internal/lsp/source: fix some invalid literal candidates

We were marking all literal candidates as addressable so we were
getting invalid candidates like "&int()". Fix it to only mark literal
struct, array, slice and map types as addressable.

I also fixed the unnamed literal candidate to pass the dereferenced
expected type. For example, if the expected type was "*[]int" we were
passing a literal type of "*[]int" which wasn't working anymore. Now
we pass "[]int" and take its address as "&[]int{}".

Change-Id: I5d0ee074d3cc91c39dd881630583e31be5a05579
Reviewed-on: https://go-review.googlesource.com/c/tools/+/212677
Run-TryBot: Muir Manders <muir@mnd.rs>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/source/completion.go

@@ -917,8 +917,9 @@ func (c *completer) lexical() error {
 		// if an object literal makes a good candidate. 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, nil)
+		t := deref(c.expectedType.objType)
+		if _, named := t.(*types.Named); !named {
+			c.literal(t, nil)
 		}
 	}
 

internal/lsp/source/completion_literal.go

@@ -65,9 +65,16 @@ func (c *completer) literal(literalType types.Type, imp *importInfo) {
 
 	// Check if an object of type literalType would match our expected type.
 	cand := candidate{
-		obj:         c.fakeObj(literalType),
-		addressable: true,
+		obj: c.fakeObj(literalType),
 	}
+
+	switch literalType.Underlying().(type) {
+	// These literal types are addressable (e.g. "&[]int{}"), others are
+	// not (e.g. can't do "&(func(){})").
+	case *types.Struct, *types.Array, *types.Slice, *types.Map:
+		cand.addressable = true
+	}
+
 	if !c.matchingCandidate(&cand) {
 		return
 	}

internal/lsp/testdata/snippets/literal_snippets.go.in

@@ -10,8 +10,12 @@ import (
 
 func _() {
 	[]int{}        //@item(litIntSlice, "[]int{}", "", "var")
+	&[]int{}       //@item(litIntSliceAddr, "&[]int{}", "", "var")
 	make([]int, 0) //@item(makeIntSlice, "make([]int, 0)", "", "func")
 
+	var _ *[]int = in //@snippet(" //", litIntSliceAddr, "&[]int{$0\\}", "&[]int{$0\\}")
+	var _ **[]int = in //@complete(" //")
+
 	var slice []int
 	slice = i //@snippet(" //", litIntSlice, "[]int{$0\\}", "[]int{$0\\}")
 	slice = m //@snippet(" //", makeIntSlice, "make([]int, ${1:})", "make([]int, ${1:0})")
@@ -164,6 +168,9 @@ func _() {
 func _() {
 	float64() //@item(litFloat64, "float64()", "float64", "var")
 
+	// don't complete to "&float64()"
+	var _ *float64 = float64 //@complete(" //")
+
 	var f float64
 	f = fl //@complete(" //", litFloat64),snippet(" //", litFloat64, "float64($0)", "float64($0)")
 

internal/lsp/testdata/summary.txt.golden

@@ -1,6 +1,6 @@
 -- summary --
-CompletionsCount = 223
-CompletionSnippetCount = 61
+CompletionsCount = 225
+CompletionSnippetCount = 62
 UnimportedCompletionsCount = 4
 DeepCompletionsCount = 5
 FuzzyCompletionsCount = 8