Merge pull request github#16457 from owen-mc/go/fix-implicitvarargsslice-type

Go: Fix `getType` on `ImplicitVarArgsSlice`

Author: owen-mc

go/ql/lib/change-notes/2024-05-08-fix-flow-variadic-builtin-variable.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Fixed a bug that stopped data flow from being followed through variadic arguments to built-in functions or to functions called using a variable.

go/ql/lib/semmle/go/dataflow/internal/DataFlowNodes.qll

@@ -455,8 +455,8 @@ module Public {
     CallNode getCallNode() { result = call }
 
     override Type getType() {
-      exists(Function f | f = call.getTarget() |
-        result = f.getParameterType(f.getNumParameter() - 1)
+      exists(SignatureType t | t = call.getCall().getCalleeType() |
+        result = t.getParameterType(t.getNumParameter() - 1)
       )
     }