fix: Normalize whitespace when comparing patch context lines (#6541)

Co-authored-by: openhands <openhands@all-hands.dev>

openhands/resolver/patching/apply.py

@@ -94,12 +94,17 @@ def apply_diff(diff, text, reverse=False, use_patch=False):
                     hunk=hunk,
                 )
             if lines[old - 1] != line:
-                raise HunkApplyException(
-                    'context line {n}, "{line}" does not match "{sl}"'.format(
-                        n=old, line=line, sl=lines[old - 1]
-                    ),
-                    hunk=hunk,
-                )
+                # Try to normalize whitespace by replacing multiple spaces with a single space
+                # This helps with patches that have different indentation levels
+                normalized_line = ' '.join(line.split())
+                normalized_source = ' '.join(lines[old - 1].split())
+                if normalized_line != normalized_source:
+                    raise HunkApplyException(
+                        'context line {n}, "{line}" does not match "{sl}"'.format(
+                            n=old, line=line, sl=lines[old - 1]
+                        ),
+                        hunk=hunk,
+                    )
 
     # for calculating the old line
     r = 0

tests/unit/test_patch_whitespace.py

@@ -0,0 +1,79 @@
+from openhands.resolver.patching.apply import apply_diff
+from openhands.resolver.patching.patch import parse_patch
+
+
+def test_patch_whitespace_mismatch():
+    """Test that the patch application succeeds even when whitespace doesn't match."""
+    # Original content has a line with spaces
+    original_content = """class Example:
+    def method(self):
+        pass
+
+    def another(self):
+        pass"""
+
+    # Patch expects an empty line (no spaces)
+    patch_text = """diff --git a/example.py b/example.py
+index 1234567..89abcdef 100644
+--- a/example.py
++++ b/example.py
+@@ -2,6 +2,10 @@ class Example:
+     def method(self):
+        pass
+
++    new_field: str = "value"
++
+     def another(self):
+        pass"""
+
+    patch = next(parse_patch(patch_text))
+    # The patch should still work because we normalize whitespace
+    new_content = apply_diff(patch, original_content)
+    assert new_content == [
+        'class Example:',
+        '    def method(self):',
+        '        pass',
+        '',
+        '    new_field: str = "value"',
+        '',
+        '    def another(self):',
+        '        pass',
+    ]
+
+
+def test_patch_whitespace_match():
+    """Test that the patch application succeeds when whitespace matches."""
+    # Original content has an empty line (no spaces)
+    original_content = """class Example:
+    def method(self):
+        pass
+
+    def another(self):
+        pass"""
+
+    # Patch expects an empty line (no spaces)
+    patch_text = """diff --git a/example.py b/example.py
+index 1234567..89abcdef 100644
+--- a/example.py
++++ b/example.py
+@@ -2,6 +2,10 @@ class Example:
+     def method(self):
+        pass
+
++    new_field: str = "value"
++
+     def another(self):
+        pass"""
+
+    patch = next(parse_patch(patch_text))
+    new_content = apply_diff(patch, original_content)
+    assert new_content == [
+        'class Example:',
+        '    def method(self):',
+        '        pass',
+        '',
+        '    new_field: str = "value"',
+        '',
+        '    def another(self):',
+        '        pass',
+    ]