Fix issue 22848: Skip codegen for template instances within unreferenced lambdas

Author: CHIKI Badreddine

compiler/src/dmd/templatesem.d

@@ -3282,6 +3282,21 @@ bool needsCodegen(TemplateInstance ti)
         return false;
     }
 
+    if (ti.enclosing)
+    {
+        if (auto fd = ti.enclosing.isFuncDeclaration())
+        {
+            if (auto fld = fd.isFuncLiteralDeclaration())
+            {
+                if (fld.tookAddressOf == 0 && fld.tok != TOK.reserved)
+                {
+                    ti.minst = null; // mark as speculative
+                    return false;
+                }
+            }
+        }
+    }
+
     // This should only be called on the primary instantiation.
     assert(ti is ti.inst);
 

compiler/test/runnable/issue22848.d

@@ -0,0 +1,20 @@
+@"
+// Test for Issue 22848
+// Undefined reference to static function in unused mixin lambda
+
+mixin template Main(alias mainFunction) {}
+
+mixin Main!(
+    ()
+    {
+        static bool pred(char c) => false;
+        accept!pred;
+    }
+);
+
+char accept(alias pred)() => pred(0);
+
+void main()
+{
+}
+"@