dosname: Change IS_RELATIVE_FILE_NAME

[Bruno Haible]

In the most important GNU package, I can see 3 uses of IS_RELATIVE_FILE_NAME:

libvirt/src/qemu/qemu_domain.c
tar/src/misc.c
coreutils/src/basename.c

In the first two, the code assumes that IS_RELATIVE_FILE_NAME(F) means that
you can append F to a directory and get a meaningful file name. But with the
current definition of IS_RELATIVE_FILE_NAME, this is not true:
IS_RELATIVE_FILE_NAME("c:") returns true, but \foo\bar\c: is not a valid file
name.

Let me fix this.

For the third occurrence, the change does not matter.


2020-03-28  Bruno Haible  <address@hidden>

        dosname: Change IS_RELATIVE_FILE_NAME.
        * lib/dosname.h (IS_RELATIVE_FILE_NAME): On native Windows, OS/2, DOS,
        change the definition so that IS_RELATIVE_FILE_NAME("c:") is false.
        * NEWS: Mention the change.

diff --git a/NEWS b/NEWS
index 3ec49f3..c9548d5 100644
--- a/NEWS
+++ b/NEWS
@@ -58,6 +58,9 @@ User visible incompatible changes
 
 Date        Modules         Changes
 
+2020-03-28  dosname         On native Windows, OS/2, DOS,
+                            IS_RELATIVE_FILE_NAME("c:") now returns false.
+
 2020-03-28  filename        The macro IS_ABSOLUTE_PATH is deprecated. Use
                             IS_ABSOLUTE_FILE_NAME instead.
                             The macro IS_PATH_WITH_DIR is deprecated. Use
diff --git a/lib/dosname.h b/lib/dosname.h
index 5782960..926a695 100644
--- a/lib/dosname.h
+++ b/lib/dosname.h
@@ -47,6 +47,7 @@
 #  define IS_ABSOLUTE_FILE_NAME(F)                              \
      (ISSLASH ((F)[0]) || FILE_SYSTEM_PREFIX_LEN (F) != 0)
 #endif
-#define IS_RELATIVE_FILE_NAME(F) (! IS_ABSOLUTE_FILE_NAME (F))
+#define IS_RELATIVE_FILE_NAME(F) \
+  (! (ISSLASH ((F)[0]) || FILE_SYSTEM_PREFIX_LEN (F) != 0))
 
 #endif /* DOSNAME_H_ */