kernel: replace ConvImmString by ImmutableString

Despite the similar name to ConvString, ConvImmString had very different
semantics. It was also used to make user supplied data immutable, something
we should not do.

Also remove a pointless CHANGED_BAG call on a T_STRING

Author: fingolfin

src/calls.c

@@ -959,7 +959,7 @@ Obj NewFunctionT (
     }
 
     /* enter the arguments and the names                               */
-    SET_NAME_FUNC(func, ConvImmString(name));
+    SET_NAME_FUNC(func, name ? ImmutableString(name) : 0);
     SET_NARG_FUNC(func, narg);
     SET_NAMS_FUNC(func, nams);
     SET_NLOC_FUNC(func, 0);
@@ -1376,10 +1376,10 @@ Obj FuncSET_NAME_FUNC(
 {
   while (!IsStringConv(name)) {
     name = ErrorReturnObj("SET_NAME_FUNC( <func>, <name> ): <name> must be a string, not a %s",
-                          (Int)TNAM_OBJ(name), 0, "YOu can return a new name to continue");
+                          (Int)TNAM_OBJ(name), 0, "You can return a new name to continue");
   }
   if (TNUM_OBJ(func) == T_FUNCTION ) {
-    SET_NAME_FUNC(func, ConvImmString(name));
+    SET_NAME_FUNC(func, ImmutableString(name));
     CHANGED_BAG(func);
   } else
     DoOperation2Args(SET_NAME_FUNC_Oper, func, name);

src/opers.c

@@ -3199,7 +3199,7 @@ void InstallGlobalFunction (
     }
     memcpy(ADDR_OBJ(oper), CONST_ADDR_OBJ(func), SIZE_OBJ(func));
 
-    SET_NAME_FUNC(oper, ConvImmString(name));
+    SET_NAME_FUNC(oper, name ? ImmutableString(name) : 0);
     CHANGED_BAG(oper);
 }
 

src/stringobj.c

@@ -1314,11 +1314,27 @@ Obj CopyToStringRep(
         } 
         CHARS_STRING(copy)[lenString] = '\0';
     }
-    CHANGED_BAG(copy);
-    return (copy);
+    return copy;
 }
 
 
+/****************************************************************************
+**
+*F  ImmutableString( <string> ) . . . copy to immutable string in string rep.
+**
+**  'ImmutableString' returns an immutable string in string representation
+**  equal to <string>. This may return <string> if it already satisfies these
+**  criteria.
+*/
+Obj ImmutableString(Obj string)
+{
+    if (!IS_STRING_REP(string) || !IS_MUTABLE_OBJ(string)) {
+        string = CopyToStringRep(string);
+        MakeImmutableString(string);
+    }
+    return string;
+}
+
 
 /****************************************************************************
 **
@@ -1386,22 +1402,6 @@ Int IsStringConv (
 }
 
 
-Obj ConvImmString(Obj str)
-{
-  Obj result;
-  size_t len;
-  if (!str || !IsStringConv(str))
-    return (Obj) 0;
-  if (!IS_MUTABLE_OBJ(str))
-    return str;
-  len = GET_LEN_STRING(str);
-  result = NEW_STRING(len);
-  memcpy(CHARS_STRING(result), CHARS_STRING(str), len);
-  MakeImmutableString(result);
-  return result;
-}
-
-
 /****************************************************************************
 **
 *F * * * * * * * * * * * * * * GAP level functions  * * * * * * * * * * * * *

src/stringobj.h

@@ -281,13 +281,24 @@ extern Int IsString (
 **
 *F  CopyToStringRep( <string> ) . . .  copy a string to string representation
 **
-**  'CopyToStringRep' copies the string <string> to a new string in string
-**  representation.
+**  'CopyToStringRep' copies the string <string> to a new mutable string in
+**  string representation.
 */
 extern Obj CopyToStringRep(
             Obj                 string );
 
 
+/****************************************************************************
+**
+*F  ImmutableString( <string> ) . . . copy to immutable string in string rep.
+**
+**  'ImmutableString' returns an immutable string in string representation
+**  equal to <string>. This may return <string> if it already satisfies these
+**  criteria.
+*/
+extern Obj ImmutableString(Obj string);
+
+
 /****************************************************************************
 **
 *F  ConvString( <string> ) . . . .  convert a string to string representation
@@ -352,9 +363,6 @@ static inline Obj MakeImmString(const Char * cstr)
 }
 
 
-Obj ConvImmString(Obj str);
-
-
 /****************************************************************************
 **
 *F  C_NEW_STRING_DYN( <string>, <cstring> ) . . . . . . . . create GAP string