1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
|
// Copyright 2023 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 simplifyslice
import (
"bytes"
_ "embed"
"fmt"
"go/ast"
"go/printer"
"go/token"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/ast/inspector"
"golang.org/x/tools/gopls/internal/util/astutil"
"golang.org/x/tools/internal/analysisinternal"
)
//go:embed doc.go
var doc string
var Analyzer = &analysis.Analyzer{
Name: "simplifyslice",
Doc: analysisinternal.MustExtractDoc(doc, "simplifyslice"),
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
URL: "https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/simplifyslice",
}
// Note: We could also simplify slice expressions of the form s[0:b] to s[:b]
// but we leave them as is since sometimes we want to be very explicit
// about the lower bound.
// An example where the 0 helps:
// x, y, z := b[0:2], b[2:4], b[4:6]
// An example where it does not:
// x, y := b[:n], b[n:]
func run(pass *analysis.Pass) (interface{}, error) {
// Gather information whether file is generated or not
generated := make(map[*token.File]bool)
for _, file := range pass.Files {
if astutil.IsGenerated(file) {
generated[pass.Fset.File(file.Pos())] = true
}
}
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{
(*ast.SliceExpr)(nil),
}
inspect.Preorder(nodeFilter, func(n ast.Node) {
if _, ok := generated[pass.Fset.File(n.Pos())]; ok {
return // skip checking if it's generated code
}
expr := n.(*ast.SliceExpr)
// - 3-index slices always require the 2nd and 3rd index
if expr.Max != nil {
return
}
s, ok := expr.X.(*ast.Ident)
// the array/slice object is a single, resolved identifier
if !ok || s.Obj == nil {
return
}
call, ok := expr.High.(*ast.CallExpr)
// the high expression is a function call with a single argument
if !ok || len(call.Args) != 1 || call.Ellipsis.IsValid() {
return
}
fun, ok := call.Fun.(*ast.Ident)
// the function called is "len" and it is not locally defined; and
// because we don't have dot imports, it must be the predefined len()
if !ok || fun.Name != "len" || fun.Obj != nil {
return
}
arg, ok := call.Args[0].(*ast.Ident)
// the len argument is the array/slice object
if !ok || arg.Obj != s.Obj {
return
}
var b bytes.Buffer
printer.Fprint(&b, pass.Fset, expr.High)
pass.Report(analysis.Diagnostic{
Pos: expr.High.Pos(),
End: expr.High.End(),
Message: fmt.Sprintf("unneeded: %s", b.String()),
SuggestedFixes: []analysis.SuggestedFix{{
Message: fmt.Sprintf("Remove '%s'", b.String()),
TextEdits: []analysis.TextEdit{{
Pos: expr.High.Pos(),
End: expr.High.End(),
NewText: []byte{},
}},
}},
})
})
return nil, nil
}
|
