3 files changed, 133 insertions, 9 deletions

diff --git a/crates/ra_ssr/src/lib.rs b/crates/ra_ssr/src/lib.rs
index 286619f59..5a71d4f31 100644
--- a/crates/ra_ssr/src/lib.rs
+++ b/crates/ra_ssr/src/lib.rs
@@ -151,8 +151,9 @@ impl<'db> MatchFinder<'db> {
     /// Returns matches for all added rules.
     pub fn matches(&self) -> SsrMatches {
         let mut matches = Vec::new();
+        let mut usage_cache = search::UsageCache::default();
         for rule in &self.rules {
-            self.find_matches_for_rule(rule, &mut matches);
+            self.find_matches_for_rule(rule, &mut usage_cache, &mut matches);
         }
         nester::nest_and_remove_collisions(matches, &self.sema)
     }
diff --git a/crates/ra_ssr/src/resolving.rs b/crates/ra_ssr/src/resolving.rs
index e9d052111..63fd217ce 100644
--- a/crates/ra_ssr/src/resolving.rs
+++ b/crates/ra_ssr/src/resolving.rs
@@ -22,6 +22,7 @@ pub(crate) struct ResolvedPattern {
 
 pub(crate) struct ResolvedPath {
     pub(crate) resolution: hir::PathResolution,
+    pub(crate) depth: u32,
 }
 
 impl ResolvedRule {
@@ -62,7 +63,7 @@ struct Resolver<'a, 'db> {
 impl Resolver<'_, '_> {
     fn resolve_pattern_tree(&self, pattern: SyntaxNode) -> Result<ResolvedPattern, SsrError> {
         let mut resolved_paths = FxHashMap::default();
-        self.resolve(pattern.clone(), &mut resolved_paths)?;
+        self.resolve(pattern.clone(), 0, &mut resolved_paths)?;
         Ok(ResolvedPattern {
             node: pattern,
             resolved_paths,
@@ -73,6 +74,7 @@ impl Resolver<'_, '_> {
     fn resolve(
         &self,
         node: SyntaxNode,
+        depth: u32,
         resolved_paths: &mut FxHashMap<SyntaxNode, ResolvedPath>,
     ) -> Result<(), SsrError> {
         use ra_syntax::ast::AstNode;
@@ -86,12 +88,12 @@ impl Resolver<'_, '_> {
                 let resolution = self
                     .resolve_path(&path)
                     .ok_or_else(|| error!("Failed to resolve path `{}`", node.text()))?;
-                resolved_paths.insert(node, ResolvedPath { resolution });
+                resolved_paths.insert(node, ResolvedPath { resolution, depth });
                 return Ok(());
             }
         }
         for node in node.children() {
-            self.resolve(node, resolved_paths)?;
+            self.resolve(node, depth + 1, resolved_paths)?;
         }
         Ok(())
     }
diff --git a/crates/ra_ssr/src/search.rs b/crates/ra_ssr/src/search.rs
index ccc2d544a..9a4e35e96 100644
--- a/crates/ra_ssr/src/search.rs
+++ b/crates/ra_ssr/src/search.rs
@@ -1,17 +1,106 @@
 //! Searching for matches.
 
-use crate::{matching, resolving::ResolvedRule, Match, MatchFinder};
+use crate::{
+    matching,
+    resolving::{ResolvedPath, ResolvedPattern, ResolvedRule},
+    Match, MatchFinder,
+};
 use ra_db::FileRange;
+use ra_ide_db::{
+    defs::Definition,
+    search::{Reference, SearchScope},
+};
 use ra_syntax::{ast, AstNode, SyntaxNode};
 
+/// A cache for the results of find_usages. This is for when we have multiple patterns that have the
+/// same path. e.g. if the pattern was `foo::Bar` that can parse as a path, an expression, a type
+/// and as a pattern. In each, the usages of `foo::Bar` are the same and we'd like to avoid finding
+/// them more than once.
+#[derive(Default)]
+pub(crate) struct UsageCache {
+    usages: Vec<(Definition, Vec<Reference>)>,
+}
+
 impl<'db> MatchFinder<'db> {
     /// Adds all matches for `rule` to `matches_out`. Matches may overlap in ways that make
     /// replacement impossible, so further processing is required in order to properly nest matches
     /// and remove overlapping matches. This is done in the `nesting` module.
-    pub(crate) fn find_matches_for_rule(&self, rule: &ResolvedRule, matches_out: &mut Vec<Match>) {
-        // FIXME: Use resolved paths in the pattern to find places to search instead of always
-        // scanning every node.
-        self.slow_scan(rule, matches_out);
+    pub(crate) fn find_matches_for_rule(
+        &self,
+        rule: &ResolvedRule,
+        usage_cache: &mut UsageCache,
+        matches_out: &mut Vec<Match>,
+    ) {
+        if pick_path_for_usages(&rule.pattern).is_none() {
+            self.slow_scan(rule, matches_out);
+            return;
+        }
+        self.find_matches_for_pattern_tree(rule, &rule.pattern, usage_cache, matches_out);
+    }
+
+    fn find_matches_for_pattern_tree(
+        &self,
+        rule: &ResolvedRule,
+        pattern: &ResolvedPattern,
+        usage_cache: &mut UsageCache,
+        matches_out: &mut Vec<Match>,
+    ) {
+        if let Some(first_path) = pick_path_for_usages(pattern) {
+            let definition: Definition = first_path.resolution.clone().into();
+            for reference in self.find_usages(usage_cache, definition) {
+                let file = self.sema.parse(reference.file_range.file_id);
+                if let Some(path) = self.sema.find_node_at_offset_with_descend::<ast::Path>(
+                    file.syntax(),
+                    reference.file_range.range.start(),
+                ) {
+                    if let Some(node_to_match) = self
+                        .sema
+                        .ancestors_with_macros(path.syntax().clone())
+                        .skip(first_path.depth as usize)
+                        .next()
+                    {
+                        if let Ok(m) =
+                            matching::get_match(false, rule, &node_to_match, &None, &self.sema)
+                        {
+                            matches_out.push(m);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn find_usages<'a>(
+        &self,
+        usage_cache: &'a mut UsageCache,
+        definition: Definition,
+    ) -> &'a [Reference] {
+        // Logically if a lookup succeeds we should just return it. Unfortunately returning it would
+        // extend the lifetime of the borrow, then we wouldn't be able to do the insertion on a
+        // cache miss. This is a limitation of NLL and is fixed with Polonius. For now we do two
+        // lookups in the case of a cache hit.
+        if usage_cache.find(&definition).is_none() {
+            let usages = definition.find_usages(&self.sema, Some(self.search_scope()));
+            usage_cache.usages.push((definition, usages));
+            return &usage_cache.usages.last().unwrap().1;
+        }
+        usage_cache.find(&definition).unwrap()
+    }
+
+    /// Returns the scope within which we want to search. We don't want un unrestricted search
+    /// scope, since we don't want to find references in external dependencies.
+    fn search_scope(&self) -> SearchScope {
+        // FIXME: We should ideally have a test that checks that we edit local roots and not library
+        // roots. This probably would require some changes to fixtures, since currently everything
+        // seems to get put into a single source root.
+        use ra_db::SourceDatabaseExt;
+        use ra_ide_db::symbol_index::SymbolsDatabase;
+        let mut files = Vec::new();
+        for &root in self.sema.db.local_roots().iter() {
+            let sr = self.sema.db.source_root(root);
+            files.extend(sr.iter());
+        }
+        SearchScope::files(&files)
     }
 
     fn slow_scan(&self, rule: &ResolvedRule, matches_out: &mut Vec<Match>) {
@@ -59,3 +148,35 @@ impl<'db> MatchFinder<'db> {
         }
     }
 }
+
+impl UsageCache {
+    fn find(&mut self, definition: &Definition) -> Option<&[Reference]> {
+        // We expect a very small number of cache entries (generally 1), so a linear scan should be
+        // fast enough and avoids the need to implement Hash for Definition.
+        for (d, refs) in &self.usages {
+            if d == definition {
+                return Some(refs);
+            }
+        }
+        None
+    }
+}
+
+/// Returns a path that's suitable for path resolution. We exclude builtin types, since they aren't
+/// something that we can find references to. We then somewhat arbitrarily pick the path that is the
+/// longest as this is hopefully more likely to be less common, making it faster to find.
+fn pick_path_for_usages(pattern: &ResolvedPattern) -> Option<&ResolvedPath> {
+    // FIXME: Take the scope of the resolved path into account. e.g. if there are any paths that are
+    // private to the current module, then we definitely would want to pick them over say a path
+    // from std. Possibly we should go further than this and intersect the search scopes for all
+    // resolved paths then search only in that scope.
+    pattern
+        .resolved_paths
+        .iter()
+        .filter(|(_, p)| {
+            !matches!(p.resolution, hir::PathResolution::Def(hir::ModuleDef::BuiltinType(_)))
+        })
+        .map(|(node, resolved)| (node.text().len(), resolved))
+        .max_by(|(a, _), (b, _)| a.cmp(b))
+        .map(|(_, resolved)| resolved)
+}