Add support for using cell ID in diffing and merging

nbdime/diffing/config.py

@@ -0,0 +1,34 @@
+
+class DiffConfig:
+    """Set of predicates/differs/other configs to pass around"""
+
+    def __init__(self, *, predicates=None, differs=None, atomic_paths=None):
+        if predicates is None:
+            from .generic import default_predicates
+            predicates = default_predicates()
+
+        if differs is None:
+            from .generic import default_differs
+            differs = default_differs()
+
+        self.predicates = predicates
+        self.differs = differs
+        self._atomic_paths = atomic_paths or {}
+
+    def diff_item_at_path(self, a, b, path):
+        """Calculate the diff for path."""
+        self.differs[path](a, b, path=path, config=self)
+
+    def is_atomic(self, x, path=None):
+        "Return True for values that diff should treat as a single atomic value."
+        try:
+            return self._atomic_paths[path]
+        except KeyError:
+            return not isinstance(x, (str, list, dict))
+
+    def __copy__(self):
+        return DiffConfig(
+            predicates=self.predicates.copy(),
+            differs=self.differs.copy(),
+            atomic_paths=self._atomic_paths.copy(),
+        )

nbdime/diffing/generic.py

@@ -10,17 +10,13 @@
 from ..diff_format import SequenceDiffBuilder, MappingDiffBuilder, validate_diff
 from ..diff_utils import count_consumed_symbols
 
+from .config import DiffConfig
 from .sequences import diff_strings_linewise, diff_sequence
 from .snakes import compute_snakes_multilevel, compute_diff_from_snakes
 
 __all__ = ["diff"]
 
 
-def is_atomic(x):
-    "Return True for values that diff should treat as a single atomic value."
-    return not isinstance(x, (str, list, dict))
-
-
 def default_predicates():
     return defaultdict(lambda: (operator.__eq__,))
 
@@ -74,18 +70,16 @@
     return s.ratio() > threshold
 
 
-def diff(a, b, path="", predicates=None, differs=None):
+def diff(a, b, path="", config=None):
     "Compute the diff of two json-like objects, list or dict or string."
 
-    if predicates is None:
-        predicates = default_predicates()
-    if differs is None:
-        differs = default_differs()
+    if config is None:
+        config = DiffConfig()
 
     if isinstance(a, list) and isinstance(b, list):
-        d = diff_lists(a, b, path=path, predicates=predicates, differs=differs)
+        d = diff_lists(a, b, path=path, config=config)
     elif isinstance(a, dict) and isinstance(b, dict):
-        d = diff_dicts(a, b, path=path, predicates=predicates, differs=differs)
+        d = diff_dicts(a, b, path=path, config=config)
     elif isinstance(a, str) and isinstance(b, str):
         # Don't pass differs/predicates as the only possible use case is to
         # use a different character differ within each line or predicates
@@ -100,35 +94,42 @@
     return d
 
 
-def diff_sequence_multilevel(a, b, path="", predicates=None, differs=None):
+def diff_string_lines(a, b, path="", config=None):
+    """Diff two lists of strings (lines)"""
+
+    # This is mainly about short-circuiting to avoid full snakes for equal content
+    # since we know we can rely on __eq__ comparison
+    if len(a) == len(b) and a == b:
+        return []
+
+    return diff_strings_linewise(a, b)
+
+
+def diff_sequence_multilevel(a, b, path="", config=None):
     """Compute diff of two lists with configurable behaviour."""
 
-    if predicates is None:
-        predicates = default_predicates()
-    if differs is None:
-        differs = default_differs()
+    if config is None:
+        config = DiffConfig()
 
     # Invoke multilevel snake computation algorithm
-    compares = predicates[path or '/']
+    compares = config.predicates[path or '/']
     snakes = compute_snakes_multilevel(a, b, compares)
 
     # Convert snakes to diff
-    return compute_diff_from_snakes(a, b, snakes, path=path, predicates=predicates, differs=differs)
+    return compute_diff_from_snakes(a, b, snakes, path=path, config=config)
 
 
-def diff_lists(a, b, path="", predicates=None, differs=None, shallow_diff=None):
+def diff_lists(a, b, path="", config=None, shallow_diff=None):
     """Compute diff of two lists with configurable behaviour."""
 
-    if predicates is None:
-        predicates = default_predicates()
-    if differs is None:
-        differs = default_differs()
+    if config is None:
+        config = DiffConfig()
 
     # If multiple compares are provided to this path, delegate to multilevel algorithm
-    compares = predicates[path or '/']
+    compares = config.predicates[path or '/']
     if len(compares) > 1:
         assert shallow_diff is None
-        return diff_sequence_multilevel(a, b, path=path, predicates=predicates, differs=differs)
+        return diff_sequence_multilevel(a, b, path=path, config=config)
 
     # First make a shallow sequence diff with custom compare,
     # unless it's provided for us
@@ -138,7 +139,7 @@
     # Next we recurse to diff items in sequence that are considered
     # similar by compares[0] in the loop below
     subpath = "/".join((path, "*"))
-    diffit = differs[subpath]
+    diffit = config.differs[subpath]
 
     # Count consumed items i,j from a,b, (i="take" in patch_list)
     i, j = 0, 0
@@ -165,8 +166,8 @@
         for k in range(n):
             aval = a[i + k]
             bval = b[j + k]
-            if not is_atomic(aval):
-                cd = diffit(aval, bval, path=subpath, predicates=predicates, differs=differs)
+            if not config.is_atomic(aval, subpath):
+                cd = diffit(aval, bval, path=subpath, config=config)
                 if cd:
                     di.patch(i + k, cd)  # FIXME: Not covered in tests, create test situation
 
@@ -186,7 +187,7 @@
     return di.validated()
 
 
-def diff_dicts(a, b, path="", predicates=None, differs=None):
+def diff_dicts(a, b, path="", config=None):
     """Compute diff of two dicts with configurable behaviour.
 
     Keys in both a and b will be handled based on
@@ -197,10 +198,8 @@
     Items not mentioned in diff are items where compare(x, y) return True.
     For other items the diff will contain delete, insert, or replace entries.
     """
-    if predicates is None:
-        predicates = default_predicates()
-    if differs is None:
-        differs = default_differs()
+    if config is None:
+        config = DiffConfig()
 
     if not isinstance(a, dict) or not isinstance(b, dict):
         raise TypeError('Arguments to diff_dicts need to be dicts, got %r and %r' % (a, b))
@@ -218,14 +217,14 @@
         avalue = a[key]
         bvalue = b[key]
         # If types are the same and nonatomic, recurse
-        if type(avalue) is type(bvalue) and not is_atomic(avalue):
-            subpath = "/".join((path, key))
-            diffit = differs[subpath]
-            dd = diffit(avalue, bvalue, path=subpath, predicates=predicates, differs=differs)
+        subpath = "/".join((path, key))
+        if type(avalue) is type(bvalue) and not config.is_atomic(avalue, path=subpath):
+            diffit = config.differs[subpath]
+            dd = diffit(avalue, bvalue, path=subpath, config=config)
             if dd:
                 di.patch(key, dd)
         else:
-            if (path or '/') in predicates:
+            if (path or '/') in config.predicates:
                 # Could also this a warning, but I think it shouldn't be done
                 raise RuntimeError(
                     "Found predicate(s) for path {} pointing to dict entry.".format(

nbdime/diffing/notebooks.py

@@ -18,8 +18,11 @@
 from ..diff_format import MappingDiffBuilder, DiffOp
 from ..utils import defaultdict2
 
-from .generic import (diff, diff_sequence_multilevel,
-                      compare_strings_approximate)
+from .config import DiffConfig
+from .generic import (
+    diff, diff_sequence_multilevel, compare_strings_approximate,
+    diff_string_lines,
+)
 
 __all__ = ["diff_notebooks"]
 
@@ -323,6 +326,7 @@ def compare_cell_moderate(x, y):
     This is used to align cells in the /cells list
     in the second multilevel diff iteration.
     """
+
     # Cell types must match
     if x["cell_type"] != y["cell_type"]:
         return False
@@ -349,6 +353,7 @@ def compare_cell_strict(x, y):
     This is used to align cells in the /cells list
     in the first multilevel diff iteration.
     """
+
     # Cell types must match
     if x["cell_type"] != y["cell_type"]:
         return False
@@ -373,8 +378,13 @@ def compare_cell_strict(x, y):
     return True
 
 
-def diff_single_outputs(a, b, path="/cells/*/outputs/*",
-                        predicates=None, differs=None):
+def compare_cell_by_ids(x, y):
+    """Compare cells x,y strictly using cell IDs"""
+    # Only consider equal if both have IDs and they match
+    return 'id' in x and 'id' in y and x['id'] == y['id']
+
+
+def diff_single_outputs(a, b, path="/cells/*/outputs/*", config=None):
     """DiffOp a pair of output cells."""
     assert path == "/cells/*/outputs/*", 'Invalid path for ouput: %r' % path
     assert a.output_type == b.output_type, 'cannot diff outputs of different types'
@@ -396,20 +406,22 @@ def diff_single_outputs(a, b, path="/cells/*/outputs/*",
                 di.append(e)
 
         # Only diff data:
-        dd = diff_mime_bundle(a.data, b.data, path=path+"/data")
+        dd = diff_mime_bundle(a.data, b.data, path=path+"/data", config=config)
         if dd:
             di.patch("data", dd)
 
         return di.validated()
     else:
-        return diff(a, b)
+        return diff(a, b, config=config)
 
 
 def add_mime_diff(key, avalue, bvalue, diffbuilder):
     # TODO: Handle output diffing with plugins?
     # I.e. image diff, svg diff, json diff, etc.
 
     mimetype = key.lower()
+    if isinstance(avalue, str) and isinstance(bvalue, str) and avalue == bvalue:
+        return
     if any(mimetype.startswith(tm) for tm in _split_mimes):
         dd = diff(avalue, bvalue)
         if dd:
@@ -418,8 +430,7 @@ def add_mime_diff(key, avalue, bvalue, diffbuilder):
         diffbuilder.replace(key, bvalue)
 
 
-def diff_attachments(a, b, path="/cells/*/attachments",
-                     predicates=None, differs=None):
+def diff_attachments(a, b, path="/cells/*/attachments", config=None):
     """Diff a pair of attachment collections"""
     assert path == "/cells/*/attachments", 'Invalid path for attachment: %r' % path
 
@@ -454,8 +465,7 @@ def diff_attachments(a, b, path="/cells/*/attachments",
     return di.validated()
 
 
-def diff_mime_bundle(a, b, path=None,
-                     predicates=None, differs=None):
+def diff_mime_bundle(a, b, path=None, config=None):
     """Diff a MIME bundle.
 
     A MIME bundle has MIME types as keys, with values that are
@@ -517,6 +527,7 @@ def ignored_diff(*args, **kwargs):
         compare_cell_approximate,
         compare_cell_moderate,
         compare_cell_strict,
+        compare_cell_by_ids,
         ],
     # Predicates to compare output cells (within one cell) in order of low-to-high precedence
     "/cells/*/outputs": [
@@ -529,12 +540,22 @@ def ignored_diff(*args, **kwargs):
 notebook_differs = defaultdict2(lambda: diff, {
     "/cells": diff_sequence_multilevel,
     "/cells/*": diff,
+    "/cells/*/source": diff_string_lines,
     "/cells/*/outputs": diff_sequence_multilevel,
     "/cells/*/outputs/*": diff_single_outputs,
     "/cells/*/attachments": diff_attachments,
     })
 
 
+notebook_config = DiffConfig(
+    predicates=notebook_predicates,
+    differs=notebook_differs,
+    atomic_paths={
+        "/cells/*/id": True
+    }
+)
+
+
 def reset_notebook_differ():
     """Reset the notebook_differs dictionary to default values."""
     # As it is a defaultdict2, simply clear all set keys to reset:
@@ -587,14 +608,12 @@ def set_notebook_diff_targets(sources=True, outputs=True, attachments=True,
 def diff_cells(a, b):
     "This is currently just used by some tests."
     path = "/cells"
-    return notebook_differs[path](
-        a, b, path=path, predicates=notebook_predicates, differs=notebook_differs)
+    return notebook_differs[path](a, b, path=path, config=notebook_config)
 
 
 def diff_item_at_path(a, b, path):
     """Calculate the diff using the configured notebook differ for path."""
-    return notebook_differs[path](
-        a, b, path=path, predicates=notebook_predicates, differs=notebook_differs)
+    return notebook_differs[path](a, b, path=path, config=notebook_config)
 
 
 def diff_notebooks(a, b):
@@ -604,4 +623,4 @@ def diff_notebooks(a, b):
     """
     if not (isinstance(a, dict) and isinstance(b, dict)):
         raise TypeError("Expected inputs to be dicts, got %r and %r" % (a, b))
-    return diff(a, b, path="", predicates=notebook_predicates, differs=notebook_differs)
+    return diff(a, b, path="", config=notebook_config)

nbdime/diffing/sequences.py

@@ -6,6 +6,7 @@
 import operator
 from collections import defaultdict
 
+from .config import DiffConfig
 from .seq_difflib import diff_sequence_difflib
 from .seq_bruteforce import diff_sequence_bruteforce
 from .seq_myers import diff_sequence_myers
@@ -37,7 +38,7 @@ def diff_sequence(a, b, compare=operator.__eq__):
         raise RuntimeError("Unknown diff_sequence_algorithm {}.".format(diff_sequence_algorithm))
 
 
-def diff_strings_by_char(a, b, path="", predicates=None, differs=None):
+def diff_strings_by_char(a, b, path="", config=None):
     "Compute char-based diff of two strings."
     assert isinstance(a, str) and isinstance(b, str), (
         'Arguments need to be string types. Got %r and %r' % (a, b))
@@ -52,12 +53,16 @@ def diff_strings_linewise(a, b):
     """
     assert isinstance(a, str) and isinstance(b, str), (
         'Arguments need to be string types. Got %r and %r' % (a, b))
+    if a == b:
+        return []
     lines_a = a.splitlines(True)
     lines_b = b.splitlines(True)
 
     from .generic import diff_lists, compare_strings_approximate
-    predicates = defaultdict(lambda: [
-        compare_strings_approximate,
-        operator.__eq__])
-    differs = defaultdict(lambda: diff_strings_by_char)
-    return diff_lists(lines_a, lines_b, predicates=predicates, differs=differs)
+    config = DiffConfig(
+        predicates=defaultdict(lambda: [
+            compare_strings_approximate,
+            operator.__eq__]),
+        differs=defaultdict(lambda: diff_strings_by_char)
+    )
+    return diff_lists(lines_a, lines_b, config=config)