+++ /dev/null
-// 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 ifaceassert defines an Analyzer that flags
-// impossible interface-interface type assertions.
-package ifaceassert
-
-import (
- "go/ast"
- "go/types"
-
- "golang.org/x/tools/go/analysis"
- "golang.org/x/tools/go/analysis/passes/inspect"
- "golang.org/x/tools/go/ast/inspector"
-)
-
-const Doc = `detect impossible interface-to-interface type assertions
-
-This checker flags type assertions v.(T) and corresponding type-switch cases
-in which the static type V of v is an interface that cannot possibly implement
-the target interface T. This occurs when V and T contain methods with the same
-name but different signatures. Example:
-
- var v interface {
- Read()
- }
- _ = v.(io.Reader)
-
-The Read method in v has a different signature than the Read method in
-io.Reader, so this assertion cannot succeed.
-`
-
-var Analyzer = &analysis.Analyzer{
- Name: "ifaceassert",
- Doc: Doc,
- Requires: []*analysis.Analyzer{inspect.Analyzer},
- Run: run,
-}
-
-// assertableTo checks whether interface v can be asserted into t. It returns
-// nil on success, or the first conflicting method on failure.
-func assertableTo(v, t types.Type) *types.Func {
- // ensure that v and t are interfaces
- V, _ := v.Underlying().(*types.Interface)
- T, _ := t.Underlying().(*types.Interface)
- if V == nil || T == nil {
- return nil
- }
- if f, wrongType := types.MissingMethod(V, T, false); wrongType {
- return f
- }
- return nil
-}
-
-func run(pass *analysis.Pass) (interface{}, error) {
- inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
- nodeFilter := []ast.Node{
- (*ast.TypeAssertExpr)(nil),
- (*ast.TypeSwitchStmt)(nil),
- }
- inspect.Preorder(nodeFilter, func(n ast.Node) {
- var (
- assert *ast.TypeAssertExpr // v.(T) expression
- targets []ast.Expr // interfaces T in v.(T)
- )
- switch n := n.(type) {
- case *ast.TypeAssertExpr:
- // take care of v.(type) in *ast.TypeSwitchStmt
- if n.Type == nil {
- return
- }
- assert = n
- targets = append(targets, n.Type)
- case *ast.TypeSwitchStmt:
- // retrieve type assertion from type switch's 'assign' field
- switch t := n.Assign.(type) {
- case *ast.ExprStmt:
- assert = t.X.(*ast.TypeAssertExpr)
- case *ast.AssignStmt:
- assert = t.Rhs[0].(*ast.TypeAssertExpr)
- }
- // gather target types from case clauses
- for _, c := range n.Body.List {
- targets = append(targets, c.(*ast.CaseClause).List...)
- }
- }
- V := pass.TypesInfo.TypeOf(assert.X)
- for _, target := range targets {
- T := pass.TypesInfo.TypeOf(target)
- if f := assertableTo(V, T); f != nil {
- pass.Reportf(
- target.Pos(),
- "impossible type assertion: no type can implement both %v and %v (conflicting types for %v method)",
- V, T, f.Name(),
- )
- }
- }
- })
- return nil, nil
-}