fsmonitor: Handle differences between Windows named pipe functions

CreateNamedPipeW is perfectly happy accepting pipe names with embedded
escape charcters (e.g. \b), WaitNamedPipeW is not and incorrectly returns
ERROR_FILE_NOT_FOUND when clearly a named pipe with the given name
exists.

For example, this path is problemmatic:
\\batfs-sb29-cifs\vmgr\sbs29\my_git_repo

In order to work around this issue, rather than using the path to the
worktree directly as the name of the pipe, instead use the hash of the
worktree path.

Author: edecosta-mw

compat/fsmonitor/fsm-ipc-win32.c

@@ -1,10 +1,24 @@
 #include "git-compat-util.h"
+#include "cache.h"
 #include "config.h"
+#include "strbuf.h"
 #include "fsmonitor-ipc.h"
 
-const char *fsmonitor_ipc__get_path(struct repository *r) {
-	static char *ret;
-	if (!ret)
-		ret = git_pathdup("fsmonitor--daemon.ipc");
-	return ret;
+const char *fsmonitor_ipc__get_path(struct repository *r)
+{
+	static const char *ipc_path = NULL;
+	git_SHA_CTX sha1ctx;
+	struct strbuf pipe_name = STRBUF_INIT;
+	unsigned char hash[GIT_MAX_RAWSZ];
+
+	if (ipc_path)
+		return ipc_path;
+
+	git_SHA1_Init(&sha1ctx);
+	git_SHA1_Update(&sha1ctx, r->worktree, strlen(r->worktree));
+	git_SHA1_Final(hash, &sha1ctx);
+
+	strbuf_addf(&pipe_name, "git-fsmonitor-%s", hash_to_hex(hash));
+	ipc_path = strbuf_detach(&pipe_name, NULL);
+	return ipc_path;
 }

compat/simple-ipc/ipc-win32.c

@@ -17,27 +17,15 @@
 static int initialize_pipe_name(const char *path, wchar_t *wpath, size_t alloc)
 {
 	int off = 0;
-	struct strbuf realpath = STRBUF_INIT;
-
-	if (!strbuf_realpath(&realpath, path, 0))
-		return -1;
+	int ret = 0;
+	char *pipe_name = xstrdup(path);
 
 	off = swprintf(wpath, alloc, L"\\\\.\\pipe\\");
-	if (xutftowcs(wpath + off, realpath.buf, alloc - off) < 0)
-		return -1;
+	if (xutftowcs(wpath + off, basename(pipe_name), alloc - off) < 0)
+		ret = -1;
 
-	/* Handle drive prefix */
-	if (wpath[off] && wpath[off + 1] == L':') {
-		wpath[off + 1] = L'_';
-		off += 2;
-	}
-
-	for (; wpath[off]; off++)
-		if (wpath[off] == L'/')
-			wpath[off] = L'\\';
-
-	strbuf_release(&realpath);
-	return 0;
+	free(pipe_name);
+	return ret;
 }
 
 static enum ipc_active_state get_active_state(wchar_t *pipe_path)