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// Copyright (c) 2023 Teddy Wing
//
// This file is part of Gocapturedrefrace.
//
// Gocapturedrefrace is free software: you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// Gocapturedrefrace is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Gocapturedrefrace. If not, see
// <https://www.gnu.org/licenses/>.
// TODO: package documentation.
package gocapturedrefrace
import (
"go/ast"
"go/token"
"go/types"
"golang.org/x/tools/go/analysis"
)
var version = "0.0.1"
var Analyzer = &analysis.Analyzer{
Name: "gocapturedrefrace",
Doc: "reports captured references in goroutine closures",
Run: run,
}
func run(pass *analysis.Pass) (interface{}, error) {
// TODO: Since we're calling ast.Inspect a bunch of times, maybe it's worthwhile using passes/inspect now.
for _, file := range pass.Files {
ast.Inspect(
file,
func(node ast.Node) bool {
// Find `go` statements.
goStmt, ok := node.(*ast.GoStmt)
if !ok {
return true
}
// Look for a function literal after the `go` statement.
funcLit, ok := goStmt.Call.Fun.(*ast.FuncLit)
if !ok {
return true
}
// Inspect closure argument list.
for _, arg := range funcLit.Type.Params.List {
// Report reference arguments.
_, ok := arg.Type.(*ast.StarExpr)
if !ok {
continue
}
pass.Reportf(
arg.Pos(),
"reference %s in goroutine closure",
arg.Names[0],
)
}
checkClosure(pass, funcLit)
return true
},
)
}
return nil, nil
}
// checkClosure reports variables used in funcLit that are captured from an
// outer scope.
func checkClosure(pass *analysis.Pass, funcLit *ast.FuncLit) {
// Get the closure's scope.
funcScope := pass.TypesInfo.Scopes[funcLit.Type]
// Build a list of assignments local to funcLit. These will be ignored as
// shadowed variables.
localVarDeclarations := findLocalVarDeclarations(pass, funcLit)
ast.Inspect(
funcLit,
func(node ast.Node) bool {
ident, ok := node.(*ast.Ident)
if !ok {
return true
}
if ident.Obj == nil {
return true
}
// Ignore shadowed variables.
for _, declarationIdent := range localVarDeclarations {
if ident == declarationIdent {
return true
}
}
// Find out whether `ident` was defined in an outer scope.
scope, scopeObj := funcScope.LookupParent(ident.Name, ident.NamePos)
// Identifier is local to the closure.
if scope == nil && scopeObj == nil {
return true
}
// Ignore non-variable identifiers.
variable, ok := scopeObj.(*types.Var)
if !ok {
return true
}
// Ignore captured callable variables, like function arguments.
_, isVariableTypeSignature := variable.Type().(*types.Signature)
if isVariableTypeSignature {
return true
}
// Identifier was defined in a different scope.
if funcScope != scope {
pass.Reportf(
ident.Pos(),
"captured reference %s in goroutine closure",
ident,
)
}
return true
},
)
}
// findLocalVarDeclarations returns a list of all variable declarations in
// funcLit.
func findLocalVarDeclarations(
pass *analysis.Pass,
funcLit *ast.FuncLit,
) (declarations []*ast.Ident) {
declarations = []*ast.Ident{}
ast.Inspect(
funcLit,
func(node ast.Node) bool {
switch node := node.(type) {
case *ast.AssignStmt:
assignments := assignmentDefinitions(node)
declarations = append(declarations, assignments...)
case *ast.GenDecl:
decls := varDeclarations(node)
if decls != nil {
declarations = append(declarations, decls...)
}
}
return true
},
)
return declarations
}
// assignmentDefinitions returns the identifiers corresponding to variable
// assignments in assignStmt, or nil if assignStmt does not declare any
// variables.
func assignmentDefinitions(
assignStmt *ast.AssignStmt,
) (assignments []*ast.Ident) {
assignments = []*ast.Ident{}
if assignStmt.Tok != token.DEFINE {
return nil
}
for _, lhs := range assignStmt.Lhs {
ident, ok := lhs.(*ast.Ident)
if !ok {
continue
}
if ident == nil {
continue
}
assignments = append(assignments, ident)
}
return assignments
}
// varDeclarations returns the identifiers corresponding to variable
// declarations in decl, or nil if decl is not a variable declaration.
func varDeclarations(decl *ast.GenDecl) (declarations []*ast.Ident) {
if decl.Tok != token.VAR {
return nil
}
declarations = []*ast.Ident{}
for _, spec := range decl.Specs {
valueSpec, ok := spec.(*ast.ValueSpec)
if !ok {
return declarations
}
for _, ident := range valueSpec.Names {
declarations = append(declarations, ident)
}
}
return declarations
}
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