internal/lsp/source: support dereferencing for completion

In cases like:

    var j *int
    var i int = <>

We will now provide "*j" as a completion candidate.

Change-Id: I1d35c2dca4864f13f7534e15b17450d784985557
Reviewed-on: https://go-review.googlesource.com/c/tools/+/215358
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

@@ -383,6 +383,9 @@ type candidate struct {
 	// makePointer is true if the candidate type name T should be made into *T.
 	makePointer bool
 
+	// dereference is true if the candidate obj should be made into *obj.
+	dereference 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 *importInfo
@@ -1776,6 +1779,15 @@ func (c *completer) matchingCandidate(cand *candidate) bool {
 		return true
 	}
 
+	// Check if dereferencing cand would match our type inference.
+	if ptr, ok := cand.obj.Type().Underlying().(*types.Pointer); ok {
+		if c.matchingCandidate(&candidate{obj: c.fakeObj(ptr.Elem())}) {
+			// Mark the candidate so we know to prepend "*" when formatting.
+			cand.dereference = true
+			return true
+		}
+	}
+
 	// Check if cand is addressable and a pointer to cand matches our type inference.
 	if cand.addressable && c.matchingCandidate(&candidate{obj: c.fakeObj(types.NewPointer(candType))}) {
 		// Mark the candidate so we know to prepend "&" when formatting.

internal/lsp/source/completion_format.go

@@ -134,7 +134,7 @@ func (c *completer) item(cand candidate) (CompletionItem, error) {
 	var prefixOp string
 	if cand.takeAddress {
 		prefixOp = "&"
-	} else if cand.makePointer {
+	} else if cand.makePointer || cand.dereference {
 		prefixOp = "*"
 	}
 

internal/lsp/testdata/address/address.go

@@ -1,6 +1,9 @@
 package address
 
-func wantsPtr(*int) {}
+func wantsPtr(*int)            {}
+func wantsVariadicPtr(...*int) {}
+
+func wantsVariadic(...int) {}
 
 type foo struct{ c int } //@item(addrFieldC, "c", "int", "field")
 
@@ -15,6 +18,8 @@ func _() {
 	wantsPtr()   //@rank(")", addrBRef, addrA),snippet(")", addrBRef, "&b", "&b")
 	wantsPtr(&b) //@snippet(")", addrB, "b", "b")
 
+	wantsVariadicPtr() //@rank(")", addrBRef, addrA),snippet(")", addrBRef, "&b", "&b")
+
 	var s foo
 	s.c          //@item(addrDeepC, "s.c", "int", "field")
 	&s.c         //@item(addrDeepCRef, "&s.c", "int", "field")
@@ -24,6 +29,13 @@ func _() {
 
 	// don't add "&" in item (it gets added as an additional edit)
 	wantsPtr(&s.c) //@snippet(")", addrFieldC, "c", "c")
+
+	// check dereferencing as well
+	var c *int
+	*c            //@item(addrCPtr, "*c", "*int", "var")
+	var _ int = _ //@rank("_ //", addrCPtr, addrA),snippet("_ //", addrCPtr, "*c", "*c")
+
+	wantsVariadic() //@rank(")", addrCPtr, addrA),snippet(")", addrCPtr, "*c", "*c")
 }
 
 func (f foo) ptr() *foo { return &f }

internal/lsp/testdata/deep/deep.go

@@ -34,7 +34,7 @@ func _() {
 		*deepCircle
 	}
 	var circle deepCircle   //@item(deepCircle, "circle", "deepCircle", "var")
-	circle.deepCircle       //@item(deepCircleField, "circle.deepCircle", "*deepCircle", "field", "deepCircle is circular.")
+	*circle.deepCircle      //@item(deepCircleField, "*circle.deepCircle", "*deepCircle", "field", "deepCircle is circular.")
 	var _ deepCircle = circ //@deep(" //", deepCircle, deepCircleField)
 }
 

internal/lsp/testdata/summary.txt.golden

@@ -1,10 +1,10 @@
 -- summary --
 CompletionsCount = 225
-CompletionSnippetCount = 63
+CompletionSnippetCount = 66
 UnimportedCompletionsCount = 9
 DeepCompletionsCount = 5
 FuzzyCompletionsCount = 8
-RankedCompletionsCount = 63
+RankedCompletionsCount = 66
 CaseSensitiveCompletionsCount = 4
 DiagnosticsCount = 35
 FoldingRangesCount = 2