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IGNORE_WHITESPACE_FEATURE.md

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Ignore Whitespace Feature

Overview

Added an "Ignore Whitespace" option to the diff viewer that allows users to toggle whether whitespace changes should be considered when comparing code.

Changes Made

Frontend Changes

1. nextjs-frontend/src/components/diff/BeyondCompareFunctionDiff.tsx

Added State:

  • Added ignoreWhitespace state variable (default: true - whitespace ignored by default)

Updated API Call:

  • Added ignore_whitespace parameter to the Rust backend API request options
  • Added ignoreWhitespace to the useEffect dependency array to trigger re-fetch when toggled

Added UI Toggle:

  • Added a checkbox control in the diff viewer header
  • Positioned next to the View Mode toggle (Unified/Side-by-Side)
  • Styled consistently with the existing UI
{/* Ignore Whitespace Toggle */}
<div className="flex items-center gap-2">
  <label className="flex items-center gap-2 cursor-pointer">
    <input
      type="checkbox"
      checked={ignoreWhitespace}
      onChange={(e) => setIgnoreWhitespace(e.target.checked)}
      className="w-4 h-4 rounded border-slate-600 bg-slate-700 text-blue-600 focus:ring-2 focus:ring-blue-500 focus:ring-offset-0 cursor-pointer"
    />
    <span className="text-xs font-medium text-slate-300">Ignore Whitespace</span>
  </label>
</div>

Backend Changes

1. crates/web-ui/src/models.rs

Updated ASTDiffOptions struct:

  • Added ignore_whitespace: bool field with #[serde(default)] attribute
  • Defaults to false when not provided
#[derive(Debug, Serialize, Deserialize)]
pub struct ASTDiffOptions {
    // ... existing fields ...
    /// Ignore whitespace when comparing lines
    #[serde(default)]
    pub ignore_whitespace: bool,
}

2. crates/web-ui/src/handlers.rs

Updated ast_diff handler:

  • Passes ignore_whitespace option to generate_lcs_line_mappings function

Updated generate_lcs_line_mappings function:

  • Added ignore_whitespace: bool parameter
  • Passes the parameter to compute_diff_operations

Updated compute_diff_operations function:

  • Added ignore_whitespace: bool parameter
  • Conditionally compares lines with or without trimming based on the flag
  • Passes the parameter to compute_lcs_table
let lines_equal = if ignore_whitespace {
    source_lines[i - 1].trim() == target_lines[j - 1].trim()
} else {
    source_lines[i - 1] == target_lines[j - 1]
};

Updated compute_lcs_table function:

  • Added ignore_whitespace: bool parameter
  • Conditionally compares lines with or without trimming in the LCS algorithm

How It Works

When ignore_whitespace = false (default):

  • Lines are compared exactly as they appear
  • Whitespace changes (indentation, trailing spaces, etc.) are detected as modifications
  • Example: " console.log()" vs " console.log()" → Modified

When ignore_whitespace = true:

  • Lines are trimmed before comparison
  • Only non-whitespace content is compared
  • Whitespace-only changes are ignored
  • Example: " console.log()" vs " console.log()" → Unchanged

Testing

A test script test_ignore_whitespace.sh was created to verify the functionality:

Test Results:

Test 1: ignore_whitespace = false

{
  "total_lines": 3,
  "added_lines": 0,
  "deleted_lines": 0,
  "modified_lines": 1,
  "unchanged_lines": 2,
  "structural_changes": 0,
  "semantic_changes": 0
}

✅ Correctly detects whitespace change as a modification

Test 2: ignore_whitespace = true

{
  "total_lines": 3,
  "added_lines": 0,
  "deleted_lines": 0,
  "modified_lines": 0,
  "unchanged_lines": 3,
  "structural_changes": 0,
  "semantic_changes": 0
}

✅ Correctly ignores whitespace change

Usage

  1. Open the diff viewer by clicking on a function pair in the comparison view
  2. Look for the "Ignore Whitespace" checkbox in the diff viewer header
  3. Toggle the checkbox to enable/disable whitespace ignoring
  4. The diff will automatically refresh when the option is changed

Implementation Notes

  • The feature currently applies to the LCS-based diff algorithm (default)
  • The AST-based diff algorithm uses structural similarity and is less affected by whitespace
  • The option is passed through the entire diff pipeline from frontend to backend
  • The implementation uses Rust's string trimming for whitespace normalization
  • The feature is backward compatible - if not specified, defaults to false

Future Enhancements

Potential improvements:

  • Add more granular whitespace options (ignore leading, ignore trailing, ignore all)
  • Add option to ignore blank lines
  • Add option to ignore case
  • Persist user preference in local storage
  • Add keyboard shortcut to toggle the option