Add a --diff-context option to control unified diff context size....

Add a --diff-context option to control unified diff context size. (!88)

Signed-off-by: Chris Lamb <lamby@debian.org>

diffoscope/config.py

@@ -39,6 +39,8 @@ class Config:
             self.reset()
 
     def reset(self):
+        self.diff_context = 7
+
         # GNU diff cannot process arbitrary large files :(
         self.max_diff_input_lines = 2 ** 22
         self.max_diff_block_lines_saved = float("inf")

diffoscope/diff.py

@@ -172,7 +172,13 @@ class DiffParser:
 
 @tool_required("diff")
 def run_diff(fifo1, fifo2, end_nl_q1, end_nl_q2):
-    cmd = [get_tool_name("diff"), "-aU7", fifo1, fifo2]
+    cmd = [
+        get_tool_name("diff"),
+        "-a",
+        "-U" + str(Config().diff_context),
+        fifo1,
+        fifo2,
+    ]
 
     logger.debug("Running %s", " ".join(cmd))
 

diffoscope/main.py

@@ -218,6 +218,14 @@ def create_parser():
 
     group2 = parser.add_argument_group("output limits")
     # everything marked with default=None below is affected by no-default-limits
+    group2.add_argument(
+        "--diff-context",
+        metavar="LINES",
+        type=int,
+        help="Lines of unified diff context to show. (default: %d)"
+        % Config().diff_context,
+        default=Config().diff_context,
+    )
     group2.add_argument(
         "--max-text-report-size",
         metavar="BYTES",
@@ -613,6 +621,7 @@ def configure(parsed_args):
         elif parsed_args.no_default_limits:
             setattr(Config(), x, float("inf"))
 
+    Config().diff_context = parsed_args.diff_context
     Config().max_page_size = parsed_args.max_page_size
     Config().max_page_diff_block_lines = parsed_args.max_page_diff_block_lines
 

tests/test_difference.py

@@ -133,3 +133,13 @@ def test_non_str_arguments_to_source1_source2():
 
         with pytest.raises(TypeError):
             Difference.from_text_readers(a, b, *x)
+
+
+def test_adjust_diff_context(monkeypatch):
+    monkeypatch.setattr(Config(), "diff_context", 2)
+    a = io.StringIO("".join(str(i) + "\n" for i in range(20)))
+    b = io.StringIO(
+        "".join(str(i if i != 10 else "x") + "\n" for i in range(20))
+    )
+    difference = Difference.from_text_readers(a, b, "a", "b")
+    assert difference.unified_diff.count("\n") == 7