internal/lsp/source: do not panic in "var func" outgoing callhierarchy

When trying to get outgoing call hierarchy from an var func like:

func main() {
    foo := func() {}
    foo()
}

gopls crashed with a panic.

This change makes it return an empty call hierarchy instead.
It also adds support for testing outgoing calls where the expected
result is 0 items, to be able to test this change.

Fixes golang/go#43376

Change-Id: Icd91bf54cb4fbd5203f5865f0ff9d81365c27d5d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/279469
Trust: Pontus Leitzler <leitzler@gmail.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Pontus Leitzler <leitzler@gmail.com>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/source/call_hierarchy.go

@@ -193,7 +193,9 @@ func OutgoingCalls(ctx context.Context, snapshot Snapshot, fh FileHandle, pos pr
 	if _, ok := identifier.Declaration.obj.Type().Underlying().(*types.Signature); !ok {
 		return nil, nil
 	}
-
+	if identifier.Declaration.node == nil {
+		return nil, nil
+	}
 	if len(identifier.Declaration.MappedRange) == 0 {
 		return nil, nil
 	}

internal/lsp/testdata/callhierarchy/callhierarchy.go

@@ -26,12 +26,14 @@ var x = func() { //@mark(hierarchyLiteral, "func"),mark(hierarchyLiteralOut, "x"
 }
 
 // D is exported to test incoming/outgoing calls across packages
-func D() { //@mark(hierarchyD, "D"),incomingcalls(hierarchyD, hierarchyA, hierarchyB, hierarchyC, hierarchyLiteral, incomingA),outgoingcalls(hierarchyD, hierarchyE, hierarchyF, hierarchyG, hierarchyLiteralOut, outgoingB)
+func D() { //@mark(hierarchyD, "D"),incomingcalls(hierarchyD, hierarchyA, hierarchyB, hierarchyC, hierarchyLiteral, incomingA),outgoingcalls(hierarchyD, hierarchyE, hierarchyF, hierarchyG, hierarchyLiteralOut, outgoingB, hierarchyFoo)
 	e()
 	x()
 	F()
 	g()
 	outgoing.B()
+	foo := func() {} //@mark(hierarchyFoo, "foo"),incomingcalls(hierarchyFoo, hierarchyD),outgoingcalls(hierarchyFoo)
+	foo()
 }
 
 func e() {} //@mark(hierarchyE, "e")

internal/lsp/testdata/summary.txt.golden

@@ -1,5 +1,5 @@
 -- summary --
-CallHierarchyCount = 1
+CallHierarchyCount = 2
 CodeLensCount = 5
 CompletionsCount = 258
 CompletionSnippetCount = 88

internal/lsp/tests/tests.go

@@ -1131,6 +1131,9 @@ func (data *Data) collectIncomingCalls(src span.Span, calls []span.Span) {
 }
 
 func (data *Data) collectOutgoingCalls(src span.Span, calls []span.Span) {
+	if data.CallHierarchy[src] == nil {
+		data.CallHierarchy[src] = &CallHierarchyResult{}
+	}
 	for _, call := range calls {
 		m, err := data.Mapper(call.URI())
 		if err != nil {
@@ -1141,19 +1144,11 @@ func (data *Data) collectOutgoingCalls(src span.Span, calls []span.Span) {
 			data.t.Fatal(err)
 		}
 		// we're only comparing protocol.range
-		if data.CallHierarchy[src] != nil {
-			data.CallHierarchy[src].OutgoingCalls = append(data.CallHierarchy[src].OutgoingCalls,
-				protocol.CallHierarchyItem{
-					URI:   protocol.DocumentURI(call.URI()),
-					Range: rng,
-				})
-		} else {
-			data.CallHierarchy[src] = &CallHierarchyResult{
-				OutgoingCalls: []protocol.CallHierarchyItem{
-					{URI: protocol.DocumentURI(call.URI()), Range: rng},
-				},
-			}
-		}
+		data.CallHierarchy[src].OutgoingCalls = append(data.CallHierarchy[src].OutgoingCalls,
+			protocol.CallHierarchyItem{
+				URI:   protocol.DocumentURI(call.URI()),
+				Range: rng,
+			})
 	}
 }