Document make-temp-name magic limitations

* doc/lispref/files.texi (Unique File Names):
* src/fileio.c (Fmake_temp_name): Document that make-temp-name
does not guarantee uniqueness on magic file names.

2 files changed, 7 insertions, 5 deletions

diff --git a/doc/lispref/files.texi b/doc/lispref/files.texi
index 2b692dbf680..d3f40a7c0c0 100644
--- a/doc/lispref/files.texi
+++ b/doc/lispref/files.texi
@@ -2547,13 +2547,14 @@ should compute the directory like this:
 @end defopt
 
 @defun make-temp-name base-name
-This function generates a string that can be used as a unique file
+This function generates a string that might be a unique file
 name.  The name starts with @var{base-name}, and has several random
 characters appended to it, which are different in each Emacs job.  It
 is like @code{make-temp-file} except that (i) it just constructs a
-name, and does not create a file, and (ii) @var{base-name} should be
-an absolute file name (on MS-DOS, this function can truncate
-@var{base-name} to fit into the 8+3 file-name limits).
+name and does not create a file, (ii) @var{base-name} should be an
+absolute file name that is not magic, and (iii) if the returned file
+name is magic, it might name an existing file.  @xref{Magic File
+Names}.
 
 @strong{Warning:} In most cases, you should not use this function; use
 @code{make-temp-file} instead!  This function is susceptible to a race
diff --git a/src/fileio.c b/src/fileio.c
index db760d9b22d..15845e39144 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -757,7 +757,8 @@ danger of generating a name being used by another Emacs process
 \(so long as only a single host can access the containing directory...).
 
 This function tries to choose a name that has no existing file.
-For this to work, PREFIX should be an absolute file name.
+For this to work, PREFIX should be an absolute file name, and PREFIX
+and the returned string should both be non-magic.
 
 There is a race condition between calling `make-temp-name' and creating the
 file, which opens all kinds of security holes.  For that reason, you should