⚡️ Speed up function get_diff_lines_count by 15% in PR #274 (skip-formatting-for-large-diffs)

[codeflash-ai]

⚡️ This pull request contains optimizations for PR #274

If you approve this dependent PR, these changes will be merged into the original PR branch skip-formatting-for-large-diffs.

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

---

📄 15% (0.15x) speedup for get_diff_lines_count in codeflash/code_utils/formatter.py

⏱️ Runtime : 3.67 milliseconds → 3.19 milliseconds (best of 257 runs)

📝 Explanation and details

Here is an optimized version of your program.
Key Improvements.

• Avoids splitting all lines and list allocation; instead, iterates only as needed and sums matches (saves both memory and runtime).
• Eliminates the inner function and replaces it with a fast inline check.

Why this is faster:

• Uses a simple for-loop instead of building a list.
• Checks first character directly—less overhead than calling startswith multiple times.
• Skips the closure.
• No intermediate list storage.

The function result and behavior are identical.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 59 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	✅ 1 Passed
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests Details

from __future__ import annotations

# imports
import pytest  # used for our unit tests
from codeflash.code_utils.formatter import get_diff_lines_count

# unit tests

# 1. Basic Test Cases

def test_empty_string():
    # Empty input should return 0
    codeflash_output = get_diff_lines_count("")

def test_no_diff_lines():
    # Input with no diff lines should return 0
    diff = " context line\n another line\n"
    codeflash_output = get_diff_lines_count(diff)

def test_single_added_line():
    # Single added line
    diff = "+added line"
    codeflash_output = get_diff_lines_count(diff)

def test_single_removed_line():
    # Single removed line
    diff = "-removed line"
    codeflash_output = get_diff_lines_count(diff)

def test_mixed_added_and_removed_lines():
    # Mixture of added and removed lines
    diff = "+added1\n-context1\n context2\n+added2\n"
    codeflash_output = get_diff_lines_count(diff)

def test_ignores_diff_headers():
    # Should not count +++ or --- lines (diff headers)
    diff = "+++ b/file.txt\n--- a/file.txt\n+added\n-context\n"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_leading_spaces():
    # Only lines starting with + or - should count, not those with leading spaces
    diff = " +not a diff line\n -not a diff line\n+real diff\n-real diff"
    codeflash_output = get_diff_lines_count(diff)

def test_multiple_lines_with_only_context():
    # Only context lines, should return 0
    diff = " context\n another context\n yet another"
    codeflash_output = get_diff_lines_count(diff)

# 2. Edge Test Cases

def test_only_diff_headers():
    # Only diff headers, should return 0
    diff = "+++ b/file.txt\n--- a/file.txt"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_plus_minus_not_at_start():
    # Lines with + or - not at the start should not count
    diff = "context + not diff\ncontext - not diff"
    codeflash_output = get_diff_lines_count(diff)

def test_empty_lines_between_diff_lines():
    # Empty lines between diff lines should not be counted
    diff = "+added1\n\n-removed1\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_starting_with_multiple_plus_minus():
    # Lines like '++added' or '--removed' (not diff headers) should count
    diff = "++added\n--removed\n+++header\n---header"
    # Only '+++header' and '---header' are headers, '++added' and '--removed' are diffs
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_only_plus_minus():
    # Lines that are just '+' or '-' should count
    diff = "+\n-\n"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_unicode_and_non_ascii():
    # Lines with unicode characters
    diff = "+añadido\n-удалено\n context\n+++ файл\n"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_tabs_and_whitespace():
    # Lines starting with + or - with tabs/spaces after
    diff = "+\tadded with tab\n- removed with space"
    codeflash_output = get_diff_lines_count(diff)

def test_only_newlines():
    # Only newlines, should return 0
    diff = "\n\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_trailing_and_leading_newlines():
    # Leading/trailing newlines should not affect result
    diff = "\n+added\n-context\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_long_line_with_plus_minus():
    # Very long diff line
    diff = "+" + "a" * 500 + "\n-" + "b" * 500
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_windows_line_endings():
    # Input with \r\n line endings
    diff = "+added1\r\n-context1\r\n context2\r\n+added2\r\n"
    # The split('\n') will work, so this should still count 3 diff lines
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_mixed_line_endings():
    # Input with mixed \n and \r\n
    diff = "+added1\n-context1\r\n context2\n+added2\r\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_blank_lines_and_headers():
    # Blank lines and headers interspersed
    diff = "\n+++ b/file\n\n--- a/file\n+added\n\n-context\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_only_plus_minus_headers():
    # Lines like '+++', '---' only (headers), should not be counted
    diff = "+++\n---"
    codeflash_output = get_diff_lines_count(diff)

# 3. Large Scale Test Cases

def test_large_number_of_added_lines():
    # 1000 added lines
    diff = "\n".join(["+line{}".format(i) for i in range(1000)])
    codeflash_output = get_diff_lines_count(diff)

def test_large_number_of_removed_lines():
    # 1000 removed lines
    diff = "\n".join(["-line{}".format(i) for i in range(1000)])
    codeflash_output = get_diff_lines_count(diff)

def test_large_mixed_diff():
    # 500 added, 500 removed, 500 context, 10 headers
    added = ["+a{}".format(i) for i in range(500)]
    removed = ["-r{}".format(i) for i in range(500)]
    context = [" context{}".format(i) for i in range(500)]
    headers = ["+++ b/file{}".format(i) for i in range(5)] + ["--- a/file{}".format(i) for i in range(5)]
    diff = "\n".join(headers + added + removed + context)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_headers_everywhere():
    # Headers interspersed with diff lines
    lines = []
    for i in range(500):
        lines.append("+++ b/file{}".format(i))
        lines.append("--- a/file{}".format(i))
        lines.append("+added{}".format(i))
        lines.append("-removed{}".format(i))
        lines.append(" context{}".format(i))
    diff = "\n".join(lines)
    # Only +added and -removed lines (not headers) should count: 2 per iteration * 500 = 1000
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_long_lines():
    # 1000 diff lines, each 500 chars long
    added = ["+" + "a"*500 for _ in range(500)]
    removed = ["-" + "b"*500 for _ in range(500)]
    diff = "\n".join(added + removed)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_only_context():
    # 1000 context lines, no diff lines
    diff = "\n".join([" context{}".format(i) for i in range(1000)])
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_blank_lines():
    # 1000 lines, half blank, half diff
    diff_lines = ["+line{}".format(i) for i in range(500)]
    blanks = [""] * 500
    diff = "\n".join(diff_lines + blanks)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_headers_and_blank_lines():
    # 1000 lines, 250 headers, 250 blank, 250 added, 250 removed
    headers = ["+++ b/file{}".format(i) for i in range(125)] + ["--- a/file{}".format(i) for i in range(125)]
    blanks = [""] * 250
    added = ["+a{}".format(i) for i in range(250)]
    removed = ["-r{}".format(i) for i in range(250)]
    diff = "\n".join(headers + blanks + added + removed)
    codeflash_output = get_diff_lines_count(diff)
# 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

# imports
import pytest  # used for our unit tests
from codeflash.code_utils.formatter import get_diff_lines_count

# unit tests

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

def test_empty_string():
    # Test with empty string input
    codeflash_output = get_diff_lines_count("")

def test_no_diff_lines():
    # Test with diff output containing no + or - lines
    diff = " context line\n another context"
    codeflash_output = get_diff_lines_count(diff)

def test_single_added_line():
    # Test with a single added line
    diff = "+added line"
    codeflash_output = get_diff_lines_count(diff)

def test_single_removed_line():
    # Test with a single removed line
    diff = "-removed line"
    codeflash_output = get_diff_lines_count(diff)

def test_mixed_added_and_removed_lines():
    # Test with mixed added and removed lines
    diff = "+add1\n-context1\n context2\n+add2\n-context2"
    codeflash_output = get_diff_lines_count(diff)

def test_ignores_diff_header_lines():
    # Test that lines starting with '+++' or '---' are ignored
    diff = "+++ b/file.txt\n--- a/file.txt\n+added\n-context"
    codeflash_output = get_diff_lines_count(diff)

def test_context_lines_with_plus_minus():
    # Test that lines with + or - not at the start are ignored
    diff = " context + not diff\n context - not diff"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_only_plus_minus():
    # Test with lines that are just '+' or '-'
    diff = "+\n-\n context"
    codeflash_output = get_diff_lines_count(diff)

def test_lines_with_spaces_before_plus_minus():
    # Test that lines with leading spaces before + or - are not counted
    diff = " +not diff\n -not diff\n+diff\n-diff"
    codeflash_output = get_diff_lines_count(diff)

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

def test_diff_with_only_header_lines():
    # Only header lines, should count as 0
    diff = "--- a/file\n+++ b/file"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_blank_lines():
    # Blank lines should not be counted
    diff = "\n\n+added\n\n-context\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_tricky_headers():
    # Headers that look like diff lines but are not
    diff = "+++added\n---removed\n+realadd\n-realrem"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_multiple_newlines():
    # Multiple newlines between diff lines
    diff = "+add1\n\n\n-context1\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_tabs_and_spaces():
    # Lines with leading tabs/spaces before + or - should not count
    diff = "\t+not diff\n    -not diff\n+diff\n-diff"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_unicode_characters():
    # Diff lines with unicode characters
    diff = "+áéíóú\n-你好\n context"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_only_newlines():
    # Input is just newlines
    diff = "\n\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_plus_minus_in_middle():
    # Lines with + or - in the middle should not count
    diff = "context + plus\ncontext - minus"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_trailing_newline():
    # Diff ending with a newline
    diff = "+add\n-remove\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_empty_lines_between_diffs():
    # Empty lines between diff lines
    diff = "+add1\n\n-add1\n\n"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_only_plus_minus_lines():
    # Only diff lines, no context
    diff = "+\n-\n+\n-"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_long_header_lines():
    # Long header lines that start with +++ or ---
    diff = "+++ some/very/long/path/to/file.txt\n--- another/path.txt\n+add\n-remove"
    codeflash_output = get_diff_lines_count(diff)

def test_diff_with_plus_plus_plus_in_middle():
    # A line like 'context +++ not header' should not be ignored as header
    diff = "context +++ not header\n+add\n-remove"
    codeflash_output = get_diff_lines_count(diff)

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

def test_large_diff_all_added():
    # Large diff with all lines added
    n = 1000
    diff = "\n".join(["+added line {}".format(i) for i in range(n)])
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_all_removed():
    # Large diff with all lines removed
    n = 1000
    diff = "\n".join(["-removed line {}".format(i) for i in range(n)])
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_mixed():
    # Large diff with mixed added, removed and context lines
    n = 333
    lines = []
    for i in range(n):
        lines.append("+added {}".format(i))
        lines.append("-removed {}".format(i))
        lines.append(" context {}".format(i))
    diff = "\n".join(lines)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_headers():
    # Large diff with headers interleaved
    n = 250
    lines = []
    for i in range(n):
        lines.append("+++ file{}.txt".format(i))
        lines.append("--- file{}.txt".format(i))
        lines.append("+add{}".format(i))
        lines.append("-rem{}".format(i))
        lines.append(" context{}".format(i))
    diff = "\n".join(lines)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_blank_lines():
    # Large diff with many blank lines
    n = 200
    lines = []
    for i in range(n):
        lines.append("")
        lines.append("+add{}".format(i))
        lines.append("")
        lines.append("-rem{}".format(i))
        lines.append("")
    diff = "\n".join(lines)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_only_headers_and_context():
    # Large diff with only headers and context, should return 0
    n = 500
    lines = []
    for i in range(n):
        lines.append("+++ file{}.txt".format(i))
        lines.append("--- file{}.txt".format(i))
        lines.append(" context{}".format(i))
    diff = "\n".join(lines)
    codeflash_output = get_diff_lines_count(diff)

def test_large_diff_with_short_lines():
    # Large diff with short + and - lines
    n = 1000
    diff = "\n".join(["+" for _ in range(n//2)] + ["-" for _ in range(n//2)])
    codeflash_output = get_diff_lines_count(diff)
# 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.formatter import get_diff_lines_count

def test_get_diff_lines_count():
    get_diff_lines_count('')

To edit these changes git checkout codeflash/optimize-pr274-2025-06-03T20.48.27 and push.