Add name variants for all arrows

CONFIG.md

@@ -143,7 +143,8 @@ Each line has the format `SOURCE ARROW TARGET` where `TARGET` is optional.
 literal delimited by `"` or `'` (e. g. `"foo\" bar/baz"`). Python's string
 escape syntax is supported. Trailing slashes are ignored. `TARGET` can be
 formatted like `SOURCE`, but it can also be a single exclamation mark without
-quotes (`!`). `ARROW` is one of `-->`, `-exact->` and `-re->`.
+quotes (`!`). `ARROW` is one of `-->`, `-exact->`, `-name->`, `-re->` and
+`-name-re->`
 
 If a rule's target is `!`, this means that when the rule matches on a path, the
 corresponding file or directory is ignored. If a rule's target is missing, the
@@ -157,6 +158,14 @@ that part of the path is replaced with `TARGET`. This means that the rule
 into `baz/xyz`. The rule `foo --> !` would ignore a directory named `foo` as
 well as all its contents.
 
+### The `-name->` arrow
+
+The `-name->` arrow works similar to the `-->` arrow, but pretends it is in the
+same directory as the file or directory it is applied to. For example, the rule
+`bar -name-> baz` would convert `foo/bar` into `foo/baz` and `foo/bar/xyz` into
+`foo/baz/xyz`. The rule `foo --> !` would ignore all files and directories named
+`foo` as well as their contents.
+
 ### The `-exact->` arrow
 
 The `-exact->` arrow requires the path to match `SOURCE` exactly. This means
@@ -165,6 +174,14 @@ but `foo/bar/xyz` would be unaffected. Also, `foo -exact-> !` would only ignore
 `foo`, but not its contents (if it has any). The examples below show why this is
 useful.
 
+### The `-name-exact->` arrow
+
+The `-name-exact->` arrow works similar to the `-exact->` arrow, but pretends it
+is in the same directory as the file or directory it is applied to. For example,
+the rule `bar -name-exact-> baz` would convert `foo/bar` into `foo/baz` but
+`foo/bar/xyz` would be unaffected. The rule `foo --> !` would ignore only ignore
+files and directories named `foo`, but not their contents.
+
 ### The `-re->` arrow
 
 The `-re->` arrow uses regular expressions. `SOURCE` is a regular expression
@@ -186,10 +203,15 @@ example `{g2.lower()}` or `{g3.replace(' ', '_')}`.
 
 [3]: <https://docs.python.org/3/library/string.html#format-string-syntax> "Format String Syntax"
 
+### The `-name-re->` arrow
+
+The `-name-re>` arrow works similar to the `-re->` arrow, but pretends it is in
+the same directory as the file or directory it is applied to.
+
 ### Example: Tutorials
 
 You have an ILIAS course with lots of tutorials, but are only interested in a
-single one?
+single one.
 
 ```
 tutorials/
@@ -236,3 +258,34 @@ To do this, you can use the most powerful of arrows: The regex arrow.
 ```
 
 Note the escaped backslashes on the `SOURCE` side.
+
+### Example: Crawl a python project
+
+You are crawling a python project and want to ignore all hidden files (files
+whose name starts with a `.`), all `__pycache__` directories and all markdown
+files (for some weird reason).
+
+```
+.gitignore
+.mypy_cache/
+.venv/
+CONFIG.md
+PFERD/
+  |- __init__.py
+  |- __main__.py
+  |- __pycache__/
+  |- authenticator.py
+  |- config.py
+  ...
+README.md
+...
+```
+
+For this task, the name arrows can be used. They are variants of the normal
+arrows that only look at the file name instead of the entire path.
+
+```
+\..* -name-re-> !
+__pycache__ -name-> !
+.*\.md -name-re-> !
+```

PFERD/transformer.py

@@ -77,6 +77,19 @@ class ExactRule(Rule):
         return False
 
 
+class NameRule(Rule):
+    def __init__(self, subrule: Rule):
+        self._subrule = subrule
+
+    def transform(self, path: PurePath) -> Union[PurePath, bool]:
+        name = PurePath(*path.parts[-1:])
+        result = self._subrule.transform(name)
+        if isinstance(result, PurePath):
+            return path.parent / result
+        else:
+            return result
+
+
 class ReRule(Rule):
     def __init__(self, left: str, right: Union[str, bool]):
         self._left = left
@@ -220,16 +233,25 @@ def parse_arrow(line: Line) -> str:
 
     name = []
     while True:
-        if c := line.get():
-            if c == "-":
-                break
+        c = line.get()
+        if not c:
+            raise RuleParseException(line, "Expected rest of arrow")
+        elif c == "-":
+            line.advance()
+            c = line.get()
+            if not c:
+                raise RuleParseException(line, "Expected rest of arrow")
+            elif c == ">":
+                line.advance()
+                break  # End of arrow
+            else:
+                name.append("-")
+                name.append(c)
         else:
             name.append(c)
-            line.advance()
-        else:
-            raise RuleParseException(line, "Expected rest of arrow")
 
-    line.expect("->")
+        line.advance()
+
     return "".join(name)
 
 
@@ -261,10 +283,16 @@ def parse_rule(line: Line) -> Rule:
     # Dispatch
     if arrowname == "":
         return NormalRule(PurePath(left), rightpath)
+    elif arrowname == "name":
+        return NameRule(NormalRule(PurePath(left), rightpath))
     elif arrowname == "exact":
         return ExactRule(PurePath(left), rightpath)
+    elif arrowname == "name-exact":
+        return NameRule(ExactRule(PurePath(left), rightpath))
     elif arrowname == "re":
         return ReRule(left, right)
+    elif arrowname == "name-re":
+        return NameRule(ReRule(left, right))
     else:
         line.index = arrowindex + 1  # For nicer error message
         raise RuleParseException(line, "Invalid arrow name")