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// Copyright 2018 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 source
import (
"context"
"go/ast"
"go/token"
"go/types"
"strings"
"time"
"golang.org/x/tools/go/ast/astutil"
"golang.org/x/tools/internal/imports"
"golang.org/x/tools/internal/lsp/fuzzy"
"golang.org/x/tools/internal/lsp/protocol"
"golang.org/x/tools/internal/lsp/snippet"
"golang.org/x/tools/internal/span"
"golang.org/x/tools/internal/telemetry/log"
"golang.org/x/tools/internal/telemetry/trace"
errors "golang.org/x/xerrors"
)
type CompletionItem struct {
// Label is the primary text the user sees for this completion item.
Label string
// Detail is supplemental information to present to the user.
// This often contains the type or return type of the completion item.
Detail string
// InsertText is the text to insert if this item is selected.
// Any of the prefix that has already been typed is not trimmed.
// The insert text does not contain snippets.
InsertText string
Kind CompletionItemKind
// An optional array of additional TextEdits that are applied when
// selecting this completion.
//
// Additional text edits should be used to change text unrelated to the current cursor position
// (for example adding an import statement at the top of the file if the completion item will
// insert an unqualified type).
AdditionalTextEdits []protocol.TextEdit
// Depth is how many levels were searched to find this completion.
// For example when completing "foo<>", "fooBar" is depth 0, and
// "fooBar.Baz" is depth 1.
Depth int
// Score is the internal relevance score.
// A higher score indicates that this completion item is more relevant.
Score float64
// snippet is the LSP snippet for the completion item. The LSP
// specification contains details about LSP snippets. For example, a
// snippet for a function with the following signature:
//
// func foo(a, b, c int)
//
// would be:
//
// foo(${1:a int}, ${2: b int}, ${3: c int})
//
// If Placeholders is false in the CompletionOptions, the above
// snippet would instead be:
//
// foo(${1:})
snippet *snippet.Builder
// Documentation is the documentation for the completion item.
Documentation string
}
// Snippet is a convenience returns the snippet if available, otherwise
// the InsertText.
// used for an item, depending on if the callee wants placeholders or not.
func (i *CompletionItem) Snippet() string {
if i.snippet != nil {
return i.snippet.String()
}
return i.InsertText
}
type CompletionItemKind int
const (
Unknown CompletionItemKind = iota
InterfaceCompletionItem
StructCompletionItem
TypeCompletionItem
ConstantCompletionItem
FieldCompletionItem
ParameterCompletionItem
VariableCompletionItem
FunctionCompletionItem
MethodCompletionItem
PackageCompletionItem
)
// Scoring constants are used for weighting the relevance of different candidates.
const (
// stdScore is the base score for all completion items.
stdScore float64 = 1.0
// highScore indicates a very relevant completion item.
highScore float64 = 10.0
// lowScore indicates an irrelevant or not useful completion item.
lowScore float64 = 0.01
)
// matcher matches a candidate's label against the user input. The
// returned score reflects the quality of the match. A score of zero
// indicates no match, and a score of one means a perfect match.
type matcher interface {
Score(candidateLabel string) (score float32)
}
// prefixMatcher implements case insensitive prefix matching.
type prefixMatcher string
func (pm prefixMatcher) Score(candidateLabel string) float32 {
if strings.HasPrefix(strings.ToLower(candidateLabel), string(pm)) {
return 1
}
return -1
}
// completer contains the necessary information for a single completion request.
type completer struct {
pkg Package
qf types.Qualifier
opts CompletionOptions
// view is the View associated with this completion request.
view View
// ctx is the context associated with this completion request.
ctx context.Context
// filename is the name of the file associated with this completion request.
filename string
// file is the AST of the file associated with this completion request.
file *ast.File
// pos is the position at which the request was triggered.
pos token.Pos
// path is the path of AST nodes enclosing the position.
path []ast.Node
// seen is the map that ensures we do not return duplicate results.
seen map[types.Object]bool
// items is the list of completion items returned.
items []CompletionItem
// surrounding describes the identifier surrounding the position.
surrounding *Selection
// expectedType contains information about the type we expect the completion
// candidate to be. It will be the zero value if no information is available.
expectedType typeInference
// enclosingFunction is the function declaration enclosing the position.
enclosingFunction *types.Signature
// enclosingCompositeLiteral contains information about the composite literal
// enclosing the position.
enclosingCompositeLiteral *compLitInfo
// deepState contains the current state of our deep completion search.
deepState deepCompletionState
// matcher matches the candidates against the surrounding prefix.
matcher matcher
// methodSetCache caches the types.NewMethodSet call, which is relatively
// expensive and can be called many times for the same type while searching
// for deep completions.
methodSetCache map[methodSetKey]*types.MethodSet
// mapper converts the positions in the file from which the completion originated.
mapper *protocol.ColumnMapper
// startTime is when we started processing this completion request. It does
// not include any time the request spent in the queue.
startTime time.Time
}
type compLitInfo struct {
// cl is the *ast.CompositeLit enclosing the position.
cl *ast.CompositeLit
// clType is the type of cl.
clType types.Type
// kv is the *ast.KeyValueExpr enclosing the position, if any.
kv *ast.KeyValueExpr
// inKey is true if we are certain the position is in the key side
// of a key-value pair.
inKey bool
// maybeInFieldName is true if inKey is false and it is possible
// we are completing a struct field name. For example,
// "SomeStruct{<>}" will be inKey=false, but maybeInFieldName=true
// because we _could_ be completing a field name.
maybeInFieldName bool
}
type methodSetKey struct {
typ types.Type
addressable bool
}
// A Selection represents the cursor position and surrounding identifier.
type Selection struct {
content string
cursor token.Pos
mappedRange
}
func (p Selection) Prefix() string {
return p.content[:p.cursor-p.spanRange.Start]
}
func (c *completer) setSurrounding(ident *ast.Ident) {
if c.surrounding != nil {
return
}
if !(ident.Pos() <= c.pos && c.pos <= ident.End()) {
return
}
c.surrounding = &Selection{
content: ident.Name,
cursor: c.pos,
mappedRange: mappedRange{
spanRange: span.NewRange(c.view.Session().Cache().FileSet(), ident.Pos(), ident.End()),
m: c.mapper,
},
}
if c.opts.FuzzyMatching {
c.matcher = fuzzy.NewMatcher(c.surrounding.Prefix(), fuzzy.Symbol)
} else {
c.matcher = prefixMatcher(strings.ToLower(c.surrounding.Prefix()))
}
}
func (c *completer) getSurrounding() *Selection {
if c.surrounding == nil {
c.surrounding = &Selection{
content: "",
cursor: c.pos,
mappedRange: mappedRange{
spanRange: span.NewRange(c.view.Session().Cache().FileSet(), c.pos, c.pos),
m: c.mapper,
},
}
}
return c.surrounding
}
// found adds a candidate completion. We will also search through the object's
// members for more candidates.
func (c *completer) found(obj types.Object, score float64, imp *imports.ImportInfo) {
if obj.Pkg() != nil && obj.Pkg() != c.pkg.GetTypes() && !obj.Exported() {
// obj is not accessible because it lives in another package and is not
// exported. Don't treat it as a completion candidate.
return
}
if c.inDeepCompletion() {
// When searching deep, just make sure we don't have a cycle in our chain.
// We don't dedupe by object because we want to allow both "foo.Baz" and
// "bar.Baz" even though "Baz" is represented the same types.Object in both.
for _, seenObj := range c.deepState.chain {
if seenObj == obj {
return
}
}
} else {
// At the top level, dedupe by object.
if c.seen[obj] {
return
}
c.seen[obj] = true
}
// If we are running out of budgeted time we must limit our search for deep
// completion candidates.
if c.shouldPrune() {
return
}
cand := candidate{
obj: obj,
score: score,
imp: imp,
}
if c.matchingCandidate(&cand) {
cand.score *= highScore
} else if isTypeName(obj) {
// If obj is a *types.TypeName that didn't otherwise match, check
// if a literal object of this type makes a good candidate.
c.literal(obj.Type())
}
// Favor shallow matches by lowering weight according to depth.
cand.score -= cand.score * float64(len(c.deepState.chain)) / 10
if cand.score < 0 {
cand.score = 0
}
cand.name = c.deepState.chainString(obj.Name())
matchScore := c.matcher.Score(cand.name)
if matchScore > 0 {
cand.score *= float64(matchScore)
// Avoid calling c.item() for deep candidates that wouldn't be in the top
// MaxDeepCompletions anyway.
if !c.inDeepCompletion() || c.deepState.isHighScore(cand.score) {
if item, err := c.item(cand); err == nil {
c.items = append(c.items, item)
} else {
log.Error(c.ctx, "error generating completion item", err)
}
}
}
c.deepSearch(obj)
}
// candidate represents a completion candidate.
type candidate struct {
// obj is the types.Object to complete to.
obj types.Object
// score is used to rank candidates.
score float64
// name is the deep object name path, e.g. "foo.bar"
name string
// expandFuncCall is true if obj should be invoked in the completion.
// For example, expandFuncCall=true yields "foo()", expandFuncCall=false yields "foo".
expandFuncCall bool
// imp is the import that needs to be added to this package in order
// for this candidate to be valid. nil if no import needed.
imp *imports.ImportInfo
}
// Completion returns a list of possible candidates for completion, given a
// a file and a position.
//
// The selection is computed based on the preceding identifier and can be used by
// the client to score the quality of the completion. For instance, some clients
// may tolerate imperfect matches as valid completion results, since users may make typos.
func Completion(ctx context.Context, view View, f GoFile, pos protocol.Position, opts CompletionOptions) ([]CompletionItem, *Selection, error) {
ctx, done := trace.StartSpan(ctx, "source.Completion")
defer done()
startTime := time.Now()
cphs, err := f.CheckPackageHandles(ctx)
if err != nil {
return nil, nil, err
}
cph := NarrowestCheckPackageHandle(cphs)
pkg, err := cph.Check(ctx)
if err != nil {
return nil, nil, err
}
ph, err := pkg.File(f.URI())
if err != nil {
return nil, nil, err
}
file, m, _, err := ph.Cached(ctx)
if err != nil {
return nil, nil, err
}
spn, err := m.PointSpan(pos)
if err != nil {
return nil, nil, err
}
rng, err := spn.Range(m.Converter)
if err != nil {
return nil, nil, err
}
// Completion is based on what precedes the cursor.
// Find the path to the position before pos.
path, _ := astutil.PathEnclosingInterval(file, rng.Start-1, rng.Start-1)
if path == nil {
return nil, nil, errors.Errorf("cannot find node enclosing position")
}
// Skip completion inside comments.
for _, g := range file.Comments {
if g.Pos() <= rng.Start && rng.Start <= g.End() {
return nil, nil, nil
}
}
// Skip completion inside any kind of literal.
if _, ok := path[0].(*ast.BasicLit); ok {
return nil, nil, nil
}
clInfo := enclosingCompositeLiteral(path, rng.Start, pkg.GetTypesInfo())
c := &completer{
pkg: pkg,
qf: qualifier(file, pkg.GetTypes(), pkg.GetTypesInfo()),
view: view,
ctx: ctx,
filename: f.URI().Filename(),
file: file,
path: path,
pos: rng.Start,
seen: make(map[types.Object]bool),
enclosingFunction: enclosingFunction(path, rng.Start, pkg.GetTypesInfo()),
enclosingCompositeLiteral: clInfo,
opts: opts,
// default to a matcher that always matches
matcher: prefixMatcher(""),
methodSetCache: make(map[methodSetKey]*types.MethodSet),
mapper: m,
startTime: startTime,
}
if opts.Deep {
// Initialize max search depth to unlimited.
c.deepState.maxDepth = -1
}
// Set the filter surrounding.
if ident, ok := path[0].(*ast.Ident); ok {
c.setSurrounding(ident)
}
c.expectedType = expectedType(c)
// Struct literals are handled entirely separately.
if c.wantStructFieldCompletions() {
if err := c.structLiteralFieldName(); err != nil {
return nil, nil, err
}
return c.items, c.getSurrounding(), nil
}
switch n := path[0].(type) {
case *ast.Ident:
// Is this the Sel part of a selector?
if sel, ok := path[1].(*ast.SelectorExpr); ok && sel.Sel == n {
if err := c.selector(sel); err != nil {
return nil, nil, err
}
return c.items, c.getSurrounding(), nil
}
// reject defining identifiers
if obj, ok := pkg.GetTypesInfo().Defs[n]; ok {
if v, ok := obj.(*types.Var); ok && v.IsField() {
// An anonymous field is also a reference to a type.
} else {
of := ""
if obj != nil {
qual := types.RelativeTo(pkg.GetTypes())
of += ", of " + types.ObjectString(obj, qual)
}
return nil, nil, errors.Errorf("this is a definition%s", of)
}
}
if err := c.lexical(); err != nil {
return nil, nil, err
}
// The function name hasn't been typed yet, but the parens are there:
// recv.‸(arg)
case *ast.TypeAssertExpr:
// Create a fake selector expression.
if err := c.selector(&ast.SelectorExpr{X: n.X}); err != nil {
return nil, nil, err
}
case *ast.SelectorExpr:
// The go parser inserts a phantom "_" Sel node when the selector is
// not followed by an identifier or a "(". The "_" isn't actually in
// the text, so don't think it is our surrounding.
// TODO: Find a way to differentiate between phantom "_" and real "_",
// perhaps by checking if "_" is present in file contents.
if n.Sel.Name != "_" || c.pos != n.Sel.Pos() {
c.setSurrounding(n.Sel)
}
if err := c.selector(n); err != nil {
return nil, nil, err
}
default:
// fallback to lexical completions
if err := c.lexical(); err != nil {
return nil, nil, err
}
}
return c.items, c.getSurrounding(), nil
}
func (c *completer) wantStructFieldCompletions() bool {
clInfo := c.enclosingCompositeLiteral
if clInfo == nil {
return false
}
return clInfo.isStruct() && (clInfo.inKey || clInfo.maybeInFieldName)
}
func (c *completer) wantTypeName() bool {
return c.expectedType.wantTypeName
}
// selector finds completions for the specified selector expression.
func (c *completer) selector(sel *ast.SelectorExpr) error {
// Is sel a qualified identifier?
if id, ok := sel.X.(*ast.Ident); ok {
if pkgname, ok := c.pkg.GetTypesInfo().Uses[id].(*types.PkgName); ok {
c.packageMembers(pkgname)
return nil
}
}
// Invariant: sel is a true selector.
tv, ok := c.pkg.GetTypesInfo().Types[sel.X]
if !ok {
return errors.Errorf("cannot resolve %s", sel.X)
}
return c.methodsAndFields(tv.Type, tv.Addressable())
}
func (c *completer) packageMembers(pkg *types.PkgName) {
scope := pkg.Imported().Scope()
for _, name := range scope.Names() {
c.found(scope.Lookup(name), stdScore, nil)
}
}
func (c *completer) methodsAndFields(typ types.Type, addressable bool) error {
mset := c.methodSetCache[methodSetKey{typ, addressable}]
if mset == nil {
if addressable && !types.IsInterface(typ) && !isPointer(typ) {
// Add methods of *T, which includes methods with receiver T.
mset = types.NewMethodSet(types.NewPointer(typ))
} else {
// Add methods of T.
mset = types.NewMethodSet(typ)
}
c.methodSetCache[methodSetKey{typ, addressable}] = mset
}
for i := 0; i < mset.Len(); i++ {
c.found(mset.At(i).Obj(), stdScore, nil)
}
// Add fields of T.
for _, f := range fieldSelections(typ) {
c.found(f, stdScore, nil)
}
return nil
}
// lexical finds completions in the lexical environment.
func (c *completer) lexical() error {
var scopes []*types.Scope // scopes[i], where i<len(path), is the possibly nil Scope of path[i].
for _, n := range c.path {
switch node := n.(type) {
case *ast.FuncDecl:
n = node.Type
case *ast.FuncLit:
n = node.Type
}
scopes = append(scopes, c.pkg.GetTypesInfo().Scopes[n])
}
scopes = append(scopes, c.pkg.GetTypes().Scope(), types.Universe)
builtinIota := types.Universe.Lookup("iota")
// Track seen variables to avoid showing completions for shadowed variables.
// This works since we look at scopes from innermost to outermost.
seen := make(map[string]struct{})
// Process scopes innermost first.
for i, scope := range scopes {
if scope == nil {
continue
}
for _, name := range scope.Names() {
declScope, obj := scope.LookupParent(name, c.pos)
if declScope != scope {
continue // Name was declared in some enclosing scope, or not at all.
}
// If obj's type is invalid, find the AST node that defines the lexical block
// containing the declaration of obj. Don't resolve types for packages.
if _, ok := obj.(*types.PkgName); !ok && obj.Type() == types.Typ[types.Invalid] {
// Match the scope to its ast.Node. If the scope is the package scope,
// use the *ast.File as the starting node.
var node ast.Node
if i < len(c.path) {
node = c.path[i]
} else if i == len(c.path) { // use the *ast.File for package scope
node = c.path[i-1]
}
if node != nil {
if resolved := resolveInvalid(obj, node, c.pkg.GetTypesInfo()); resolved != nil {
obj = resolved
}
}
}
// Don't suggest "iota" outside of const decls.
if obj == builtinIota && !c.inConstDecl() {
continue
}
// If we haven't already added a candidate for an object with this name.
if _, ok := seen[obj.Name()]; !ok {
seen[obj.Name()] = struct{}{}
c.found(obj, stdScore, nil)
}
}
}
if c.opts.Unimported {
// Suggest packages that have not been imported yet.
pkgs, err := CandidateImports(c.ctx, c.view, c.filename)
if err != nil {
return err
}
score := stdScore
// Rank unimported packages significantly lower than other results.
score *= 0.07
for _, pkg := range pkgs {
if _, ok := seen[pkg.IdentName]; !ok {
// Do not add the unimported packages to seen, since we can have
// multiple packages of the same name as completion suggestions, since
// only one will be chosen.
obj := types.NewPkgName(0, nil, pkg.IdentName, types.NewPackage(pkg.StmtInfo.ImportPath, pkg.IdentName))
c.found(obj, score, &pkg.StmtInfo)
}
}
}
if c.expectedType.objType != nil {
// If we have an expected type and it is _not_ a named type, see
// if an object literal makes a good candidate. Named types are
// handled during the normal lexical object search. For example,
// if our expected type is "[]int", this will add a candidate of
// "[]int{}".
if _, named := deref(c.expectedType.objType).(*types.Named); !named {
c.literal(c.expectedType.objType)
}
}
return nil
}
func (c *completer) inConstDecl() bool {
for _, n := range c.path {
if decl, ok := n.(*ast.GenDecl); ok && decl.Tok == token.CONST {
return true
}
}
return false
}
// structLiteralFieldName finds completions for struct field names inside a struct literal.
func (c *completer) structLiteralFieldName() error {
clInfo := c.enclosingCompositeLiteral
// Mark fields of the composite literal that have already been set,
// except for the current field.
addedFields := make(map[*types.Var]bool)
for _, el := range clInfo.cl.Elts {
if kvExpr, ok := el.(*ast.KeyValueExpr); ok {
if clInfo.kv == kvExpr {
continue
}
if key, ok := kvExpr.Key.(*ast.Ident); ok {
if used, ok := c.pkg.GetTypesInfo().Uses[key]; ok {
if usedVar, ok := used.(*types.Var); ok {
addedFields[usedVar] = true
}
}
}
}
}
switch t := clInfo.clType.(type) {
case *types.Struct:
for i := 0; i < t.NumFields(); i++ {
field := t.Field(i)
if !addedFields[field] {
c.found(field, highScore, nil)
}
}
// Add lexical completions if we aren't certain we are in the key part of a
// key-value pair.
if clInfo.maybeInFieldName {
return c.lexical()
}
default:
return c.lexical()
}
return nil
}
func (cl *compLitInfo) isStruct() bool {
_, ok := cl.clType.(*types.Struct)
return ok
}
// enclosingCompositeLiteral returns information about the composite literal enclosing the
// position.
func enclosingCompositeLiteral(path []ast.Node, pos token.Pos, info *types.Info) *compLitInfo {
for _, n := range path {
switch n := n.(type) {
case *ast.CompositeLit:
// The enclosing node will be a composite literal if the user has just
// opened the curly brace (e.g. &x{<>) or the completion request is triggered
// from an already completed composite literal expression (e.g. &x{foo: 1, <>})
//
// The position is not part of the composite literal unless it falls within the
// curly braces (e.g. "foo.Foo<>Struct{}").
if !(n.Lbrace <= pos && pos <= n.Rbrace) {
return nil
}
tv, ok := info.Types[n]
if !ok {
return nil
}
clInfo := compLitInfo{
cl: n,
clType: deref(tv.Type).Underlying(),
}
var (
expr ast.Expr
hasKeys bool
)
for _, el := range n.Elts {
// Remember the expression that the position falls in, if any.
if el.Pos() <= pos && pos <= el.End() {
expr = el
}
if kv, ok := el.(*ast.KeyValueExpr); ok {
hasKeys = true
// If expr == el then we know the position falls in this expression,
// so also record kv as the enclosing *ast.KeyValueExpr.
if expr == el {
clInfo.kv = kv
break
}
}
}
if clInfo.kv != nil {
// If in a *ast.KeyValueExpr, we know we are in the key if the position
// is to the left of the colon (e.g. "Foo{F<>: V}".
clInfo.inKey = pos <= clInfo.kv.Colon
} else if hasKeys {
// If we aren't in a *ast.KeyValueExpr but the composite literal has
// other *ast.KeyValueExprs, we must be on the key side of a new
// *ast.KeyValueExpr (e.g. "Foo{F: V, <>}").
clInfo.inKey = true
} else {
switch clInfo.clType.(type) {
case *types.Struct:
if len(n.Elts) == 0 {
// If the struct literal is empty, next could be a struct field
// name or an expression (e.g. "Foo{<>}" could become "Foo{F:}"
// or "Foo{someVar}").
clInfo.maybeInFieldName = true
} else if len(n.Elts) == 1 {
// If there is one expression and the position is in that expression
// and the expression is an identifier, we may be writing a field
// name or an expression (e.g. "Foo{F<>}").
_, clInfo.maybeInFieldName = expr.(*ast.Ident)
}
case *types.Map:
// If we aren't in a *ast.KeyValueExpr we must be adding a new key
// to the map.
clInfo.inKey = true
}
}
return &clInfo
default:
if breaksExpectedTypeInference(n) {
return nil
}
}
}
return nil
}
// enclosingFunction returns the signature of the function enclosing the given position.
func enclosingFunction(path []ast.Node, pos token.Pos, info *types.Info) *types.Signature {
for _, node := range path {
switch t := node.(type) {
case *ast.FuncDecl:
if obj, ok := info.Defs[t.Name]; ok {
return obj.Type().(*types.Signature)
}
case *ast.FuncLit:
if typ, ok := info.Types[t]; ok {
return typ.Type.(*types.Signature)
}
}
}
return nil
}
func (c *completer) expectedCompositeLiteralType() types.Type {
clInfo := c.enclosingCompositeLiteral
switch t := clInfo.clType.(type) {
case *types.Slice:
if clInfo.inKey {
return types.Typ[types.Int]
}
return t.Elem()
case *types.Array:
if clInfo.inKey {
return types.Typ[types.Int]
}
return t.Elem()
case *types.Map:
if clInfo.inKey {
return t.Key()
}
return t.Elem()
case *types.Struct:
// If we are completing a key (i.e. field name), there is no expected type.
if clInfo.inKey {
return nil
}
// If we are in a key-value pair, but not in the key, then we must be on the
// value side. The expected type of the value will be determined from the key.
if clInfo.kv != nil {
if key, ok := clInfo.kv.Key.(*ast.Ident); ok {
for i := 0; i < t.NumFields(); i++ {
if field := t.Field(i); field.Name() == key.Name {
return field.Type()
}
}
}
} else {
// If we aren't in a key-value pair and aren't in the key, we must be using
// implicit field names.
// The order of the literal fields must match the order in the struct definition.
// Find the element that the position belongs to and suggest that field's type.
if i := indexExprAtPos(c.pos, clInfo.cl.Elts); i < t.NumFields() {
return t.Field(i).Type()
}
}
}
return nil
}
// typeModifier represents an operator that changes the expected type.
type typeModifier int
const (
star typeModifier = iota // dereference operator for expressions, pointer indicator for types
reference // reference ("&") operator
chanRead // channel read ("<-") operator
)
// typeInference holds information we have inferred about a type that can be
// used at the current position.
type typeInference struct {
// objType is the desired type of an object used at the query position.
objType types.Type
// variadic is true if objType is a slice type from an initial
// variadic param.
variadic bool
// wantTypeName is true if we expect the name of a type.
wantTypeName bool
// modifiers are prefixes such as "*", "&" or "<-" that influence how
// a candidate type relates to the expected type.
modifiers []typeModifier
// assertableFrom is a type that must be assertable to our candidate type.
assertableFrom types.Type
// convertibleTo is a type our candidate type must be convertible to.
convertibleTo types.Type
}
// expectedType returns information about the expected type for an expression at
// the query position.
func expectedType(c *completer) typeInference {
if ti := expectTypeName(c); ti.wantTypeName {
return ti
}
if c.enclosingCompositeLiteral != nil {
return typeInference{objType: c.expectedCompositeLiteralType()}
}
var (
modifiers []typeModifier
variadic bool
typ types.Type
convertibleTo types.Type
)
Nodes:
for i, node := range c.path {
switch node := node.(type) {
case *ast.BinaryExpr:
// Determine if query position comes from left or right of op.
e := node.X
if c.pos < node.OpPos {
e = node.Y
}
if tv, ok := c.pkg.GetTypesInfo().Types[e]; ok {
typ = tv.Type
break Nodes
}
case *ast.AssignStmt:
// Only rank completions if you are on the right side of the token.
if c.pos > node.TokPos {
i := indexExprAtPos(c.pos, node.Rhs)
if i >= len(node.Lhs) {
i = len(node.Lhs) - 1
}
if tv, ok := c.pkg.GetTypesInfo().Types[node.Lhs[i]]; ok {
typ = tv.Type
break Nodes
}
}
return typeInference{}
case *ast.CallExpr:
// Only consider CallExpr args if position falls between parens.
if node.Lparen <= c.pos && c.pos <= node.Rparen {
// For type conversions like "int64(foo)" we can only infer our
// desired type is convertible to int64.
if typ := typeConversion(node, c.pkg.GetTypesInfo()); typ != nil {
convertibleTo = typ
break Nodes
}
if tv, ok := c.pkg.GetTypesInfo().Types[node.Fun]; ok {
if sig, ok := tv.Type.(*types.Signature); ok {
if sig.Params().Len() == 0 {
return typeInference{}
}
i := indexExprAtPos(c.pos, node.Args)
// Make sure not to run past the end of expected parameters.
if i >= sig.Params().Len() {
i = sig.Params().Len() - 1
}
typ = sig.Params().At(i).Type()
variadic = sig.Variadic() && i == sig.Params().Len()-1
break Nodes
}
}
}
return typeInference{}
case *ast.ReturnStmt:
if sig := c.enclosingFunction; sig != nil {
// Find signature result that corresponds to our return statement.
if resultIdx := indexExprAtPos(c.pos, node.Results); resultIdx < len(node.Results) {
if resultIdx < sig.Results().Len() {
typ = sig.Results().At(resultIdx).Type()
break Nodes
}
}
}
return typeInference{}
case *ast.CaseClause:
if swtch, ok := findSwitchStmt(c.path[i+1:], c.pos, node).(*ast.SwitchStmt); ok {
if tv, ok := c.pkg.GetTypesInfo().Types[swtch.Tag]; ok {
typ = tv.Type
break Nodes
}
}
return typeInference{}
case *ast.SliceExpr:
// Make sure position falls within the brackets (e.g. "foo[a:<>]").
if node.Lbrack < c.pos && c.pos <= node.Rbrack {
typ = types.Typ[types.Int]
break Nodes
}
return typeInference{}
case *ast.IndexExpr:
// Make sure position falls within the brackets (e.g. "foo[<>]").
if node.Lbrack < c.pos && c.pos <= node.Rbrack {
if tv, ok := c.pkg.GetTypesInfo().Types[node.X]; ok {
switch t := tv.Type.Underlying().(type) {
case *types.Map:
typ = t.Key()
case *types.Slice, *types.Array:
typ = types.Typ[types.Int]
default:
return typeInference{}
}
break Nodes
}
}
return typeInference{}
case *ast.SendStmt:
// Make sure we are on right side of arrow (e.g. "foo <- <>").
if c.pos > node.Arrow+1 {
if tv, ok := c.pkg.GetTypesInfo().Types[node.Chan]; ok {
if ch, ok := tv.Type.Underlying().(*types.Chan); ok {
typ = ch.Elem()
break Nodes
}
}
}
return typeInference{}
case *ast.StarExpr:
modifiers = append(modifiers, star)
case *ast.UnaryExpr:
switch node.Op {
case token.AND:
modifiers = append(modifiers, reference)
case token.ARROW:
modifiers = append(modifiers, chanRead)
}
default:
if breaksExpectedTypeInference(node) {
return typeInference{}
}
}
}
return typeInference{
variadic: variadic,
objType: typ,
modifiers: modifiers,
convertibleTo: convertibleTo,
}
}
// applyTypeModifiers applies the list of type modifiers to a type.
func (ti typeInference) applyTypeModifiers(typ types.Type) types.Type {
for _, mod := range ti.modifiers {
switch mod {
case star:
// For every "*" deref operator, remove a pointer layer from candidate type.
typ = deref(typ)
case reference:
// For every "&" ref operator, add another pointer layer to candidate type.
typ = types.NewPointer(typ)
case chanRead:
// For every "<-" operator, remove a layer of channelness.
if ch, ok := typ.(*types.Chan); ok {
typ = ch.Elem()
}
}
}
return typ
}
// applyTypeNameModifiers applies the list of type modifiers to a type name.
func (ti typeInference) applyTypeNameModifiers(typ types.Type) types.Type {
for _, mod := range ti.modifiers {
switch mod {
case star:
// For every "*" indicator, add a pointer layer to type name.
typ = types.NewPointer(typ)
}
}
return typ
}
// findSwitchStmt returns an *ast.CaseClause's corresponding *ast.SwitchStmt or
// *ast.TypeSwitchStmt. path should start from the case clause's first ancestor.
func findSwitchStmt(path []ast.Node, pos token.Pos, c *ast.CaseClause) ast.Stmt {
// Make sure position falls within a "case <>:" clause.
if exprAtPos(pos, c.List) == nil {
return nil
}
// A case clause is always nested within a block statement in a switch statement.
if len(path) < 2 {
return nil
}
if _, ok := path[0].(*ast.BlockStmt); !ok {
return nil
}
switch s := path[1].(type) {
case *ast.SwitchStmt:
return s
case *ast.TypeSwitchStmt:
return s
default:
return nil
}
}
// breaksExpectedTypeInference reports if an expression node's type is unrelated
// to its child expression node types. For example, "Foo{Bar: x.Baz(<>)}" should
// expect a function argument, not a composite literal value.
func breaksExpectedTypeInference(n ast.Node) bool {
switch n.(type) {
case *ast.FuncLit, *ast.CallExpr, *ast.TypeAssertExpr, *ast.IndexExpr, *ast.SliceExpr, *ast.CompositeLit:
return true
default:
return false
}
}
// expectTypeName returns information about the expected type name at position.
func expectTypeName(c *completer) typeInference {
var (
wantTypeName bool
modifiers []typeModifier
assertableFrom types.Type
)
Nodes:
for i, p := range c.path {
switch n := p.(type) {
case *ast.FuncDecl:
// Expect type names in a function declaration receiver, params and results.
if r := n.Recv; r != nil && r.Pos() <= c.pos && c.pos <= r.End() {
wantTypeName = true
break Nodes
}
if t := n.Type; t != nil {
if p := t.Params; p != nil && p.Pos() <= c.pos && c.pos <= p.End() {
wantTypeName = true
break Nodes
}
if r := t.Results; r != nil && r.Pos() <= c.pos && c.pos <= r.End() {
wantTypeName = true
break Nodes
}
}
return typeInference{}
case *ast.CaseClause:
// Expect type names in type switch case clauses.
if swtch, ok := findSwitchStmt(c.path[i+1:], c.pos, n).(*ast.TypeSwitchStmt); ok {
// The case clause types must be assertable from the type switch parameter.
ast.Inspect(swtch.Assign, func(n ast.Node) bool {
if ta, ok := n.(*ast.TypeAssertExpr); ok {
assertableFrom = c.pkg.GetTypesInfo().TypeOf(ta.X)
return false
}
return true
})
wantTypeName = true
break Nodes
}
return typeInference{}
case *ast.TypeAssertExpr:
// Expect type names in type assert expressions.
if n.Lparen < c.pos && c.pos <= n.Rparen {
// The type in parens must be assertable from the expression type.
assertableFrom = c.pkg.GetTypesInfo().TypeOf(n.X)
wantTypeName = true
break Nodes
}
return typeInference{}
case *ast.StarExpr:
modifiers = append(modifiers, star)
default:
if breaksExpectedTypeInference(p) {
return typeInference{}
}
}
}
return typeInference{
wantTypeName: wantTypeName,
modifiers: modifiers,
assertableFrom: assertableFrom,
}
}
// matchingType reports whether a type matches the expected type.
func (c *completer) matchingType(T types.Type) bool {
fakeObj := types.NewVar(token.NoPos, c.pkg.GetTypes(), "", T)
return c.matchingCandidate(&candidate{obj: fakeObj})
}
// matchingCandidate reports whether a candidate matches our type
// inferences.
func (c *completer) matchingCandidate(cand *candidate) bool {
if isTypeName(cand.obj) {
return c.matchingTypeName(cand)
}
objType := cand.obj.Type()
// Default to invoking *types.Func candidates. This is so function
// completions in an empty statement (or other cases with no expected type)
// are invoked by default.
cand.expandFuncCall = isFunc(cand.obj)
typeMatches := func(candType types.Type) bool {
// Take into account any type modifiers on the expected type.
candType = c.expectedType.applyTypeModifiers(candType)
if c.expectedType.objType != nil {
wantType := types.Default(c.expectedType.objType)
// Handle untyped values specially since AssignableTo gives false negatives
// for them (see https://golang.org/issue/32146).
if candBasic, ok := candType.(*types.Basic); ok && candBasic.Info()&types.IsUntyped > 0 {
if wantBasic, ok := wantType.Underlying().(*types.Basic); ok {
// Check that their constant kind (bool|int|float|complex|string) matches.
// This doesn't take into account the constant value, so there will be some
// false positives due to integer sign and overflow.
return candBasic.Info()&types.IsConstType == wantBasic.Info()&types.IsConstType
}
return false
}
// AssignableTo covers the case where the types are equal, but also handles
// cases like assigning a concrete type to an interface type.
return types.AssignableTo(candType, wantType)
}
return false
}
if typeMatches(objType) {
// If obj's type matches, we don't want to expand to an invocation of obj.
cand.expandFuncCall = false
return true
}
// Try using a function's return type as its type.
if sig, ok := objType.Underlying().(*types.Signature); ok && sig.Results().Len() == 1 {
if typeMatches(sig.Results().At(0).Type()) {
// If obj's return value matches the expected type, we need to invoke obj
// in the completion.
cand.expandFuncCall = true
return true
}
}
if c.expectedType.convertibleTo != nil {
return types.ConvertibleTo(objType, c.expectedType.convertibleTo)
}
return false
}
func (c *completer) matchingTypeName(cand *candidate) bool {
if !c.wantTypeName() {
return false
}
// Take into account any type name modifier prefixes.
actual := c.expectedType.applyTypeNameModifiers(cand.obj.Type())
if c.expectedType.assertableFrom != nil {
// Don't suggest the starting type in type assertions. For example,
// if "foo" is an io.Writer, don't suggest "foo.(io.Writer)".
if types.Identical(c.expectedType.assertableFrom, actual) {
return false
}
if intf, ok := c.expectedType.assertableFrom.Underlying().(*types.Interface); ok {
if !types.AssertableTo(intf, actual) {
return false
}
}
}
// Default to saying any type name is a match.
return true
}