internal/lsp: add literal completion candidates

Add support for literal completion candidates such as "[]int{}" or
"make([]int, 0)". We support both named and unnamed types. I used the
existing type matching logic, so, for example, if the expected type is
an interface, we will suggest literal candidates that implement the
interface.

The literal candidates have a lower score than normal matching
candidates, so they shouldn't be disruptive in cases where you don't
want a literal candidate.

This commit adds support for slice, array, struct, map, and channel
literal candidates since they are pretty similar. Functions will be
supported in a subsequent commit.

I also added support for setting a snippet's final tab stop. This is
useful if you want the cursor to end up somewhere other than the
character after the snippet.

Change-Id: Id3b74260fff4d61703989b422267021b00cec005
Reviewed-on: https://go-review.googlesource.com/c/tools/+/193698
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/completion.go

@@ -73,6 +73,12 @@ func (s *Server) toProtocolCompletionItems(candidates []source.CompletionItem, r
 			insertText = candidate.Snippet()
 		}
 
+		// This can happen if the client has snippets disabled but the
+		// candidate only supports snippet insertion.
+		if insertText == "" {
+			continue
+		}
+
 		item := protocol.CompletionItem{
 			Label:  candidate.Label,
 			Detail: candidate.Detail,

internal/lsp/lsp_test.go

@@ -180,7 +180,7 @@ func (r *runner) Completion(t *testing.T, data tests.Completions, snippets tests
 				}
 			}
 			if got == nil {
-				t.Fatalf("%s: couldn't find completion matching %q", src.URI(), wantItem.Label)
+				t.Fatalf("%s:%d: couldn't find completion matching %q", src.URI(), src.Start().Line(), wantItem.Label)
 			}
 			var expected string
 			if usePlaceholders {

internal/lsp/snippet/snippet_builder.go

@@ -50,6 +50,13 @@ func (b *Builder) WritePlaceholder(fn func(*Builder)) {
 	b.sb.WriteByte('}')
 }
 
+// WriteFinalTabstop marks where cursor ends up after the user has
+// cycled through all the normal tab stops. It defaults to the
+// character after the snippet.
+func (b *Builder) WriteFinalTabstop() {
+	fmt.Fprint(&b.sb, "$0")
+}
+
 // In addition to '\', '}', and '$', snippet choices also use '|' and ',' as
 // meta characters, so they must be escaped within the choices.
 var choiceReplacer = strings.NewReplacer(

internal/lsp/snippet/snippet_builder_test.go

@@ -48,4 +48,9 @@ func TestSnippetBuilder(t *testing.T) {
 	expect(`${1|one,{ \} \$ \| " \, / \\,three|}`, func(b *Builder) {
 		b.WriteChoice([]string{"one", `{ } $ | " , / \`, "three"})
 	})
+
+	expect("$0 hello", func(b *Builder) {
+		b.WriteFinalTabstop()
+		b.WriteText(" hello")
+	})
 }

internal/lsp/source/completion.go

@@ -306,8 +306,12 @@ func (c *completer) found(obj types.Object, score float64, imp *imports.ImportIn
 		imp:   imp,
 	}
 
-	if c.matchingType(&cand) {
+	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.
@@ -651,6 +655,18 @@ func (c *completer) lexical() error {
 			}
 		}
 	}
+
+	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 := c.expectedType.objType.(*types.Named); !named {
+			c.literal(c.expectedType.objType)
+		}
+	}
+
 	return nil
 }
 
@@ -880,6 +896,10 @@ 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
 
@@ -907,6 +927,7 @@ func expectedType(c *completer) typeInference {
 
 	var (
 		modifiers     []typeModifier
+		variadic      bool
 		typ           types.Type
 		convertibleTo types.Type
 	)
@@ -958,6 +979,7 @@ Nodes:
 							i = sig.Params().Len() - 1
 						}
 						typ = sig.Params().At(i).Type()
+						variadic = sig.Variadic() && i == sig.Params().Len()-1
 						break Nodes
 					}
 				}
@@ -1033,6 +1055,7 @@ Nodes:
 	}
 
 	return typeInference{
+		variadic:      variadic,
 		objType:       typ,
 		modifiers:     modifiers,
 		convertibleTo: convertibleTo,
@@ -1176,9 +1199,15 @@ Nodes:
 	}
 }
 
-// matchingType reports whether an object is a good completion candidate
-// in the context of the expected type.
-func (c *completer) matchingType(cand *candidate) bool {
+// 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)
 	}

internal/lsp/source/completion_literal.go

@@ -0,0 +1,164 @@
+// 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 source
+
+import (
+	"go/types"
+	"strings"
+
+	"golang.org/x/tools/internal/lsp/snippet"
+)
+
+// literal generates composite literal and make() completion items.
+func (c *completer) literal(literalType types.Type) {
+	if c.expectedType.objType == nil {
+		return
+	}
+
+	// Don't provide literal candidates for variadic function arguments.
+	// For example, don't provide "[]interface{}{}" in "fmt.Print(<>)".
+	if c.expectedType.variadic {
+		return
+	}
+
+	// Avoid literal candidates if the expected type is an empty
+	// interface. It isn't very useful to suggest a literal candidate of
+	// every possible type.
+	if isEmptyInterface(c.expectedType.objType) {
+		return
+	}
+
+	// We handle unnamed literal completions explicitly before searching
+	// for candidates. Avoid named-type literal completions for
+	// unnamed-type expected type since that results in duplicate
+	// candidates. For example, in
+	//
+	// type mySlice []int
+	// var []int = <>
+	//
+	// don't offer "mySlice{}" since we have already added a candidate
+	// of "[]int{}".
+	if _, named := literalType.(*types.Named); named {
+		if _, named := deref(c.expectedType.objType).(*types.Named); !named {
+			return
+		}
+	}
+
+	// Check if an object of type literalType or *literalType would
+	// match our expected type.
+	if !c.matchingType(literalType) {
+		literalType = types.NewPointer(literalType)
+
+		if !c.matchingType(literalType) {
+			return
+		}
+	}
+
+	ptr, isPointer := literalType.(*types.Pointer)
+	if isPointer {
+		literalType = ptr.Elem()
+	}
+
+	typeName := types.TypeString(literalType, c.qf)
+
+	// A type name of "[]int" doesn't work very will with the matcher
+	// since "[" isn't a valid identifier prefix. Here we strip off the
+	// slice (and array) prefix yielding just "int".
+	matchName := typeName
+	switch t := literalType.(type) {
+	case *types.Slice:
+		matchName = types.TypeString(t.Elem(), c.qf)
+	case *types.Array:
+		matchName = types.TypeString(t.Elem(), c.qf)
+	}
+
+	// If prefix matches the type name, client may want a composite literal.
+	if score := c.matcher.Score(matchName); score >= 0 {
+		if isPointer {
+			typeName = "&" + typeName
+		}
+
+		switch t := literalType.Underlying().(type) {
+		case *types.Struct, *types.Array, *types.Slice, *types.Map:
+			c.compositeLiteral(t, typeName, float64(score))
+		}
+	}
+
+	// If prefix matches "make", client may want a "make()"
+	// invocation. We also include the type name to allow for more
+	// flexible fuzzy matching.
+	if score := c.matcher.Score("make." + matchName); !isPointer && score >= 0 {
+		switch literalType.Underlying().(type) {
+		case *types.Slice:
+			// The second argument to "make()" for slices is required, so default to "0".
+			c.makeCall(typeName, "0", float64(score))
+		case *types.Map, *types.Chan:
+			// Maps and channels don't require the second argument, so omit
+			// to keep things simple for now.
+			c.makeCall(typeName, "", float64(score))
+		}
+	}
+}
+
+// literalCandidateScore is the base score for literal candidates.
+// Literal candidates match the expected type so they should be high
+// scoring, but we want them ranked below lexical objects of the
+// correct type, so scale down highScore.
+const literalCandidateScore = highScore / 2
+
+// compositeLiteral adds a composite literal completion item for the given typeName.
+func (c *completer) compositeLiteral(T types.Type, typeName string, matchScore float64) {
+	snip := &snippet.Builder{}
+	snip.WriteText(typeName + "{")
+	// Don't put the tab stop inside the composite literal curlies "{}"
+	// for structs that have no fields.
+	if strct, ok := T.(*types.Struct); !ok || strct.NumFields() > 0 {
+		snip.WriteFinalTabstop()
+	}
+	snip.WriteText("}")
+
+	nonSnippet := typeName + "{}"
+
+	c.items = append(c.items, CompletionItem{
+		Label:      nonSnippet,
+		InsertText: nonSnippet,
+		Score:      matchScore * literalCandidateScore,
+		Kind:       VariableCompletionItem,
+		snippet:    snip,
+	})
+}
+
+// makeCall adds a completion item for a "make()" call given a specific type.
+func (c *completer) makeCall(typeName string, secondArg string, matchScore float64) {
+	// Keep it simple and don't add any placeholders for optional "make()" arguments.
+
+	snip := &snippet.Builder{}
+	snip.WriteText("make(" + typeName)
+	if secondArg != "" {
+		snip.WriteText(", ")
+		snip.WritePlaceholder(func(b *snippet.Builder) {
+			if c.opts.Placeholders {
+				b.WriteText(secondArg)
+			}
+		})
+	}
+	snip.WriteText(")")
+
+	var nonSnippet strings.Builder
+	nonSnippet.WriteString("make(" + typeName)
+	if secondArg != "" {
+		nonSnippet.WriteString(", ")
+		nonSnippet.WriteString(secondArg)
+	}
+	nonSnippet.WriteByte(')')
+
+	c.items = append(c.items, CompletionItem{
+		Label:      nonSnippet.String(),
+		InsertText: nonSnippet.String(),
+		Score:      matchScore * literalCandidateScore,
+		Kind:       FunctionCompletionItem,
+		snippet:    snip,
+	})
+}

internal/lsp/source/util.go

@@ -329,6 +329,11 @@ func isFunc(obj types.Object) bool {
 	return ok
 }
 
+func isEmptyInterface(T types.Type) bool {
+	intf, _ := T.(*types.Interface)
+	return intf != nil && intf.NumMethods() == 0
+}
+
 // typeConversion returns the type being converted to if call is a type
 // conversion expression.
 func typeConversion(call *ast.CallExpr, info *types.Info) types.Type {

internal/lsp/testdata/nested_complit/nested_complit.go.in

@@ -7,7 +7,8 @@ type ncBar struct { //@item(structNCBar, "ncBar", "struct{...}", "struct")
 }
 
 func _() {
+	[]ncFoo{} //@item(litNCFoo, "[]ncFoo{}", "", "var")
 	_ := ncBar{
-		baz: [] //@complete(" //", structNCBar, structNCFoo)
+		baz: [] //@complete(" //", litNCFoo, structNCBar, structNCFoo)
 	}
 }

internal/lsp/testdata/snippets/literal_snippets.go

@@ -0,0 +1,98 @@
+package snippets
+
+func _() {
+	[]int{}        //@item(litIntSlice, "[]int{}", "", "var")
+	make([]int, 0) //@item(makeIntSlice, "make([]int, 0)", "", "func")
+
+	var slice []int
+	slice = i //@snippet(" //", litIntSlice, "[]int{$0\\}", "[]int{$0\\}")
+	slice = m //@snippet(" //", makeIntSlice, "make([]int, ${1:})", "make([]int, ${1:0})")
+}
+
+func _() {
+	type namedInt []int
+
+	namedInt{}        //@item(litNamedSlice, "namedInt{}", "", "var")
+	make(namedInt, 0) //@item(makeNamedSlice, "make(namedInt, 0)", "", "func")
+
+	var namedSlice namedInt
+	namedSlice = n //@snippet(" //", litNamedSlice, "namedInt{$0\\}", "namedInt{$0\\}")
+	namedSlice = m //@snippet(" //", makeNamedSlice, "make(namedInt, ${1:})", "make(namedInt, ${1:0})")
+}
+
+func _() {
+	make(chan int) //@item(makeChan, "make(chan int)", "", "func")
+
+	var ch chan int
+	ch = m //@snippet(" //", makeChan, "make(chan int)", "make(chan int)")
+}
+
+func _() {
+	map[string]struct{}{}     //@item(litMap, "map[string]struct{}{}", "", "var")
+	make(map[string]struct{}) //@item(makeMap, "make(map[string]struct{})", "", "func")
+
+	var m map[string]struct{}
+	m = m //@snippet(" //", litMap, "map[string]struct{\\}{$0\\}", "map[string]struct{\\}{$0\\}")
+	m = m //@snippet(" //", makeMap, "make(map[string]struct{\\})", "make(map[string]struct{\\})")
+
+	struct{}{} //@item(litEmptyStruct, "struct{}{}", "", "var")
+
+	m["hi"] = s //@snippet(" //", litEmptyStruct, "struct{\\}{\\}", "struct{\\}{\\}")
+}
+
+func _() {
+	type myStruct struct{ i int }
+
+	myStruct{}  //@item(litStruct, "myStruct{}", "", "var")
+	&myStruct{} //@item(litStructPtr, "&myStruct{}", "", "var")
+
+	var ms myStruct
+	ms = m //@snippet(" //", litStruct, "myStruct{$0\\}", "myStruct{$0\\}")
+
+	var msPtr *myStruct
+	msPtr = m //@snippet(" //", litStructPtr, "&myStruct{$0\\}", "&myStruct{$0\\}")
+
+	msPtr = &m //@snippet(" //", litStruct, "myStruct{$0\\}", "myStruct{$0\\}")
+}
+
+type myImpl struct{}
+
+func (myImpl) foo() {}
+
+func (*myImpl) bar() {}
+
+func _() {
+	type myIntf interface {
+		foo()
+	}
+
+	myImpl{} //@item(litImpl, "myImpl{}", "", "var")
+
+	var mi myIntf
+	mi = m //@snippet(" //", litImpl, "myImpl{\\}", "myImpl{\\}")
+
+	// only satisfied by pointer to myImpl
+	type myPtrIntf interface {
+		bar()
+	}
+
+	&myImpl{} //@item(litImplPtr, "&myImpl{}", "", "var")
+
+	var mpi myPtrIntf
+	mpi = m //@snippet(" //", litImplPtr, "&myImpl{\\}", "&myImpl{\\}")
+}
+
+func _() {
+	var s struct{ i []int } //@item(litSliceField, "i", "[]int", "field")
+	var foo []int
+	// no literal completions after selector
+	foo = s.i //@complete(" //", litSliceField)
+}
+
+func _() {
+	type myStruct struct{ i int } //@item(litStructType, "myStruct", "struct{...}", "struct")
+
+	foo := func(s string, args ...myStruct) {}
+	// Don't give literal slice candidate for variadic arg.
+	foo("", myStruct) //@complete(")", litStructType)
+}

internal/lsp/tests/tests.go

@@ -30,8 +30,8 @@ import (
 // We hardcode the expected number of test cases to ensure that all tests
 // are being executed. If a test is added, this number must be changed.
 const (
-	ExpectedCompletionsCount       = 162
-	ExpectedCompletionSnippetCount = 16
+	ExpectedCompletionsCount       = 164
+	ExpectedCompletionSnippetCount = 29
 	ExpectedDiagnosticsCount       = 21
 	ExpectedFormatCount            = 6
 	ExpectedImportCount            = 2