returns the package name for the given import path.
+var importPathToName = importPathToNameBasic
+
+// importPathToNameBasic assumes the package name is the base of import path.
+func importPathToNameBasic(importPath string) (packageName string) {
+	return path.Base(importPath)
+}
+
+type pkg struct {
+	importpath string // full pkg import path, e.g. "net/http"
+	dir        string // absolute file path to pkg directory e.g. "/usr/lib/go/src/fmt"
+}
+
+// findImport searches for a package with the given symbols.
+// If no package is found, findImport returns "".
+// Declared as a variable rather than a function so goimports can be easily
+// extended by adding a file with an init function.
+var findImport = findImportStdlib
+
+type visitFn func(node ast.Node) ast.Visitor
+
+func (fn visitFn) Visit(node ast.Node) ast.Visitor {
+	return fn(node)
+}
+
+func findImportStdlib(shortPkg string, symbols map[string]bool) (importPath string, rename bool, err error) {
+	for symbol := range symbols {
+		path := stdlib[shortPkg+"."+symbol]
+		if path == "" {
+			return "", false, nil
+		}
+		if importPath != "" && importPath != path {
+			// Ambiguous. Symbols pointed to different things.
+			return "", false, nil
+		}
+		importPath = path
+	}
+	return importPath, false, nil
+}

playground/internal/imports/gen.go

@@ -0,0 +1,5 @@
+//go:generate go run mkapi.go -output=gopherjs.txt -gopath github.com/gopherjs/gopherjs/js
+//go:generate go run mkstdlib.go -output=zstdlib
+//go:generate rm gopherjs.txt
+
+package imports