the POSIX 2008 behaviour of realpath is not available everywhere so we
provide a simple wrapper function.  We use (and provide) the gnu
extension canonicalize_file_name to make it cleaner to test for the
feature we need; otherwise we have to rely on realpath segfaulting if
the second argument is null.
---
 compat/Makefile.local                |  4 ++++
 compat/canonicalize_file_name.c      | 18 ++++++++++++++++++
 compat/compat.h                      |  8 ++++++++
 compat/have_canonicalize_file_name.c | 10 ++++++++++
 configure                            | 16 ++++++++++++++++
 notmuch-config.c                     |  2 +-
 6 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 compat/canonicalize_file_name.c
 create mode 100644 compat/have_canonicalize_file_name.c

diff --git a/compat/Makefile.local b/compat/Makefile.local
index b0d5417..bcb9f0e 100644
--- a/compat/Makefile.local
+++ b/compat/Makefile.local
@@ -5,6 +5,10 @@ extra_cflags += -I$(srcdir)/$(dir)
 
 notmuch_compat_srcs :=
 
+ifneq ($(HAVE_CANONICALIZE_FILE_NAME),1)
+notmuch_compat_srcs += $(dir)/canonicalize_file_name.c
+endif
+
 ifneq ($(HAVE_GETLINE),1)
 notmuch_compat_srcs += $(dir)/getline.c $(dir)/getdelim.c
 endif
diff --git a/compat/canonicalize_file_name.c b/compat/canonicalize_file_name.c
new file mode 100644
index 0000000..e92c0f6
--- /dev/null
+++ b/compat/canonicalize_file_name.c
@@ -0,0 +1,18 @@
+#include "compat.h"
+#include <limits.h>
+#undef _GNU_SOURCE
+#include <stdlib.h>
+
+char *
+canonicalize_file_name (const char * path)
+{
+#ifdef PATH_MAX
+    char *resolved_path =  malloc (PATH_MAX+1);
+    if (resolved_path == NULL)
+	return NULL;
+
+    return realpath (path, resolved_path);
+#else
+#error undefined PATH_MAX _and_ missing canonicalize_file_name not supported
+#endif
+}
diff --git a/compat/compat.h b/compat/compat.h
index 5a402d5..634d505 100644
--- a/compat/compat.h
+++ b/compat/compat.h
@@ -37,6 +37,14 @@ extern "C" {
 #define _POSIX_PTHREAD_SEMANTICS 1
 #endif
 
+#if !HAVE_CANONICALIZE_FILE_NAME
+/* we only call this function from C, and this makes testing easier */
+#ifndef __cplusplus
+char *
+canonicalize_file_name (const char *path);
+#endif
+#endif
+
 #if !HAVE_GETLINE
 #include <stdio.h>
 #include <unistd.h>
diff --git a/compat/have_canonicalize_file_name.c b/compat/have_canonicalize_file_name.c
new file mode 100644
index 0000000..24c848e
--- /dev/null
+++ b/compat/have_canonicalize_file_name.c
@@ -0,0 +1,10 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+
+int main()
+{
+    char *found;
+    char *string;
+
+    found = canonicalize_file_name (string);
+}
diff --git a/configure b/configure
index 13b6062..5b7c941 100755
--- a/configure
+++ b/configure
@@ -526,6 +526,18 @@ EOF
     exit 1
 fi
 
+printf "Checking for canonicalize_file_name... "
+if ${CC} -o compat/have_canonicalize_file_name "$srcdir"/compat/have_canonicalize_file_name.c > /dev/null 2>&1
+then
+    printf "Yes.\n"
+    have_canonicalize_file_name=1
+else
+    printf "No (will use our own instead).\n"
+    have_canonicalize_file_name=0
+fi
+rm -f compat/have_canonicalize_file_name
+
+
 printf "Checking for getline... "
 if ${CC} -o compat/have_getline "$srcdir"/compat/have_getline.c > /dev/null 2>&1
 then
@@ -751,6 +763,10 @@ zsh_completion_dir = ${ZSHCOMLETIONDIR:=\$(prefix)/share/zsh/functions/Completio
 
 # Whether the getline function is available (if not, then notmuch will
 # build its own version)
+HAVE_CANONICALIZE_FILE_NAME = ${have_canonicalize_file_name}
+
+# Whether the getline function is available (if not, then notmuch will
+# build its own version)
 HAVE_GETLINE = ${have_getline}
 
 # Whether the strcasestr function is available (if not, then notmuch will
diff --git a/notmuch-config.c b/notmuch-config.c
index 8d28653..4886d36 100644
--- a/notmuch-config.c
+++ b/notmuch-config.c
@@ -454,7 +454,7 @@ notmuch_config_save (notmuch_config_t *config)
     }
 
     /* Try not to overwrite symlinks. */
-    filename = realpath (config->filename, NULL);
+    filename = canonicalize_file_name (config->filename);
     if (! filename) {
 	if (errno == ENOENT) {
 	    filename = strdup (config->filename);
-- 
1.8.5.2