blob: 742f48f6a1ddf738e9d6ba0161a53959991f8c6f [file] [log] [blame]
// Copyright 2019 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 cache
import (
"bytes"
"context"
"fmt"
"go/ast"
"go/parser"
"go/scanner"
"go/token"
"go/types"
"reflect"
"strconv"
"strings"
"golang.org/x/tools/internal/event"
"golang.org/x/tools/internal/lsp/debug/tag"
"golang.org/x/tools/internal/lsp/diff"
"golang.org/x/tools/internal/lsp/diff/myers"
"golang.org/x/tools/internal/lsp/protocol"
"golang.org/x/tools/internal/lsp/source"
"golang.org/x/tools/internal/memoize"
"golang.org/x/tools/internal/span"
errors "golang.org/x/xerrors"
)
// parseKey uniquely identifies a parsed Go file.
type parseKey struct {
file source.FileIdentity
mode source.ParseMode
}
type parseGoHandle struct {
handle *memoize.Handle
file source.FileHandle
mode source.ParseMode
}
type parseGoData struct {
parsed *source.ParsedGoFile
// If true, we adjusted the AST to make it type check better, and
// it may not match the source code.
fixed bool
err error // any other errors
}
func (s *snapshot) parseGoHandle(ctx context.Context, fh source.FileHandle, mode source.ParseMode) *parseGoHandle {
key := parseKey{
file: fh.FileIdentity(),
mode: mode,
}
if pgh := s.getGoFile(key); pgh != nil {
return pgh
}
parseHandle := s.generation.Bind(key, func(ctx context.Context, arg memoize.Arg) interface{} {
snapshot := arg.(*snapshot)
return parseGo(ctx, snapshot.FileSet(), fh, mode)
}, nil)
pgh := &parseGoHandle{
handle: parseHandle,
file: fh,
mode: mode,
}
return s.addGoFile(key, pgh)
}
func (pgh *parseGoHandle) String() string {
return pgh.File().URI().Filename()
}
func (pgh *parseGoHandle) File() source.FileHandle {
return pgh.file
}
func (pgh *parseGoHandle) Mode() source.ParseMode {
return pgh.mode
}
func (s *snapshot) ParseGo(ctx context.Context, fh source.FileHandle, mode source.ParseMode) (*source.ParsedGoFile, error) {
pgh := s.parseGoHandle(ctx, fh, mode)
pgf, _, err := s.parseGo(ctx, pgh)
return pgf, err
}
func (s *snapshot) parseGo(ctx context.Context, pgh *parseGoHandle) (*source.ParsedGoFile, bool, error) {
if pgh.mode == source.ParseExported {
panic("only type checking should use Exported")
}
d, err := pgh.handle.Get(ctx, s.generation, s)
if err != nil {
return nil, false, err
}
data := d.(*parseGoData)
return data.parsed, data.fixed, data.err
}
type astCacheKey struct {
pkg packageHandleKey
uri span.URI
}
func (s *snapshot) astCacheData(ctx context.Context, spkg source.Package, pos token.Pos) (*astCacheData, error) {
pkg := spkg.(*pkg)
pkgHandle := s.getPackage(pkg.m.ID, pkg.mode)
if pkgHandle == nil {
return nil, fmt.Errorf("could not reconstruct package handle for %v", pkg.m.ID)
}
tok := s.FileSet().File(pos)
if tok == nil {
return nil, fmt.Errorf("no file for pos %v", pos)
}
pgf, err := pkg.File(span.URIFromPath(tok.Name()))
if err != nil {
return nil, err
}
astHandle := s.generation.Bind(astCacheKey{pkgHandle.key, pgf.URI}, func(ctx context.Context, arg memoize.Arg) interface{} {
return buildASTCache(pgf)
}, nil)
d, err := astHandle.Get(ctx, s.generation, s)
if err != nil {
return nil, err
}
data := d.(*astCacheData)
if data.err != nil {
return nil, data.err
}
return data, nil
}
func (s *snapshot) PosToDecl(ctx context.Context, spkg source.Package, pos token.Pos) (ast.Decl, error) {
data, err := s.astCacheData(ctx, spkg, pos)
if err != nil {
return nil, err
}
return data.posToDecl[pos], nil
}
func (s *snapshot) PosToField(ctx context.Context, spkg source.Package, pos token.Pos) (*ast.Field, error) {
data, err := s.astCacheData(ctx, spkg, pos)
if err != nil {
return nil, err
}
return data.posToField[pos], nil
}
type astCacheData struct {
err error
posToDecl map[token.Pos]ast.Decl
posToField map[token.Pos]*ast.Field
}
// buildASTCache builds caches to aid in quickly going from the typed
// world to the syntactic world.
func buildASTCache(pgf *source.ParsedGoFile) *astCacheData {
var (
// path contains all ancestors, including n.
path []ast.Node
// decls contains all ancestors that are decls.
decls []ast.Decl
)
data := &astCacheData{
posToDecl: make(map[token.Pos]ast.Decl),
posToField: make(map[token.Pos]*ast.Field),
}
ast.Inspect(pgf.File, func(n ast.Node) bool {
if n == nil {
lastP := path[len(path)-1]
path = path[:len(path)-1]
if len(decls) > 0 && decls[len(decls)-1] == lastP {
decls = decls[:len(decls)-1]
}
return false
}
path = append(path, n)
switch n := n.(type) {
case *ast.Field:
addField := func(f ast.Node) {
if f.Pos().IsValid() {
data.posToField[f.Pos()] = n
if len(decls) > 0 {
data.posToDecl[f.Pos()] = decls[len(decls)-1]
}
}
}
// Add mapping for *ast.Field itself. This handles embedded
// fields which have no associated *ast.Ident name.
addField(n)
// Add mapping for each field name since you can have
// multiple names for the same type expression.
for _, name := range n.Names {
addField(name)
}
// Also map "X" in "...X" to the containing *ast.Field. This
// makes it easy to format variadic signature params
// properly.
if elips, ok := n.Type.(*ast.Ellipsis); ok && elips.Elt != nil {
addField(elips.Elt)
}
case *ast.FuncDecl:
decls = append(decls, n)
if n.Name != nil && n.Name.Pos().IsValid() {
data.posToDecl[n.Name.Pos()] = n
}
case *ast.GenDecl:
decls = append(decls, n)
for _, spec := range n.Specs {
switch spec := spec.(type) {
case *ast.TypeSpec:
if spec.Name != nil && spec.Name.Pos().IsValid() {
data.posToDecl[spec.Name.Pos()] = n
}
case *ast.ValueSpec:
for _, id := range spec.Names {
if id != nil && id.Pos().IsValid() {
data.posToDecl[id.Pos()] = n
}
}
}
}
}
return true
})
return data
}
func parseGo(ctx context.Context, fset *token.FileSet, fh source.FileHandle, mode source.ParseMode) *parseGoData {
ctx, done := event.Start(ctx, "cache.parseGo", tag.File.Of(fh.URI().Filename()))
defer done()
if fh.Kind() != source.Go {
return &parseGoData{err: errors.Errorf("cannot parse non-Go file %s", fh.URI())}
}
src, err := fh.Read()
if err != nil {
return &parseGoData{err: err}
}
parserMode := parser.AllErrors | parser.ParseComments
if mode == source.ParseHeader {
parserMode = parser.ImportsOnly | parser.ParseComments
}
file, err := parser.ParseFile(fset, fh.URI().Filename(), src, parserMode)
var parseErr scanner.ErrorList
if err != nil {
// We passed a byte slice, so the only possible error is a parse error.
parseErr = err.(scanner.ErrorList)
}
tok := fset.File(file.Pos())
if tok == nil {
// file.Pos is the location of the package declaration. If there was
// none, we can't find the token.File that ParseFile created, and we
// have no choice but to recreate it.
tok = fset.AddFile(fh.URI().Filename(), -1, len(src))
tok.SetLinesForContent(src)
}
fixed := false
// If there were parse errors, attempt to fix them up.
if parseErr != nil {
// Fix any badly parsed parts of the AST.
fixed = fixAST(ctx, file, tok, src)
for i := 0; i < 10; i++ {
// Fix certain syntax errors that render the file unparseable.
newSrc := fixSrc(file, tok, src)
if newSrc == nil {
break
}
// If we thought there was something to fix 10 times in a row,
// it is likely we got stuck in a loop somehow. Log out a diff
// of the last changes we made to aid in debugging.
if i == 9 {
edits, err := myers.ComputeEdits(fh.URI(), string(src), string(newSrc))
if err != nil {
event.Error(ctx, "error generating fixSrc diff", err, tag.File.Of(tok.Name()))
} else {
unified := diff.ToUnified("before", "after", string(src), edits)
event.Log(ctx, fmt.Sprintf("fixSrc loop - last diff:\n%v", unified), tag.File.Of(tok.Name()))
}
}
newFile, _ := parser.ParseFile(fset, fh.URI().Filename(), newSrc, parserMode)
if newFile != nil {
// Maintain the original parseError so we don't try formatting the doctored file.
file = newFile
src = newSrc
tok = fset.File(file.Pos())
fixed = fixAST(ctx, file, tok, src)
}
}
}
return &parseGoData{
parsed: &source.ParsedGoFile{
URI: fh.URI(),
Mode: mode,
Src: src,
File: file,
Tok: tok,
Mapper: &protocol.ColumnMapper{
URI: fh.URI(),
Converter: span.NewTokenConverter(fset, tok),
Content: src,
},
ParseErr: parseErr,
},
fixed: fixed,
}
}
// An unexportedFilter removes as much unexported AST from a set of Files as possible.
type unexportedFilter struct {
uses map[string]bool
}
// Filter records uses of unexported identifiers and filters out all other
// unexported declarations.
func (f *unexportedFilter) Filter(files []*ast.File) {
// Iterate to fixed point -- unexported types can include other unexported types.
oldLen := len(f.uses)
for {
for _, file := range files {
f.recordUses(file)
}
if len(f.uses) == oldLen {
break
}
oldLen = len(f.uses)
}
for _, file := range files {
var newDecls []ast.Decl
for _, decl := range file.Decls {
if f.filterDecl(decl) {
newDecls = append(newDecls, decl)
}
}
file.Decls = newDecls
file.Scope = nil
file.Unresolved = nil
file.Comments = nil
trimAST(file)
}
}
func (f *unexportedFilter) keep(ident *ast.Ident) bool {
return ast.IsExported(ident.Name) || f.uses[ident.Name]
}
func (f *unexportedFilter) filterDecl(decl ast.Decl) bool {
switch decl := decl.(type) {
case *ast.FuncDecl:
if ident := recvIdent(decl); ident != nil && !f.keep(ident) {
return false
}
return f.keep(decl.Name)
case *ast.GenDecl:
if decl.Tok == token.CONST {
// Constants can involve iota, and iota is hard to deal with.
return true
}
var newSpecs []ast.Spec
for _, spec := range decl.Specs {
if f.filterSpec(spec) {
newSpecs = append(newSpecs, spec)
}
}
decl.Specs = newSpecs
return len(newSpecs) != 0
case *ast.BadDecl:
return false
}
panic(fmt.Sprintf("unknown ast.Decl %T", decl))
}
func (f *unexportedFilter) filterSpec(spec ast.Spec) bool {
switch spec := spec.(type) {
case *ast.ImportSpec:
return true
case *ast.ValueSpec:
var newNames []*ast.Ident
for _, name := range spec.Names {
if f.keep(name) {
newNames = append(newNames, name)
}
}
spec.Names = newNames
return len(spec.Names) != 0
case *ast.TypeSpec:
if !f.keep(spec.Name) {
return false
}
switch typ := spec.Type.(type) {
case *ast.StructType:
f.filterFieldList(typ.Fields)
case *ast.InterfaceType:
f.filterFieldList(typ.Methods)
}
return true
}
panic(fmt.Sprintf("unknown ast.Spec %T", spec))
}
func (f *unexportedFilter) filterFieldList(fields *ast.FieldList) {
var newFields []*ast.Field
for _, field := range fields.List {
if len(field.Names) == 0 {
// Keep embedded fields: they can export methods and fields.
newFields = append(newFields, field)
}
for _, name := range field.Names {
if f.keep(name) {
newFields = append(newFields, field)
break
}
}
}
fields.List = newFields
}
func (f *unexportedFilter) recordUses(file *ast.File) {
for _, decl := range file.Decls {
switch decl := decl.(type) {
case *ast.FuncDecl:
// Ignore methods on dropped types.
if ident := recvIdent(decl); ident != nil && !f.keep(ident) {
break
}
// Ignore functions with dropped names.
if !f.keep(decl.Name) {
break
}
f.recordFuncType(decl.Type)
case *ast.GenDecl:
for _, spec := range decl.Specs {
switch spec := spec.(type) {
case *ast.ValueSpec:
for i, name := range spec.Names {
// Don't mess with constants -- iota is hard.
if f.keep(name) || decl.Tok == token.CONST {
f.recordIdents(spec.Type)
if len(spec.Values) > i {
f.recordIdents(spec.Values[i])
}
}
}
case *ast.TypeSpec:
switch typ := spec.Type.(type) {
case *ast.StructType:
f.recordFieldUses(false, typ.Fields)
case *ast.InterfaceType:
f.recordFieldUses(false, typ.Methods)
}
}
}
}
}
}
// recvIdent returns the identifier of a method receiver, e.g. *int.
func recvIdent(decl *ast.FuncDecl) *ast.Ident {
if decl.Recv == nil || len(decl.Recv.List) == 0 {
return nil
}
x := decl.Recv.List[0].Type
if star, ok := x.(*ast.StarExpr); ok {
x = star.X
}
if ident, ok := x.(*ast.Ident); ok {
return ident
}
return nil
}
// recordIdents records unexported identifiers in an Expr in uses.
// These may be types, e.g. in map[key]value, function names, e.g. in foo(),
// or simple variable references. References that will be discarded, such
// as those in function literal bodies, are ignored.
func (f *unexportedFilter) recordIdents(x ast.Expr) {
ast.Inspect(x, func(n ast.Node) bool {
if n == nil {
return false
}
if complit, ok := n.(*ast.CompositeLit); ok {
// We clear out composite literal contents; just record their type.
f.recordIdents(complit.Type)
return false
}
if flit, ok := n.(*ast.FuncLit); ok {
f.recordFuncType(flit.Type)
return false
}
if ident, ok := n.(*ast.Ident); ok && !ast.IsExported(ident.Name) {
f.uses[ident.Name] = true
}
return true
})
}
// recordFuncType records the types mentioned by a function type.
func (f *unexportedFilter) recordFuncType(x *ast.FuncType) {
f.recordFieldUses(true, x.Params)
f.recordFieldUses(true, x.Results)
}
// recordFieldUses records unexported identifiers used in fields, which may be
// struct members, interface members, or function parameter/results.
func (f *unexportedFilter) recordFieldUses(isParams bool, fields *ast.FieldList) {
if fields == nil {
return
}
for _, field := range fields.List {
if isParams {
// Parameter types of retained functions need to be retained.
f.recordIdents(field.Type)
continue
}
if ft, ok := field.Type.(*ast.FuncType); ok {
// Function declarations in interfaces need all their types retained.
f.recordFuncType(ft)
continue
}
if len(field.Names) == 0 {
// Embedded fields might contribute exported names.
f.recordIdents(field.Type)
}
for _, name := range field.Names {
// We only need normal fields if they're exported.
if ast.IsExported(name.Name) {
f.recordIdents(field.Type)
break
}
}
}
}
// ProcessErrors records additional uses from errors, returning the new uses
// and any unexpected errors.
func (f *unexportedFilter) ProcessErrors(errors []types.Error) (map[string]bool, []types.Error) {
var unexpected []types.Error
missing := map[string]bool{}
for _, err := range errors {
if strings.Contains(err.Msg, "missing return") {
continue
}
const undeclared = "undeclared name: "
if strings.HasPrefix(err.Msg, undeclared) {
missing[strings.TrimPrefix(err.Msg, undeclared)] = true
f.uses[strings.TrimPrefix(err.Msg, undeclared)] = true
continue
}
unexpected = append(unexpected, err)
}
return missing, unexpected
}
// trimAST clears any part of the AST not relevant to type checking
// expressions at pos.
func trimAST(file *ast.File) {
ast.Inspect(file, func(n ast.Node) bool {
if n == nil {
return false
}
switch n := n.(type) {
case *ast.FuncDecl:
n.Body = nil
case *ast.BlockStmt:
n.List = nil
case *ast.CaseClause:
n.Body = nil
case *ast.CommClause:
n.Body = nil
case *ast.CompositeLit:
// types.Info.Types for long slice/array literals are particularly
// expensive. Try to clear them out.
at, ok := n.Type.(*ast.ArrayType)
if !ok {
// Composite literal. No harm removing all its fields.
n.Elts = nil
break
}
// Removing the elements from an ellipsis array changes its type.
// Try to set the length explicitly so we can continue.
if _, ok := at.Len.(*ast.Ellipsis); ok {
length, ok := arrayLength(n)
if !ok {
break
}
at.Len = &ast.BasicLit{
Kind: token.INT,
Value: fmt.Sprint(length),
ValuePos: at.Len.Pos(),
}
}
n.Elts = nil
}
return true
})
}
// arrayLength returns the length of some simple forms of ellipsis array literal.
// Notably, it handles the tables in golang.org/x/text.
func arrayLength(array *ast.CompositeLit) (int, bool) {
litVal := func(expr ast.Expr) (int, bool) {
lit, ok := expr.(*ast.BasicLit)
if !ok {
return 0, false
}
val, err := strconv.ParseInt(lit.Value, 10, 64)
if err != nil {
return 0, false
}
return int(val), true
}
largestKey := -1
for _, elt := range array.Elts {
kve, ok := elt.(*ast.KeyValueExpr)
if !ok {
continue
}
switch key := kve.Key.(type) {
case *ast.BasicLit:
if val, ok := litVal(key); ok && largestKey < val {
largestKey = val
}
case *ast.BinaryExpr:
// golang.org/x/text uses subtraction (and only subtraction) in its indices.
if key.Op != token.SUB {
break
}
x, ok := litVal(key.X)
if !ok {
break
}
y, ok := litVal(key.Y)
if !ok {
break
}
if val := x - y; largestKey < val {
largestKey = val
}
}
}
if largestKey != -1 {
return largestKey + 1, true
}
return len(array.Elts), true
}
// fixAST inspects the AST and potentially modifies any *ast.BadStmts so that it can be
// type-checked more effectively.
func fixAST(ctx context.Context, n ast.Node, tok *token.File, src []byte) (fixed bool) {
var err error
walkASTWithParent(n, func(n, parent ast.Node) bool {
switch n := n.(type) {
case *ast.BadStmt:
if fixed = fixDeferOrGoStmt(n, parent, tok, src); fixed {
// Recursively fix in our fixed node.
_ = fixAST(ctx, parent, tok, src)
} else {
err = errors.Errorf("unable to parse defer or go from *ast.BadStmt: %v", err)
}
return false
case *ast.BadExpr:
if fixed = fixArrayType(n, parent, tok, src); fixed {
// Recursively fix in our fixed node.
_ = fixAST(ctx, parent, tok, src)
return false
}
// Fix cases where parser interprets if/for/switch "init"
// statement as "cond" expression, e.g.:
//
// // "i := foo" is init statement, not condition.
// for i := foo
//
fixInitStmt(n, parent, tok, src)
return false
case *ast.SelectorExpr:
// Fix cases where a keyword prefix results in a phantom "_" selector, e.g.:
//
// foo.var<> // want to complete to "foo.variance"
//
fixPhantomSelector(n, tok, src)
return true
case *ast.BlockStmt:
switch parent.(type) {
case *ast.SwitchStmt, *ast.TypeSwitchStmt, *ast.SelectStmt:
// Adjust closing curly brace of empty switch/select
// statements so we can complete inside them.
fixEmptySwitch(n, tok, src)
}
return true
default:
return true
}
})
return fixed
}
// walkASTWithParent walks the AST rooted at n. The semantics are
// similar to ast.Inspect except it does not call f(nil).
func walkASTWithParent(n ast.Node, f func(n ast.Node, parent ast.Node) bool) {
var ancestors []ast.Node
ast.Inspect(n, func(n ast.Node) (recurse bool) {
defer func() {
if recurse {
ancestors = append(ancestors, n)
}
}()
if n == nil {
ancestors = ancestors[:len(ancestors)-1]
return false
}
var parent ast.Node
if len(ancestors) > 0 {
parent = ancestors[len(ancestors)-1]
}
return f(n, parent)
})
}
// fixSrc attempts to modify the file's source code to fix certain
// syntax errors that leave the rest of the file unparsed.
func fixSrc(f *ast.File, tok *token.File, src []byte) (newSrc []byte) {
walkASTWithParent(f, func(n, parent ast.Node) bool {
if newSrc != nil {
return false
}
switch n := n.(type) {
case *ast.BlockStmt:
newSrc = fixMissingCurlies(f, n, parent, tok, src)
case *ast.SelectorExpr:
newSrc = fixDanglingSelector(n, tok, src)
}
return newSrc == nil
})
return newSrc
}
// fixMissingCurlies adds in curly braces for block statements that
// are missing curly braces. For example:
//
// if foo
//
// becomes
//
// if foo {}
func fixMissingCurlies(f *ast.File, b *ast.BlockStmt, parent ast.Node, tok *token.File, src []byte) []byte {
// If the "{" is already in the source code, there isn't anything to
// fix since we aren't missing curlies.
if b.Lbrace.IsValid() {
braceOffset := tok.Offset(b.Lbrace)
if braceOffset < len(src) && src[braceOffset] == '{' {
return nil
}
}
parentLine := tok.Line(parent.Pos())
if parentLine >= tok.LineCount() {
// If we are the last line in the file, no need to fix anything.
return nil
}
// Insert curlies at the end of parent's starting line. The parent
// is the statement that contains the block, e.g. *ast.IfStmt. The
// block's Pos()/End() can't be relied upon because they are based
// on the (missing) curly braces. We assume the statement is a
// single line for now and try sticking the curly braces at the end.
insertPos := tok.LineStart(parentLine+1) - 1
// Scootch position backwards until it's not in a comment. For example:
//
// if foo<> // some amazing comment |
// someOtherCode()
//
// insertPos will be located at "|", so we back it out of the comment.
didSomething := true
for didSomething {
didSomething = false
for _, c := range f.Comments {
if c.Pos() < insertPos && insertPos <= c.End() {
insertPos = c.Pos()
didSomething = true
}
}
}
// Bail out if line doesn't end in an ident or ".". This is to avoid
// cases like below where we end up making things worse by adding
// curlies:
//
// if foo &&
// bar<>
switch precedingToken(insertPos, tok, src) {
case token.IDENT, token.PERIOD:
// ok
default:
return nil
}
var buf bytes.Buffer
buf.Grow(len(src) + 3)
buf.Write(src[:tok.Offset(insertPos)])
// Detect if we need to insert a semicolon to fix "for" loop situations like:
//
// for i := foo(); foo<>
//
// Just adding curlies is not sufficient to make things parse well.
if fs, ok := parent.(*ast.ForStmt); ok {
if _, ok := fs.Cond.(*ast.BadExpr); !ok {
if xs, ok := fs.Post.(*ast.ExprStmt); ok {
if _, ok := xs.X.(*ast.BadExpr); ok {
buf.WriteByte(';')
}
}
}
}
// Insert "{}" at insertPos.
buf.WriteByte('{')
buf.WriteByte('}')
buf.Write(src[tok.Offset(insertPos):])
return buf.Bytes()
}
// fixEmptySwitch moves empty switch/select statements' closing curly
// brace down one line. This allows us to properly detect incomplete
// "case" and "default" keywords as inside the switch statement. For
// example:
//
// switch {
// def<>
// }
//
// gets parsed like:
//
// switch {
// }
//
// Later we manually pull out the "def" token, but we need to detect
// that our "<>" position is inside the switch block. To do that we
// move the curly brace so it looks like:
//
// switch {
//
// }
//
func fixEmptySwitch(body *ast.BlockStmt, tok *token.File, src []byte) {
// We only care about empty switch statements.
if len(body.List) > 0 || !body.Rbrace.IsValid() {
return
}
// If the right brace is actually in the source code at the
// specified position, don't mess with it.
braceOffset := tok.Offset(body.Rbrace)
if braceOffset < len(src) && src[braceOffset] == '}' {
return
}
braceLine := tok.Line(body.Rbrace)
if braceLine >= tok.LineCount() {
// If we are the last line in the file, no need to fix anything.
return
}
// Move the right brace down one line.
body.Rbrace = tok.LineStart(braceLine + 1)
}
// fixDanglingSelector inserts real "_" selector expressions in place
// of phantom "_" selectors. For example:
//
// func _() {
// x.<>
// }
// var x struct { i int }
//
// To fix completion at "<>", we insert a real "_" after the "." so the
// following declaration of "x" can be parsed and type checked
// normally.
func fixDanglingSelector(s *ast.SelectorExpr, tok *token.File, src []byte) []byte {
if !isPhantomUnderscore(s.Sel, tok, src) {
return nil
}
if !s.X.End().IsValid() {
return nil
}
// Insert directly after the selector's ".".
insertOffset := tok.Offset(s.X.End()) + 1
if src[insertOffset-1] != '.' {
return nil
}
var buf bytes.Buffer
buf.Grow(len(src) + 1)
buf.Write(src[:insertOffset])
buf.WriteByte('_')
buf.Write(src[insertOffset:])
return buf.Bytes()
}
// fixPhantomSelector tries to fix selector expressions with phantom
// "_" selectors. In particular, we check if the selector is a
// keyword, and if so we swap in an *ast.Ident with the keyword text. For example:
//
// foo.var
//
// yields a "_" selector instead of "var" since "var" is a keyword.
func fixPhantomSelector(sel *ast.SelectorExpr, tok *token.File, src []byte) {
if !isPhantomUnderscore(sel.Sel, tok, src) {
return
}
// Only consider selectors directly abutting the selector ".". This
// avoids false positives in cases like:
//
// foo. // don't think "var" is our selector
// var bar = 123
//
if sel.Sel.Pos() != sel.X.End()+1 {
return
}
maybeKeyword := readKeyword(sel.Sel.Pos(), tok, src)
if maybeKeyword == "" {
return
}
replaceNode(sel, sel.Sel, &ast.Ident{
Name: maybeKeyword,
NamePos: sel.Sel.Pos(),
})
}
// isPhantomUnderscore reports whether the given ident is a phantom
// underscore. The parser sometimes inserts phantom underscores when
// it encounters otherwise unparseable situations.
func isPhantomUnderscore(id *ast.Ident, tok *token.File, src []byte) bool {
if id == nil || id.Name != "_" {
return false
}
// Phantom underscore means the underscore is not actually in the
// program text.
offset := tok.Offset(id.Pos())
return len(src) <= offset || src[offset] != '_'
}
// fixInitStmt fixes cases where the parser misinterprets an
// if/for/switch "init" statement as the "cond" conditional. In cases
// like "if i := 0" the user hasn't typed the semicolon yet so the
// parser is looking for the conditional expression. However, "i := 0"
// are not valid expressions, so we get a BadExpr.
func fixInitStmt(bad *ast.BadExpr, parent ast.Node, tok *token.File, src []byte) {
if !bad.Pos().IsValid() || !bad.End().IsValid() {
return
}
// Try to extract a statement from the BadExpr.
stmtBytes := src[tok.Offset(bad.Pos()) : tok.Offset(bad.End()-1)+1]
stmt, err := parseStmt(bad.Pos(), stmtBytes)
if err != nil {
return
}
// If the parent statement doesn't already have an "init" statement,
// move the extracted statement into the "init" field and insert a
// dummy expression into the required "cond" field.
switch p := parent.(type) {
case *ast.IfStmt:
if p.Init != nil {
return
}
p.Init = stmt
p.Cond = &ast.Ident{
Name: "_",
NamePos: stmt.End(),
}
case *ast.ForStmt:
if p.Init != nil {
return
}
p.Init = stmt
p.Cond = &ast.Ident{
Name: "_",
NamePos: stmt.End(),
}
case *ast.SwitchStmt:
if p.Init != nil {
return
}
p.Init = stmt
p.Tag = nil
}
}
// readKeyword reads the keyword starting at pos, if any.
func readKeyword(pos token.Pos, tok *token.File, src []byte) string {
var kwBytes []byte
for i := tok.Offset(pos); i < len(src); i++ {
// Use a simplified identifier check since keywords are always lowercase ASCII.
if src[i] < 'a' || src[i] > 'z' {
break
}
kwBytes = append(kwBytes, src[i])
// Stop search at arbitrarily chosen too-long-for-a-keyword length.
if len(kwBytes) > 15 {
return ""
}
}
if kw := string(kwBytes); token.Lookup(kw).IsKeyword() {
return kw
}
return ""
}
// fixArrayType tries to parse an *ast.BadExpr into an *ast.ArrayType.
// go/parser often turns lone array types like "[]int" into BadExprs
// if it isn't expecting a type.
func fixArrayType(bad *ast.BadExpr, parent ast.Node, tok *token.File, src []byte) bool {
// Our expected input is a bad expression that looks like "[]someExpr".
from := bad.Pos()
to := bad.End()
if !from.IsValid() || !to.IsValid() {
return false
}
exprBytes := make([]byte, 0, int(to-from)+3)
// Avoid doing tok.Offset(to) since that panics if badExpr ends at EOF.
// It also panics if the position is not in the range of the file, and
// badExprs may not necessarily have good positions, so check first.
if !source.InRange(tok, from) {
return false
}
if !source.InRange(tok, to-1) {
return false
}
fromOffset := tok.Offset(from)
toOffset := tok.Offset(to-1) + 1
exprBytes = append(exprBytes, src[fromOffset:toOffset]...)
exprBytes = bytes.TrimSpace(exprBytes)
// If our expression ends in "]" (e.g. "[]"), add a phantom selector
// so we can complete directly after the "[]".
if len(exprBytes) > 0 && exprBytes[len(exprBytes)-1] == ']' {
exprBytes = append(exprBytes, '_')
}
// Add "{}" to turn our ArrayType into a CompositeLit. This is to
// handle the case of "[...]int" where we must make it a composite
// literal to be parseable.
exprBytes = append(exprBytes, '{', '}')
expr, err := parseExpr(from, exprBytes)
if err != nil {
return false
}
cl, _ := expr.(*ast.CompositeLit)
if cl == nil {
return false
}
at, _ := cl.Type.(*ast.ArrayType)
if at == nil {
return false
}
return replaceNode(parent, bad, at)
}
// precedingToken scans src to find the token preceding pos.
func precedingToken(pos token.Pos, tok *token.File, src []byte) token.Token {
s := &scanner.Scanner{}
s.Init(tok, src, nil, 0)
var lastTok token.Token
for {
p, t, _ := s.Scan()
if t == token.EOF || p >= pos {
break
}
lastTok = t
}
return lastTok
}
// fixDeferOrGoStmt tries to parse an *ast.BadStmt into a defer or a go statement.
//
// go/parser packages a statement of the form "defer x." as an *ast.BadStmt because
// it does not include a call expression. This means that go/types skips type-checking
// this statement entirely, and we can't use the type information when completing.
// Here, we try to generate a fake *ast.DeferStmt or *ast.GoStmt to put into the AST,
// instead of the *ast.BadStmt.
func fixDeferOrGoStmt(bad *ast.BadStmt, parent ast.Node, tok *token.File, src []byte) bool {
// Check if we have a bad statement containing either a "go" or "defer".
s := &scanner.Scanner{}
s.Init(tok, src, nil, 0)
var (
pos token.Pos
tkn token.Token
)
for {
if tkn == token.EOF {
return false
}
if pos >= bad.From {
break
}
pos, tkn, _ = s.Scan()
}
var stmt ast.Stmt
switch tkn {
case token.DEFER:
stmt = &ast.DeferStmt{
Defer: pos,
}
case token.GO:
stmt = &ast.GoStmt{
Go: pos,
}
default:
return false
}
var (
from, to, last token.Pos
lastToken token.Token
braceDepth int
phantomSelectors []token.Pos
)
FindTo:
for {
to, tkn, _ = s.Scan()
if from == token.NoPos {
from = to
}
switch tkn {
case token.EOF:
break FindTo
case token.SEMICOLON:
// If we aren't in nested braces, end of statement means
// end of expression.
if braceDepth == 0 {
break FindTo
}
case token.LBRACE:
braceDepth++
}
// This handles the common dangling selector case. For example in
//
// defer fmt.
// y := 1
//
// we notice the dangling period and end our expression.
//
// If the previous token was a "." and we are looking at a "}",
// the period is likely a dangling selector and needs a phantom
// "_". Likewise if the current token is on a different line than
// the period, the period is likely a dangling selector.
if lastToken == token.PERIOD && (tkn == token.RBRACE || tok.Line(to) > tok.Line(last)) {
// Insert phantom "_" selector after the dangling ".".
phantomSelectors = append(phantomSelectors, last+1)
// If we aren't in a block then end the expression after the ".".
if braceDepth == 0 {
to = last + 1
break
}
}
lastToken = tkn
last = to
switch tkn {
case token.RBRACE:
braceDepth--
if braceDepth <= 0 {
if braceDepth == 0 {
// +1 to include the "}" itself.
to += 1
}
break FindTo
}
}
}
if !from.IsValid() || tok.Offset(from) >= len(src) {
return false
}
if !to.IsValid() || tok.Offset(to) >= len(src) {
return false
}
// Insert any phantom selectors needed to prevent dangling "." from messing
// up the AST.
exprBytes := make([]byte, 0, int(to-from)+len(phantomSelectors))
for i, b := range src[tok.Offset(from):tok.Offset(to)] {
if len(phantomSelectors) > 0 && from+token.Pos(i) == phantomSelectors[0] {
exprBytes = append(exprBytes, '_')
phantomSelectors = phantomSelectors[1:]
}
exprBytes = append(exprBytes, b)
}
if len(phantomSelectors) > 0 {
exprBytes = append(exprBytes, '_')
}
expr, err := parseExpr(from, exprBytes)
if err != nil {
return false
}
// Package the expression into a fake *ast.CallExpr and re-insert
// into the function.
call := &ast.CallExpr{
Fun: expr,
Lparen: to,
Rparen: to,
}
switch stmt := stmt.(type) {
case *ast.DeferStmt:
stmt.Call = call
case *ast.GoStmt:
stmt.Call = call
}
return replaceNode(parent, bad, stmt)
}
// parseStmt parses the statement in src and updates its position to
// start at pos.
func parseStmt(pos token.Pos, src []byte) (ast.Stmt, error) {
// Wrap our expression to make it a valid Go file we can pass to ParseFile.
fileSrc := bytes.Join([][]byte{
[]byte("package fake;func _(){"),
src,
[]byte("}"),
}, nil)
// Use ParseFile instead of ParseExpr because ParseFile has
// best-effort behavior, whereas ParseExpr fails hard on any error.
fakeFile, err := parser.ParseFile(token.NewFileSet(), "", fileSrc, 0)
if fakeFile == nil {
return nil, errors.Errorf("error reading fake file source: %v", err)
}
// Extract our expression node from inside the fake file.
if len(fakeFile.Decls) == 0 {
return nil, errors.Errorf("error parsing fake file: %v", err)
}
fakeDecl, _ := fakeFile.Decls[0].(*ast.FuncDecl)
if fakeDecl == nil || len(fakeDecl.Body.List) == 0 {
return nil, errors.Errorf("no statement in %s: %v", src, err)
}
stmt := fakeDecl.Body.List[0]
// parser.ParseFile returns undefined positions.
// Adjust them for the current file.
offsetPositions(stmt, pos-1-(stmt.Pos()-1))
return stmt, nil
}
// parseExpr parses the expression in src and updates its position to
// start at pos.
func parseExpr(pos token.Pos, src []byte) (ast.Expr, error) {
stmt, err := parseStmt(pos, src)
if err != nil {
return nil, err
}
exprStmt, ok := stmt.(*ast.ExprStmt)
if !ok {
return nil, errors.Errorf("no expr in %s: %v", src, err)
}
return exprStmt.X, nil
}
var tokenPosType = reflect.TypeOf(token.NoPos)
// offsetPositions applies an offset to the positions in an ast.Node.
func offsetPositions(n ast.Node, offset token.Pos) {
ast.Inspect(n, func(n ast.Node) bool {
if n == nil {
return false
}
v := reflect.ValueOf(n).Elem()
switch v.Kind() {
case reflect.Struct:
for i := 0; i < v.NumField(); i++ {
f := v.Field(i)
if f.Type() != tokenPosType {
continue
}
if !f.CanSet() {
continue
}
f.SetInt(f.Int() + int64(offset))
}
}
return true
})
}
// replaceNode updates parent's child oldChild to be newChild. It
// returns whether it replaced successfully.
func replaceNode(parent, oldChild, newChild ast.Node) bool {
if parent == nil || oldChild == nil || newChild == nil {
return false
}
parentVal := reflect.ValueOf(parent).Elem()
if parentVal.Kind() != reflect.Struct {
return false
}
newChildVal := reflect.ValueOf(newChild)
tryReplace := func(v reflect.Value) bool {
if !v.CanSet() || !v.CanInterface() {
return false
}
// If the existing value is oldChild, we found our child. Make
// sure our newChild is assignable and then make the swap.
if v.Interface() == oldChild && newChildVal.Type().AssignableTo(v.Type()) {
v.Set(newChildVal)
return true
}
return false
}
// Loop over parent's struct fields.
for i := 0; i < parentVal.NumField(); i++ {
f := parentVal.Field(i)
switch f.Kind() {
// Check interface and pointer fields.
case reflect.Interface, reflect.Ptr:
if tryReplace(f) {
return true
}
// Search through any slice fields.
case reflect.Slice:
for i := 0; i < f.Len(); i++ {
if tryReplace(f.Index(i)) {
return true
}
}
}
}
return false
}