⚡️ Speed up function generate_candidates by 4,183% in PR #363 (part-1-windows-fixes)

[codeflash-ai]

⚡️ This pull request contains optimizations for PR #363

If you approve this dependent PR, these changes will be merged into the original PR branch part-1-windows-fixes.

This PR will be automatically closed if the original PR is merged.

---

📄 4,183% (41.83x) speedup for generate_candidates in codeflash/code_utils/coverage_utils.py

⏱️ Runtime : 245 milliseconds → 5.73 milliseconds (best of 36 runs)

📝 Explanation and details

The optimized code achieves a 4182% speedup by eliminating expensive Path object creation and manipulation within the loop.

Key optimizations:

1. Pre-compute path parts: Instead of repeatedly calling current_path.parent and creating new Path objects, the code uses source_code_path.parts to get all path components upfront as a tuple.

2. Replace Path operations with string concatenation: The original code's bottleneck was (Path(current_path.name) / last_added).as_posix() which created Path objects and converted them to POSIX format in every iteration. The optimized version uses simple f-string formatting: f"{parts[i]}/{last_added}".

3. Index-based iteration: Rather than walking up the directory tree using current_path.parent, it uses a reverse range loop over the parts indices, which is much faster than Path navigation.

Performance impact by test case type:

• Deeply nested paths see the most dramatic improvements (up to 7573% faster for 1000-level nesting) because they eliminate the most Path object creations
• Simple 1-2 level paths still benefit significantly (200-400% faster) from avoiding even a few Path operations
• Edge cases with special characters or unicode maintain the same speedup ratios, showing the optimization is universally effective

The line profiler confirms the original bottleneck: 94.3% of time was spent on Path object creation (candidate_path = (Path(current_path.name) / last_added).as_posix()), which is now replaced with lightweight string operations.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	✅ 49 Passed
🌀 Generated Regression Tests	✅ 1046 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	✅ 1 Passed
📊 Tests Coverage	100.0%

⚙️ Existing Unit Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
test_code_utils.py::test_generate_candidates	72.4μs	9.09μs	697%✅

🌀 Generated Regression Tests and Runtime

from __future__ import annotations

from pathlib import Path

# imports
import pytest  # used for our unit tests
from codeflash.code_utils.coverage_utils import generate_candidates

# unit tests

# ------------------------------
# BASIC TEST CASES
# ------------------------------

def test_single_file_in_root():
    # Basic: File in root directory
    path = Path("foo.py")
    expected = {"foo.py"}
    # The only candidate should be the file name itself, since parent is '.'
    codeflash_output = generate_candidates(path) # 8.84μs -> 5.66μs (56.1% faster)

def test_file_in_one_level_subdir():
    # Basic: File in one-level subdirectory
    path = Path("bar/foo.py")
    expected = {
        "foo.py",
        "bar/foo.py"
    }
    # Candidates: file name, and full path
    codeflash_output = generate_candidates(path) # 18.7μs -> 5.67μs (230% faster)

def test_file_in_two_level_subdir():
    # Basic: File in two-level subdirectory
    path = Path("baz/bar/foo.py")
    expected = {
        "foo.py",
        "bar/foo.py",
        "baz/bar/foo.py"
    }
    # Candidates: file name, bar/foo.py, baz/bar/foo.py
    codeflash_output = generate_candidates(path) # 27.1μs -> 6.29μs (331% faster)

def test_file_with_dot_in_name():
    # Basic: File with dot in name
    path = Path("src/main.test.py")
    expected = {
        "main.test.py",
        "src/main.test.py"
    }
    codeflash_output = generate_candidates(path) # 18.2μs -> 5.49μs (232% faster)

def test_file_with_multiple_extensions():
    # Basic: File with multiple extensions
    path = Path("src/foo.tar.gz")
    expected = {
        "foo.tar.gz",
        "src/foo.tar.gz"
    }
    codeflash_output = generate_candidates(path) # 18.1μs -> 5.50μs (229% faster)

# ------------------------------
# EDGE TEST CASES
# ------------------------------

def test_file_in_deeply_nested_dir():
    # Edge: Deeply nested (but < 1000) directory
    path = Path("a/b/c/d/e/f/g/h/i/j/foo.py")
    expected = set()
    # Build expected candidates
    parts = path.parts
    # Start with file name
    expected.add(parts[-1])
    last_added = parts[-1]
    for i in range(len(parts)-2, -1, -1):
        candidate = Path(parts[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())
    codeflash_output = generate_candidates(path) # 80.0μs -> 3.76μs (2029% faster)

def test_file_with_spaces_and_special_chars():
    # Edge: File with spaces and special characters
    path = Path("weird dir/!@#$/foo bar.py")
    expected = {
        "foo bar.py",
        "!@$/foo bar.py",
        "weird dir/!@$/foo bar.py"
    }
    expected.add(path.as_posix())
    codeflash_output = generate_candidates(path) # 24.4μs -> 3.78μs (545% faster)

def test_file_with_unicode():
    # Edge: File with unicode characters
    path = Path("src/测试.py")
    expected = {
        "测试.py",
        "src/测试.py"
    }
    codeflash_output = generate_candidates(path) # 18.6μs -> 5.64μs (230% faster)

def test_file_with_empty_parent():
    # Edge: File with no parent (e.g., Path("foo.py"))
    path = Path("foo.py")
    expected = {"foo.py"}
    codeflash_output = generate_candidates(path) # 7.98μs -> 5.32μs (50.1% faster)

def test_file_with_dot_parent():
    # Edge: File in '.' directory
    path = Path("./foo.py")
    expected = {"foo.py"}
    codeflash_output = generate_candidates(path) # 8.14μs -> 5.18μs (57.1% faster)

def test_file_with_dotdot_parent():
    # Edge: File in '..' directory
    path = Path("../foo.py")
    expected = {"foo.py", "../foo.py"}
    codeflash_output = generate_candidates(path) # 18.0μs -> 5.36μs (236% faster)

def test_file_with_empty_string():
    # Edge: Empty string path
    path = Path("")
    expected = {""}
    codeflash_output = generate_candidates(path) # 7.75μs -> 5.15μs (50.6% faster)

def test_file_with_trailing_slash():
    # Edge: Path with trailing slash (should be treated as directory, not file)
    path = Path("src/foo.py/")
    # Path("src/foo.py/") is a directory, not a file, so name is empty string
    expected = {""}
    codeflash_output = generate_candidates(path) # 18.0μs -> 5.38μs (235% faster)

def test_file_with_multiple_dotdot():
    # Edge: Path with multiple '..'
    path = Path("../../foo.py")
    expected = {"foo.py", "../foo.py", "../../foo.py"}
    codeflash_output = generate_candidates(path) # 26.6μs -> 6.13μs (334% faster)

def test_file_with_absolute_path():
    # Edge: Absolute path
    path = Path("/home/user/project/foo.py")
    expected = {
        "foo.py",
        "project/foo.py",
        "user/project/foo.py",
        "home/user/project/foo.py",
        "/home/user/project/foo.py"
    }
    codeflash_output = generate_candidates(path) # 34.0μs -> 7.07μs (381% faster)

def test_file_with_mixed_separators():
    # Edge: Path with mixed separators (simulate Windows)
    path = Path("src\\bar/foo.py")
    # Path will normalize separators, so candidates should be correct
    expected = {
        "foo.py",
        "bar/foo.py",
        "src/bar/foo.py"
    }
    expected.add(path.as_posix())
    codeflash_output = generate_candidates(path) # 16.1μs -> 3.27μs (394% faster)

# ------------------------------
# LARGE SCALE TEST CASES
# ------------------------------

def test_large_number_of_nested_dirs():
    # Large scale: Deeply nested path (1000 levels)
    depth = 1000
    dirs = [f"dir{i}" for i in range(depth)]
    path = Path("/".join(dirs) + "/file.py")
    expected = set()
    # Start with file name
    last_added = "file.py"
    expected.add(last_added)
    for i in range(depth-1, -1, -1):
        candidate = Path(dirs[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())
    codeflash_output = generate_candidates(path) # 77.0ms -> 1.02ms (7433% faster)

def test_large_number_of_candidates_per_dir():
    # Large scale: Path with 1000 sibling directories, but only one file
    # Only the path to the file matters, so this is similar to above
    depth = 5
    dirs = [f"dir{i}" for i in range(depth)]
    path = Path("/".join(dirs) + "/file.py")
    expected = set()
    last_added = "file.py"
    expected.add(last_added)
    for i in range(depth-1, -1, -1):
        candidate = Path(dirs[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())
    codeflash_output = generate_candidates(path) # 43.9μs -> 4.22μs (940% faster)

def test_large_file_name():
    # Large scale: Very long file name
    long_name = "a" * 255 + ".py"
    path = Path("src/" + long_name)
    expected = {long_name, f"src/{long_name}"}
    codeflash_output = generate_candidates(path) # 18.5μs -> 5.81μs (218% faster)

def test_large_path_and_file_name():
    # Large scale: Very long path and file name
    depth = 50
    dirs = ["a"*20 for _ in range(depth)]
    long_name = "b"*200 + ".py"
    path = Path("/".join(dirs) + "/" + long_name)
    expected = set()
    last_added = long_name
    expected.add(last_added)
    for i in range(depth-1, -1, -1):
        candidate = Path(dirs[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())
    codeflash_output = generate_candidates(path) # 512μs -> 20.0μs (2462% faster)

# ------------------------------
# DETERMINISM TEST CASE
# ------------------------------

def test_determinism():
    # Determinism: Calling twice returns same result
    path = Path("foo/bar/baz.py")
    codeflash_output = generate_candidates(path); result1 = codeflash_output # 26.4μs -> 6.22μs (325% faster)
    codeflash_output = generate_candidates(path); result2 = codeflash_output # 18.7μs -> 1.74μs (973% faster)

# ------------------------------
# INVALID INPUT TEST CASES
# ------------------------------

def test_non_path_input_raises():
    # Should raise TypeError if not Path
    with pytest.raises(AttributeError):
        generate_candidates("foo/bar.py") # 2.98μs -> 2.78μs (7.53% faster)

def test_none_input_raises():
    # Should raise AttributeError if None
    with pytest.raises(AttributeError):
        generate_candidates(None) # 2.46μs -> 2.44μs (0.450% faster)

# ------------------------------
# CASE SENSITIVITY TEST CASE
# ------------------------------

def test_case_sensitivity():
    # On case-sensitive systems, names are distinct
    path = Path("src/Foo.py")
    expected = {"Foo.py", "src/Foo.py"}
    codeflash_output = generate_candidates(path) # 18.4μs -> 5.74μs (220% faster)

def test_case_insensitivity():
    # On case-insensitive systems, names may be treated the same, but function should not modify case
    path = Path("src/foo.py")
    expected = {"foo.py", "src/foo.py"}
    codeflash_output = generate_candidates(path) # 17.6μs -> 5.59μs (216% faster)

# ------------------------------
# DOT FILE TEST CASE
# ------------------------------

def test_dot_file():
    # File starting with dot
    path = Path("src/.hidden.py")
    expected = {".hidden.py", "src/.hidden.py"}
    codeflash_output = generate_candidates(path) # 17.7μs -> 5.53μs (219% faster)

# ------------------------------
# EXTENSIONLESS FILE TEST CASE
# ------------------------------

def test_extensionless_file():
    # File with no extension
    path = Path("src/Makefile")
    expected = {"Makefile", "src/Makefile"}
    codeflash_output = generate_candidates(path) # 17.3μs -> 5.40μs (220% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
from __future__ import annotations

from pathlib import Path

# imports
import pytest  # used for our unit tests
from codeflash.code_utils.coverage_utils import generate_candidates

# unit tests

# --------------------------
# Basic Test Cases
# --------------------------

def test_basic_single_file_in_root():
    # Test a file in the root directory
    path = Path("main.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 8.35μs -> 5.35μs (56.0% faster)

def test_basic_file_in_one_subdir():
    # Test a file in a single subdirectory
    path = Path("src/module.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 18.1μs -> 5.38μs (237% faster)
    # Candidates: file name, subdir/file, full path
    expected = {"module.py", "src/module.py"}

def test_basic_file_in_two_subdirs():
    # Test a file in nested subdirectories
    path = Path("src/utils/helper.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 26.4μs -> 6.27μs (321% faster)
    expected = {
        "helper.py",
        "utils/helper.py",
        "src/utils/helper.py"
    }

def test_basic_file_with_dot_in_name():
    # File with multiple dots in the name
    path = Path("src/my.module.test.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 17.9μs -> 5.37μs (234% faster)
    expected = {
        "my.module.test.py",
        "src/my.module.test.py"
    }

# --------------------------
# Edge Test Cases
# --------------------------

def test_edge_empty_path():
    # Path is empty string (should treat as current directory)
    path = Path("")
    codeflash_output = generate_candidates(path); result = codeflash_output # 7.95μs -> 5.05μs (57.4% faster)

def test_edge_file_in_deep_nested_dirs():
    # File in deeply nested directories
    path = Path("a/b/c/d/e/f/g/h/i/j/file.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 85.4μs -> 7.72μs (1006% faster)
    # Should include file.py, j/file.py, i/j/file.py, ..., a/b/c/d/e/f/g/h/i/j/file.py
    expected = set()
    # Build expected set
    parts = path.parts
    expected.add("file.py")
    last_added = "file.py"
    # Walk up the path from the deepest directory to the root
    for i in range(len(parts)-2, -1, -1):
        candidate = Path(parts[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())

def test_edge_file_with_spaces_and_special_chars():
    # File name with spaces and special characters
    path = Path("src/dir with spaces/@special$file!.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 26.4μs -> 5.90μs (347% faster)
    expected = {
        "@special$file!.py",
        "dir with spaces/@special$file!.py",
        "src/dir with spaces/@special$file!.py"
    }

def test_edge_file_with_unicode_chars():
    # File name with unicode characters
    path = Path("src/üñîçødë.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 17.4μs -> 5.45μs (219% faster)
    expected = {
        "üñîçødë.py",
        "src/üñîçødë.py"
    }

def test_edge_file_with_hidden_file():
    # Hidden file (starts with dot)
    path = Path(".config/.hidden")
    codeflash_output = generate_candidates(path); result = codeflash_output # 17.1μs -> 5.20μs (229% faster)
    expected = {
        ".hidden",
        ".config/.hidden"
    }

def test_edge_file_in_absolute_path():
    # Absolute path
    path = Path("/usr/local/bin/script.sh")
    codeflash_output = generate_candidates(path); result = codeflash_output # 33.9μs -> 7.09μs (378% faster)
    # Should include script.sh, bin/script.sh, local/bin/script.sh, usr/local/bin/script.sh, /usr/local/bin/script.sh
    expected = {
        "script.sh",
        "bin/script.sh",
        "local/bin/script.sh",
        "usr/local/bin/script.sh",
        "/usr/local/bin/script.sh"
    }

def test_edge_file_with_trailing_slash():
    # Path with trailing slash (should be treated as a directory, not a file)
    path = Path("src/module.py/")
    codeflash_output = generate_candidates(path); result = codeflash_output # 17.3μs -> 5.28μs (228% faster)
    # Path("src/module.py/").name == "module.py", so same as normal file
    expected = {
        "module.py",
        "src/module.py"
    }

def test_edge_file_with_dot_dot_segments():
    # Path with parent directory references
    path = Path("src/../module.py")
    codeflash_output = generate_candidates(path); result = codeflash_output # 25.7μs -> 5.99μs (329% faster)
    # Path.parts: ('src', '..', 'module.py')
    expected = {
        "module.py",
        "../module.py",
        "src/../module.py"
    }

def test_edge_file_is_dot():
    # Path is '.' (current directory)
    path = Path(".")
    codeflash_output = generate_candidates(path); result = codeflash_output # 7.69μs -> 5.12μs (50.3% faster)

def test_edge_file_is_dot_dot():
    # Path is '..' (parent directory)
    path = Path("..")
    codeflash_output = generate_candidates(path); result = codeflash_output # 7.91μs -> 5.23μs (51.1% faster)

# --------------------------
# Large Scale Test Cases
# --------------------------

def test_large_scale_deeply_nested_path():
    # Test with a path 1000 directories deep
    dirs = [f"dir{i}" for i in range(1, 1000)]
    file_name = "bigfile.py"
    path = Path("/".join(dirs + [file_name]))
    codeflash_output = generate_candidates(path); result = codeflash_output # 77.2ms -> 1.01ms (7573% faster)
    # Should include file_name, and for each parent dir, the candidate path, plus the full path
    expected = set()
    expected.add(file_name)
    last_added = file_name
    for i in range(len(dirs)-1, -1, -1):
        candidate = Path(dirs[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())

def test_large_scale_many_files_in_one_dir():
    # Test with many files in one directory
    dir_name = "bigdir"
    files = [f"file{i}.txt" for i in range(1000)]
    for file_name in files:
        path = Path(f"{dir_name}/{file_name}")
        codeflash_output = generate_candidates(path); result = codeflash_output # 9.75ms -> 2.08ms (368% faster)
        expected = {file_name, f"{dir_name}/{file_name}"}

def test_large_scale_long_file_name():
    # Test with a very long file name
    file_name = "a" * 255 + ".py"
    path = Path(f"src/{file_name}")
    codeflash_output = generate_candidates(path); result = codeflash_output # 19.5μs -> 6.03μs (224% faster)
    expected = {file_name, f"src/{file_name}"}

def test_large_scale_long_dir_names():
    # Test with long directory names
    dir_name = "b" * 200
    file_name = "file.py"
    path = Path(f"{dir_name}/{file_name}")
    codeflash_output = generate_candidates(path); result = codeflash_output # 19.0μs -> 5.68μs (235% faster)
    expected = {file_name, f"{dir_name}/{file_name}"}

def test_large_scale_absolute_path_many_dirs():
    # Test with an absolute path with many directories
    dirs = [f"absdir{i}" for i in range(1, 1000)]
    file_name = "absfile.py"
    path = Path("/" + "/".join(dirs + [file_name]))
    codeflash_output = generate_candidates(path); result = codeflash_output # 79.9ms -> 1.36ms (5767% faster)
    expected = set()
    expected.add(file_name)
    last_added = file_name
    for i in range(len(dirs)-1, -1, -1):
        candidate = Path(dirs[i]) / last_added
        expected.add(candidate.as_posix())
        last_added = candidate.as_posix()
    expected.add(path.as_posix())
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
from codeflash.code_utils.coverage_utils import generate_candidates
from pathlib import Path

def test_generate_candidates():
    generate_candidates(Path())

🔎 Concolic Coverage Tests and Runtime

Test File::Test Function	Original ⏱️	Optimized ⏱️	Speedup
codeflash_concolic_f8a6zz_s/tmpwxgbfa1y/test_concolic_coverage.py::test_generate_candidates	8.77μs	5.49μs	59.7%✅

To edit these changes git checkout codeflash/optimize-pr363-2025-09-29T22.03.01 and push.