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typecheck.go
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// Copyright 2011 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 main
import (
"fmt"
"go/ast"
"go/parser"
"go/token"
exec "internal/execabs"
"os"
"path/filepath"
"reflect"
"runtime"
"strings"
)
// Partial type checker.
//
// The fact that it is partial is very important: the input is
// an AST and a description of some type information to
// assume about one or more packages, but not all the
// packages that the program imports. The checker is
// expected to do as much as it can with what it has been
// given. There is not enough information supplied to do
// a full type check, but the type checker is expected to
// apply information that can be derived from variable
// declarations, function and method returns, and type switches
// as far as it can, so that the caller can still tell the types
// of expression relevant to a particular fix.
//
// TODO(rsc,gri): Replace with go/typechecker.
// Doing that could be an interesting test case for go/typechecker:
// the constraints about working with partial information will
// likely exercise it in interesting ways. The ideal interface would
// be to pass typecheck a map from importpath to package API text
// (Go source code), but for now we use data structures (TypeConfig, Type).
//
// The strings mostly use gofmt form.
//
// A Field or FieldList has as its type a comma-separated list
// of the types of the fields. For example, the field list
// x, y, z int
// has type "int, int, int".
// The prefix "type " is the type of a type.
// For example, given
// var x int
// type T int
// x's type is "int" but T's type is "type int".
// mkType inserts the "type " prefix.
// getType removes it.
// isType tests for it.
func mkType(t string) string {
return "type " + t
}
func getType(t string) string {
if !isType(t) {
return ""
}
return t[len("type "):]
}
func isType(t string) bool {
return strings.HasPrefix(t, "type ")
}
// TypeConfig describes the universe of relevant types.
// For ease of creation, the types are all referred to by string
// name (e.g., "reflect.Value"). TypeByName is the only place
// where the strings are resolved.
type TypeConfig struct {
Type map[string]*Type
Var map[string]string
Func map[string]string
// External maps from a name to its type.
// It provides additional typings not present in the Go source itself.
// For now, the only additional typings are those generated by cgo.
External map[string]string
}
// typeof returns the type of the given name, which may be of
// the form "x" or "p.X".
func (cfg *TypeConfig) typeof(name string) string {
if cfg.Var != nil {
if t := cfg.Var[name]; t != "" {
return t
}
}
if cfg.Func != nil {
if t := cfg.Func[name]; t != "" {
return "func()" + t
}
}
return ""
}
// Type describes the Fields and Methods of a type.
// If the field or method cannot be found there, it is next
// looked for in the Embed list.
type Type struct {
Field map[string]string // map field name to type
Method map[string]string // map method name to comma-separated return types (should start with "func ")
Embed []string // list of types this type embeds (for extra methods)
Def string // definition of named type
}
// dot returns the type of "typ.name", making its decision
// using the type information in cfg.
func (typ *Type) dot(cfg *TypeConfig, name string) string {
if typ.Field != nil {
if t := typ.Field[name]; t != "" {
return t
}
}
if typ.Method != nil {
if t := typ.Method[name]; t != "" {
return t
}
}
for _, e := range typ.Embed {
etyp := cfg.Type[e]
if etyp != nil {
if t := etyp.dot(cfg, name); t != "" {
return t
}
}
}
return ""
}
// typecheck type checks the AST f assuming the information in cfg.
// It returns two maps with type information:
// typeof maps AST nodes to type information in gofmt string form.
// assign maps type strings to lists of expressions that were assigned
// to values of another type that were assigned to that type.
func typecheck(cfg *TypeConfig, f *ast.File) (typeof map[any]string, assign map[string][]any) {
typeof = make(map[any]string)
assign = make(map[string][]any)
cfg1 := &TypeConfig{}
*cfg1 = *cfg // make copy so we can add locally
copied := false
// If we import "C", add types of cgo objects.
cfg.External = map[string]string{}
cfg1.External = cfg.External
if imports(f, "C") {
// Run cgo on gofmtFile(f)
// Parse, extract decls from _cgo_gotypes.go
// Map _Ctype_* types to C.* types.
err := func() error {
txt, err := gofmtFile(f)
if err != nil {
return err
}
dir, err := os.MkdirTemp(os.TempDir(), "fix_cgo_typecheck")
if err != nil {
return err
}
defer os.RemoveAll(dir)
err = os.WriteFile(filepath.Join(dir, "in.go"), txt, 0600)
if err != nil {
return err
}
cmd := exec.Command(filepath.Join(runtime.GOROOT(), "bin", "go"), "tool", "cgo", "-objdir", dir, "-srcdir", dir, "in.go")
err = cmd.Run()
if err != nil {
return err
}
out, err := os.ReadFile(filepath.Join(dir, "_cgo_gotypes.go"))
if err != nil {
return err
}
cgo, err := parser.ParseFile(token.NewFileSet(), "cgo.go", out, 0)
if err != nil {
return err
}
for _, decl := range cgo.Decls {
fn, ok := decl.(*ast.FuncDecl)
if !ok {
continue
}
if strings.HasPrefix(fn.Name.Name, "_Cfunc_") {
var params, results []string
for _, p := range fn.Type.Params.List {
t := gofmt(p.Type)
t = strings.ReplaceAll(t, "_Ctype_", "C.")
params = append(params, t)
}
for _, r := range fn.Type.Results.List {
t := gofmt(r.Type)
t = strings.ReplaceAll(t, "_Ctype_", "C.")
results = append(results, t)
}
cfg.External["C."+fn.Name.Name[7:]] = joinFunc(params, results)
}
}
return nil
}()
if err != nil {
fmt.Fprintf(os.Stderr, "go fix: warning: no cgo types: %s\n", err)
}
}
// gather function declarations
for _, decl := range f.Decls {
fn, ok := decl.(*ast.FuncDecl)
if !ok {
continue
}
typecheck1(cfg, fn.Type, typeof, assign)
t := typeof[fn.Type]
if fn.Recv != nil {
// The receiver must be a type.
rcvr := typeof[fn.Recv]
if !isType(rcvr) {
if len(fn.Recv.List) != 1 {
continue
}
rcvr = mkType(gofmt(fn.Recv.List[0].Type))
typeof[fn.Recv.List[0].Type] = rcvr
}
rcvr = getType(rcvr)
if rcvr != "" && rcvr[0] == '*' {
rcvr = rcvr[1:]
}
typeof[rcvr+"."+fn.Name.Name] = t
} else {
if isType(t) {
t = getType(t)
} else {
t = gofmt(fn.Type)
}
typeof[fn.Name] = t
// Record typeof[fn.Name.Obj] for future references to fn.Name.
typeof[fn.Name.Obj] = t
}
}
// gather struct declarations
for _, decl := range f.Decls {
d, ok := decl.(*ast.GenDecl)
if ok {
for _, s := range d.Specs {
switch s := s.(type) {
case *ast.TypeSpec:
if cfg1.Type[s.Name.Name] != nil {
break
}
if !copied {
copied = true
// Copy map lazily: it's time.
cfg1.Type = make(map[string]*Type)
for k, v := range cfg.Type {
cfg1.Type[k] = v
}
}
t := &Type{Field: map[string]string{}}
cfg1.Type[s.Name.Name] = t
switch st := s.Type.(type) {
case *ast.StructType:
for _, f := range st.Fields.List {
for _, n := range f.Names {
t.Field[n.Name] = gofmt(f.Type)
}
}
case *ast.ArrayType, *ast.StarExpr, *ast.MapType:
t.Def = gofmt(st)
}
}
}
}
}
typecheck1(cfg1, f, typeof, assign)
return typeof, assign
}
func makeExprList(a []*ast.Ident) []ast.Expr {
var b []ast.Expr
for _, x := range a {
b = append(b, x)
}
return b
}
// Typecheck1 is the recursive form of typecheck.
// It is like typecheck but adds to the information in typeof
// instead of allocating a new map.
func typecheck1(cfg *TypeConfig, f any, typeof map[any]string, assign map[string][]any) {
// set sets the type of n to typ.
// If isDecl is true, n is being declared.
set := func(n ast.Expr, typ string, isDecl bool) {
if typeof[n] != "" || typ == "" {
if typeof[n] != typ {
assign[typ] = append(assign[typ], n)
}
return
}
typeof[n] = typ
// If we obtained typ from the declaration of x
// propagate the type to all the uses.
// The !isDecl case is a cheat here, but it makes
// up in some cases for not paying attention to
// struct fields. The real type checker will be
// more accurate so we won't need the cheat.
if id, ok := n.(*ast.Ident); ok && id.Obj != nil && (isDecl || typeof[id.Obj] == "") {
typeof[id.Obj] = typ
}
}
// Type-check an assignment lhs = rhs.
// If isDecl is true, this is := so we can update
// the types of the objects that lhs refers to.
typecheckAssign := func(lhs, rhs []ast.Expr, isDecl bool) {
if len(lhs) > 1 && len(rhs) == 1 {
if _, ok := rhs[0].(*ast.CallExpr); ok {
t := split(typeof[rhs[0]])
// Lists should have same length but may not; pair what can be paired.
for i := 0; i < len(lhs) && i < len(t); i++ {
set(lhs[i], t[i], isDecl)
}
return
}
}
if len(lhs) == 1 && len(rhs) == 2 {
// x = y, ok
rhs = rhs[:1]
} else if len(lhs) == 2 && len(rhs) == 1 {
// x, ok = y
lhs = lhs[:1]
}
// Match as much as we can.
for i := 0; i < len(lhs) && i < len(rhs); i++ {
x, y := lhs[i], rhs[i]
if typeof[y] != "" {
set(x, typeof[y], isDecl)
} else {
set(y, typeof[x], false)
}
}
}
expand := func(s string) string {
typ := cfg.Type[s]
if typ != nil && typ.Def != "" {
return typ.Def
}
return s
}
// The main type check is a recursive algorithm implemented
// by walkBeforeAfter(n, before, after).
// Most of it is bottom-up, but in a few places we need
// to know the type of the function we are checking.
// The before function records that information on
// the curfn stack.
var curfn []*ast.FuncType
before := func(n any) {
// push function type on stack
switch n := n.(type) {
case *ast.FuncDecl:
curfn = append(curfn, n.Type)
case *ast.FuncLit:
curfn = append(curfn, n.Type)
}
}
// After is the real type checker.
after := func(n any) {
if n == nil {
return
}
if false && reflect.TypeOf(n).Kind() == reflect.Pointer { // debugging trace
defer func() {
if t := typeof[n]; t != "" {
pos := fset.Position(n.(ast.Node).Pos())
fmt.Fprintf(os.Stderr, "%s: typeof[%s] = %s\n", pos, gofmt(n), t)
}
}()
}
switch n := n.(type) {
case *ast.FuncDecl, *ast.FuncLit:
// pop function type off stack
curfn = curfn[:len(curfn)-1]
case *ast.FuncType:
typeof[n] = mkType(joinFunc(split(typeof[n.Params]), split(typeof[n.Results])))
case *ast.FieldList:
// Field list is concatenation of sub-lists.
t := ""
for _, field := range n.List {
if t != "" {
t += ", "
}
t += typeof[field]
}
typeof[n] = t
case *ast.Field:
// Field is one instance of the type per name.
all := ""
t := typeof[n.Type]
if !isType(t) {
// Create a type, because it is typically *T or *p.T
// and we might care about that type.
t = mkType(gofmt(n.Type))
typeof[n.Type] = t
}
t = getType(t)
if len(n.Names) == 0 {
all = t
} else {
for _, id := range n.Names {
if all != "" {
all += ", "
}
all += t
typeof[id.Obj] = t
typeof[id] = t
}
}
typeof[n] = all
case *ast.ValueSpec:
// var declaration. Use type if present.
if n.Type != nil {
t := typeof[n.Type]
if !isType(t) {
t = mkType(gofmt(n.Type))
typeof[n.Type] = t
}
t = getType(t)
for _, id := range n.Names {
set(id, t, true)
}
}
// Now treat same as assignment.
typecheckAssign(makeExprList(n.Names), n.Values, true)
case *ast.AssignStmt:
typecheckAssign(n.Lhs, n.Rhs, n.Tok == token.DEFINE)
case *ast.Ident:
// Identifier can take its type from underlying object.
if t := typeof[n.Obj]; t != "" {
typeof[n] = t
}
case *ast.SelectorExpr:
// Field or method.
name := n.Sel.Name
if t := typeof[n.X]; t != "" {
t = strings.TrimPrefix(t, "*") // implicit *
if typ := cfg.Type[t]; typ != nil {
if t := typ.dot(cfg, name); t != "" {
typeof[n] = t
return
}
}
tt := typeof[t+"."+name]
if isType(tt) {
typeof[n] = getType(tt)
return
}
}
// Package selector.
if x, ok := n.X.(*ast.Ident); ok && x.Obj == nil {
str := x.Name + "." + name
if cfg.Type[str] != nil {
typeof[n] = mkType(str)
return
}
if t := cfg.typeof(x.Name + "." + name); t != "" {
typeof[n] = t
return
}
}
case *ast.CallExpr:
// make(T) has type T.
if isTopName(n.Fun, "make") && len(n.Args) >= 1 {
typeof[n] = gofmt(n.Args[0])
return
}
// new(T) has type *T
if isTopName(n.Fun, "new") && len(n.Args) == 1 {
typeof[n] = "*" + gofmt(n.Args[0])
return
}
// Otherwise, use type of function to determine arguments.
t := typeof[n.Fun]
if t == "" {
t = cfg.External[gofmt(n.Fun)]
}
in, out := splitFunc(t)
if in == nil && out == nil {
return
}
typeof[n] = join(out)
for i, arg := range n.Args {
if i >= len(in) {
break
}
if typeof[arg] == "" {
typeof[arg] = in[i]
}
}
case *ast.TypeAssertExpr:
// x.(type) has type of x.
if n.Type == nil {
typeof[n] = typeof[n.X]
return
}
// x.(T) has type T.
if t := typeof[n.Type]; isType(t) {
typeof[n] = getType(t)
} else {
typeof[n] = gofmt(n.Type)
}
case *ast.SliceExpr:
// x[i:j] has type of x.
typeof[n] = typeof[n.X]
case *ast.IndexExpr:
// x[i] has key type of x's type.
t := expand(typeof[n.X])
if strings.HasPrefix(t, "[") || strings.HasPrefix(t, "map[") {
// Lazy: assume there are no nested [] in the array
// length or map key type.
if _, elem, ok := strings.Cut(t, "]"); ok {
typeof[n] = elem
}
}
case *ast.StarExpr:
// *x for x of type *T has type T when x is an expr.
// We don't use the result when *x is a type, but
// compute it anyway.
t := expand(typeof[n.X])
if isType(t) {
typeof[n] = "type *" + getType(t)
} else if strings.HasPrefix(t, "*") {
typeof[n] = t[len("*"):]
}
case *ast.UnaryExpr:
// &x for x of type T has type *T.
t := typeof[n.X]
if t != "" && n.Op == token.AND {
typeof[n] = "*" + t
}
case *ast.CompositeLit:
// T{...} has type T.
typeof[n] = gofmt(n.Type)
// Propagate types down to values used in the composite literal.
t := expand(typeof[n])
if strings.HasPrefix(t, "[") { // array or slice
// Lazy: assume there are no nested [] in the array length.
if _, et, ok := strings.Cut(t, "]"); ok {
for _, e := range n.Elts {
if kv, ok := e.(*ast.KeyValueExpr); ok {
e = kv.Value
}
if typeof[e] == "" {
typeof[e] = et
}
}
}
}
if strings.HasPrefix(t, "map[") { // map
// Lazy: assume there are no nested [] in the map key type.
if kt, vt, ok := strings.Cut(t[len("map["):], "]"); ok {
for _, e := range n.Elts {
if kv, ok := e.(*ast.KeyValueExpr); ok {
if typeof[kv.Key] == "" {
typeof[kv.Key] = kt
}
if typeof[kv.Value] == "" {
typeof[kv.Value] = vt
}
}
}
}
}
if typ := cfg.Type[t]; typ != nil && len(typ.Field) > 0 { // struct
for _, e := range n.Elts {
if kv, ok := e.(*ast.KeyValueExpr); ok {
if ft := typ.Field[fmt.Sprintf("%s", kv.Key)]; ft != "" {
if typeof[kv.Value] == "" {
typeof[kv.Value] = ft
}
}
}
}
}
case *ast.ParenExpr:
// (x) has type of x.
typeof[n] = typeof[n.X]
case *ast.RangeStmt:
t := expand(typeof[n.X])
if t == "" {
return
}
var key, value string
if t == "string" {
key, value = "int", "rune"
} else if strings.HasPrefix(t, "[") {
key = "int"
_, value, _ = strings.Cut(t, "]")
} else if strings.HasPrefix(t, "map[") {
if k, v, ok := strings.Cut(t[len("map["):], "]"); ok {
key, value = k, v
}
}
changed := false
if n.Key != nil && key != "" {
changed = true
set(n.Key, key, n.Tok == token.DEFINE)
}
if n.Value != nil && value != "" {
changed = true
set(n.Value, value, n.Tok == token.DEFINE)
}
// Ugly failure of vision: already type-checked body.
// Do it again now that we have that type info.
if changed {
typecheck1(cfg, n.Body, typeof, assign)
}
case *ast.TypeSwitchStmt:
// Type of variable changes for each case in type switch,
// but go/parser generates just one variable.
// Repeat type check for each case with more precise
// type information.
as, ok := n.Assign.(*ast.AssignStmt)
if !ok {
return
}
varx, ok := as.Lhs[0].(*ast.Ident)
if !ok {
return
}
t := typeof[varx]
for _, cas := range n.Body.List {
cas := cas.(*ast.CaseClause)
if len(cas.List) == 1 {
// Variable has specific type only when there is
// exactly one type in the case list.
if tt := typeof[cas.List[0]]; isType(tt) {
tt = getType(tt)
typeof[varx] = tt
typeof[varx.Obj] = tt
typecheck1(cfg, cas.Body, typeof, assign)
}
}
}
// Restore t.
typeof[varx] = t
typeof[varx.Obj] = t
case *ast.ReturnStmt:
if len(curfn) == 0 {
// Probably can't happen.
return
}
f := curfn[len(curfn)-1]
res := n.Results
if f.Results != nil {
t := split(typeof[f.Results])
for i := 0; i < len(res) && i < len(t); i++ {
set(res[i], t[i], false)
}
}
case *ast.BinaryExpr:
// Propagate types across binary ops that require two args of the same type.
switch n.Op {
case token.EQL, token.NEQ: // TODO: more cases. This is enough for the cftype fix.
if typeof[n.X] != "" && typeof[n.Y] == "" {
typeof[n.Y] = typeof[n.X]
}
if typeof[n.X] == "" && typeof[n.Y] != "" {
typeof[n.X] = typeof[n.Y]
}
}
}
}
walkBeforeAfter(f, before, after)
}
// Convert between function type strings and lists of types.
// Using strings makes this a little harder, but it makes
// a lot of the rest of the code easier. This will all go away
// when we can use go/typechecker directly.
// splitFunc splits "func(x,y,z) (a,b,c)" into ["x", "y", "z"] and ["a", "b", "c"].
func splitFunc(s string) (in, out []string) {
if !strings.HasPrefix(s, "func(") {
return nil, nil
}
i := len("func(") // index of beginning of 'in' arguments
nparen := 0
for j := i; j < len(s); j++ {
switch s[j] {
case '(':
nparen++
case ')':
nparen--
if nparen < 0 {
// found end of parameter list
out := strings.TrimSpace(s[j+1:])
if len(out) >= 2 && out[0] == '(' && out[len(out)-1] == ')' {
out = out[1 : len(out)-1]
}
return split(s[i:j]), split(out)
}
}
}
return nil, nil
}
// joinFunc is the inverse of splitFunc.
func joinFunc(in, out []string) string {
outs := ""
if len(out) == 1 {
outs = " " + out[0]
} else if len(out) > 1 {
outs = " (" + join(out) + ")"
}
return "func(" + join(in) + ")" + outs
}
// split splits "int, float" into ["int", "float"] and splits "" into [].
func split(s string) []string {
out := []string{}
i := 0 // current type being scanned is s[i:j].
nparen := 0
for j := 0; j < len(s); j++ {
switch s[j] {
case ' ':
if i == j {
i++
}
case '(':
nparen++
case ')':
nparen--
if nparen < 0 {
// probably can't happen
return nil
}
case ',':
if nparen == 0 {
if i < j {
out = append(out, s[i:j])
}
i = j + 1
}
}
}
if nparen != 0 {
// probably can't happen
return nil
}
if i < len(s) {
out = append(out, s[i:])
}
return out
}
// join is the inverse of split.
func join(x []string) string {
return strings.Join(x, ", ")
}