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// 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 simplifycompositelit defines an Analyzer that simplifies composite literals.
// https://github.com/golang/go/blob/master/src/cmd/gofmt/simplify.go
// https://golang.org/cmd/gofmt/#hdr-The_simplify_command
package simplifycompositelit
import (
"bytes"
"fmt"
"go/ast"
"go/printer"
"go/token"
"reflect"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/ast/inspector"
)
const Doc = `check for composite literal simplifications
An array, slice, or map composite literal of the form:
[]T{T{}, T{}}
will be simplified to:
[]T{{}, {}}
This is one of the simplifications that "gofmt -s" applies.`
var Analyzer = &analysis.Analyzer{
Name: "simplifycompositelit",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
}
func run(pass *analysis.Pass) (interface{}, error) {
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{(*ast.CompositeLit)(nil)}
inspect.Preorder(nodeFilter, func(n ast.Node) {
expr := n.(*ast.CompositeLit)
outer := expr
var keyType, eltType ast.Expr
switch typ := outer.Type.(type) {
case *ast.ArrayType:
eltType = typ.Elt
case *ast.MapType:
keyType = typ.Key
eltType = typ.Value
}
if eltType == nil {
return
}
var ktyp reflect.Value
if keyType != nil {
ktyp = reflect.ValueOf(keyType)
}
typ := reflect.ValueOf(eltType)
for _, x := range outer.Elts {
// look at value of indexed/named elements
if t, ok := x.(*ast.KeyValueExpr); ok {
if keyType != nil {
simplifyLiteral(pass, ktyp, keyType, t.Key)
}
x = t.Value
}
simplifyLiteral(pass, typ, eltType, x)
}
})
return nil, nil
}
func simplifyLiteral(pass *analysis.Pass, typ reflect.Value, astType, x ast.Expr) {
// if the element is a composite literal and its literal type
// matches the outer literal's element type exactly, the inner
// literal type may be omitted
if inner, ok := x.(*ast.CompositeLit); ok && match(typ, reflect.ValueOf(inner.Type)) {
var b bytes.Buffer
printer.Fprint(&b, pass.Fset, inner.Type)
createDiagnostic(pass, inner.Type.Pos(), inner.Type.End(), b.String())
}
// if the outer literal's element type is a pointer type *T
// and the element is & of a composite literal of type T,
// the inner &T may be omitted.
if ptr, ok := astType.(*ast.StarExpr); ok {
if addr, ok := x.(*ast.UnaryExpr); ok && addr.Op == token.AND {
if inner, ok := addr.X.(*ast.CompositeLit); ok {
if match(reflect.ValueOf(ptr.X), reflect.ValueOf(inner.Type)) {
var b bytes.Buffer
printer.Fprint(&b, pass.Fset, inner.Type)
// Account for the & by subtracting 1 from typ.Pos().
createDiagnostic(pass, inner.Type.Pos()-1, inner.Type.End(), "&"+b.String())
}
}
}
}
}
func createDiagnostic(pass *analysis.Pass, start, end token.Pos, typ string) {
pass.Report(analysis.Diagnostic{
Pos: start,
End: end,
Message: "redundant type from array, slice, or map composite literal",
SuggestedFixes: []analysis.SuggestedFix{{
Message: fmt.Sprintf("Remove '%s'", typ),
TextEdits: []analysis.TextEdit{{
Pos: start,
End: end,
NewText: []byte{},
}},
}},
})
}
// match reports whether pattern matches val,
// recording wildcard submatches in m.
// If m == nil, match checks whether pattern == val.
// from https://github.com/golang/go/blob/26154f31ad6c801d8bad5ef58df1e9263c6beec7/src/cmd/gofmt/rewrite.go#L160
func match(pattern, val reflect.Value) bool {
// Otherwise, pattern and val must match recursively.
if !pattern.IsValid() || !val.IsValid() {
return !pattern.IsValid() && !val.IsValid()
}
if pattern.Type() != val.Type() {
return false
}
// Special cases.
switch pattern.Type() {
case identType:
// For identifiers, only the names need to match
// (and none of the other *ast.Object information).
// This is a common case, handle it all here instead
// of recursing down any further via reflection.
p := pattern.Interface().(*ast.Ident)
v := val.Interface().(*ast.Ident)
return p == nil && v == nil || p != nil && v != nil && p.Name == v.Name
case objectPtrType, positionType:
// object pointers and token positions always match
return true
case callExprType:
// For calls, the Ellipsis fields (token.Position) must
// match since that is how f(x) and f(x...) are different.
// Check them here but fall through for the remaining fields.
p := pattern.Interface().(*ast.CallExpr)
v := val.Interface().(*ast.CallExpr)
if p.Ellipsis.IsValid() != v.Ellipsis.IsValid() {
return false
}
}
p := reflect.Indirect(pattern)
v := reflect.Indirect(val)
if !p.IsValid() || !v.IsValid() {
return !p.IsValid() && !v.IsValid()
}
switch p.Kind() {
case reflect.Slice:
if p.Len() != v.Len() {
return false
}
for i := 0; i < p.Len(); i++ {
if !match(p.Index(i), v.Index(i)) {
return false
}
}
return true
case reflect.Struct:
for i := 0; i < p.NumField(); i++ {
if !match(p.Field(i), v.Field(i)) {
return false
}
}
return true
case reflect.Interface:
return match(p.Elem(), v.Elem())
}
// Handle token integers, etc.
return p.Interface() == v.Interface()
}
// Values/types for special cases.
var (
identType = reflect.TypeOf((*ast.Ident)(nil))
objectPtrType = reflect.TypeOf((*ast.Object)(nil))
positionType = reflect.TypeOf(token.NoPos)
callExprType = reflect.TypeOf((*ast.CallExpr)(nil))
)
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