Don't store docstrings of preloaded .el files in etc/DOC

Since the location of those files changes between build time and
installation time, this requires to tweak the file name used in those
(#$ . NNN) references during the dump so they don't hardcode the build
directory.  We do it in the same way as was already done for those
same file names in `load-history`, except we convert them back to
absolute file names more lazily (i.e. when fetching the actual
docstring rather than at startup), which requires remembering the
`lisp-dir` computed at startup in the new `lisp-directory` variable.

* src/Makefile.in ($(etc)/DOC): Don't scan Lisp files any more.

* src/lread.c (Fload): Use relative file names for `load-file-name`
when preloading for the dump, like we already did for `current-load-list`.
(read_list): Don't zero-out dynamic docstring references during the
preload since they won't be filled later by Snarf-documentation any more.
(read1): Remove the hash-hack for doc references that were zeroed.

* lisp/startup.el (lisp-directory): New variable.
(command-line): Set it.

* src/doc.c (get_doc_string): Use `lisp-directory` for dynamic
docstring references using relative file names.
(syms_of_doc): Add `Qlisp_directory`.

* lib-src/make-docfile.c (scan_file): Don't handle `.el` or `.elc`
files any more.
(IS_SLASH): Remove macro, not used any more.
(skip_white, read_lisp_symbol, search_lisp_doc_at_eol)
(scan_lisp_file): Remove functions, not used any more.

* doc/lispref/loading.texi (Library Search): Mention `lisp-directory`.

3 files changed, 13 insertions, 48 deletions

diff --git a/src/Makefile.in b/src/Makefile.in
index ea4a7207ffb..76e4675c2a7 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -642,13 +642,11 @@ endif
 ## for the first time, this prevents any variation between configurations
 ## in the contents of the DOC file.
 ##
-$(etc)/DOC: lisp.mk $(libsrc)/make-docfile$(EXEEXT) $(doc_obj) $(lisp)
+$(etc)/DOC: $(libsrc)/make-docfile$(EXEEXT) $(doc_obj)
 	$(AM_V_GEN)$(MKDIR_P) $(etc)
 	$(AM_V_at)rm -f $(etc)/DOC
 	$(AM_V_at)$(libsrc)/make-docfile -d $(srcdir) \
 	  $(SOME_MACHINE_OBJECTS) $(doc_obj) > $(etc)/DOC
-	$(AM_V_at)$(libsrc)/make-docfile -a $(etc)/DOC -d $(lispsource) \
-	  $(shortlisp)
 
 $(libsrc)/make-docfile$(EXEEXT) $(libsrc)/make-fingerprint$(EXEEXT): \
   $(lib)/libgnu.a
diff --git a/src/doc.c b/src/doc.c
index 6be023bb934..129d3a517b7 100644
--- a/src/doc.c
+++ b/src/doc.c
@@ -84,16 +84,19 @@ get_doc_string (Lisp_Object filepos, bool unibyte, bool definition)
   char *from, *to, *name, *p, *p1;
   Lisp_Object file, pos;
   ptrdiff_t count = SPECPDL_INDEX ();
+  Lisp_Object dir;
   USE_SAFE_ALLOCA;
 
   if (FIXNUMP (filepos))
     {
       file = Vdoc_file_name;
+      dir = Vdoc_directory;
       pos = filepos;
     }
   else if (CONSP (filepos))
     {
       file = XCAR (filepos);
+      dir = Fsymbol_value (Qlisp_directory);
       pos = XCDR (filepos);
     }
   else
@@ -101,7 +104,7 @@ get_doc_string (Lisp_Object filepos, bool unibyte, bool definition)
 
   EMACS_INT position = eabs (XFIXNUM (pos));
 
-  if (!STRINGP (Vdoc_directory))
+  if (!STRINGP (dir))
     return Qnil;
 
   if (!STRINGP (file))
@@ -113,7 +116,7 @@ get_doc_string (Lisp_Object filepos, bool unibyte, bool definition)
   Lisp_Object tem = Ffile_name_absolute_p (file);
   file = ENCODE_FILE (file);
   Lisp_Object docdir
-    = NILP (tem) ? ENCODE_FILE (Vdoc_directory) : empty_unibyte_string;
+    = NILP (tem) ? ENCODE_FILE (dir) : empty_unibyte_string;
   ptrdiff_t docdir_sizemax = SBYTES (docdir) + 1;
   if (will_dump_p ())
     docdir_sizemax = max (docdir_sizemax, sizeof sibling_etc);
@@ -703,6 +706,7 @@ See variable `text-quoting-style'.  */)
 void
 syms_of_doc (void)
 {
+  DEFSYM (Qlisp_directory, "lisp-directory");
   DEFSYM (Qsubstitute_command_keys, "substitute-command-keys");
   DEFSYM (Qfunction_documentation, "function-documentation");
   DEFSYM (Qgrave, "grave");
diff --git a/src/lread.c b/src/lread.c
index 49925764146..55b3d473dce 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -1545,7 +1545,7 @@ Return t if the file exists and loads successfully.  */)
 	message_with_string ("Loading %s...", file, 1);
     }
 
-  specbind (Qload_file_name, found_eff);
+  specbind (Qload_file_name, hist_file_name);
   specbind (Qload_true_file_name, found);
   specbind (Qinhibit_file_name_operation, Qnil);
   specbind (Qload_in_progress, Qt);
@@ -3224,23 +3224,6 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 		    Fstring_as_unibyte (AREF (tmp, COMPILED_BYTECODE)));
 	    }
 
-	  if (COMPILED_DOC_STRING < ASIZE (tmp)
-	      && EQ (AREF (tmp, COMPILED_DOC_STRING), make_fixnum (0)))
-	    {
-	      /* read_list found a docstring like '(#$ . 5521)' and treated it
-		 as 0.  This placeholder 0 would lead to accidental sharing in
-		 purecopy's hash-consing, so replace it with a (hopefully)
-		 unique integer placeholder, which is negative so that it is
-		 not confused with a DOC file offset (the USE_LSB_TAG shift
-		 relies on the fact that VALMASK is one bit narrower than
-		 INTMASK).  Eventually Snarf-documentation should replace the
-		 placeholder with the actual docstring.  */
-	      verify (INTMASK & ~VALMASK);
-	      EMACS_UINT hash = ((XHASH (tmp) >> USE_LSB_TAG)
-				 | (INTMASK - INTMASK / 2));
-	      ASET (tmp, COMPILED_DOC_STRING, make_ufixnum (hash));
-	    }
-
 	  XSETPVECTYPE (vec, PVEC_COMPILED);
 	  return tmp;
 	}
@@ -4208,31 +4191,13 @@ read_list (bool flag, Lisp_Object readcharfun)
 
       /* While building, if the list starts with #$, treat it specially.  */
       if (EQ (elt, Vload_file_name)
-	  && ! NILP (elt)
-	  && !NILP (Vpurify_flag))
+	  && ! NILP (elt))
 	{
-	  if (NILP (Vdoc_file_name))
-	    /* We have not yet called Snarf-documentation, so assume
-	       this file is described in the DOC file
-	       and Snarf-documentation will fill in the right value later.
-	       For now, replace the whole list with 0.  */
-	    doc_reference = 1;
-	  else
-	    /* We have already called Snarf-documentation, so make a relative
-	       file name for this file, so it can be found properly
-	       in the installed Lisp directory.
-	       We don't use Fexpand_file_name because that would make
-	       the directory absolute now.  */
-	    {
-	      AUTO_STRING (dot_dot_lisp, "../lisp/");
-	      elt = concat2 (dot_dot_lisp, Ffile_name_nondirectory (elt));
-	    }
+	  if (!NILP (Vpurify_flag))
+	    doc_reference = 0;
+	  else if (load_force_doc_strings)
+	    doc_reference = 2;
 	}
-      else if (EQ (elt, Vload_file_name)
-	       && ! NILP (elt)
-	       && load_force_doc_strings)
-	doc_reference = 2;
-
       if (ch)
 	{
 	  if (flag > 0)
@@ -4253,8 +4218,6 @@ read_list (bool flag, Lisp_Object readcharfun)
 
 	      if (ch == ')')
 		{
-		  if (doc_reference == 1)
-		    return make_fixnum (0);
 		  if (doc_reference == 2 && FIXNUMP (XCDR (val)))
 		    {
 		      char *saved = NULL;