Re: How does one find out what file a library has been loaded from?

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Wed, Jul 20, 2022 at 11:47:11 +0000, Alan Mackenzie wrote:

> On Tue, Jul 19, 2022 at 22:13:53 +0300, Eli Zaretskii wrote:
> > > Date: Tue, 19 Jul 2022 17:07:09 +0000
> > > Cc: emacs-devel@gnu.org
> > > From: Alan Mackenzie <acm@muc.de>

[ .... ]

> If it loads a .eln file, and says it has loaded a .elc file, that is an
> untruth.  Not a "sort of not quite true", but a blatant untruth.  I had
> a look at the relevant code in lread.c some while ago.

> > But if you are bothered by that detail, I'm okay with having a note
> > there regarding *.eln files.  (Somehow, I'm not sure you will settle
> > for that.)

> I will write a patch for the doc string and another for the Elisp manual.
> I'm not happy with the state of things, but will probably have to accept
> it.

[ .... ]

Here's a first preliminary effort at amending loading.texi:



diff --git a/doc/lispref/loading.texi b/doc/lispref/loading.texi
index 54fc16ec9f..32ab08fcfd 100644
--- a/doc/lispref/loading.texi
+++ b/doc/lispref/loading.texi
@@ -1033,11 +1033,11 @@ Where Defined
 @cindex where was a symbol defined
 
 @defun symbol-file symbol &optional type
-This function returns the name of the file that defined @var{symbol}.
-If @var{type} is @code{nil}, then any kind of definition is acceptable.
-If @var{type} is @code{defun}, @code{defvar}, or @code{defface}, that
-specifies function definition, variable definition, or face definition
-only.
+This function returns a file name associated with the file that
+defined @var{symbol} (@pxref{eln files}).  If @var{type} is
+@code{nil}, then any kind of definition is acceptable.  If @var{type}
+is @code{defun}, @code{defvar}, or @code{defface}, that specifies
+function definition, variable definition, or face definition only.
 
 The value is normally an absolute file name.  It can also be @code{nil},
 if the definition is not associated with any file.  If @var{symbol}
@@ -1049,14 +1049,15 @@ Where Defined
 @code{load-history}.
 
 @defvar load-history
-The value of this variable is an alist that associates the names of
-loaded library files with the names of the functions and variables
-they defined, as well as the features they provided or required.
+The value of this variable is an alist that associates names
+associated with loaded library files (@pxref{eln files}) with the
+names of the functions and variables the files defined, as well as the
+features they provided or required.
 
 Each element in this alist describes one loaded library (including
 libraries that are preloaded at startup).  It is a list whose @sc{car}
-is the absolute file name of the library (a string).  The rest of the
-list elements have these forms:
+is an absolute file name associated with the library (a string)
+(@pxref{eln files}).  The rest of the list elements have these forms:
 
 @table @code
 @item @var{var}
@@ -1083,9 +1084,30 @@ Where Defined
 @code{eval-buffer} on a buffer that is not visiting a file.
 @end defvar
 
-  The command @code{eval-region} updates @code{load-history}, but does so
-by adding the symbols defined to the element for the file being visited,
-rather than replacing that element.  @xref{Eval}.
+@anchor{eln files} For backwards compatibility, @code{load-history}
+stores and @code{symbol-file} returns the name of a notional byte
+compiled @file{.elc} file in the same directory as its source file
+when the real file loaded from is a natively compiled file elsewhere.
+This @file{.elc} file may or may not actually exist.  For other files,
+their absolute file names are used.  If you want to find the actual
+file loaded from, and you suspect if may really be a native compiled
+file, something like the following should help.  You need to know the
+name of a function which hasn't been advised, say @var{foo}, defined
+in the suspected native compiled file.  Then
+
+@lisp
+(let ((foo-fun (symbol-function #'FOO)))
+       (and foo-fun (subr-native-elisp-p foo-fun)
+            (native-comp-unit-file (subr-native-comp-unit foo-fun))))
+@end lisp
+
+@noindent
+will return either the name of the native compiled file defining
+@var{foo}, or @code{nil} if there is no such file.
+
+The command @code{eval-region} updates @code{load-history}, but does
+so by adding the symbols defined to the element for the file being
+visited, rather than replacing that element.  @xref{Eval}.
 
 @kindex function-history @r{(function symbol property)}
 In addition to @code{load-history}, every function keeps track of its


-- 
Alan Mackenzie (Nuremberg, Germany).