Add (:documentation <form>) for dynamically-generated docstrings

* lisp/emacs-lisp/bytecomp.el:
(byte-compile-initial-macro-environment): Use macroexp-progn.
(byte-compile-cl-warn): Don't silence use of cl-macroexpand-all.
(byte-compile-file-form-defvar-function): Rename from
byte-compile-file-form-define-abbrev-table.
(defvaralias, byte-compile-file-form-custom-declare-variable): Use it.
(byte-compile): Use byte-compile-top-level rather than
byte-compile-lambda so we can compile non-values.
(byte-compile-form): Add warnings for failed uses of lexical vars via
quoted symbols.
(byte-compile-unfold-bcf): Improve message for failed inlining.
(byte-compile-make-closure): Handle new format of internal-make-closure
for dynamically-generated docstrings.

* lisp/emacs-lisp/cconv.el (cconv--convert-function):
Add `docstring' argument.
(cconv-convert): Use it to handle the new (:documentation ...) form.
(cconv-analyze-form): Handle the new (:documentation ...) form.

* src/eval.c (Ffunction): Handle the new (:documentation ...) form.
(syms_of_eval): Declare `:documentation'.

1 files changed, 18 insertions, 4 deletions

diff --git a/src/eval.c b/src/eval.c
index b98b224e622..e828da9288f 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -575,10 +575,23 @@ usage: (function ARG)  */)
   if (!NILP (Vinternal_interpreter_environment)
       && CONSP (quoted)
       && EQ (XCAR (quoted), Qlambda))
-    /* This is a lambda expression within a lexical environment;
-       return an interpreted closure instead of a simple lambda.  */
-    return Fcons (Qclosure, Fcons (Vinternal_interpreter_environment,
-                                   XCDR (quoted)));
+    { /* This is a lambda expression within a lexical environment;
+         return an interpreted closure instead of a simple lambda.  */
+      Lisp_Object cdr = XCDR (quoted);
+      Lisp_Object tmp = cdr;
+      if (CONSP (tmp)
+          && (tmp = XCDR (tmp), CONSP (tmp))
+          && (tmp = XCAR (tmp), CONSP (tmp))
+          && (EQ (QCdocumentation, XCAR (tmp))))
+        { /* Handle the special (:documentation <form>) to build the docstring
+             dynamically.  */
+          Lisp_Object docstring = eval_sub (Fcar (XCDR (tmp)));
+          CHECK_STRING (docstring);
+          cdr = Fcons (XCAR (cdr), Fcons (docstring, XCDR (XCDR (cdr))));
+        }
+      return Fcons (Qclosure, Fcons (Vinternal_interpreter_environment,
+                                     cdr));
+    }
   else
     /* Simply quote the argument.  */
     return quoted;
@@ -3668,6 +3681,7 @@ before making `inhibit-quit' nil.  */);
   DEFSYM (Qand_rest, "&rest");
   DEFSYM (Qand_optional, "&optional");
   DEFSYM (Qclosure, "closure");
+  DEFSYM (QCdocumentation, ":documentation");
   DEFSYM (Qdebug, "debug");
 
   DEFVAR_LISP ("inhibit-debugger", Vinhibit_debugger,