mirror of
https://github.com/golang/go
synced 2024-11-06 11:26:12 -07:00
1fd976651f
The code for `gofmt -s` directly modifies the AST, since the ASTs are not long-lived. Some of this code made it into our analysis implementations, causing very strange bugs to manifest. Added a regression test for this specific case. Fixes golang/go#38267 Change-Id: I235620adcbf2bbc7027c6d83ff2c7fe74729062e Reviewed-on: https://go-review.googlesource.com/c/tools/+/227299 Run-TryBot: Rebecca Stambler <rstambler@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Heschi Kreinick <heschi@google.com>
95 lines
2.7 KiB
Go
95 lines
2.7 KiB
Go
// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package simplifyslice defines an Analyzer that simplifies slice statements.
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// https://github.com/golang/go/blob/master/src/cmd/gofmt/simplify.go
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// https://golang.org/cmd/gofmt/#hdr-The_simplify_command
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package simplifyslice
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import (
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"bytes"
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"fmt"
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"go/ast"
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"go/printer"
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"golang.org/x/tools/go/analysis"
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"golang.org/x/tools/go/analysis/passes/inspect"
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"golang.org/x/tools/go/ast/inspector"
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)
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const Doc = `check for slice simplifications
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A slice expression of the form:
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s[a:len(s)]
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will be simplified to:
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s[a:]
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This is one of the simplifications that "gofmt -s" applies.`
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var Analyzer = &analysis.Analyzer{
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Name: "simplifyslice",
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Doc: Doc,
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Requires: []*analysis.Analyzer{inspect.Analyzer},
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Run: run,
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}
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// Note: We could also simplify slice expressions of the form s[0:b] to s[:b]
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// but we leave them as is since sometimes we want to be very explicit
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// about the lower bound.
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// An example where the 0 helps:
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// x, y, z := b[0:2], b[2:4], b[4:6]
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// An example where it does not:
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// x, y := b[:n], b[n:]
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func run(pass *analysis.Pass) (interface{}, error) {
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inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
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nodeFilter := []ast.Node{
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(*ast.SliceExpr)(nil),
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}
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inspect.Preorder(nodeFilter, func(n ast.Node) {
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expr := n.(*ast.SliceExpr)
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// - 3-index slices always require the 2nd and 3rd index
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if expr.Max != nil {
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return
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}
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s, ok := expr.X.(*ast.Ident)
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// the array/slice object is a single, resolved identifier
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if !ok || s.Obj == nil {
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return
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}
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call, ok := expr.High.(*ast.CallExpr)
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// the high expression is a function call with a single argument
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if !ok || len(call.Args) != 1 || call.Ellipsis.IsValid() {
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return
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}
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fun, ok := call.Fun.(*ast.Ident)
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// the function called is "len" and it is not locally defined; and
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// because we don't have dot imports, it must be the predefined len()
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if !ok || fun.Name != "len" || fun.Obj != nil {
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return
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}
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arg, ok := call.Args[0].(*ast.Ident)
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// the len argument is the array/slice object
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if !ok || arg.Obj != s.Obj {
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return
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}
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var b bytes.Buffer
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printer.Fprint(&b, pass.Fset, expr.High)
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pass.Report(analysis.Diagnostic{
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Pos: expr.High.Pos(),
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End: expr.High.End(),
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Message: fmt.Sprintf("unneeded: %s", b.String()),
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SuggestedFixes: []analysis.SuggestedFix{{
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Message: fmt.Sprintf("Remove '%s'", b.String()),
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TextEdits: []analysis.TextEdit{{
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Pos: expr.High.Pos(),
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End: expr.High.End(),
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NewText: []byte{},
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}},
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}},
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})
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})
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return nil, nil
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}
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