[PATCH v4 1/2] abspath: add a function to resolve paths with missing components

["brian m. carlson" <sandals@xxxxxxxxxxxxxxxxxxxx>]

We'd like to canonicalize paths such that we can preserve any number of
trailing components that may be missing.  Let's add a function to do
that, allowing either one or an unlimited number of components to
canonicalize, and make strbuf_realpath a wrapper around it that allows
just one component.

Signed-off-by: brian m. carlson <sandals@xxxxxxxxxxxxxxxxxxxx>
---
 abspath.c | 13 ++++++++++++-
 cache.h   |  2 ++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/abspath.c b/abspath.c
index 6f15a418bb..e6630b3618 100644
--- a/abspath.c
+++ b/abspath.c
@@ -80,6 +80,17 @@ static void get_root_part(struct strbuf *resolved, struct strbuf *remaining)
  */
 char *strbuf_realpath(struct strbuf *resolved, const char *path,
 		      int die_on_error)
+{
+	return strbuf_realpath_missing(resolved, path, 0, die_on_error);
+}
+
+/*
+ * Just like strbuf_realpath, but allows specifying how many missing components
+ * are permitted.  If many_missing is true, an arbitrary number of path
+ * components may be missing; otherwise, only the last component may be missing.
+ */
+char *strbuf_realpath_missing(struct strbuf *resolved, const char *path,
+			      int many_missing, int die_on_error)
 {
 	struct strbuf remaining = STRBUF_INIT;
 	struct strbuf next = STRBUF_INIT;
@@ -129,7 +140,7 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path,
 
 		if (lstat(resolved->buf, &st)) {
 			/* error out unless this was the last component */
-			if (errno != ENOENT || remaining.len) {
+			if (errno != ENOENT || (!many_missing && remaining.len)) {
 				if (die_on_error)
 					die_errno("Invalid path '%s'",
 						  resolved->buf);
diff --git a/cache.h b/cache.h
index e986cf4ea9..a1386235fc 100644
--- a/cache.h
+++ b/cache.h
@@ -1320,6 +1320,8 @@ static inline int is_absolute_path(const char *path)
 int is_directory(const char *);
 char *strbuf_realpath(struct strbuf *resolved, const char *path,
 		      int die_on_error);
+char *strbuf_realpath_missing(struct strbuf *resolved, const char *path,
+			      int missing_components, int die_on_error);
 char *real_pathdup(const char *path, int die_on_error);
 const char *absolute_path(const char *path);
 char *absolute_pathdup(const char *path);