Add a new function child_path.

child_path returns a pointer to the first component in a child path
that comes after a parent path.  This does not depend on trying to
stat() the paths since they may describe remote paths but instead
relies on filename parsing.  The function requires that the child path
describe a filename that contains at least one component below the
parent path and returns a pointer to the first component.

gdb/ChangeLog:

	* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add
	unittests/child-path-selftests.c.
	* common/pathstuff.c (child_path): New function.
	* common/pathstuff.h (child_path): New prototype.
	* unittests/child-path-selftests.c: New file.

1 files changed, 6 insertions, 0 deletions

diff --git a/gdb/common/pathstuff.h b/gdb/common/pathstuff.h
index c264e78..67072a4 100644
--- a/gdb/common/pathstuff.h
+++ b/gdb/common/pathstuff.h
@@ -48,6 +48,12 @@ extern gdb::unique_xmalloc_ptr<char>
 
 extern gdb::unique_xmalloc_ptr<char> gdb_abspath (const char *path);
 
+/* If the path in CHILD is a child of the path in PARENT, return a
+   pointer to the first component in the CHILD's pathname below the
+   PARENT.  Otherwise, return NULL.  */
+
+extern const char *child_path (const char *parent, const char *child);
+
 /* Return whether PATH contains a directory separator character.  */
 
 extern bool contains_dir_separator (const char *path);