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// Copyright 2021 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.
//go:build go1.18
// +build go1.18
package infertypeargs
import (
"go/ast"
"go/token"
"go/types"
"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/internal/typeparams"
)
func run(pass *analysis.Pass) (interface{}, error) {
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{
(*ast.CallExpr)(nil),
}
inspect.Preorder(nodeFilter, func(node ast.Node) {
call := node.(*ast.CallExpr)
x, lbrack, indices, rbrack := typeparams.UnpackIndexExpr(call.Fun)
ident := calledIdent(x)
if ident == nil || len(indices) == 0 {
return // no explicit args, nothing to do
}
// Confirm that instantiation actually occurred at this ident.
idata, ok := typeparams.GetInstances(pass.TypesInfo)[ident]
if !ok {
return // something went wrong, but fail open
}
instance := idata.Type
// Start removing argument expressions from the right, and check if we can
// still infer the call expression.
required := len(indices) // number of type expressions that are required
for i := len(indices) - 1; i >= 0; i-- {
var fun ast.Expr
if i == 0 {
// No longer an index expression: just use the parameterized operand.
fun = x
} else {
fun = typeparams.PackIndexExpr(x, lbrack, indices[:i], indices[i-1].End())
}
newCall := &ast.CallExpr{
Fun: fun,
Lparen: call.Lparen,
Args: call.Args,
Ellipsis: call.Ellipsis,
Rparen: call.Rparen,
}
info := new(types.Info)
typeparams.InitInstanceInfo(info)
if err := types.CheckExpr(pass.Fset, pass.Pkg, call.Pos(), newCall, info); err != nil {
// Most likely inference failed.
break
}
newIData := typeparams.GetInstances(info)[ident]
newInstance := newIData.Type
if !types.Identical(instance, newInstance) {
// The inferred result type does not match the original result type, so
// this simplification is not valid.
break
}
required = i
}
if required < len(indices) {
var start, end token.Pos
var edit analysis.TextEdit
if required == 0 {
start, end = lbrack, rbrack+1 // erase the entire index
edit = analysis.TextEdit{Pos: start, End: end}
} else {
start = indices[required].Pos()
end = rbrack
// erase from end of last arg to include last comma & white-spaces
edit = analysis.TextEdit{Pos: indices[required-1].End(), End: end}
}
pass.Report(analysis.Diagnostic{
Pos: start,
End: end,
Message: "unnecessary type arguments",
SuggestedFixes: []analysis.SuggestedFix{{
Message: "simplify type arguments",
TextEdits: []analysis.TextEdit{edit},
}},
})
}
})
return nil, nil
}
func calledIdent(x ast.Expr) *ast.Ident {
switch x := x.(type) {
case *ast.Ident:
return x
case *ast.SelectorExpr:
return x.Sel
}
return nil
}
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