Add a test.

ql/test/library-tests/semmle/go/dataflow/CallGraph/getACallee.expected

@@ -1,2 +1,5 @@
 missingCallee
 spuriousCallee
+| main.go:44:3:44:7 | call to m | main.go:17:1:17:17 | function declaration |
+| main.go:44:3:44:7 | call to m | main.go:21:1:21:20 | function declaration |
+| main.go:56:2:56:6 | call to m | main.go:21:1:21:20 | function declaration |

ql/test/library-tests/semmle/go/dataflow/CallGraph/main.go

@@ -35,5 +35,23 @@ func test(x *s1, y s2, z s3, b mybool, i I) {
 }
 
 func test2(v interface{}) {
-	v.(interface{ m(int) }).m(0)       // callee: s3.m
+	v.(interface{ m(int) }).m(0) // callee: s3.m
+}
+
+func test3(v I) {
+	if v == nil {
+		v = s1{}
+		v.m() // callee: s1.m
+	}
+	v.m() // callee: s1.m callee: s2.m callee: mybool.m
+}
+
+func test4(b bool) {
+	var v I
+	if b {
+		v = s1{}
+	} else {
+		v = &s2{}
+	}
+	v.m() // callee: s1.m callee: s2.m
 }

ql/test/library-tests/semmle/go/dataflow/CallGraph/viableCallee.expected

@@ -0,0 +1,2 @@
+missingCallee
+spuriousCallee

ql/test/library-tests/semmle/go/dataflow/CallGraph/viableCallee.ql

@@ -0,0 +1,26 @@
+import go
+import semmle.go.dataflow.internal.DataFlowDispatch
+
+/**
+ * Gets a string `val` such that there is a comment on the same line as `l`
+ * that contains the substring `key: val`.
+ */
+string metadata(Locatable l, string key) {
+  exists(string f, int line, Comment c, string kv |
+    l.hasLocationInfo(f, line, _, _, _) and
+    c.hasLocationInfo(f, line, _, _, _) and
+    kv = c.getText().regexpFind("\\b(\\w+: \\S+)", _, _) and
+    key = kv.regexpCapture("(\\w+): (\\S+)", 1) and
+    result = kv.regexpCapture("(\\w+): (\\S+)", 2)
+  )
+}
+
+query predicate missingCallee(DataFlow::CallNode call, FuncDef callee) {
+  metadata(call.asExpr(), "callee") = metadata(callee, "name") and
+  not viableCallable(call.asExpr()) = callee
+}
+
+query predicate spuriousCallee(DataFlow::CallNode call, FuncDef callee) {
+  viableCallable(call.asExpr()) = callee and
+  not metadata(call.asExpr(), "callee") = metadata(callee, "name")
+}