525 lines
18 KiB
Rust
525 lines
18 KiB
Rust
//! Snippet extraction for search results; contentless FTS5 has no
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//! `snippet()`. Output is structural (window text plus byte ranges), never
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//! markup. Matching folds ASCII case only, as full-text verification does:
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//! `cafe` neither finds nor marks `café`.
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#[derive(Debug, Clone)]
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pub struct Options {
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/// Approximate byte budget for the returned window: a soft target, since
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/// matches expand the window so a hit is never cut off.
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pub approx_bytes: usize,
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}
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impl Default for Options {
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fn default() -> Self {
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Options { approx_bytes: 200 }
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}
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}
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/// A context window from a document plus the match positions inside it.
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#[derive(Debug, Clone, PartialEq, Eq)]
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pub struct Snippet {
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/// The excerpt, sliced verbatim from the source text.
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pub window: String,
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/// Byte ranges *into `window`*, sorted, non-overlapping (overlapping
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/// term hits are coalesced), always on char boundaries.
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pub ranges: Vec<(usize, usize)>,
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/// Content exists before/after the window.
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pub truncated_start: bool,
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pub truncated_end: bool,
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}
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impl Snippet {
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fn empty() -> Snippet {
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Snippet {
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window: String::new(),
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ranges: Vec::new(),
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truncated_start: false,
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truncated_end: false,
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}
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}
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}
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/// Extract against a haystack the caller has already ASCII-folded. `folded`
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/// must be `text.to_ascii_lowercase()`: the fold preserves byte length, so
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/// offsets found in it slice the original.
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///
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/// Returns the window and how many occurrences of `term` it found before
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/// touching ranges were coalesced, the count the full-text pass ranks on. A
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/// blank term matches nothing, but a padded term is searched as given, never
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/// trimmed.
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pub fn extract_folded(text: &str, folded: &str, term: &str, opts: &Options) -> (Snippet, usize) {
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debug_assert_eq!(folded.len(), text.len(), "ASCII folding preserves length");
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if text.is_empty() {
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return (Snippet::empty(), 0);
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}
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if term.trim().is_empty() {
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return (head_window(text, opts.approx_bytes), 0);
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}
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// Borrow when the term is already folded, as every cascade call's is,
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// to avoid an allocation per candidate row.
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let pattern: std::borrow::Cow<'_, str> = if term.bytes().any(|b| b.is_ascii_uppercase()) {
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std::borrow::Cow::Owned(term.to_ascii_lowercase())
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} else {
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std::borrow::Cow::Borrowed(term)
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};
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// `memmem`, not `str::match_indices`: measured faster on whole-body
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// scans. The walk runs to the end (the count must see every occurrence),
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// but matches past the window's right edge are not stored.
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let mut matches: Vec<(usize, usize)> = Vec::new();
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let mut found = 0usize;
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// The window's right edge once the first match fixes it, from the same
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// [`window_bounds`] the window itself uses.
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let mut keep_below: Option<usize> = None;
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// The end of the last kept match, so a chain of touching occurrences
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// (`abab…` for `ab`) that starts inside the window and continues past
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// it stays intact for `coalesce_overlapping` and the expansion step.
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let mut chain_end = 0usize;
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for at in memchr::memmem::find_iter(folded.as_bytes(), pattern.as_bytes()) {
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// Before any dropping: two abutting occurrences are two hits for
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// ranking even though they paint as one highlight.
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found += 1;
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let bound = *keep_below.get_or_insert_with(|| window_bounds(text, at, opts.approx_bytes).1);
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if at >= bound && at > chain_end {
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// Past the edge and not chained to anything kept: keep counting,
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// stop storing.
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continue;
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}
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chain_end = at + pattern.len();
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matches.push((at, chain_end));
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}
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if matches.is_empty() {
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return (head_window(text, opts.approx_bytes), 0);
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}
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// One term's occurrences arrive in order and never overlap; only
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// abutting ones merge.
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let matches = coalesce_overlapping(matches);
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let (win_start, mut win_end) = window_bounds(text, matches[0].0, opts.approx_bytes);
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// A match straddling the right edge is fully included, not cut mid-hit.
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if let Some((_, end)) = matches.iter().rfind(|(s, _)| *s < win_end) {
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if *end > win_end {
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win_end = text.ceil_char_boundary(*end);
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}
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}
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let ranges = matches
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.iter()
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.filter(|(s, e)| *e > win_start && *s < win_end)
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.map(|(s, e)| {
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(
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(*s).max(win_start) - win_start,
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(*e).min(win_end) - win_start,
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)
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})
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.collect();
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(
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Snippet {
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window: text[win_start..win_end].to_string(),
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ranges,
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truncated_start: win_start > 0,
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truncated_end: win_end < text.len(),
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},
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found,
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)
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}
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/// The window cut around a match that starts at `first`: from a third of
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/// `budget` before it, rounded down to a char boundary, to `budget` past that
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/// unrounded start, rounded up. The third keeps the hit off the left edge.
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fn window_bounds(text: &str, first: usize, budget: usize) -> (usize, usize) {
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let start = first.saturating_sub(budget / 3);
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let end = (start + budget).min(text.len());
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(
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text.floor_char_boundary(start),
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text.ceil_char_boundary(end),
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)
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}
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/// Clamp `range` into `text` and widen it to the nearest char boundaries.
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/// Callers take ranges from byte-level matchers, so an endpoint can land
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/// inside a multi-byte character, where slicing panics.
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fn aligned_range(text: &str, range: (usize, usize)) -> (usize, usize) {
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let start = range.0.min(text.len());
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let end = range.1.clamp(start, text.len());
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(
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text.floor_char_boundary(start),
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text.ceil_char_boundary(end),
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)
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}
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/// The whole of `text` as the window, with `range` marked: the shape the name
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/// and path tiers use. `window` is the field verbatim, so the ranges index the
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/// field the column is already painting.
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pub fn whole_field(text: &str, range: (usize, usize)) -> Snippet {
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if text.is_empty() {
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return Snippet::empty();
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}
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let (start, end) = aligned_range(text, range);
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Snippet {
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window: text.to_string(),
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ranges: if end > start {
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vec![(start, end)]
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} else {
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Vec::new()
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},
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truncated_start: false,
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truncated_end: false,
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}
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}
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/// Build a snippet window around one known match range in `text`. The range
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/// is clamped into `text` and widened to char boundaries.
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pub fn window_around(text: &str, range: (usize, usize), opts: &Options) -> Snippet {
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if text.is_empty() {
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return Snippet::empty();
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}
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let (ms, me) = aligned_range(text, range);
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let (win_start, win_end) = window_bounds(text, ms, opts.approx_bytes);
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// The whole match stays inside the window.
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let win_end = win_end.max(me);
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let ranges = if me > ms {
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vec![(ms - win_start, me - win_start)]
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} else {
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Vec::new()
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};
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Snippet {
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window: text[win_start..win_end].to_string(),
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ranges,
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truncated_start: win_start > 0,
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truncated_end: win_end < text.len(),
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}
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}
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/// Count non-overlapping occurrences of `term` in `text`, byte for byte: a
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/// case-insensitive count passes both already folded.
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pub fn count_occurrences(text: &str, term: &str) -> usize {
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if term.is_empty() || text.len() < term.len() {
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return 0;
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}
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memchr::memmem::find_iter(text.as_bytes(), term.as_bytes()).count()
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}
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/// The first `n` bytes of `text` (char-aligned) as a match-less window.
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fn head_window(text: &str, n: usize) -> Snippet {
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let cut = text.floor_char_boundary(n);
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Snippet {
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window: text[..cut].to_string(),
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ranges: Vec::new(),
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truncated_start: false,
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truncated_end: cut < text.len(),
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}
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}
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/// Merge adjacent/overlapping ranges. Input must be sorted by start.
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fn coalesce_overlapping(v: Vec<(usize, usize)>) -> Vec<(usize, usize)> {
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let mut out = Vec::with_capacity(v.len());
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let mut it = v.into_iter();
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let Some(mut cur) = it.next() else {
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return out;
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};
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for next in it {
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if next.0 <= cur.1 {
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cur.1 = cur.1.max(next.1);
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} else {
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out.push(cur);
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cur = next;
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}
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}
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out.push(cur);
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out
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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fn extract(text: &str, term: &str, opts: &Options) -> Snippet {
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extract_folded(text, &text.to_ascii_lowercase(), term, opts).0
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}
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fn extract_counted(text: &str, term: &str, opts: &Options) -> (Snippet, usize) {
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extract_folded(text, &text.to_ascii_lowercase(), term, opts)
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}
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fn opts_small() -> Options {
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Options { approx_bytes: 40 }
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}
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/// The count is occurrences, not the highlights they coalesce into.
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#[test]
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fn extract_folded_counts_occurrences_not_ranges() {
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let text = "abab and ab";
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let (s, n) = extract_counted(text, "ab", &opts_small());
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assert_eq!(n, 3, "three occurrences");
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assert_eq!(
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n,
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count_occurrences(text, "ab"),
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"must agree with count_occurrences"
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);
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assert_eq!(s.ranges.len(), 2, "the abutting pair paints as one range");
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}
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/// A disagreement here would change which rows survive the pass.
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#[test]
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fn extract_folded_count_agrees_with_count_occurrences() {
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let cases: &[(&str, &str)] = &[
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("no hits at all", "zzz"),
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("one hit here", "hit"),
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("Hit hit HIT", "hit"),
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("aaaa", "aa"),
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("", "x"),
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("short", "much longer than the haystack"),
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("ünïcode ünïcode", "ünïcode"),
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];
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for (text, term) in cases {
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let folded = text.to_ascii_lowercase();
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let (_, n) = extract_folded(text, &folded, term, &opts_small());
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assert_eq!(
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n,
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count_occurrences(&folded, &term.to_ascii_lowercase()),
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"count mismatch for {:?} in {:?}",
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term,
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text
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);
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}
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}
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/// The owning and borrowing branches of the fold must find the same
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/// matches.
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#[test]
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fn extract_folded_needle_case_does_not_change_matches() {
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let text = "The Needle and the needle";
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let folded = text.to_ascii_lowercase();
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let (upper, n_upper) = extract_folded(text, &folded, "Needle", &opts_small());
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let (lower, n_lower) = extract_folded(text, &folded, "needle", &opts_small());
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assert_eq!(n_upper, 2);
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assert_eq!(n_upper, n_lower);
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assert_eq!(upper.ranges, lower.ranges);
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assert_eq!(upper.window, lower.window);
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}
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/// An empty needle would match at every byte offset.
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#[test]
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fn extract_folded_ignores_blank_terms() {
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let text = "some text";
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let folded = text.to_ascii_lowercase();
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for term in ["", " ", "\t"] {
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let (s, n) = extract_folded(text, &folded, term, &opts_small());
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assert_eq!(n, 0, "blank term {:?} counted", term);
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assert!(s.ranges.is_empty(), "blank term {:?} highlighted", term);
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}
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}
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/// A term with surrounding space is searched as given, never trimmed.
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#[test]
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fn extract_folded_does_not_trim_a_padded_term() {
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let text = "needle needlework";
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let folded = text.to_ascii_lowercase();
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let (_, n) = extract_folded(text, &folded, "needle ", &opts_small());
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assert_eq!(n, 1, "only the occurrence followed by a space");
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assert_eq!(n, count_occurrences(&folded, "needle "));
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}
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/// The `Snippet::ranges` contract egui's LayoutJob sections rely on.
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fn assert_ranges_valid(s: &Snippet) {
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let mut prev_end = 0;
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for &(a, b) in &s.ranges {
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assert!(a < b, "empty/inverted range {:?}", (a, b));
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assert!(b <= s.window.len(), "range {:?} beyond window", (a, b));
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assert!(a >= prev_end, "overlapping ranges");
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assert!(s.window.is_char_boundary(a) && s.window.is_char_boundary(b));
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prev_end = b;
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}
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}
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fn marked(s: &Snippet) -> Vec<&str> {
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s.ranges.iter().map(|&(a, b)| &s.window[a..b]).collect()
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}
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/// Occurrences past the window's right edge are counted but not kept; a
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/// bound leaking into either side would be a ranking change or a missing
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/// highlight.
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#[test]
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fn occurrences_past_the_window_are_counted_but_not_kept() {
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let unit = "needle filler filler ";
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let text = unit.repeat(400);
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let (snip, found) = extract_counted(&text, "needle", &opts_small());
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assert_eq!(found, 400, "every occurrence must still be counted");
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assert_ranges_valid(&snip);
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assert!(!snip.ranges.is_empty());
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assert!(snip.truncated_end, "there is a great deal more body");
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for &(a, b) in &snip.ranges {
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assert_eq!(&snip.window[a..b], "needle");
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}
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let win_at = text
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.find(&snip.window)
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.expect("the window is a slice of the text");
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let expected = memchr::memmem::find_iter(text.as_bytes(), b"needle")
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.filter(|at| *at >= win_at && *at < win_at + snip.window.len())
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.count();
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assert_eq!(
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snip.ranges.len(),
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expected,
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"every occurrence inside the window must be marked"
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);
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}
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/// The case the chain rule exists for: a chain that starts inside the
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/// window can run past its right edge, and dropping at the edge would
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/// cut the highlight short.
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#[test]
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fn a_coalescing_chain_is_not_cut_at_the_window_edge() {
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let text = "ab".repeat(400);
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let (snip, found) = extract_counted(&text, "ab", &opts_small());
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assert_eq!(found, 400, "non-overlapping occurrences, all counted");
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assert_ranges_valid(&snip);
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assert_eq!(snip.ranges.len(), 1, "one chain, one highlight");
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// An unbroken chain grows the window to the whole text; without the
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// chain rule the window is 40 bytes, which "range == whole window"
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// alone cannot tell apart.
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assert_eq!(
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snip.window.len(),
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text.len(),
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"the window must grow to cover the coalesced run"
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);
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assert!(
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!snip.truncated_end,
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"nothing is left past a full-length window"
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);
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assert_eq!(
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snip.ranges[0],
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(0, text.len()),
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"one highlight over the lot"
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);
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}
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#[test]
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fn empty_text_returns_empty() {
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let s = extract("", "foo", &Options::default());
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assert_eq!(s, Snippet::empty());
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}
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#[test]
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fn a_blank_term_returns_head_marked_truncated() {
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let long = "abcdefghijklmnop".repeat(10);
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let s = extract(&long, "", &opts_small());
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assert!(s.truncated_end);
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assert!(!s.truncated_start);
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assert!(s.ranges.is_empty());
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assert!(s.window.len() <= 40);
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}
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#[test]
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fn a_blank_term_untruncated() {
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let s = extract("short text", "", &opts_small());
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assert_eq!(s.window, "short text");
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assert!(!s.truncated_end && !s.truncated_start);
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}
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#[test]
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fn simple_match_range() {
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let s = extract("the quick brown fox", "quick", &opts_small());
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assert_eq!(marked(&s), vec!["quick"]);
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assert_ranges_valid(&s);
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}
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#[test]
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fn case_insensitive_match_reports_original_case() {
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let s = extract("The QUICK brown fox", "quick", &opts_small());
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assert_eq!(marked(&s), vec!["QUICK"]);
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}
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#[test]
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fn window_truncation_flags_on_both_sides() {
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let text = "prefix ".repeat(20) + "MATCH in middle " + &"suffix ".repeat(20);
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let s = extract(&text, "MATCH", &opts_small());
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assert!(s.truncated_start);
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assert!(s.truncated_end);
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assert_eq!(marked(&s), vec!["MATCH"]);
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}
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#[test]
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fn match_at_start_not_truncated_left() {
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let s = extract(
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"MATCH right at the start of this paragraph",
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"match",
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&opts_small(),
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);
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assert!(!s.truncated_start);
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assert_eq!(s.ranges[0].0, 0);
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}
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#[test]
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fn no_match_returns_head_without_ranges() {
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let text = "alpha beta gamma delta epsilon zeta eta theta iota kappa";
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let s = extract(text, "nomatch", &opts_small());
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assert!(s.ranges.is_empty());
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assert!(s.window.starts_with("alpha"));
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}
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#[test]
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fn utf8_boundaries_hold_with_multibyte_text() {
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let text = "café café café café café café café café café café";
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let s = extract(text, "café", &opts_small());
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assert!(!s.ranges.is_empty());
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assert_ranges_valid(&s);
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for m in marked(&s) {
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assert_eq!(m, "café");
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
fn match_near_right_edge_is_fully_included() {
|
|
let prefix = "x".repeat(30);
|
|
let text = format!("{}{}", prefix, "LONGMATCHTERMTEXT");
|
|
let s = extract(&text, "LONGMATCHTERMTEXT", &opts_small());
|
|
assert_eq!(marked(&s), vec!["LONGMATCHTERMTEXT"]);
|
|
}
|
|
|
|
#[test]
|
|
fn window_around_basic() {
|
|
let text = "prefix ".repeat(20) + "NEEDLE" + &" suffix".repeat(20);
|
|
let at = text.find("NEEDLE").unwrap();
|
|
let s = window_around(&text, (at, at + 6), &opts_small());
|
|
assert_eq!(marked(&s), vec!["NEEDLE"]);
|
|
assert!(s.truncated_start && s.truncated_end);
|
|
assert_ranges_valid(&s);
|
|
}
|
|
|
|
#[test]
|
|
fn window_around_clamps_out_of_bounds() {
|
|
let s = window_around("tiny", (2, 999), &opts_small());
|
|
assert_eq!(s.window, "tiny");
|
|
assert_eq!(s.ranges, vec![(2, 4)]);
|
|
// Fully out-of-range → no ranges, but never a panic.
|
|
let s = window_around("tiny", (999, 1000), &opts_small());
|
|
assert!(s.ranges.is_empty());
|
|
}
|
|
|
|
#[test]
|
|
fn window_around_aligns_multibyte_boundaries() {
|
|
let text = "ééééééééé needle ééééééééé";
|
|
let s = window_around(text, (1, 3), &opts_small());
|
|
assert_ranges_valid(&s);
|
|
}
|
|
|
|
#[test]
|
|
fn count_occurrences_cases() {
|
|
assert_eq!(count_occurrences("aaaa", "aaa"), 1, "non-overlapping");
|
|
assert_eq!(count_occurrences("abcABC", "abc"), 1, "byte for byte");
|
|
assert_eq!(count_occurrences("", "x"), 0);
|
|
assert_eq!(count_occurrences("xyz", ""), 0);
|
|
assert_eq!(count_occurrences("no hits here", "zzz"), 0);
|
|
assert_eq!(count_occurrences("ab ab ab", "ab"), 3);
|
|
}
|
|
}
|