(cl-type-of): New function to return more precise types (bug#69739)

* src/data.c (Fcl_type_of): New function, extracted from `Ftype_of`.
Make it return more precise types for symbols, integers, and subrs.
(Ftype_of): Use it.
(syms_of_data): Define the corresponding new symbols and defsubr
the new function.

* doc/lispref/objects.texi (Type Predicates): Document it.

* src/comp.c (emit_limple_insn): Use `Fcl_type_of`.

* lisp/emacs-lisp/cl-preloaded.el (subr): Demote it to `atom`.
(subr-native-elisp, subr-primitive): Add `compiled-function` as
parent instead.
(special-form): New type.

* lisp/obsolete/eieio-core.el (cl--generic-struct-tag):
* lisp/emacs-lisp/cl-generic.el (cl--generic-typeof-generalizer):
Use `cl-type-of`.
cl--generic--unreachable-types): Update accordingly.

test/src/data-tests.el (data-tests--cl-type-of): New test.

2 files changed, 36 insertions, 6 deletions

diff --git a/src/comp.c b/src/comp.c
index 3f989c722d4..76cf1f3ab6e 100644
--- a/src/comp.c
+++ b/src/comp.c
@@ -2442,7 +2442,7 @@ emit_limple_insn (Lisp_Object insn)
     {
       Lisp_Object arg1 = arg[1];
 
-      if (EQ (Ftype_of (arg1), Qcomp_mvar))
+      if (EQ (Fcl_type_of (arg1), Qcomp_mvar))
 	res = emit_mvar_rval (arg1);
       else if (EQ (FIRST (arg1), Qcall))
 	res = emit_limple_call (XCDR (arg1));
diff --git a/src/data.c b/src/data.c
index 35f4c82c68f..5d6b6e0ba9d 100644
--- a/src/data.c
+++ b/src/data.c
@@ -193,16 +193,37 @@ DEFUN ("null", Fnull, Snull, 1, 1, 0,
 DEFUN ("type-of", Ftype_of, Stype_of, 1, 1, 0,
        doc: /* Return a symbol representing the type of OBJECT.
 The symbol returned names the object's basic type;
-for example, (type-of 1) returns `integer'.  */)
+for example, (type-of 1) returns `integer'.
+Contrary to `cl-type-of', the returned type is not always the most
+precise type possible, because instead this function tries to preserve
+compatibility with the return value of previous Emacs versions.  */)
+  (Lisp_Object object)
+{
+  return SYMBOLP (object)    ? Qsymbol
+         : INTEGERP (object) ? Qinteger
+         : SUBRP (object)    ? Qsubr
+         : Fcl_type_of (object);
+}
+
+DEFUN ("cl-type-of", Fcl_type_of, Scl_type_of, 1, 1, 0,
+       doc: /* Return a symbol representing the type of OBJECT.
+The returned symbol names the most specific possible type of the object.
+for example, (cl-type-of nil) returns `null'.
+The specific type returned may change depending on Emacs versions,
+so we recommend you use `cl-typep', `cl-typecase', or other predicates
+rather than compare the return value of this function against
+a fixed set of types.  */)
   (Lisp_Object object)
 {
   switch (XTYPE (object))
     {
     case_Lisp_Int:
-      return Qinteger;
+      return Qfixnum;
 
     case Lisp_Symbol:
-      return Qsymbol;
+      return NILP (object) ? Qnull
+             : EQ (object, Qt) ? Qboolean
+             : Qsymbol;
 
     case Lisp_String:
       return Qstring;
@@ -215,7 +236,7 @@ for example, (type-of 1) returns `integer'.  */)
       switch (PSEUDOVECTOR_TYPE (XVECTOR (object)))
         {
         case PVEC_NORMAL_VECTOR: return Qvector;
-	case PVEC_BIGNUM: return Qinteger;
+	case PVEC_BIGNUM: return Qbignum;
 	case PVEC_MARKER: return Qmarker;
 	case PVEC_SYMBOL_WITH_POS: return Qsymbol_with_pos;
 	case PVEC_OVERLAY: return Qoverlay;
@@ -224,7 +245,10 @@ for example, (type-of 1) returns `integer'.  */)
         case PVEC_WINDOW_CONFIGURATION: return Qwindow_configuration;
         case PVEC_PROCESS: return Qprocess;
         case PVEC_WINDOW: return Qwindow;
-        case PVEC_SUBR: return Qsubr;
+        case PVEC_SUBR:
+          return XSUBR (object)->max_args == UNEVALLED ? Qspecial_form
+                 : SUBR_NATIVE_COMPILEDP (object) ? Qsubr_native_elisp
+                 : Qsubr_primitive;
         case PVEC_COMPILED: return Qcompiled_function;
         case PVEC_BUFFER: return Qbuffer;
         case PVEC_CHAR_TABLE: return Qchar_table;
@@ -4202,7 +4226,9 @@ syms_of_data (void)
 	     "Variable binding depth exceeds max-specpdl-size");
 
   /* Types that type-of returns.  */
+  DEFSYM (Qboolean, "boolean");
   DEFSYM (Qinteger, "integer");
+  DEFSYM (Qbignum, "bignum");
   DEFSYM (Qsymbol, "symbol");
   DEFSYM (Qstring, "string");
   DEFSYM (Qcons, "cons");
@@ -4218,6 +4244,9 @@ syms_of_data (void)
   DEFSYM (Qprocess, "process");
   DEFSYM (Qwindow, "window");
   DEFSYM (Qsubr, "subr");
+  DEFSYM (Qspecial_form, "special-form");
+  DEFSYM (Qsubr_primitive, "subr-primitive");
+  DEFSYM (Qsubr_native_elisp, "subr-native-elisp");
   DEFSYM (Qcompiled_function, "compiled-function");
   DEFSYM (Qbuffer, "buffer");
   DEFSYM (Qframe, "frame");
@@ -4255,6 +4284,7 @@ syms_of_data (void)
   defsubr (&Seq);
   defsubr (&Snull);
   defsubr (&Stype_of);
+  defsubr (&Scl_type_of);
   defsubr (&Slistp);
   defsubr (&Snlistp);
   defsubr (&Sconsp);