Changed @generated body purity error (#32627)

* Changed @generated body purity error

* change error message in tests for nonpure generated function

Author: oxinabox

src/method.c

@@ -413,7 +413,7 @@ JL_DLLEXPORT jl_code_info_t *jl_code_for_staged(jl_method_instance_t *linfo)
                     ptls->in_pure_callback = 0;
                     jl_toplevel_eval(def->module, (jl_value_t*)func);
                 }
-                jl_error("generated function body is not pure. this likely means it contains a closure or comprehension.");
+                jl_error("The function body AST defined by this @generated function is not pure. This likely means it contains a closure or comprehension.");
             }
 
             jl_array_t *stmts = (jl_array_t*)func->code;

test/core.jl

@@ -4942,7 +4942,7 @@ gVararg(a::fVararg(Int)) = length(a)
     false
 catch e
     (e::ErrorException).msg
-end == "generated function body is not pure. this likely means it contains a closure or comprehension."
+end == "The function body AST defined by this @generated function is not pure. This likely means it contains a closure or comprehension."
 
 let x = 1
     global g18444