⚡️ Speed up method JavaAssertTransformer._find_balanced_braces by 71% in PR #1199 (omni-java)

[codeflash-ai]

⚡️ This pull request contains optimizations for PR #1199

If you approve this dependent PR, these changes will be merged into the original PR branch omni-java.

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

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📄 71% (0.71x) speedup for JavaAssertTransformer._find_balanced_braces in codeflash/languages/java/remove_asserts.py

⏱️ Runtime : 4.83 milliseconds → 2.82 milliseconds (best of 138 runs)

📝 Explanation and details

This optimization achieves a 71% speedup (from 4.83ms to 2.82ms) by eliminating redundant operations inside a hot loop that parses Java code character-by-character to find balanced braces.

Key Optimizations:

1. Cached String Length: The optimization hoists len(code) outside the loop (storing it as code_len), eliminating ~30,500 redundant length calculations per execution. The line profiler shows the loop condition went from 10.7ms (15.8% of time) to 8.57ms (13.9%), saving ~2ms.

2. Eliminated Repeated Indexing: The original code computed prev_char = code[pos - 1] if pos > 0 else "" on every iteration (~10.4ms, 15.3% of time). The optimized version maintains prev_char as a variable updated at the end of each iteration, completely eliminating this 30,500-hit operation and its conditional check.

3. Preserved Correctness: The optimization carefully initializes prev_char = code[open_brace_pos] before the loop to maintain identical behavior - the first iteration compares against the opening brace character, matching the original's code[pos-1] when pos = open_brace_pos + 1.

Performance Characteristics:

The test results show consistent improvements across all scenarios:

• Large-scale tests see the biggest gains (72-85% faster) - parsing 1000+ character strings or 500+ statements benefits most from eliminating repeated operations
• Nested structures improve 40-68% - deeply nested braces require more iterations, amplifying the per-iteration savings
• Simple cases still improve 6-29% - even small inputs benefit from reduced overhead

This is a classic loop optimization that trades a small amount of memory (one extra variable + one cached length) for significant runtime improvements in a character-by-character parser that's likely called frequently when processing Java test code.

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 103 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Click to see Generated Regression Tests

import pytest  # used for our unit tests
from codeflash.languages.java.remove_asserts import JavaAssertTransformer

def test_basic_balanced_braces_simple():
    # Basic scenario: a single, simple pair of braces with plain content.
    transformer = JavaAssertTransformer("dummy")  # create an instance
    code = "prefix {inner} suffix"  # code containing braces
    open_pos = code.index("{")  # find the open brace position
    content, end_pos = transformer._find_balanced_braces(code, open_pos) # 2.60μs -> 2.35μs (11.0% faster)

def test_invalid_open_brace_position_and_non_brace_char():
    transformer = JavaAssertTransformer("dummy")
    code = "no braces here"
    # Position beyond the end should return (None, -1)
    content, pos = transformer._find_balanced_braces(code, len(code) + 5) # 500ns -> 551ns (9.26% slower)
    # Position within string but not a '{' should also return (None, -1)
    content2, pos2 = transformer._find_balanced_braces("abc{}", 0) # 431ns -> 470ns (8.30% slower)

def test_nested_braces():
    # Nested braces should be handled by depth counting.
    transformer = JavaAssertTransformer("dummy")
    code = "{a{b{c}d}e}"  # multiple nested braces
    content, end_pos = transformer._find_balanced_braces(code, 0) # 3.47μs -> 2.96μs (17.3% faster)

def test_braces_inside_string_ignored():
    # Braces that appear inside string literals must not affect brace balancing.
    transformer = JavaAssertTransformer("dummy")
    # The inner braces are inside a double-quoted string literal.
    code = '{ "not{brace}" }'
    content, end_pos = transformer._find_balanced_braces(code, 0) # 4.02μs -> 3.29μs (22.2% faster)

def test_brace_inside_char_literal_ignored():
    # A single character literal containing a brace should not be treated as a structural brace.
    transformer = JavaAssertTransformer("dummy")
    # Use a char literal '}' inside the braces. Use double-quoted Python string to embed single quotes.
    code = "{ '}' }"
    content, end_pos = transformer._find_balanced_braces(code, 0) # 2.92μs -> 2.47μs (17.8% faster)

def test_unbalanced_braces_returns_none():
    # When there is no matching closing brace the function should indicate failure.
    transformer = JavaAssertTransformer("dummy")
    code = "{ unclosed ..."
    content, pos = transformer._find_balanced_braces(code, 0) # 3.24μs -> 2.50μs (29.2% faster)

def test_escaped_quotes_do_not_start_string():
    # An escaped quote (preceded by a backslash) must not toggle in_string,
    # so braces that follow should still be interpreted as structural braces.
    transformer = JavaAssertTransformer("dummy")
    # Build a string where double quotes are preceded by backslashes so they should NOT be treated as string delimiters.
    # In Python literal we write backslashes as \\ and double quotes as \", so the Java snippet becomes: { \"{inner}\" }
    code = "{ \\\"{inner}\\\" }"
    content, end_pos = transformer._find_balanced_braces(code, 0) # 4.00μs -> 3.35μs (19.5% faster)

def test_large_nested_braces_performance():
    # Large-scale test: many nested brace pairs to test scalability.
    # Keep total steps < 1000 per instructions; choose 200 nested pairs (400 braces + 1 char inside).
    transformer = JavaAssertTransformer("dummy")
    n = 200  # nested depth
    inner_char = "X"
    code = "{" * n + inner_char + "}" * n  # e.g., "{{{...X...}}}"
    # Call at the outermost brace
    content, end_pos = transformer._find_balanced_braces(code, 0) # 66.2μs -> 41.9μs (57.9% faster)
    # The returned content should be the inner text (everything except the outermost braces)
    expected_inner = "{" * (n - 1) + inner_char + "}" * (n - 1)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

import pytest
from codeflash.languages.java.parser import get_java_analyzer
from codeflash.languages.java.remove_asserts import JavaAssertTransformer

class TestFindBalancedBraces:
    """Test suite for JavaAssertTransformer._find_balanced_braces method."""

    # ==================== BASIC TEST CASES ====================
    # These tests verify fundamental functionality under normal conditions.

    def test_basic_empty_braces(self):
        """Test finding content in simple empty braces."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 1.58μs -> 1.49μs (6.03% faster)

    def test_basic_single_statement(self):
        """Test finding content with a single simple statement."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{int x = 5;}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 3.26μs -> 2.69μs (21.3% faster)

    def test_basic_multiple_statements(self):
        """Test finding content with multiple statements."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{int x = 5; int y = 10;}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.90μs -> 3.87μs (26.7% faster)

    def test_basic_nested_braces(self):
        """Test finding content with nested braces."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{if (true) {x = 1;}}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.56μs -> 3.68μs (24.0% faster)

    def test_basic_string_with_brace(self):
        """Test that braces inside strings are not counted."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "{}"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.54μs -> 3.77μs (20.5% faster)

    def test_basic_char_literal_single_quote(self):
        """Test that single quotes in char literals are handled correctly."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{char c = '{'; }"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.05μs -> 3.26μs (24.3% faster)

    def test_basic_escaped_quote_in_string(self):
        """Test that escaped quotes in strings don't affect parsing."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "\\""; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.56μs -> 3.74μs (22.0% faster)

    # ==================== EDGE CASES ====================
    # These tests evaluate extreme or unusual conditions.

    def test_edge_invalid_starting_position(self):
        """Test with position that doesn't point to opening brace."""
        transformer = JavaAssertTransformer("testMethod")
        code = "int x = {5};"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 570ns -> 601ns (5.16% slower)

    def test_edge_position_out_of_bounds(self):
        """Test with position beyond string length."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{}"
        content, end_pos = transformer._find_balanced_braces(code, 10) # 511ns -> 461ns (10.8% faster)

    def test_edge_unclosed_braces(self):
        """Test with unclosed braces."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{int x = 5;"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 2.75μs -> 2.24μs (22.8% faster)

    def test_edge_extra_closing_braces(self):
        """Test handling when there are extra closing braces after balanced pair."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{int x = 5;}}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 3.29μs -> 2.77μs (18.8% faster)

    def test_edge_string_with_escaped_backslash_then_quote(self):
        """Test escaped backslash followed by quote in string."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "\\\\\\\""; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 5.00μs -> 3.92μs (27.6% faster)

    def test_edge_empty_string_literal(self):
        """Test empty string literal."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = ""; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.25μs -> 3.43μs (24.0% faster)

    def test_edge_empty_char_literal(self):
        """Test edge case with char literal."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{char c = ' '; }"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.09μs -> 3.29μs (24.4% faster)

    def test_edge_mixed_quotes(self):
        """Test code with both single and double quotes."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "it\'s"; char c = \'"\'; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 7.12μs -> 5.53μs (28.8% faster)

    def test_edge_nested_deeply(self):
        """Test deeply nested braces."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{{{{{x = 1;}}}}}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.00μs -> 3.29μs (21.7% faster)

    def test_edge_string_contains_escape_sequences(self):
        """Test strings with various escape sequences."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "a\\nb\\tc"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 5.17μs -> 4.10μs (26.2% faster)

    def test_edge_char_with_escape_sequence(self):
        """Test char literal with escape sequence."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{char c = '\\n'; }"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.23μs -> 3.44μs (23.0% faster)

    def test_edge_quote_after_escaped_backslash(self):
        """Test quote immediately after escaped backslash."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "test\\\\"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.55μs -> 3.56μs (27.9% faster)

    def test_edge_single_char_content(self):
        """Test braces with single character content."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{x}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 1.89μs -> 1.75μs (8.04% faster)

    def test_edge_only_whitespace(self):
        """Test braces containing only whitespace."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{   \n  \t  }"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 3.12μs -> 2.56μs (21.8% faster)

    def test_edge_string_with_newline(self):
        """Test string literal containing actual newline (if supported)."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "line1";\n}'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.98μs -> 3.95μs (26.1% faster)

    def test_edge_multiple_string_literals(self):
        """Test multiple string literals in sequence."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "first" + "second"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 6.38μs -> 4.92μs (29.7% faster)

    def test_edge_alternating_single_double_quotes(self):
        """Test alternating single and double quotes."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{s = "a\'b" + \'c"d\'; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 5.07μs -> 4.17μs (21.6% faster)

    def test_edge_backslash_not_before_quote(self):
        """Test backslash not used as escape character."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{String s = "a\\b"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.73μs -> 3.76μs (25.9% faster)

    def test_edge_position_at_last_character(self):
        """Test when opening brace is at very end of string."""
        transformer = JavaAssertTransformer("testMethod")
        code = "int x ="
        content, end_pos = transformer._find_balanced_braces(code, len(code) - 1) # 631ns -> 631ns (0.000% faster)

    def test_edge_string_with_quote_char_mix(self):
        """Test complex mix of quotes and characters."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{x = "\'" + "\\""; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.62μs -> 3.70μs (25.0% faster)

    def test_edge_closing_brace_immediately_after_opening(self):
        """Test empty braces edge case."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 1.54μs -> 1.50μs (2.66% faster)

    def test_edge_string_before_and_after_nested_brace(self):
        """Test strings surrounding nested braces."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{"before" {x} "after"}'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 5.07μs -> 4.04μs (25.6% faster)

    def test_edge_escaped_backslash_in_char(self):
        """Test escaped backslash in character literal."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{char c = '\\\\'; }"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 3.86μs -> 3.04μs (27.0% faster)

    def test_edge_double_quote_in_char_literal(self):
        """Test double quote inside character literal."""
        transformer = JavaAssertTransformer("testMethod")
        code = '{char c = \'"\'; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.15μs -> 3.40μs (22.1% faster)

    def test_edge_single_quote_in_string_literal(self):
        """Test single quote inside string literal."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{String s = \"'\"; }"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 4.52μs -> 3.66μs (23.5% faster)

    # ==================== LARGE SCALE TEST CASES ====================
    # These tests assess performance and scalability with large data samples.

    def test_large_many_statements(self):
        """Test with many statements inside braces."""
        transformer = JavaAssertTransformer("testMethod")
        # Create code with 500 statements
        statements = "; ".join([f"x{i} = {i}" for i in range(500)])
        code = "{" + statements + ";}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 943μs -> 548μs (72.0% faster)

    def test_large_many_nested_levels(self):
        """Test with deeply nested braces (up to 100 levels)."""
        transformer = JavaAssertTransformer("testMethod")
        # Create 100 levels of nesting
        open_braces = "{" * 100
        close_braces = "}" * 100
        code = open_braces + "x" + close_braces
        content, end_pos = transformer._find_balanced_braces(code, 0) # 30.1μs -> 21.6μs (39.6% faster)

    def test_large_long_string_literal(self):
        """Test with very long string literal."""
        transformer = JavaAssertTransformer("testMethod")
        # Create string with 1000 characters
        long_string = "a" * 1000
        code = '{String s = "' + long_string + '"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 142μs -> 78.8μs (81.2% faster)

    def test_large_mixed_quotes_many_times(self):
        """Test with alternating quotes many times."""
        transformer = JavaAssertTransformer("testMethod")
        # Create 250 pairs of alternating string and char literals
        parts = []
        for i in range(250):
            parts.append(f'"str{i}"')
            parts.append(f"'c{i}'")
        code = "{" + " + ".join(parts) + ";}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 747μs -> 432μs (72.9% faster)

    def test_large_escaped_sequences_many(self):
        """Test with many escape sequences."""
        transformer = JavaAssertTransformer("testMethod")
        # Create string with many escape sequences
        escape_string = "\\n\\t\\r\\\\" * 250
        code = '{String s = "' + escape_string + '"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 283μs -> 152μs (85.2% faster)

    def test_large_nested_with_strings(self):
        """Test deeply nested braces with strings at each level."""
        transformer = JavaAssertTransformer("testMethod")
        # Create 50 levels of nesting with strings
        code = "{"
        for i in range(50):
            code += f'String s{i} = "level{i}"; {{'
        code += "x"
        code += "}" * 51
        content, end_pos = transformer._find_balanced_braces(code, 0) # 203μs -> 121μs (68.1% faster)

    def test_large_many_char_literals(self):
        """Test with many character literals."""
        transformer = JavaAssertTransformer("testMethod")
        # Create 500 character literals
        parts = [f"'c{i}'" for i in range(500)]
        code = "{" + ", ".join(parts) + ";}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 606μs -> 343μs (76.2% faster)

    def test_large_complex_mixed_scenario(self):
        """Test large code with mixed complexity."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{"
        # Add nested structure with strings and chars
        for i in range(100):
            code += f'if (true) {{ String s = "str{i}"; char c = \'c{i}\'; x{i} = {i}; '
        code += "y = 1;"
        code += "}" * 100
        content, end_pos = transformer._find_balanced_braces(code, 0) # 956μs -> 554μs (72.6% faster)

    def test_large_position_in_middle(self):
        """Test finding balanced braces when opening brace is in middle of large code."""
        transformer = JavaAssertTransformer("testMethod")
        # Create code where we start from a brace in the middle
        prefix = 'String s = "prefix"; '
        middle_code = "{int x = 5; int y = 10;}"
        code = prefix + middle_code
        start_pos = len(prefix)
        content, end_pos = transformer._find_balanced_braces(code, start_pos) # 4.94μs -> 3.83μs (29.1% faster)

    def test_large_alternating_braces_and_strings(self):
        """Test alternating between nested braces and string literals."""
        transformer = JavaAssertTransformer("testMethod")
        code = "{"
        for i in range(100):
            code += f'{{ String s = "test{i}"; }}'
        code += "}"
        content, end_pos = transformer._find_balanced_braces(code, 0) # 385μs -> 230μs (67.3% faster)

    def test_large_single_string_with_many_escapes(self):
        """Test single very long string with many escape sequences."""
        transformer = JavaAssertTransformer("testMethod")
        # Create alternating characters and escapes
        long_content = ("a" + "\\\\" + "b" + "\\n" + "c" + "\\t") * 250
        code = '{String s = "' + long_content + '"; }'
        content, end_pos = transformer._find_balanced_braces(code, 0) # 313μs -> 171μs (82.8% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

To edit these changes git checkout codeflash/optimize-pr1199-2026-02-04T01.49.20 and push.