From b742303c94549529ba285d4ced79c454d53d446a Mon Sep 17 00:00:00 2001
From: Dianne Skoll <dianne@skoll.ca>
Date: Thu, 14 May 2026 10:08:23 -0400
Subject: [PATCH] Add warnings if we try to PUSH or FUNSET a built-in function.

---
 src/err.h      |  5 ++++-
 src/userfns.c  | 16 ++++++++++++++++
 tests/test.cmp |  7 ++++++-
 tests/test.rem |  6 ++++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/err.h b/src/err.h
index 732d1311..5f143e51 100644
--- a/src/err.h
+++ b/src/err.h
@@ -139,7 +139,8 @@
 #define E_EXPECTING_EOXPR   115
 #define E_EXPECTING_ATOM    116
 #define E_BAD_VAL_FOR_SYSVAR 117
-
+#define E_UNSET_BUILTIN_FUNC 118
+#define E_PUSH_BUILTIN_FUNC  119
 #ifdef MK_GLOBALS
 #undef EXTERN
 #define EXTERN
@@ -274,6 +275,8 @@ EXTERN char *ErrMsg[]
 /* E_EXPECTING_EOXPR */    "Expecting operator or end-of-expression",
 /* E_EXPECTING_ATOM */     "Expecting constant, variable, function call or (expression)",
 /* E_BAD_VAL_FOR_SYSVAR */ "Invalid value for system variable",
+/* E_UNSET_BUILTIN_FUNC */ "Attempt to unset built-in function",
+/* E_PUSH_BUILTIN_FUNC */  "Attempt to PUSH built-in function",
 }
 #endif /* MK_GLOBALS */
 ;
diff --git a/src/userfns.c b/src/userfns.c
index 1eda626b..38ee1884 100644
--- a/src/userfns.c
+++ b/src/userfns.c
@@ -449,6 +449,13 @@ static void DestroyUserFunc(UserFunc *f)
 /***************************************************************/
 static void FUnset(char const *name)
 {
+    if (!Hush) {
+        if (FindBuiltinFunc(name)) {
+            if (warning_level("06.02.06")) {
+                Eprint("%s: `%s'", GetErr(E_UNSET_BUILTIN_FUNC), name);
+            }
+        }
+    }
     UserFunc *f = FindUserFunc(name);
     if (f) {
         hash_table_delete(&FuncHash, f);
@@ -715,6 +722,15 @@ int PushUserFuncs(ParsePtr p)
             return E_BAD_ID;
         }
 
+        if (FindBuiltinFunc(name)) {
+            if (!Hush) {
+                if (warning_level("06.02.06")) {
+                    Eprint("%s: `%s'", GetErr(E_PUSH_BUILTIN_FUNC), name);
+                }
+            }
+            DBufFree(&buf);
+            continue;
+        }
         r = add_func_to_push(name, pf);
 
         DBufFree(&buf);
diff --git a/tests/test.cmp b/tests/test.cmp
index d59b04be..41114844 100644
--- a/tests/test.cmp
+++ b/tests/test.cmp
@@ -16771,7 +16771,10 @@ mbupper("öÖçÇéôñÑÉÊ") => "ÖÖÇÇÉÔÑÑÉÊ"
 mblower("öÖçÇéôñÑÉÊ") => "ööççéôññéê"
 upper("öÖçÇéôñÑÉÊ") => "öÖçÇéôñÑÉÊ"
 lower("öÖçÇéôñÑÉÊ") => "öÖçÇéôñÑÉÊ"
-DynBuf Mallocs: 1132 mallocs; 31873408 bytes
+../tests/test.rem(1915): Attempt to redefine built-in function: `max'
+../tests/test.rem(1916): Attempt to unset built-in function: `max'
+../tests/test.rem(1917): Attempt to PUSH built-in function: `max'
+DynBuf Mallocs: 1134 mallocs; 31873536 bytes
 Variable hash table statistics:
   Entries: 100146; Buckets: 87719; Non-empty Buckets: 66303
   Maxlen: 5; Minlen: 0; Avglen: 1.142; Stddev: 0.878; Avg nonempty len: 1.510
@@ -25201,6 +25204,8 @@ TRANSLATE "Maximum expression complexity exceeded" ""
 TRANSLATE "Expecting operator or end-of-expression" ""
 TRANSLATE "Expecting constant, variable, function call or (expression)" ""
 TRANSLATE "Invalid value for system variable" ""
+TRANSLATE "Attempt to unset built-in function" ""
+TRANSLATE "Attempt to PUSH built-in function" ""
 
 # Other Messages
 TRANSLATE "%s function `%s' defined at %s(%s) does not use its argument" ""
diff --git a/tests/test.rem b/tests/test.rem
index b91362b2..411de1d5 100644
--- a/tests/test.rem
+++ b/tests/test.rem
@@ -1911,6 +1911,12 @@ SET a upper("öÖçÇéôñÑÉÊ")
 SET a lower("öÖçÇéôñÑÉÊ")
 DEBUG -x
 
+# Warnings about defining/unsetting/pushing built-in functions
+FSET max(x) x*2
+FUNSET max
+PUSH-FUNCS max a b c
+POP-FUNCS
+
 # Don't want Remind to queue reminders
 EXIT