internal/lsp/analysis: add simplify-slice pass from "gofmt -s"
This is one of the simplifications that "gofmt -s" applies.
https://golang.org/cmd/gofmt/#hdr-The_simplify_command
A slice expression of the form:
s[a:len(s)]
will be simplified to:
s[a:]
Updates golang/go#37221
Change-Id: Ibd4dedaadc9b129d5d39524f0c1ccc8a95bf7e0d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/223659
Run-TryBot: Rohan Challa <rohan@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
diff --git a/gopls/doc/analyzers.md b/gopls/doc/analyzers.md
index 9ebbaec..5ddd525 100644
--- a/gopls/doc/analyzers.md
+++ b/gopls/doc/analyzers.md
@@ -364,6 +364,23 @@
Default value: `true`.
+### **simplifyslice**
+
+check for slice simplifications
+
+A slice expression of the form:
+```go
+s[a:len(s)]
+```
+will be simplified to:
+```go
+s[a:]
+```
+
+This is one of the simplifications that "gofmt -s" applies.
+
+Default value: `true`.
+
### **sortslice**
check the argument type of sort.Slice
diff --git a/internal/lsp/analysis/simplifyslice/simplifyslice.go b/internal/lsp/analysis/simplifyslice/simplifyslice.go
new file mode 100644
index 0000000..01a6bc3
--- /dev/null
+++ b/internal/lsp/analysis/simplifyslice/simplifyslice.go
@@ -0,0 +1,96 @@
+// 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 simplifyslice defines an Analyzer that simplifies slice statements.
+// https://github.com/golang/go/blob/master/src/cmd/gofmt/simplify.go
+// https://golang.org/cmd/gofmt/#hdr-The_simplify_command
+package simplifyslice
+
+import (
+ "bytes"
+ "fmt"
+ "go/ast"
+ "go/printer"
+
+ "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 slice simplifications
+
+A slice expression of the form:
+ s[a:len(s)]
+will be simplified to:
+ s[a:]
+
+This is one of the simplifications that "gofmt -s" applies.`
+
+var Analyzer = &analysis.Analyzer{
+ Name: "simplifyslice",
+ Doc: Doc,
+ Requires: []*analysis.Analyzer{inspect.Analyzer},
+ Run: run,
+}
+
+// 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) {
+ inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+ nodeFilter := []ast.Node{
+ (*ast.SliceExpr)(nil),
+ }
+ inspect.Preorder(nodeFilter, func(n ast.Node) {
+ 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
+ }
+ old := expr.High
+ var b bytes.Buffer
+ printer.Fprint(&b, pass.Fset, old)
+ pass.Report(analysis.Diagnostic{
+ Pos: old.Pos(),
+ End: old.End(),
+ Message: fmt.Sprintf("unneeded: %s", b.String()),
+ SuggestedFixes: []analysis.SuggestedFix{{
+ Message: fmt.Sprintf("Remove '%s'", b.String()),
+ TextEdits: []analysis.TextEdit{{
+ Pos: old.Pos(),
+ End: old.End(),
+ NewText: []byte{},
+ }},
+ }},
+ })
+ expr.High = old
+ })
+ return nil, nil
+}
diff --git a/internal/lsp/analysis/simplifyslice/simplifyslice_test.go b/internal/lsp/analysis/simplifyslice/simplifyslice_test.go
new file mode 100644
index 0000000..91db76a
--- /dev/null
+++ b/internal/lsp/analysis/simplifyslice/simplifyslice_test.go
@@ -0,0 +1,17 @@
+// 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 simplifyslice_test
+
+import (
+ "testing"
+
+ "golang.org/x/tools/go/analysis/analysistest"
+ "golang.org/x/tools/internal/lsp/analysis/simplifyslice"
+)
+
+func Test(t *testing.T) {
+ testdata := analysistest.TestData()
+ analysistest.RunWithSuggestedFixes(t, testdata, simplifyslice.Analyzer, "a")
+}
diff --git a/internal/lsp/analysis/simplifyslice/testdata/src/a/a.go b/internal/lsp/analysis/simplifyslice/testdata/src/a/a.go
new file mode 100644
index 0000000..2079210
--- /dev/null
+++ b/internal/lsp/analysis/simplifyslice/testdata/src/a/a.go
@@ -0,0 +1,70 @@
+// 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 testdata
+
+var (
+ a [10]byte
+ b [20]float32
+ s []int
+ t struct {
+ s []byte
+ }
+
+ _ = a[0:]
+ _ = a[1:10]
+ _ = a[2:len(a)] // want "unneeded: len\\(a\\)"
+ _ = a[3:(len(a))]
+ _ = a[len(a)-1 : len(a)] // want "unneeded: len\\(a\\)"
+ _ = a[2:len(a):len(a)]
+
+ _ = a[:]
+ _ = a[:10]
+ _ = a[:len(a)] // want "unneeded: len\\(a\\)"
+ _ = a[:(len(a))]
+ _ = a[:len(a)-1]
+ _ = a[:len(a):len(a)]
+
+ _ = s[0:]
+ _ = s[1:10]
+ _ = s[2:len(s)] // want "unneeded: len\\(s\\)"
+ _ = s[3:(len(s))]
+ _ = s[len(a) : len(s)-1]
+ _ = s[0:len(b)]
+ _ = s[2:len(s):len(s)]
+
+ _ = s[:]
+ _ = s[:10]
+ _ = s[:len(s)] // want "unneeded: len\\(s\\)"
+ _ = s[:(len(s))]
+ _ = s[:len(s)-1]
+ _ = s[:len(b)]
+ _ = s[:len(s):len(s)]
+
+ _ = t.s[0:]
+ _ = t.s[1:10]
+ _ = t.s[2:len(t.s)]
+ _ = t.s[3:(len(t.s))]
+ _ = t.s[len(a) : len(t.s)-1]
+ _ = t.s[0:len(b)]
+ _ = t.s[2:len(t.s):len(t.s)]
+
+ _ = t.s[:]
+ _ = t.s[:10]
+ _ = t.s[:len(t.s)]
+ _ = t.s[:(len(t.s))]
+ _ = t.s[:len(t.s)-1]
+ _ = t.s[:len(b)]
+ _ = t.s[:len(t.s):len(t.s)]
+)
+
+func _() {
+ s := s[0:len(s)] // want "unneeded: len\\(s\\)"
+ _ = s
+}
+
+func m() {
+ maps := []int{}
+ _ = maps[1:len(maps)] // want "unneeded: len\\(maps\\)"
+}
diff --git a/internal/lsp/analysis/simplifyslice/testdata/src/a/a.go.golden b/internal/lsp/analysis/simplifyslice/testdata/src/a/a.go.golden
new file mode 100644
index 0000000..45c7914
--- /dev/null
+++ b/internal/lsp/analysis/simplifyslice/testdata/src/a/a.go.golden
@@ -0,0 +1,70 @@
+// 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 testdata
+
+var (
+ a [10]byte
+ b [20]float32
+ s []int
+ t struct {
+ s []byte
+ }
+
+ _ = a[0:]
+ _ = a[1:10]
+ _ = a[2:] // want "unneeded: len\\(a\\)"
+ _ = a[3:(len(a))]
+ _ = a[len(a)-1:] // want "unneeded: len\\(a\\)"
+ _ = a[2:len(a):len(a)]
+
+ _ = a[:]
+ _ = a[:10]
+ _ = a[:] // want "unneeded: len\\(a\\)"
+ _ = a[:(len(a))]
+ _ = a[:len(a)-1]
+ _ = a[:len(a):len(a)]
+
+ _ = s[0:]
+ _ = s[1:10]
+ _ = s[2:] // want "unneeded: len\\(s\\)"
+ _ = s[3:(len(s))]
+ _ = s[len(a) : len(s)-1]
+ _ = s[0:len(b)]
+ _ = s[2:len(s):len(s)]
+
+ _ = s[:]
+ _ = s[:10]
+ _ = s[:] // want "unneeded: len\\(s\\)"
+ _ = s[:(len(s))]
+ _ = s[:len(s)-1]
+ _ = s[:len(b)]
+ _ = s[:len(s):len(s)]
+
+ _ = t.s[0:]
+ _ = t.s[1:10]
+ _ = t.s[2:len(t.s)]
+ _ = t.s[3:(len(t.s))]
+ _ = t.s[len(a) : len(t.s)-1]
+ _ = t.s[0:len(b)]
+ _ = t.s[2:len(t.s):len(t.s)]
+
+ _ = t.s[:]
+ _ = t.s[:10]
+ _ = t.s[:len(t.s)]
+ _ = t.s[:(len(t.s))]
+ _ = t.s[:len(t.s)-1]
+ _ = t.s[:len(b)]
+ _ = t.s[:len(t.s):len(t.s)]
+)
+
+func _() {
+ s := s[0:] // want "unneeded: len\\(s\\)"
+ _ = s
+}
+
+func m() {
+ maps := []int{}
+ _ = maps[1:] // want "unneeded: len\\(maps\\)"
+}
diff --git a/internal/lsp/source/options.go b/internal/lsp/source/options.go
index d967857..37fe965 100644
--- a/internal/lsp/source/options.go
+++ b/internal/lsp/source/options.go
@@ -38,6 +38,7 @@
"golang.org/x/tools/go/analysis/passes/unusedresult"
"golang.org/x/tools/internal/lsp/analysis/simplifycompositelit"
"golang.org/x/tools/internal/lsp/analysis/simplifyrange"
+ "golang.org/x/tools/internal/lsp/analysis/simplifyslice"
"golang.org/x/tools/internal/lsp/analysis/unusedparams"
"golang.org/x/tools/internal/lsp/debug/tag"
"golang.org/x/tools/internal/lsp/diff"
@@ -517,5 +518,6 @@
// gofmt -s suite:
simplifycompositelit.Analyzer.Name: {Analyzer: simplifycompositelit.Analyzer, Enabled: true, HighConfidence: true},
simplifyrange.Analyzer.Name: {Analyzer: simplifyrange.Analyzer, Enabled: true, HighConfidence: true},
+ simplifyslice.Analyzer.Name: {Analyzer: simplifyslice.Analyzer, Enabled: true, HighConfidence: true},
}
}
