completions: Offer ../ and ./ again (#9477)

Inadvertently broken in a2d816710f,
this made `cd .` no longer offer `cd ../` (same for general file completions
like `ls .`, which only offers dotfiles)

src/wildcard.cpp

@@ -679,7 +679,7 @@ class wildcard_expander_t {
     }
 
     // Helper to resolve using our prefix.
-    dir_iter_t open_dir(const wcstring &base_dir) const {
+    dir_iter_t open_dir(const wcstring &base_dir, bool dotdot = false) const {
         wcstring path = this->working_directory;
         append_path_component(path, base_dir);
         if (flags & expand_flag::special_for_cd) {
@@ -687,7 +687,7 @@ class wildcard_expander_t {
             // for example, cd ../<tab> should complete "without resolving symlinks".
             path = normalize_path(path);
         }
-        return dir_iter_t(path);
+        return dir_iter_t(path, dotdot);
     }
 
    public:
@@ -952,7 +952,8 @@ void wildcard_expander_t::expand(const wcstring &base_dir, const wchar_t *wc,
             }
         }
 
-        dir_iter_t dir = open_dir(base_dir);
+        // return "." and ".." entries if we're doing completions
+        dir_iter_t dir = open_dir(base_dir, /* return . and .. */ flags & expand_flag::for_completions);
         if (dir.valid()) {
             if (is_last_segment) {
                 // Last wildcard segment, nonempty wildcard.

src/wutil.cpp

@@ -172,12 +172,13 @@ void dir_iter_t::entry_t::do_stat() const {
     }
 }
 
-dir_iter_t::dir_iter_t(const wcstring &path) {
+dir_iter_t::dir_iter_t(const wcstring &path, bool withdot) {
     dir_.reset(wopendir(path));
     if (!dir_) {
         error_ = errno;
         return;
     }
+    withdot_ = withdot;
     entry_.dirfd_ = dirfd(&*dir_);
 }
 
@@ -211,8 +212,9 @@ const dir_iter_t::entry_t *dir_iter_t::next() {
         error_ = errno;
         return nullptr;
     }
-    // Skip . and ..
-    if (!strcmp(dent->d_name, ".") || !strcmp(dent->d_name, "..")) {
+    // Skip . and ..,
+    // unless we've been told not to.
+    if (!withdot_ && (!strcmp(dent->d_name, ".") || !strcmp(dent->d_name, ".."))) {
         return next();
     }
     entry_.reset();

src/wutil.h

@@ -171,12 +171,15 @@ enum class dir_entry_type_t : uint8_t {
 /// symlink, or if the caller asks for the stat buffer.
 /// Symlinks are followed.
 class dir_iter_t : noncopyable_t {
+   private:
+    /// Whether this dir_iter considers the "." and ".." filesystem entries.
+    bool withdot_{false};
    public:
     struct entry_t;
 
     /// Open a directory at a given path. On failure, \p error() will return the error code.
     /// Note opendir is guaranteed to set close-on-exec by POSIX (hooray).
-    explicit dir_iter_t(const wcstring &path);
+    explicit dir_iter_t(const wcstring &path, bool withdot = false);
 
     /// Advance this iterator.
     /// \return a pointer to the entry, or nullptr if the entry is finished, or an error occurred.

tests/checks/cd.fish

@@ -267,3 +267,7 @@ begin
     # CHECK: $PWD is absolute
     cd ../../..
 end
+
+complete -C'cd .'
+# CHECK: ../
+# CHECK: ./