internal/lsp/source/completion/postfix_snippets.go - tools - Git at Google

 // Copyright 2020 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 completion

 import (
 	"context"
 	"fmt"
 	"go/ast"
 	"go/token"
 	"go/types"
 	"log"
 	"reflect"
 	"strings"
 	"sync"
 	"text/template"

 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/imports"
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/snippet"
 	"golang.org/x/tools/internal/lsp/source"
 )

 // Postfix snippets are artificial methods that allow the user to
 // compose common operations in an "argument oriented" fashion. For
 // example, instead of "sort.Slice(someSlice, ...)" a user can expand
 // "someSlice.sort!".

 // postfixTmpl represents a postfix snippet completion candidate.
 type postfixTmpl struct {
 	// label is the completion candidate's label presented to the user.
 	label string

 	// details is passed along to the client as the candidate's details.
 	details string

 	// body is the template text. See postfixTmplArgs for details on the
 	// facilities available to the template.
 	body string

 	tmpl *template.Template
 }

 // postfixTmplArgs are the template execution arguments available to
 // the postfix snippet templates.
 type postfixTmplArgs struct {
 	// StmtOK is true if it is valid to replace the selector with a
 	// statement. For example:
 	//
 	//    func foo() {
 	//      bar.sort! // statement okay
 	//
 	//      someMethod(bar.sort!) // statement not okay
 	//    }
 	StmtOK bool

 	// X is the textual SelectorExpr.X. For example, when completing
 	// "foo.bar.print!", "X" is "foo.bar".
 	X string

 	// Obj is the types.Object of SelectorExpr.X, if any.
 	Obj types.Object

 	// Type is the type of "foo.bar" in "foo.bar.print!".
 	Type types.Type

 	scope          *types.Scope
 	snip           snippet.Builder
 	importIfNeeded func(pkgPath string, scope *types.Scope) (name string, edits []protocol.TextEdit, err error)
 	edits          []protocol.TextEdit
 	qf             types.Qualifier
 	varNames       map[string]bool
 }

 var postfixTmpls = []postfixTmpl{{
 	label:   "sort",
 	details: "sort.Slice()",
 	body: `{{if and (eq .Kind "slice") .StmtOK -}}
 {{.Import "sort"}}.Slice({{.X}}, func({{.VarName nil "i"}}, {{.VarName nil "j"}} int) bool {
 	{{.Cursor}}
 })
 {{- end}}`,
 }, {
 	label:   "last",
 	details: "s[len(s)-1]",
 	body: `{{if and (eq .Kind "slice") .Obj -}}
 {{.X}}[len({{.X}})-1]
 {{- end}}`,
 }, {
 	label:   "reverse",
 	details: "reverse slice",
 	body: `{{if and (eq .Kind "slice") .StmtOK -}}
 {{$i := .VarName nil "i"}}{{$j := .VarName nil "j" -}}
 for {{$i}}, {{$j}} := 0, len({{.X}})-1; {{$i}} < {{$j}}; {{$i}}, {{$j}} = {{$i}}+1, {{$j}}-1 {
 	{{.X}}[{{$i}}], {{.X}}[{{$j}}] = {{.X}}[{{$j}}], {{.X}}[{{$i}}]
 }
 {{end}}`,
 }, {
 	label:   "range",
 	details: "range over slice",
 	body: `{{if and (eq .Kind "slice") .StmtOK -}}
 for {{.VarName nil "i"}}, {{.VarName .ElemType "v"}} := range {{.X}} {
 	{{.Cursor}}
 }
 {{- end}}`,
 }, {
 	label:   "append",
 	details: "append and re-assign slice",
 	body: `{{if and (eq .Kind "slice") .StmtOK .Obj -}}
 {{.X}} = append({{.X}}, {{.Cursor}})
 {{- end}}`,
 }, {
 	label:   "append",
 	details: "append to slice",
 	body: `{{if and (eq .Kind "slice") (not .StmtOK) -}}
 append({{.X}}, {{.Cursor}})
 {{- end}}`,
 }, {
 	label:   "copy",
 	details: "duplicate slice",
 	body: `{{if and (eq .Kind "slice") .StmtOK .Obj -}}
 {{$v := (.VarName nil (printf "%sCopy" .X))}}{{$v}} := make([]{{.TypeName .ElemType}}, len({{.X}}))
 copy({{$v}}, {{.X}})
 {{end}}`,
 }, {
 	label:   "range",
 	details: "range over map",
 	body: `{{if and (eq .Kind "map") .StmtOK -}}
 for {{.VarName .KeyType "k"}}, {{.VarName .ElemType "v"}} := range {{.X}} {
 	{{.Cursor}}
 }
 {{- end}}`,
 }, {
 	label:   "clear",
 	details: "clear map contents",
 	body: `{{if and (eq .Kind "map") .StmtOK -}}
 {{$k := (.VarName .KeyType "k")}}for {{$k}} := range {{.X}} {
 	delete({{.X}}, {{$k}})
 }
 {{end}}`,
 }, {
 	label:   "keys",
 	details: "create slice of keys",
 	body: `{{if and (eq .Kind "map") .StmtOK -}}
 {{$keysVar := (.VarName nil "keys")}}{{$keysVar}} := make([]{{.TypeName .KeyType}}, 0, len({{.X}}))
 {{$k := (.VarName .KeyType "k")}}for {{$k}} := range {{.X}} {
 	{{$keysVar}} = append({{$keysVar}}, {{$k}})
 }
 {{end}}`,
 }, {
 	label:   "var",
 	details: "assign to variables",
 	body: `{{if and (eq .Kind "tuple") .StmtOK -}}
 {{$a := .}}{{range $i, $v := .Tuple}}{{if $i}}, {{end}}{{$a.VarName $v.Type $v.Name}}{{end}} := {{.X}}
 {{- end}}`,
 }, {
 	label:   "var",
 	details: "assign to variable",
 	body: `{{if and (ne .Kind "tuple") .StmtOK -}}
 {{.VarName .Type ""}} := {{.X}}
 {{- end}}`,
 }, {
 	label:   "print",
 	details: "print to stdout",
 	body: `{{if and (ne .Kind "tuple") .StmtOK -}}
 {{.Import "fmt"}}.Printf("{{.EscapeQuotes .X}}: %v\n", {{.X}})
 {{- end}}`,
 }, {
 	label:   "print",
 	details: "print to stdout",
 	body: `{{if and (eq .Kind "tuple") .StmtOK -}}
 {{.Import "fmt"}}.Println({{.X}})
 {{- end}}`,
 }, {
 	label:   "split",
 	details: "split string",
 	body: `{{if (eq (.TypeName .Type) "string") -}}
 {{.Import "strings"}}.Split({{.X}}, "{{.Cursor}}")
 {{- end}}`,
 }, {
 	label:   "join",
 	details: "join string slice",
 	body: `{{if and (eq .Kind "slice") (eq (.TypeName .ElemType) "string") -}}
 {{.Import "strings"}}.Join({{.X}}, "{{.Cursor}}")
 {{- end}}`,
 }}

 // Cursor indicates where the client's cursor should end up after the
 // snippet is done.
 func (a *postfixTmplArgs) Cursor() string {
 	a.snip.WriteFinalTabstop()
 	return ""
 }

 // Import makes sure the package corresponding to path is imported,
 // returning the identifier to use to refer to the package.
 func (a *postfixTmplArgs) Import(path string) (string, error) {
 	name, edits, err := a.importIfNeeded(path, a.scope)
 	if err != nil {
 		return "", fmt.Errorf("couldn't import %q: %w", path, err)
 	}
 	a.edits = append(a.edits, edits...)
 	return name, nil
 }

 func (a *postfixTmplArgs) EscapeQuotes(v string) string {
 	return strings.ReplaceAll(v, `"`, `\\"`)
 }

 // ElemType returns the Elem() type of xType, if applicable.
 func (a *postfixTmplArgs) ElemType() types.Type {
 	if e, _ := a.Type.(interface{ Elem() types.Type }); e != nil {
 		return e.Elem()
 	}
 	return nil
 }

 // Kind returns the underlying kind of type, e.g. "slice", "struct",
 // etc.
 func (a *postfixTmplArgs) Kind() string {
 	t := reflect.TypeOf(a.Type.Underlying())
 	return strings.ToLower(strings.TrimPrefix(t.String(), "*types."))
 }

 // KeyType returns the type of X's key. KeyType panics if X is not a
 // map.
 func (a *postfixTmplArgs) KeyType() types.Type {
 	return a.Type.Underlying().(*types.Map).Key()
 }

 // Tuple returns the tuple result vars if X is a call expression.
 func (a *postfixTmplArgs) Tuple() []*types.Var {
 	tuple, _ := a.Type.(*types.Tuple)
 	if tuple == nil {
 		return nil
 	}

 	typs := make([]*types.Var, 0, tuple.Len())
 	for i := 0; i < tuple.Len(); i++ {
 		typs = append(typs, tuple.At(i))
 	}
 	return typs
 }

 // TypeName returns the textual representation of type t.
 func (a *postfixTmplArgs) TypeName(t types.Type) (string, error) {
 	if t == nil || t == types.Typ[types.Invalid] {
 		return "", fmt.Errorf("invalid type: %v", t)
 	}
 	return types.TypeString(t, a.qf), nil
 }

 // VarName returns a suitable variable name for the type t. If t
 // implements the error interface, "err" is used. If t is not a named
 // type then nonNamedDefault is used. Otherwise a name is made by
 // abbreviating the type name. If the resultant name is already in
 // scope, an integer is appended to make a unique name.
 func (a *postfixTmplArgs) VarName(t types.Type, nonNamedDefault string) string {
 	if t == nil {
 		t = types.Typ[types.Invalid]
 	}

 	var name string
 	if types.Implements(t, errorIntf) {
 		name = "err"
 	} else if _, isNamed := source.Deref(t).(*types.Named); !isNamed {
 		name = nonNamedDefault
 	}

 	if name == "" {
 		name = types.TypeString(t, func(p *types.Package) string {
 			return ""
 		})
 		name = abbreviateTypeName(name)
 	}

 	if dot := strings.LastIndex(name, "."); dot > -1 {
 		name = name[dot+1:]
 	}

 	uniqueName := name
 	for i := 2; ; i++ {
 		if s, _ := a.scope.LookupParent(uniqueName, token.NoPos); s == nil && !a.varNames[uniqueName] {
 			break
 		}
 		uniqueName = fmt.Sprintf("%s%d", name, i)
 	}

 	a.varNames[uniqueName] = true

 	return uniqueName
 }

 func (c *completer) addPostfixSnippetCandidates(ctx context.Context, sel *ast.SelectorExpr) {
 	if !c.opts.postfix {
 		return
 	}

 	initPostfixRules()

 	if sel == nil || sel.Sel == nil {
 		return
 	}

 	selType := c.pkg.GetTypesInfo().TypeOf(sel.X)
 	if selType == nil {
 		return
 	}

 	// Skip empty tuples since there is no value to operate on.
 	if tuple, ok := selType.Underlying().(*types.Tuple); ok && tuple == nil {
 		return
 	}

 	tokFile := c.snapshot.FileSet().File(c.pos)

 	// Only replace sel with a statement if sel is already a statement.
 	var stmtOK bool
 	for i, n := range c.path {
 		if n == sel && i < len(c.path)-1 {
 			switch p := c.path[i+1].(type) {
 			case *ast.ExprStmt:
 				stmtOK = true
 			case *ast.AssignStmt:
 				// In cases like:
 				//
 				//   foo.<>
 				//   bar = 123
 				//
 				// detect that "foo." makes up the entire statement since the
 				// apparent selector spans lines.
 				stmtOK = tokFile.Line(c.pos) < tokFile.Line(p.TokPos)
 			}
 			break
 		}
 	}

 	scope := c.pkg.GetTypes().Scope().Innermost(c.pos)
 	if scope == nil {
 		return
 	}

 	// afterDot is the position after selector dot, e.g. "|" in
 	// "foo.|print".
 	afterDot := sel.Sel.Pos()

 	// We must detect dangling selectors such as:
 	//
 	//    foo.<>
 	//    bar
 	//
 	// and adjust afterDot so that we don't mistakenly delete the
 	// newline thinking "bar" is part of our selector.
 	if startLine := tokFile.Line(sel.Pos()); startLine != tokFile.Line(afterDot) {
 		if tokFile.Line(c.pos) != startLine {
 			return
 		}
 		afterDot = c.pos
 	}

 	for _, rule := range postfixTmpls {
 		// When completing foo.print<>, "print" is naturally overwritten,
 		// but we need to also remove "foo." so the snippet has a clean
 		// slate.
 		edits, err := c.editText(sel.Pos(), afterDot, "")
 		if err != nil {
 			event.Error(ctx, "error calculating postfix edits", err)
 			return
 		}

 		tmplArgs := postfixTmplArgs{
 			X:              source.FormatNode(c.snapshot.FileSet(), sel.X),
 			StmtOK:         stmtOK,
 			Obj:            exprObj(c.pkg.GetTypesInfo(), sel.X),
 			Type:           selType,
 			qf:             c.qf,
 			importIfNeeded: c.importIfNeeded,
 			scope:          scope,
 			varNames:       make(map[string]bool),
 		}

 		// Feed the template straight into the snippet builder. This
 		// allows templates to build snippets as they are executed.
 		err = rule.tmpl.Execute(&tmplArgs.snip, &tmplArgs)
 		if err != nil {
 			event.Error(ctx, "error executing postfix template", err)
 			continue
 		}

 		if strings.TrimSpace(tmplArgs.snip.String()) == "" {
 			continue
 		}

 		score := c.matcher.Score(rule.label)
 		if score <= 0 {
 			continue
 		}

 		c.items = append(c.items, CompletionItem{
 			Label:               rule.label + "!",
 			Detail:              rule.details,
 			Score:               float64(score) * 0.01,
 			Kind:                protocol.SnippetCompletion,
 			snippet:             &tmplArgs.snip,
 			AdditionalTextEdits: append(edits, tmplArgs.edits...),
 		})
 	}
 }

 var postfixRulesOnce sync.Once

 func initPostfixRules() {
 	postfixRulesOnce.Do(func() {
 		var idx int
 		for _, rule := range postfixTmpls {
 			var err error
 			rule.tmpl, err = template.New("postfix_snippet").Parse(rule.body)
 			if err != nil {
 				log.Panicf("error parsing postfix snippet template: %v", err)
 			}
 			postfixTmpls[idx] = rule
 			idx++
 		}
 		postfixTmpls = postfixTmpls[:idx]
 	})
 }

 // importIfNeeded returns the package identifier and any necessary
 // edits to import package pkgPath.
 func (c *completer) importIfNeeded(pkgPath string, scope *types.Scope) (string, []protocol.TextEdit, error) {
 	defaultName := imports.ImportPathToAssumedName(pkgPath)

 	// Check if file already imports pkgPath.
 	for _, s := range c.file.Imports {
 		if source.ImportPath(s) == pkgPath {
 			if s.Name == nil {
 				return defaultName, nil, nil
 			}
 			if s.Name.Name != "_" {
 				return s.Name.Name, nil, nil
 			}
 		}
 	}

 	// Give up if the package's name is already in use by another object.
 	if _, obj := scope.LookupParent(defaultName, token.NoPos); obj != nil {
 		return "", nil, fmt.Errorf("import name %q of %q already in use", defaultName, pkgPath)
 	}

 	edits, err := c.importEdits(&importInfo{
 		importPath: pkgPath,
 	})
 	if err != nil {
 		return "", nil, err
 	}

 	return defaultName, edits, nil
 }
	// Copyright 2020 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 completion

	import (
	"context"
	"fmt"
	"go/ast"
	"go/token"
	"go/types"
	"log"
	"reflect"
	"strings"
	"sync"
	"text/template"

	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/imports"
	"golang.org/x/tools/internal/lsp/protocol"
	"golang.org/x/tools/internal/lsp/snippet"
	"golang.org/x/tools/internal/lsp/source"
	)

	// Postfix snippets are artificial methods that allow the user to
	// compose common operations in an "argument oriented" fashion. For
	// example, instead of "sort.Slice(someSlice, ...)" a user can expand
	// "someSlice.sort!".

	// postfixTmpl represents a postfix snippet completion candidate.
	type postfixTmpl struct {
	// label is the completion candidate's label presented to the user.
	label string

	// details is passed along to the client as the candidate's details.
	details string

	// body is the template text. See postfixTmplArgs for details on the
	// facilities available to the template.
	body string

	tmpl *template.Template
	}

	// postfixTmplArgs are the template execution arguments available to
	// the postfix snippet templates.
	type postfixTmplArgs struct {
	// StmtOK is true if it is valid to replace the selector with a
	// statement. For example:
	//
	// func foo() {
	// bar.sort! // statement okay
	//
	// someMethod(bar.sort!) // statement not okay
	// }
	StmtOK bool

	// X is the textual SelectorExpr.X. For example, when completing
	// "foo.bar.print!", "X" is "foo.bar".
	X string

	// Obj is the types.Object of SelectorExpr.X, if any.
	Obj types.Object

	// Type is the type of "foo.bar" in "foo.bar.print!".
	Type types.Type

	scope *types.Scope
	snip snippet.Builder
	importIfNeeded func(pkgPath string, scope *types.Scope) (name string, edits []protocol.TextEdit, err error)
	edits []protocol.TextEdit
	qf types.Qualifier
	varNames map[string]bool
	}

	var postfixTmpls = []postfixTmpl{{
	label: "sort",
	details: "sort.Slice()",
	body: `{{if and (eq .Kind "slice") .StmtOK -}}
	{{.Import "sort"}}.Slice({{.X}}, func({{.VarName nil "i"}}, {{.VarName nil "j"}} int) bool {
	{{.Cursor}}
	})
	{{- end}}`,
	}, {
	label: "last",
	details: "s[len(s)-1]",
	body: `{{if and (eq .Kind "slice") .Obj -}}
	{{.X}}[len({{.X}})-1]
	{{- end}}`,
	}, {
	label: "reverse",
	details: "reverse slice",
	body: `{{if and (eq .Kind "slice") .StmtOK -}}
	{{$i := .VarName nil "i"}}{{$j := .VarName nil "j" -}}
	for {{$i}}, {{$j}} := 0, len({{.X}})-1; {{$i}} < {{$j}}; {{$i}}, {{$j}} = {{$i}}+1, {{$j}}-1 {
	{{.X}}[{{$i}}], {{.X}}[{{$j}}] = {{.X}}[{{$j}}], {{.X}}[{{$i}}]
	}
	{{end}}`,
	}, {
	label: "range",
	details: "range over slice",
	body: `{{if and (eq .Kind "slice") .StmtOK -}}
	for {{.VarName nil "i"}}, {{.VarName .ElemType "v"}} := range {{.X}} {
	{{.Cursor}}
	}
	{{- end}}`,
	}, {
	label: "append",
	details: "append and re-assign slice",
	body: `{{if and (eq .Kind "slice") .StmtOK .Obj -}}
	{{.X}} = append({{.X}}, {{.Cursor}})
	{{- end}}`,
	}, {
	label: "append",
	details: "append to slice",
	body: `{{if and (eq .Kind "slice") (not .StmtOK) -}}
	append({{.X}}, {{.Cursor}})
	{{- end}}`,
	}, {
	label: "copy",
	details: "duplicate slice",
	body: `{{if and (eq .Kind "slice") .StmtOK .Obj -}}
	{{$v := (.VarName nil (printf "%sCopy" .X))}}{{$v}} := make([]{{.TypeName .ElemType}}, len({{.X}}))
	copy({{$v}}, {{.X}})
	{{end}}`,
	}, {
	label: "range",
	details: "range over map",
	body: `{{if and (eq .Kind "map") .StmtOK -}}
	for {{.VarName .KeyType "k"}}, {{.VarName .ElemType "v"}} := range {{.X}} {
	{{.Cursor}}
	}
	{{- end}}`,
	}, {
	label: "clear",
	details: "clear map contents",
	body: `{{if and (eq .Kind "map") .StmtOK -}}
	{{$k := (.VarName .KeyType "k")}}for {{$k}} := range {{.X}} {
	delete({{.X}}, {{$k}})
	}
	{{end}}`,
	}, {
	label: "keys",
	details: "create slice of keys",
	body: `{{if and (eq .Kind "map") .StmtOK -}}
	{{$keysVar := (.VarName nil "keys")}}{{$keysVar}} := make([]{{.TypeName .KeyType}}, 0, len({{.X}}))
	{{$k := (.VarName .KeyType "k")}}for {{$k}} := range {{.X}} {
	{{$keysVar}} = append({{$keysVar}}, {{$k}})
	}
	{{end}}`,
	}, {
	label: "var",
	details: "assign to variables",
	body: `{{if and (eq .Kind "tuple") .StmtOK -}}
	{{$a := .}}{{range $i, $v := .Tuple}}{{if $i}}, {{end}}{{$a.VarName $v.Type $v.Name}}{{end}} := {{.X}}
	{{- end}}`,
	}, {
	label: "var",
	details: "assign to variable",
	body: `{{if and (ne .Kind "tuple") .StmtOK -}}
	{{.VarName .Type ""}} := {{.X}}
	{{- end}}`,
	}, {
	label: "print",
	details: "print to stdout",
	body: `{{if and (ne .Kind "tuple") .StmtOK -}}
	{{.Import "fmt"}}.Printf("{{.EscapeQuotes .X}}: %v\n", {{.X}})
	{{- end}}`,
	}, {
	label: "print",
	details: "print to stdout",
	body: `{{if and (eq .Kind "tuple") .StmtOK -}}
	{{.Import "fmt"}}.Println({{.X}})
	{{- end}}`,
	}, {
	label: "split",
	details: "split string",
	body: `{{if (eq (.TypeName .Type) "string") -}}
	{{.Import "strings"}}.Split({{.X}}, "{{.Cursor}}")
	{{- end}}`,
	}, {
	label: "join",
	details: "join string slice",
	body: `{{if and (eq .Kind "slice") (eq (.TypeName .ElemType) "string") -}}
	{{.Import "strings"}}.Join({{.X}}, "{{.Cursor}}")
	{{- end}}`,
	}}

	// Cursor indicates where the client's cursor should end up after the
	// snippet is done.
	func (a *postfixTmplArgs) Cursor() string {
	a.snip.WriteFinalTabstop()
	return ""
	}

	// Import makes sure the package corresponding to path is imported,
	// returning the identifier to use to refer to the package.
	func (a *postfixTmplArgs) Import(path string) (string, error) {
	name, edits, err := a.importIfNeeded(path, a.scope)
	if err != nil {
	return "", fmt.Errorf("couldn't import %q: %w", path, err)
	}
	a.edits = append(a.edits, edits...)
	return name, nil
	}

	func (a *postfixTmplArgs) EscapeQuotes(v string) string {
	return strings.ReplaceAll(v, `"`, `\\"`)
	}

	// ElemType returns the Elem() type of xType, if applicable.
	func (a *postfixTmplArgs) ElemType() types.Type {
	if e, _ := a.Type.(interface{ Elem() types.Type }); e != nil {
	return e.Elem()
	}
	return nil
	}

	// Kind returns the underlying kind of type, e.g. "slice", "struct",
	// etc.
	func (a *postfixTmplArgs) Kind() string {
	t := reflect.TypeOf(a.Type.Underlying())
	return strings.ToLower(strings.TrimPrefix(t.String(), "*types."))
	}

	// KeyType returns the type of X's key. KeyType panics if X is not a
	// map.
	func (a *postfixTmplArgs) KeyType() types.Type {
	return a.Type.Underlying().(*types.Map).Key()
	}

	// Tuple returns the tuple result vars if X is a call expression.
	func (a postfixTmplArgs) Tuple() []types.Var {
	tuple, _ := a.Type.(*types.Tuple)
	if tuple == nil {
	return nil
	}

	typs := make([]*types.Var, 0, tuple.Len())
	for i := 0; i < tuple.Len(); i++ {
	typs = append(typs, tuple.At(i))
	}
	return typs
	}

	// TypeName returns the textual representation of type t.
	func (a *postfixTmplArgs) TypeName(t types.Type) (string, error) {
	if t == nil \|\| t == types.Typ[types.Invalid] {
	return "", fmt.Errorf("invalid type: %v", t)
	}
	return types.TypeString(t, a.qf), nil
	}

	// VarName returns a suitable variable name for the type t. If t
	// implements the error interface, "err" is used. If t is not a named
	// type then nonNamedDefault is used. Otherwise a name is made by
	// abbreviating the type name. If the resultant name is already in
	// scope, an integer is appended to make a unique name.
	func (a *postfixTmplArgs) VarName(t types.Type, nonNamedDefault string) string {
	if t == nil {
	t = types.Typ[types.Invalid]
	}

	var name string
	if types.Implements(t, errorIntf) {
	name = "err"
	} else if _, isNamed := source.Deref(t).(*types.Named); !isNamed {
	name = nonNamedDefault
	}

	if name == "" {
	name = types.TypeString(t, func(p *types.Package) string {
	return ""
	})
	name = abbreviateTypeName(name)
	}

	if dot := strings.LastIndex(name, "."); dot > -1 {
	name = name[dot+1:]
	}

	uniqueName := name
	for i := 2; ; i++ {
	if s, _ := a.scope.LookupParent(uniqueName, token.NoPos); s == nil && !a.varNames[uniqueName] {
	break
	}
	uniqueName = fmt.Sprintf("%s%d", name, i)
	}

	a.varNames[uniqueName] = true

	return uniqueName
	}

	func (c completer) addPostfixSnippetCandidates(ctx context.Context, sel ast.SelectorExpr) {
	if !c.opts.postfix {
	return
	}

	initPostfixRules()

	if sel == nil \|\| sel.Sel == nil {
	return
	}

	selType := c.pkg.GetTypesInfo().TypeOf(sel.X)
	if selType == nil {
	return
	}

	// Skip empty tuples since there is no value to operate on.
	if tuple, ok := selType.Underlying().(*types.Tuple); ok && tuple == nil {
	return
	}

	tokFile := c.snapshot.FileSet().File(c.pos)

	// Only replace sel with a statement if sel is already a statement.
	var stmtOK bool
	for i, n := range c.path {
	if n == sel && i < len(c.path)-1 {
	switch p := c.path[i+1].(type) {
	case *ast.ExprStmt:
	stmtOK = true
	case *ast.AssignStmt:
	// In cases like:
	//
	// foo.<>
	// bar = 123
	//
	// detect that "foo." makes up the entire statement since the
	// apparent selector spans lines.
	stmtOK = tokFile.Line(c.pos) < tokFile.Line(p.TokPos)
	}
	break
	}
	}

	scope := c.pkg.GetTypes().Scope().Innermost(c.pos)
	if scope == nil {
	return
	}

	// afterDot is the position after selector dot, e.g. "\|" in
	// "foo.\|print".
	afterDot := sel.Sel.Pos()

	// We must detect dangling selectors such as:
	//
	// foo.<>
	// bar
	//
	// and adjust afterDot so that we don't mistakenly delete the
	// newline thinking "bar" is part of our selector.
	if startLine := tokFile.Line(sel.Pos()); startLine != tokFile.Line(afterDot) {
	if tokFile.Line(c.pos) != startLine {
	return
	}
	afterDot = c.pos
	}

	for _, rule := range postfixTmpls {
	// When completing foo.print<>, "print" is naturally overwritten,
	// but we need to also remove "foo." so the snippet has a clean
	// slate.
	edits, err := c.editText(sel.Pos(), afterDot, "")
	if err != nil {
	event.Error(ctx, "error calculating postfix edits", err)
	return
	}

	tmplArgs := postfixTmplArgs{
	X: source.FormatNode(c.snapshot.FileSet(), sel.X),
	StmtOK: stmtOK,
	Obj: exprObj(c.pkg.GetTypesInfo(), sel.X),
	Type: selType,
	qf: c.qf,
	importIfNeeded: c.importIfNeeded,
	scope: scope,
	varNames: make(map[string]bool),
	}

	// Feed the template straight into the snippet builder. This
	// allows templates to build snippets as they are executed.
	err = rule.tmpl.Execute(&tmplArgs.snip, &tmplArgs)
	if err != nil {
	event.Error(ctx, "error executing postfix template", err)
	continue
	}

	if strings.TrimSpace(tmplArgs.snip.String()) == "" {
	continue
	}

	score := c.matcher.Score(rule.label)
	if score <= 0 {
	continue
	}

	c.items = append(c.items, CompletionItem{
	Label: rule.label + "!",
	Detail: rule.details,
	Score: float64(score) * 0.01,
	Kind: protocol.SnippetCompletion,
	snippet: &tmplArgs.snip,
	AdditionalTextEdits: append(edits, tmplArgs.edits...),
	})
	}
	}

	var postfixRulesOnce sync.Once

	func initPostfixRules() {
	postfixRulesOnce.Do(func() {
	var idx int
	for _, rule := range postfixTmpls {
	var err error
	rule.tmpl, err = template.New("postfix_snippet").Parse(rule.body)
	if err != nil {
	log.Panicf("error parsing postfix snippet template: %v", err)
	}
	postfixTmpls[idx] = rule
	idx++
	}
	postfixTmpls = postfixTmpls[:idx]
	})
	}

	// importIfNeeded returns the package identifier and any necessary
	// edits to import package pkgPath.
	func (c completer) importIfNeeded(pkgPath string, scope types.Scope) (string, []protocol.TextEdit, error) {
	defaultName := imports.ImportPathToAssumedName(pkgPath)

	// Check if file already imports pkgPath.
	for _, s := range c.file.Imports {
	if source.ImportPath(s) == pkgPath {
	if s.Name == nil {
	return defaultName, nil, nil
	}
	if s.Name.Name != "_" {
	return s.Name.Name, nil, nil
	}
	}
	}

	// Give up if the package's name is already in use by another object.
	if _, obj := scope.LookupParent(defaultName, token.NoPos); obj != nil {
	return "", nil, fmt.Errorf("import name %q of %q already in use", defaultName, pkgPath)
	}

	edits, err := c.importEdits(&importInfo{
	importPath: pkgPath,
	})
	if err != nil {
	return "", nil, err
	}

	return defaultName, edits, nil
	}