git-changebar: Fix in-repository paths on Windows

Git uses its own path representation for files inside its tree, which
follows the UNIX path style (forward slashes).  So properly convert
internal paths from native to Git paths.

See libgit2/libgit2#3012

Part of Issue geany#214.

git-changebar/src/gcb-plugin.c

@@ -290,6 +290,58 @@ monitor_head_ref (git_repository *repo,
   return monitor;
 }
 
+/* checks whether @path points somewhere inside @dir and returns the pointer
+ * inside @path starting the relative path, or NULL */
+static const gchar *
+path_dir_contains (const gchar *dir,
+                   const gchar *path)
+{
+#ifdef G_OS_WIN32
+  /* FIXME: handle drive letters and such */
+# define NORM_PATH_CH(c) (((c) == '\\') ? '/' : (c))
+#else
+# define NORM_PATH_CH(c) (c)
+#endif
+
+  g_return_val_if_fail (dir != NULL, NULL);
+  g_return_val_if_fail (path != NULL, NULL);
+
+  while (*dir && NORM_PATH_CH (*dir) == NORM_PATH_CH (*path)) {
+    dir++, path++;
+  }
+
+  return *dir ? NULL : path;
+}
+
+/* gets the Git path for @repo pointing to @sys_path, or NULL */
+static gchar *
+get_path_in_repository (git_repository *repo,
+                        const gchar    *sys_path)
+{
+  const gchar  *workdir   = git_repository_workdir (repo);
+  const gchar  *rel_path  = path_dir_contains (workdir, sys_path);
+
+#ifdef G_OS_WIN32
+  if (rel_path) {
+    /* we want an internal Git path, which uses UNIX format */
+    gchar  *p;
+    gchar  *repo_path = g_strdup (rel_path);
+
+    for (p = repo_path; *p; p++) {
+      if (*p == '\\') {
+        *p = '/';
+      }
+    }
+
+    return repo_path;
+  }
+
+  return NULL;
+#else
+  return g_strdup (rel_path);
+#endif
+}
+
 static gpointer
 worker_thread (gpointer data)
 {
@@ -303,7 +355,7 @@ worker_thread (gpointer data)
     const gchar *path = job->path;
 
     if (repo && (job->force ||
-                 ! g_str_has_prefix (path, git_repository_workdir (repo)))) {
+                 ! path_dir_contains (path, git_repository_workdir (repo)))) {
       /* FIXME: this can fail with nested repositories */
       git_repository_free (repo);
       repo = NULL;
@@ -330,12 +382,14 @@ worker_thread (gpointer data)
       }
     }
 
+    job->blob = NULL;
     if (repo) {
-      const gchar *relpath = path + strlen (git_repository_workdir (repo));
+      gchar *relpath = get_path_in_repository (repo, path);
 
-      job->blob = repo_get_file_blob (repo, relpath);
-    } else {
-      job->blob = NULL;
+      if (relpath) {
+        job->blob = repo_get_file_blob (repo, relpath);
+        g_free (relpath);
+      }
     }
 
     g_idle_add_full (G_PRIORITY_LOW, report_work_in_idle, job, free_job);