Fix Makefile tab handling in patch application

- Add special case to preserve tabs in Makefiles
- Disable whitespace normalization for Makefiles
- Add tests to verify tab preservation and whitespace handling

openhands/resolver/patching/apply.py

@@ -97,17 +97,26 @@ def apply_diff(
                     hunk=hunk,
                 )
             if lines[old - 1] != line:
-                # 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:
+                # For Makefiles, we need to preserve tabs since they are significant
+                if diff.header.new_path and diff.header.new_path.endswith('Makefile'):
                     raise HunkApplyException(
                         'context line {n}, "{line}" does not match "{sl}"'.format(
                             n=old, line=line, sl=lines[old - 1]
                         ),
                         hunk=hunk,
                     )
+                else:
+                    # 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_makefile_patch3.py

@@ -0,0 +1,61 @@
+from openhands.resolver.patching.apply import apply_diff
+from openhands.resolver.patching.patch import parse_patch
+
+
+def test_makefile_parsing():
+    """Test that we can correctly parse a Makefile with tabs."""
+    # Create a simple Makefile with a tab
+    makefile_content = "all:\n\techo hello\n"
+    lines = makefile_content.splitlines()
+    assert lines == ['all:', '\techo hello']
+    
+    # Create a patch that adds a new target
+    patch_text = """diff --git a/Makefile b/Makefile
+index 1234567..89abcdef 100
+--- a/Makefile
++++ b/Makefile
+@@ -1,2 +1,4 @@
+ all:
+-	echo hello
++	echo hello
++test:
++	echo test"""
+
+    patch = next(parse_patch(patch_text))
+    new_content = apply_diff(patch, makefile_content)
+    
+    # Verify that tabs are preserved in the output
+    expected = [
+        'all:',
+        '\techo hello',
+        'test:',
+        '\techo test',
+    ]
+    assert new_content == expected
+
+
+def test_makefile_whitespace_normalization():
+    """Test that whitespace normalization is disabled for Makefiles."""
+    # Create a simple Makefile with a tab
+    makefile_content = "all:\n\techo hello\n"
+    lines = makefile_content.splitlines()
+    assert lines == ['all:', '\techo hello']
+    
+    # Create a patch that has spaces instead of tabs
+    patch_text = """diff --git a/Makefile b/Makefile
+index 1234567..89abcdef 100
+--- a/Makefile
++++ b/Makefile
+@@ -1,2 +1,4 @@
+ all:
+-    echo hello
++    echo hello
++test:
++    echo test"""
+
+    patch = next(parse_patch(patch_text))
+    try:
+        new_content = apply_diff(patch, makefile_content)
+        assert False, "Expected HunkApplyException due to tab vs space mismatch"
+    except Exception as e:
+        assert "does not match" in str(e)