1 files changed, 98 insertions, 0 deletions

diff --git a/crates/ra_ssr/src/nester.rs b/crates/ra_ssr/src/nester.rs
new file mode 100644
index 000000000..b3e20579b
--- /dev/null
+++ b/crates/ra_ssr/src/nester.rs
@@ -0,0 +1,98 @@
+//! Converts a flat collection of matches into a nested form suitable for replacement. When there
+//! are multiple matches for a node, or that overlap, priority is given to the earlier rule. Nested
+//! matches are only permitted if the inner match is contained entirely within a placeholder of an
+//! outer match.
+//!
+//! For example, if our search pattern is `foo(foo($a))` and the code had `foo(foo(foo(foo(42))))`,
+//! then we'll get 3 matches, however only the outermost and innermost matches can be accepted. The
+//! middle match would take the second `foo` from the outer match.
+
+use crate::{Match, SsrMatches};
+use ra_syntax::SyntaxNode;
+use rustc_hash::FxHashMap;
+
+pub(crate) fn nest_and_remove_collisions(
+    mut matches: Vec<Match>,
+    sema: &hir::Semantics<ra_ide_db::RootDatabase>,
+) -> SsrMatches {
+    // We sort the matches by depth then by rule index. Sorting by depth means that by the time we
+    // see a match, any parent matches or conflicting matches will have already been seen. Sorting
+    // by rule_index means that if there are two matches for the same node, the rule added first
+    // will take precedence.
+    matches.sort_by(|a, b| a.depth.cmp(&b.depth).then_with(|| a.rule_index.cmp(&b.rule_index)));
+    let mut collector = MatchCollector::default();
+    for m in matches {
+        collector.add_match(m, sema);
+    }
+    collector.into()
+}
+
+#[derive(Default)]
+struct MatchCollector {
+    matches_by_node: FxHashMap<SyntaxNode, Match>,
+}
+
+impl MatchCollector {
+    /// Attempts to add `m` to matches. If it conflicts with an existing match, it is discarded. If
+    /// it is entirely within the a placeholder of an existing match, then it is added as a child
+    /// match of the existing match.
+    fn add_match(&mut self, m: Match, sema: &hir::Semantics<ra_ide_db::RootDatabase>) {
+        let matched_node = m.matched_node.clone();
+        if let Some(existing) = self.matches_by_node.get_mut(&matched_node) {
+            try_add_sub_match(m, existing, sema);
+            return;
+        }
+        for ancestor in sema.ancestors_with_macros(m.matched_node.clone()) {
+            if let Some(existing) = self.matches_by_node.get_mut(&ancestor) {
+                try_add_sub_match(m, existing, sema);
+                return;
+            }
+        }
+        self.matches_by_node.insert(matched_node, m);
+    }
+}
+
+/// Attempts to add `m` as a sub-match of `existing`.
+fn try_add_sub_match(
+    m: Match,
+    existing: &mut Match,
+    sema: &hir::Semantics<ra_ide_db::RootDatabase>,
+) {
+    for p in existing.placeholder_values.values_mut() {
+        // Note, no need to check if p.range.file is equal to m.range.file, since we
+        // already know we're within `existing`.
+        if p.range.range.contains_range(m.range.range) {
+            // Convert the inner matches in `p` into a temporary MatchCollector. When
+            // we're done, we then convert it back into an SsrMatches. If we expected
+            // lots of inner matches, it might be worthwhile keeping a MatchCollector
+            // around for each placeholder match. However we expect most placeholder
+            // will have 0 and a few will have 1. More than that should hopefully be
+            // exceptional.
+            let mut collector = MatchCollector::default();
+            for m in std::mem::replace(&mut p.inner_matches.matches, Vec::new()) {
+                collector.matches_by_node.insert(m.matched_node.clone(), m);
+            }
+            collector.add_match(m, sema);
+            p.inner_matches = collector.into();
+            break;
+        }
+    }
+}
+
+impl From<MatchCollector> for SsrMatches {
+    fn from(mut match_collector: MatchCollector) -> Self {
+        let mut matches = SsrMatches::default();
+        for (_, m) in match_collector.matches_by_node.drain() {
+            matches.matches.push(m);
+        }
+        matches.matches.sort_by(|a, b| {
+            // Order matches by file_id then by start range. This should be sufficient since ranges
+            // shouldn't be overlapping.
+            a.range
+                .file_id
+                .cmp(&b.range.file_id)
+                .then_with(|| a.range.range.start().cmp(&b.range.range.start()))
+        });
+        matches
+    }
+}