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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"
"golang.org/x/tools/go/ast/astutil"
"golang.org/x/tools/internal/event"
"golang.org/x/tools/internal/lsp/protocol"
errors "golang.org/x/xerrors"
)
func SignatureHelp(ctx context.Context, snapshot Snapshot, fh FileHandle, pos protocol.Position) (*protocol.SignatureInformation, int, error) {
ctx, done := event.Start(ctx, "source.SignatureHelp")
defer done()
pkg, pgf, err := GetParsedFile(ctx, snapshot, fh, NarrowestPackage)
if err != nil {
return nil, 0, errors.Errorf("getting file for SignatureHelp: %w", err)
}
spn, err := pgf.Mapper.PointSpan(pos)
if err != nil {
return nil, 0, err
}
rng, err := spn.Range(pgf.Mapper.Converter)
if err != nil {
return nil, 0, err
}
// Find a call expression surrounding the query position.
var callExpr *ast.CallExpr
path, _ := astutil.PathEnclosingInterval(pgf.File, rng.Start, rng.Start)
if path == nil {
return nil, 0, errors.Errorf("cannot find node enclosing position")
}
FindCall:
for _, node := range path {
switch node := node.(type) {
case *ast.CallExpr:
if rng.Start >= node.Lparen && rng.Start <= node.Rparen {
callExpr = node
break FindCall
}
case *ast.FuncLit, *ast.FuncType:
// The user is within an anonymous function,
// which may be the parameter to the *ast.CallExpr.
// Don't show signature help in this case.
return nil, 0, errors.Errorf("no signature help within a function declaration")
}
}
if callExpr == nil || callExpr.Fun == nil {
return nil, 0, errors.Errorf("cannot find an enclosing function")
}
qf := Qualifier(pgf.File, pkg.GetTypes(), pkg.GetTypesInfo())
// Get the object representing the function, if available.
// There is no object in certain cases such as calling a function returned by
// a function (e.g. "foo()()").
var obj types.Object
switch t := callExpr.Fun.(type) {
case *ast.Ident:
obj = pkg.GetTypesInfo().ObjectOf(t)
case *ast.SelectorExpr:
obj = pkg.GetTypesInfo().ObjectOf(t.Sel)
}
// Handle builtin functions separately.
if obj, ok := obj.(*types.Builtin); ok {
return builtinSignature(ctx, snapshot, callExpr, obj.Name(), rng.Start)
}
// Get the type information for the function being called.
sigType := pkg.GetTypesInfo().TypeOf(callExpr.Fun)
if sigType == nil {
return nil, 0, errors.Errorf("cannot get type for Fun %[1]T (%[1]v)", callExpr.Fun)
}
sig, _ := sigType.Underlying().(*types.Signature)
if sig == nil {
return nil, 0, errors.Errorf("cannot find signature for Fun %[1]T (%[1]v)", callExpr.Fun)
}
activeParam := activeParameter(callExpr, sig.Params().Len(), sig.Variadic(), rng.Start)
var (
name string
comment *ast.CommentGroup
)
if obj != nil {
node, err := objToDecl(ctx, snapshot, pkg, obj)
if err != nil {
return nil, 0, err
}
rng, err := objToMappedRange(snapshot, pkg, obj)
if err != nil {
return nil, 0, err
}
decl := Declaration{
obj: obj,
node: node,
}
decl.MappedRange = append(decl.MappedRange, rng)
d, err := HoverInfo(ctx, pkg, decl.obj, decl.node)
if err != nil {
return nil, 0, err
}
name = obj.Name()
comment = d.comment
} else {
name = "func"
}
s := NewSignature(ctx, snapshot, pkg, sig, comment, qf)
paramInfo := make([]protocol.ParameterInformation, 0, len(s.params))
for _, p := range s.params {
paramInfo = append(paramInfo, protocol.ParameterInformation{Label: p})
}
return &protocol.SignatureInformation{
Label: name + s.Format(),
Documentation: s.doc,
Parameters: paramInfo,
}, activeParam, nil
}
func builtinSignature(ctx context.Context, snapshot Snapshot, callExpr *ast.CallExpr, name string, pos token.Pos) (*protocol.SignatureInformation, int, error) {
sig, err := NewBuiltinSignature(ctx, snapshot, name)
if err != nil {
return nil, 0, err
}
paramInfo := make([]protocol.ParameterInformation, 0, len(sig.params))
for _, p := range sig.params {
paramInfo = append(paramInfo, protocol.ParameterInformation{Label: p})
}
activeParam := activeParameter(callExpr, len(sig.params), sig.variadic, pos)
return &protocol.SignatureInformation{
Label: sig.name + sig.Format(),
Documentation: sig.doc,
Parameters: paramInfo,
}, activeParam, nil
}
func activeParameter(callExpr *ast.CallExpr, numParams int, variadic bool, pos token.Pos) (activeParam int) {
if len(callExpr.Args) == 0 {
return 0
}
// First, check if the position is even in the range of the arguments.
start, end := callExpr.Lparen, callExpr.Rparen
if !(start <= pos && pos <= end) {
return 0
}
for _, expr := range callExpr.Args {
if start == token.NoPos {
start = expr.Pos()
}
end = expr.End()
if start <= pos && pos <= end {
break
}
// Don't advance the active parameter for the last parameter of a variadic function.
if !variadic || activeParam < numParams-1 {
activeParam++
}
start = expr.Pos() + 1 // to account for commas
}
return activeParam
}
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