index: make lazy check less lazy

We got many reports where the 'lazy check' didn't work too well for
people... so make it a bit less lazy, so it'll just work for more
people.

In practice, never skip _directories_ unless they're leaf directories;
this avoids the mtime-does-not-bubble-up problem.

lib/index/mu-indexer.cc

@@ -115,12 +115,16 @@ Indexer::Private::handler (const std::string& fullpath, struct stat *statbuf,
                            Scanner::HandleType htype)
 {
         switch (htype) {
-        case Scanner::HandleType::EnterDir: {
+        case Scanner::HandleType::EnterDir:
+        case Scanner::HandleType::EnterNewCur: {
                 // in lazy-mode, we ignore this dir if its dirstamp suggest it
                 // is up-to-date (this is _not_ always true; hence we call it
-                // lazy-mode)
+                // lazy-mode); only for actual message dirs, since the dir
+                // tstamps may not bubble up.
                 dirstamp_ = store_.dirstamp(fullpath);
-                if (conf_.lazy_check && dirstamp_ == statbuf->st_mtime) {
+                if (conf_.lazy_check &&
+                    dirstamp_ == statbuf->st_mtime &&
+                    htype == Scanner::HandleType::EnterNewCur) {
                         g_debug("skip %s (seems up-to-date)", fullpath.c_str());
                         return false;
                 }

lib/index/mu-scanner.cc

@@ -96,14 +96,15 @@ Scanner::Private::process_dentry (const std::string& path, struct dirent *dentry
         }
 
         if (S_ISDIR(statbuf.st_mode)) {
-
-                const auto res = handler_(fullpath, &statbuf, Scanner::HandleType::EnterDir);
-                if (!res) {
-                        //g_debug ("skipping dir %s", fullpath.c_str());
+                const auto new_cur = is_new_cur(dentry->d_name);
+                const auto htype   = new_cur ?
+                        Scanner::HandleType::EnterNewCur :
+                        Scanner::HandleType::EnterDir;
+                const auto res     = handler_(fullpath, &statbuf, htype);
+                if (!res)
                         return true; // skip
-                }
 
-                process_dir (fullpath, is_new_cur(dentry->d_name));
+                process_dir (fullpath, new_cur);
 
                 return handler_(fullpath, &statbuf, Scanner::HandleType::LeaveDir);
 

lib/index/mu-scanner.hh

@@ -42,7 +42,12 @@ namespace Mu {
 ///
 class Scanner {
 public:
-        enum struct HandleType { File, EnterDir, LeaveDir };
+        enum struct HandleType {
+                File,
+                EnterNewCur, /* cur/ or new/ */
+                EnterDir, /* some other directory */
+                LeaveDir
+        };
 
         /// Prototype for a handler function
         using Handler     = std::function<bool(const std::string& fullpath,