Feature: Implements the treat-unmeasured-as-uncovered flag

diff_cover/diff_cover_tool.py

@@ -54,6 +54,9 @@
 TOTAL_PERCENT_FLOAT_HELP = (
     "Show total coverage/quality as a float rounded to 2 decimal places"
 )
+TREAT_UNMEASURED_AS_UNCOVERED_HELP = (
+    "Treat lines in the diff that are absent from the coverage report as uncovered"
+)
 
 LOGGER = logging.getLogger(__name__)
 
@@ -190,6 +193,12 @@ def parse_coverage_args(argv):
         default=None,
         help=TOTAL_PERCENT_FLOAT_HELP,
     )
+    parser.add_argument(
+        "--treat-unmeasured-as-uncovered",
+        action="store_true",
+        default=None,
+        help=TREAT_UNMEASURED_AS_UNCOVERED_HELP,
+    )
 
     defaults = {
         "show_uncovered": False,
@@ -204,6 +213,7 @@ def parse_coverage_args(argv):
         "quiet": False,
         "expand_coverage_report": False,
         "total_percent_float": False,
+        "treat_unmeasured_as_uncovered": False,
     }
 
     return get_config(parser=parser, argv=argv, defaults=defaults, tool=Tool.DIFF_COVER)
@@ -225,6 +235,7 @@ def generate_coverage_report(
     show_uncovered=False,
     expand_coverage_report=False,
     total_percent_float=False,
+    treat_unmeasured_as_uncovered=False,
 ):
     """
     Generate the diff coverage report, using kwargs from `parse_args()`.
@@ -237,6 +248,7 @@ def generate_coverage_report(
         include_untracked=include_untracked,
         exclude=exclude,
         include=include,
+        filter_blank_lines=treat_unmeasured_as_uncovered,
     )
 
     xml_roots = [
@@ -263,7 +275,11 @@ def generate_coverage_report(
         if css_url is not None:
             css_url = os.path.relpath(css_file, os.path.dirname(html_report))
         reporter = HtmlReportGenerator(
-            coverage, diff, css_url=css_url, total_percent_float=total_percent_float
+            coverage,
+            diff,
+            css_url=css_url,
+            total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         with open_file(html_report, "wb") as output_file:
             reporter.generate_report(output_file)
@@ -274,15 +290,21 @@ def generate_coverage_report(
     if "json" in report_formats:
         json_report = report_formats["json"] or JSON_REPORT_DEFAULT_PATH
         reporter = JsonReportGenerator(
-            coverage, diff, total_percent_float=total_percent_float
+            coverage,
+            diff,
+            total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         with open_file(json_report, "wb") as output_file:
             reporter.generate_report(output_file)
 
     if "markdown" in report_formats:
         markdown_report = report_formats["markdown"] or MARKDOWN_REPORT_DEFAULT_PATH
         reporter = MarkdownReportGenerator(
-            coverage, diff, total_percent_float=total_percent_float
+            coverage,
+            diff,
+            total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         with open_file(markdown_report, "wb") as output_file:
             reporter.generate_report(output_file)
@@ -294,6 +316,7 @@ def generate_coverage_report(
             diff,
             report_formats["github-annotations"],
             total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         reporter.generate_report(sys.stdout.buffer)
 
@@ -303,6 +326,7 @@ def generate_coverage_report(
         diff,
         show_uncovered,
         total_percent_float=total_percent_float,
+        treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
     )
     output_file = io.BytesIO() if quiet else sys.stdout.buffer
 
@@ -400,6 +424,7 @@ def main(argv=None, directory=None):
         show_uncovered=arg_dict["show_uncovered"],
         expand_coverage_report=arg_dict["expand_coverage_report"],
         total_percent_float=arg_dict["total_percent_float"],
+        treat_unmeasured_as_uncovered=arg_dict["treat_unmeasured_as_uncovered"],
     )
 
     if percent_covered >= fail_under:

diff_cover/diff_reporter.py

@@ -117,6 +117,7 @@ def __init__(
         supported_extensions=None,
         exclude=None,
         include=None,
+        filter_blank_lines=False,
     ):
         """
         Configure the reporter to use `git_diff` as the wrapper
@@ -148,6 +149,7 @@ def __init__(
         self._ignore_unstaged = ignore_unstaged
         self._include_untracked = include_untracked
         self._supported_extensions = supported_extensions
+        self._filter_blank_lines = filter_blank_lines
 
         # Cache diff information as a dictionary
         # with file path keys and line number list values
@@ -377,6 +379,9 @@ def _parse_lines(self, diff_lines):
         where `ADDED_LINES` and `DELETED_LINES` are lists of line
         numbers added/deleted respectively.
 
+        If `self._filter_blank_lines` is True, blank/whitespace-only
+        added lines are excluded from `ADDED_LINES`.
+
         Raises a `GitDiffError` if the diff lines are in an invalid format.
         """
 
@@ -399,8 +404,10 @@ def _parse_lines(self, diff_lines):
                 # calling this method, we're guaranteed to have a source
                 # file specified.  We check anyway just to be safe.
                 if current_line_new is not None:
-                    # Store the added line
-                    added_lines.append(current_line_new)
+                    # Skip blank/whitespace-only added lines when filtering
+                    if not self._filter_blank_lines or line[1:].strip():
+                        # Store the added line
+                        added_lines.append(current_line_new)
 
                     # Increment the line number in the file
                     current_line_new += 1

diff_cover/report_generator.py

@@ -11,14 +11,21 @@
 
 from diff_cover.snippets import Snippet
 from diff_cover.util import to_unix_path
+from diff_cover.violationsreporters.base import Violation
 
 
 class DiffViolations:
     """
     Class to capture violations generated by a particular diff
     """
 
-    def __init__(self, violations, measured_lines, diff_lines):
+    def __init__(
+        self,
+        violations,
+        measured_lines,
+        diff_lines,
+        treat_unmeasured_as_uncovered=False,
+    ):
         self.lines = {violation.line for violation in violations}.intersection(
             diff_lines
         )
@@ -36,13 +43,28 @@ def __init__(self, violations, measured_lines, diff_lines):
         else:
             self.measured_lines = set(measured_lines).intersection(diff_lines)
 
+            # When enabled and coverage data exists for this file,
+            # treat diff lines absent from the coverage report as uncovered.
+            if treat_unmeasured_as_uncovered and self.measured_lines:
+                unmeasured_diff_lines = set(diff_lines) - set(measured_lines)
+                for line_num in unmeasured_diff_lines:
+                    self.measured_lines.add(line_num)
+                    self.lines.add(line_num)
+                    self.violations.add(Violation(line_num, None))
+
 
 class BaseReportGenerator(ABC):
     """
     Generate a diff coverage report.
     """
 
-    def __init__(self, violations_reporter, diff_reporter, total_percent_float=False):
+    def __init__(
+        self,
+        violations_reporter,
+        diff_reporter,
+        total_percent_float=False,
+        treat_unmeasured_as_uncovered=False,
+    ):
         """
         Configure the report generator to build a report
         from `violations_reporter` (of type BaseViolationReporter)
@@ -51,6 +73,7 @@ def __init__(self, violations_reporter, diff_reporter, total_percent_float=False
         self._violations = violations_reporter
         self._diff = diff_reporter
         self._total_percent_float = total_percent_float
+        self._treat_unmeasured_as_uncovered = treat_unmeasured_as_uncovered
         self._diff_violations_dict = None
 
         self._cache_violations = None
@@ -204,6 +227,7 @@ def _diff_violations(self):
                         violations.get(to_unix_path(src_path), []),
                         self._violations.measured_lines(src_path),
                         self._diff.lines_changed(src_path),
+                        treat_unmeasured_as_uncovered=self._treat_unmeasured_as_uncovered,
                     )
                     for src_path in src_paths_changed
                 }
@@ -213,6 +237,7 @@ def _diff_violations(self):
                         self._violations.violations(src_path),
                         self._violations.measured_lines(src_path),
                         self._diff.lines_changed(src_path),
+                        treat_unmeasured_as_uncovered=self._treat_unmeasured_as_uncovered,
                     )
                     for src_path in src_paths_changed
                 }
@@ -295,11 +320,13 @@ def __init__(
         diff_reporter,
         css_url=None,
         total_percent_float=False,
+        treat_unmeasured_as_uncovered=False,
     ):
         super().__init__(
             violations_reporter,
             diff_reporter,
             total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         self.css_url = css_url
 
@@ -438,11 +465,13 @@ def __init__(
         diff_reporter,
         show_uncovered=False,
         total_percent_float=False,
+        treat_unmeasured_as_uncovered=False,
     ):
         super().__init__(
             violations_reporter,
             diff_reporter,
             total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         self.include_snippets = show_uncovered
 
@@ -464,11 +493,13 @@ def __init__(
         diff_reporter,
         annotations_type,
         total_percent_float=False,
+        treat_unmeasured_as_uncovered=False,
     ):
         super().__init__(
             violations_reporter,
             diff_reporter,
             total_percent_float=total_percent_float,
+            treat_unmeasured_as_uncovered=treat_unmeasured_as_uncovered,
         )
         self.annotations_type = annotations_type
 

tests/test_diff_reporter.py

@@ -466,6 +466,63 @@ def test_git_diff_error(
             diff.lines_changed("subdir/file1.py")
 
 
+def test_blank_lines_included_by_default(diff, git_diff):
+    """Without filter_blank_lines, blank added lines are included in lines_changed()."""
+    diff_str = dedent("""
+        diff --git a/file.py b/file.py
+        @@ -1,3 +1,6 @@
+         existing line
+        +
+        +def something():
+        +    print("hello")
+        +
+        +
+        """)
+
+    _set_git_diff_output(diff, git_diff, diff_str, "", "")
+
+    # All added lines are included (default behavior preserved)
+    assert diff.lines_changed("file.py") == [2, 3, 4, 5, 6]
+
+
+def test_blank_lines_filtered_when_flag_set(git_diff):
+    """With filter_blank_lines=True, blank added lines are excluded from lines_changed()."""
+    diff = GitDiffReporter(git_diff=git_diff, filter_blank_lines=True)
+    diff_str = dedent("""
+        diff --git a/file.py b/file.py
+        @@ -1,3 +1,6 @@
+         existing line
+        +
+        +def something():
+        +    print("hello")
+        +
+        +
+        """)
+
+    _set_git_diff_output(diff, git_diff, diff_str, "", "")
+
+    # Only non-blank added lines are included
+    assert diff.lines_changed("file.py") == [3, 4]
+
+
+def test_whitespace_only_lines_filtered_when_flag_set(git_diff):
+    """With filter_blank_lines=True, whitespace-only added lines are excluded."""
+    diff = GitDiffReporter(git_diff=git_diff, filter_blank_lines=True)
+    diff_str = dedent("""
+        diff --git a/file.py b/file.py
+        @@ -1,1 +1,4 @@
+         existing line
+        +    \t
+        +code_line
+        +
+        """)
+
+    _set_git_diff_output(diff, git_diff, diff_str, "", "")
+
+    # Only non-blank added line is included
+    assert diff.lines_changed("file.py") == [3]
+
+
 def test_plus_sign_in_hunk_bug(diff, git_diff):
     # This was a bug that caused a parse error
     diff_str = dedent("""