forked from golang/tools
/
statements.go
305 lines (260 loc) · 7.66 KB
/
statements.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
// Copyright 2020 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 completion
import (
"fmt"
"go/ast"
"go/token"
"go/types"
"golang.org/x/tools/internal/lsp/protocol"
"golang.org/x/tools/internal/lsp/snippet"
"golang.org/x/tools/internal/lsp/source"
)
// addStatementCandidates adds full statement completion candidates
// appropriate for the current context.
func (c *completer) addStatementCandidates() {
c.addErrCheckAndReturn()
c.addAssignAppend()
}
// addAssignAppend offers a completion candidate of the form:
//
// someSlice = append(someSlice, )
//
// It will offer the "append" completion in two situations:
//
// 1. Position is in RHS of assign, prefix matches "append", and
// corresponding LHS object is a slice. For example,
// "foo = ap<>" completes to "foo = append(foo, )".
//
// Or
//
// 2. Prefix is an ident or selector in an *ast.ExprStmt (i.e.
// beginning of statement), and our best matching candidate is a
// slice. For example: "foo.ba" completes to "foo.bar = append(foo.bar, )".
func (c *completer) addAssignAppend() {
if len(c.path) < 3 {
return
}
ident, _ := c.path[0].(*ast.Ident)
if ident == nil {
return
}
var (
// sliceText is the full name of our slice object, e.g. "s.abc" in
// "s.abc = app<>".
sliceText string
// needsLHS is true if we need to prepend the LHS slice name and
// "=" to our candidate.
needsLHS = false
fset = c.snapshot.FileSet()
)
switch n := c.path[1].(type) {
case *ast.AssignStmt:
// We are already in an assignment. Make sure our prefix matches "append".
if c.matcher.Score("append") <= 0 {
return
}
exprIdx := exprAtPos(c.pos, n.Rhs)
if exprIdx == len(n.Rhs) || exprIdx > len(n.Lhs)-1 {
return
}
lhsType := c.pkg.GetTypesInfo().TypeOf(n.Lhs[exprIdx])
if lhsType == nil {
return
}
// Make sure our corresponding LHS object is a slice.
if _, isSlice := lhsType.Underlying().(*types.Slice); !isSlice {
return
}
// The name or our slice is whatever's in the LHS expression.
sliceText = source.FormatNode(fset, n.Lhs[exprIdx])
case *ast.SelectorExpr:
// Make sure we are a selector at the beginning of a statement.
if _, parentIsExprtStmt := c.path[2].(*ast.ExprStmt); !parentIsExprtStmt {
return
}
// So far we only know the first part of our slice name. For
// example in "s.a<>" we only know our slice begins with "s."
// since the user could still be typing.
sliceText = source.FormatNode(fset, n.X) + "."
needsLHS = true
case *ast.ExprStmt:
needsLHS = true
default:
return
}
var (
label string
snip snippet.Builder
score = highScore
)
if needsLHS {
// Offer the long form assign + append candidate if our best
// candidate is a slice.
bestItem := c.topCandidate()
if bestItem == nil || bestItem.obj == nil || bestItem.obj.Type() == nil {
return
}
if _, isSlice := bestItem.obj.Type().Underlying().(*types.Slice); !isSlice {
return
}
// Don't rank the full form assign + append candidate above the
// slice itself.
score = bestItem.Score - 0.01
// Fill in rest of sliceText now that we have the object name.
sliceText += bestItem.Label
// Fill in the candidate's LHS bits.
label = fmt.Sprintf("%s = ", bestItem.Label)
snip.WriteText(label)
}
snip.WriteText(fmt.Sprintf("append(%s, ", sliceText))
snip.WritePlaceholder(nil)
snip.WriteText(")")
c.items = append(c.items, CompletionItem{
Label: label + fmt.Sprintf("append(%s, )", sliceText),
Kind: protocol.FunctionCompletion,
Score: score,
snippet: &snip,
})
}
// topCandidate returns the strictly highest scoring candidate
// collected so far. If the top two candidates have the same score,
// nil is returned.
func (c *completer) topCandidate() *CompletionItem {
var bestItem, secondBestItem *CompletionItem
for i := range c.items {
if bestItem == nil || c.items[i].Score > bestItem.Score {
bestItem = &c.items[i]
} else if secondBestItem == nil || c.items[i].Score > secondBestItem.Score {
secondBestItem = &c.items[i]
}
}
// If secondBestItem has the same score, bestItem isn't
// the strict best.
if secondBestItem != nil && secondBestItem.Score == bestItem.Score {
return nil
}
return bestItem
}
// addErrCheckAndReturn offers a completion candidate of the form:
//
// if err != nil {
// return nil, err
// }
//
// The position must be in a function that returns an error, and the
// statement preceding the position must be an assignment where the
// final LHS object is an error. addErrCheckAndReturn will synthesize
// zero values as necessary to make the return statement valid.
func (c *completer) addErrCheckAndReturn() {
if len(c.path) < 2 || c.enclosingFunc == nil || !c.opts.placeholders {
return
}
var (
errorType = types.Universe.Lookup("error").Type()
result = c.enclosingFunc.sig.Results()
)
// Make sure our enclosing function returns an error.
if result.Len() == 0 || !types.Identical(result.At(result.Len()-1).Type(), errorType) {
return
}
prevLine := prevStmt(c.pos, c.path)
if prevLine == nil {
return
}
// Make sure our preceding statement was as assignment.
assign, _ := prevLine.(*ast.AssignStmt)
if assign == nil || len(assign.Lhs) == 0 {
return
}
lastAssignee := assign.Lhs[len(assign.Lhs)-1]
// Make sure the final assignee is an error.
if !types.Identical(c.pkg.GetTypesInfo().TypeOf(lastAssignee), errorType) {
return
}
var (
// errText is e.g. "err" in "foo, err := bar()".
errText = source.FormatNode(c.snapshot.FileSet(), lastAssignee)
// Whether we need to include the "if" keyword in our candidate.
needsIf = true
)
// "_" isn't a real object.
if errText == "_" {
return
}
// Below we try to detect if the user has already started typing "if
// err" so we can replace what they've typed with our complete
// statement.
switch n := c.path[0].(type) {
case *ast.Ident:
switch c.path[1].(type) {
case *ast.ExprStmt:
// This handles:
//
// f, err := os.Open("foo")
// i<>
// Make sure they are typing "if".
if c.matcher.Score("if") <= 0 {
return
}
case *ast.IfStmt:
// This handles:
//
// f, err := os.Open("foo")
// if er<>
// Make sure they are typing the error's name.
if c.matcher.Score(errText) <= 0 {
return
}
needsIf = false
default:
return
}
case *ast.IfStmt:
// This handles:
//
// f, err := os.Open("foo")
// if <>
// Avoid false positives by ensuring the if's cond is a bad
// expression. For example, don't offer the completion in cases
// like "if <> somethingElse".
if _, bad := n.Cond.(*ast.BadExpr); !bad {
return
}
// If "if" is our direct prefix, we need to include it in our
// candidate since the existing "if" will be overwritten.
needsIf = c.pos == n.Pos()+token.Pos(len("if"))
}
// Build up a snippet that looks like:
//
// if err != nil {
// return <zero value>, ..., ${1:err}
// }
//
// We make the error a placeholder so it is easy to alter the error.
var snip snippet.Builder
if needsIf {
snip.WriteText("if ")
}
snip.WriteText(fmt.Sprintf("%s != nil {\n\treturn ", errText))
for i := 0; i < result.Len()-1; i++ {
snip.WriteText(formatZeroValue(result.At(i).Type(), c.qf))
snip.WriteText(", ")
}
snip.WritePlaceholder(func(b *snippet.Builder) {
b.WriteText(errText)
})
snip.WriteText("\n}")
label := fmt.Sprintf("%[1]s != nil { return %[1]s }", errText)
if needsIf {
label = "if " + label
}
c.items = append(c.items, CompletionItem{
Label: label,
// There doesn't seem to be a more appropriate kind.
Kind: protocol.KeywordCompletion,
Score: highScore,
snippet: &snip,
})
}