manual: Improve documentation of get_current_dir_name. [BZ #6889]

This is a minor rewording to clarify the behaviour of
get_current_dir_name.  Additionally, the @vindex is moved above the
@deftypefun so that following links give a better result with regard
to context.

	[BZ #6889]
	* manual/filesys.texi (get_current_dir_name): Clarify
	behaviour.

2 files changed, 14 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index d6262e5746..35bf20ac11 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-02-19  Rical Jasan  <ricaljasan@pacific.net>
+
+	[BZ #6889]
+	* manual/filesys.texi (get_current_dir_name): Clarify behaviour.
+
 2018-02-18  Aurelien Jarno  <aurelien@aurel32.net>
 
 	[BZ #22818]
diff --git a/manual/filesys.texi b/manual/filesys.texi
index ca77996902..cc70a6b7ee 100644
--- a/manual/filesys.texi
+++ b/manual/filesys.texi
@@ -147,19 +147,20 @@ necessarily enough space to contain the directory name.  That is why
 this function is deprecated.
 @end deftypefn
 
+@vindex PWD
 @deftypefun {char *} get_current_dir_name (void)
 @standards{GNU, unistd.h}
 @safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{} @acsfd{}}}
 @c Besides getcwd, which this function calls as a fallback, it calls
 @c getenv, with the potential thread-safety issues that brings about.
-@vindex PWD
-This @code{get_current_dir_name} function is basically equivalent to
-@w{@code{getcwd (NULL, 0)}}.  The only difference is that the value of
-the @code{PWD} variable is returned if this value is correct.  This is a
-subtle difference which is visible if the path described by the
-@code{PWD} value is using one or more symbol links in which case the
-value returned by @code{getcwd} can resolve the symbol links and
-therefore yield a different result.
+The @code{get_current_dir_name} function is basically equivalent to
+@w{@code{getcwd (NULL, 0)}}, except the value of the @env{PWD}
+environment variable is first examined, and if it does in fact
+correspond to the current directory, that value is returned.  This is
+a subtle difference which is visible if the path described by the
+value in @env{PWD} is using one or more symbolic links, in which case
+the value returned by @code{getcwd} would resolve the symbolic links
+and therefore yield a different result.
 
 This function is a GNU extension.
 @end deftypefun