Minimal changes to allow multiline suggestions.

I'm trying to be the least invasive;
But the idea is to allow access to previous lines when rendering a line
in order to shift them down; and display multiline sugestions.

With this I can add minimal modification into IPython that allows
multiline suggestion (typically would be created by an LLM – while not a
big fan, there is a lot of requests for it.

I'm going to assume there is no willingness tochange the current API
for transformers to get at least a ranges of lines instead of lines,
it would be easier to handle.

I do not include any update to the transformers we use in IPython to
display those completions; but once battled tested a bit more, I'm happy
to contribute it as well.

Author: Carreau

src/prompt_toolkit/layout/controls.py

@@ -667,7 +667,11 @@ def _create_get_processed_line_func(
 
         merged_processor = merge_processors(input_processors)
 
-        def transform(lineno: int, fragments: StyleAndTextTuples) -> _ProcessedLine:
+        def transform(
+            lineno: int,
+            fragments: StyleAndTextTuples,
+            get_line: Callable[[int], StyleAndTextTuples],
+        ) -> _ProcessedLine:
             "Transform the fragments for a given line number."
 
             # Get cursor position at this line.
@@ -679,7 +683,14 @@ def source_to_display(i: int) -> int:
 
             transformation = merged_processor.apply_transformation(
                 TransformationInput(
-                    self, document, lineno, source_to_display, fragments, width, height
+                    self,
+                    document,
+                    lineno,
+                    source_to_display,
+                    fragments,
+                    width,
+                    height,
+                    get_line,
                 )
             )
 
@@ -697,7 +708,7 @@ def get_processed_line(i: int) -> _ProcessedLine:
                 try:
                     return cache[i]
                 except KeyError:
-                    processed_line = transform(i, get_line(i))
+                    processed_line = transform(i, get_line(i), get_line)
                     cache[i] = processed_line
                     return processed_line
 

src/prompt_toolkit/layout/processors.py

@@ -10,7 +10,7 @@
 
 import re
 from abc import ABCMeta, abstractmethod
-from typing import TYPE_CHECKING, Callable, Hashable, cast
+from typing import TYPE_CHECKING, Callable, Hashable, cast, Optional
 
 from prompt_toolkit.application.current import get_app
 from prompt_toolkit.cache import SimpleCache
@@ -86,6 +86,9 @@ class TransformationInput:
         previous processors into account.)
     :param fragments: List of fragments that we can transform. (Received from the
         previous processor.)
+    :param get_line: Optional ; a callable that returns the fragments of another
+        line in the  current buffer; This can be used to create processors capable
+        of affecting transforms across multiple lines.
     """
 
     def __init__(
@@ -97,6 +100,7 @@ def __init__(
         fragments: StyleAndTextTuples,
         width: int,
         height: int,
+        get_line: Optional[Callable[[int], StyleAndTextTuples]] = None,
     ) -> None:
         self.buffer_control = buffer_control
         self.document = document
@@ -105,6 +109,7 @@ def __init__(
         self.fragments = fragments
         self.width = width
         self.height = height
+        self.get_line = get_line
 
     def unpack(
         self,
@@ -987,6 +992,7 @@ def source_to_display(i: int) -> int:
                     fragments,
                     ti.width,
                     ti.height,
+                    ti.get_line,
                 )
             )
             fragments = transformation.fragments