Generalize dirEntries to take a pred as parameter

Author: nordlow

std/file.d

@@ -4616,7 +4616,8 @@ enum SpanMode
         ["animals", "plants"]));
 }
 
-private struct DirIteratorImpl
+private struct DirIteratorImpl(alias pred = (const scope ref DirEntry entry) => true)
+// TODO: if (is(typeof(pred(DirEntry.init)) : bool))
 {
   @safe:
     SpanMode _mode;
@@ -4720,6 +4721,8 @@ private struct DirIteratorImpl
 
         bool mayStepIn()
         {
+            if (pred(_cur))
+                return false;
             return _followSymlink ? _cur.isDir : _cur.isDir && !_cur.isSymlink;
         }
     }
@@ -4863,11 +4866,12 @@ private struct DirIteratorImpl
     }
 }
 
-struct DirIterator
+struct DirIterator(alias pred = (const scope ref DirEntry entry) => true)
+// TODO: if (is(typeof(pred(DirEntry.init)) : bool))
 {
 @safe:
 private:
-    RefCounted!(DirIteratorImpl, RefCountedAutoInitialize.no) impl;
+    RefCounted!(DirIteratorImpl!(pred), RefCountedAutoInitialize.no) impl;
     this(string pathname, SpanMode mode, bool followSymlink) @trusted
     {
         impl = typeof(impl)(pathname, mode, followSymlink);
@@ -4957,7 +4961,12 @@ foreach (d; dFiles)
  +/
 auto dirEntries(string path, SpanMode mode, bool followSymlink = true)
 {
-    return DirIterator(path, mode, followSymlink);
+    return DirIterator!()(path, mode, followSymlink);
+}
+auto dirEntries(alias pred)(string path, SpanMode mode, bool followSymlink = true)
+// TODO: if (is(typeof(pred(DirEntry.init)) : bool))
+{
+    return DirIterator!(pred)(path, mode, followSymlink);
 }
 
 /// Duplicate functionality of D1's `std.file.listdir()`:
@@ -5064,7 +5073,7 @@ auto dirEntries(string path, string pattern, SpanMode mode,
     import std.path : globMatch, baseName;
 
     bool f(DirEntry de) { return globMatch(baseName(de.name), pattern); }
-    return filter!f(DirIterator(path, mode, followSymlink));
+    return filter!f(DirIterator!()(path, mode, followSymlink));
 }
 
 @safe unittest