Fix shared Go CFG expression and return-edge regressions

Agent-Logs-Url: https://github.com/github/codeql/sessions/3f96ead2-cda4-479c-9e37-f38ace035870

Co-authored-by: owen-mc <62447351+owen-mc@users.noreply.github.com>

Author: Copilot

go/ql/lib/semmle/go/controlflow/ControlFlowGraph.qll

@@ -340,7 +340,10 @@ module ControlFlow {
    * cannot return normally, but never fails to hold of a function that can return normally.
    */
   predicate mayReturnNormally(FuncDecl f) {
-    exists(GoCfg::ControlFlow::NormalExitNode exit | exit.getEnclosingCallable() = f)
+    exists(GoCfg::ControlFlow::NormalExitNode exit |
+      exit.getEnclosingCallable() = f and
+      exists(exit.getAPredecessor())
+    )
   }
 
   /**

go/ql/lib/semmle/go/controlflow/ControlFlowGraphShared.qll

@@ -79,8 +79,7 @@ module GoCfg {
       or
       not node instanceof Callable and
       not exists(node.getEnclosingFunction()) and
-      result = node.getFile() and
-      result instanceof Callable
+      result = node.getFile()
     }
 
     class Stmt = Go::Stmt;
@@ -292,6 +291,10 @@ module GoCfg {
     predicate preOrderExpr(Ast::Expr e) { none() }
 
     predicate postOrInOrder(Ast::AstNode n) {
+      n instanceof Go::ReferenceExpr
+      or
+      n instanceof Go::BasicLit
+      or
       n instanceof Go::CallExpr and
       not n = any(Go::DeferStmt defer).getCall() and
       not n = any(Go::GoStmt go_).getCall()
@@ -633,6 +636,12 @@ module GoCfg {
         c.hasLabel(TGoLabel(lbl.getLabel()))
       )
       or
+      exists(Go::FuncDef fd |
+        ast = fd.getBody() and
+        c.getSuccessorType() instanceof ReturnSuccessor and
+        n.isAfter(fd.getBody())
+      )
+      or
       exists(Go::LabeledStmt lbl, Go::FuncDef fd |
         ast = fd.getBody() and
         n.isBefore(lbl) and
@@ -841,6 +850,13 @@ module GoCfg {
           n1.isAfter(lastChild) and n2.isAdditional(ret, getFirstReturnEpilogueTag(ret))
         )
         or
+        exists(Ast::AstNode lastChild | lastChild = getLastRankedChild(ret) |
+          // After last expr → return node directly if there is no return epilogue
+          not exists(getFirstReturnEpilogueTag(ret)) and
+          n1.isAfter(lastChild) and
+          n2.isIn(ret)
+        )
+        or
         // No expressions → before → return node directly
         not exists(getRankedChild(ret, _)) and
         n1.isBefore(ret) and