Struct IstanbulFileCoverage 

pub struct IstanbulFileCoverage { /* private fields */ }

Pre-processed per-function coverage data for a single file, derived from Istanbul coverage-final.json.

Implementations

impl IstanbulFileCoverage

pub fn lookup(&self, name: &str, line: u32, col: u32) -> Option<f64>

Look up coverage for a function by name, start line, and start column.

Resolution order:

1. Exact (name, line, col) match.
2. Name-only fuzzy match within ±2 lines (tolerates formatter drift), tie-broken by smallest (line, col) distance from the target.
3. Anonymous fallback: among Istanbul (anonymous_N) entries within ±2 lines, pick the one closest in (line, col) to the target. Bail only if two candidates tie on distance, which would be genuinely ambiguous.

Step 3 covers arrow-function exports where fallow extracts the binding identifier (const myHandler = () => {...} yields myHandler) while Istanbul records the function as anonymous. load_istanbul_coverage indexes declaration aliases so standard Istanbul producers still participate in this fallback. See issues #155, #166, #181, and #370.

When the map is relocated (recorded against a different checkout of the project, as in the audit base-worktree pass), a distance-free name match runs between steps 2 and 3: if every entry named name carries the same coverage value, that value is returned regardless of line drift. Unrelated edits can shift a function arbitrarily far between the two checkouts, and when all same-named candidates agree the choice among them cannot matter (#2347). Same-checkout lookups keep the bounded fuzz, which protects against stale coverage data.