From f6ab61c80dfafd7fabb95aa88af6be14d1fc6767 Mon Sep 17 00:00:00 2001
From: Lewis Russell <lewis6991@gmail.com>
Date: Thu, 26 Feb 2026 16:05:53 +0000
Subject: [PATCH] fix(module): stabilize fuzzy require resolution across
 duplicate suffix matches

When multiple indexed modules share the same trailing require path (for
example plugin/treesitter-context.lua and lua/treesitter-context.lua),
fuzzy lookup previously returned the first inserted candidate. Because
indexing/insertion order can vary, require('treesitter-context') could
intermittently resolve to different files and sometimes degrade to any
when a non-exporting candidate won.

This change makes fuzzy resolution deterministic by selecting the best
match using:
- smallest leading-segment count before the requested module path
- lexicographic full-module-name tie-break for stable ordering

This preserves existing fuzzy behavior while removing insertion-order
flakiness.
---
 .../src/db_index/module/mod.rs                | 45 +++++++++++++------
 .../src/db_index/module/test.rs               | 23 ++++++++++
 2 files changed, 54 insertions(+), 14 deletions(-)

diff --git a/crates/emmylua_code_analysis/src/db_index/module/mod.rs b/crates/emmylua_code_analysis/src/db_index/module/mod.rs
index 5b2b9773d..5f21b6661 100644
--- a/crates/emmylua_code_analysis/src/db_index/module/mod.rs
+++ b/crates/emmylua_code_analysis/src/db_index/module/mod.rs
@@ -254,23 +254,40 @@ impl LuaModuleIndex {
         self.file_module_map.get(file_id)
     }
 
+    /// Find a module by suffix when exact lookup fails.
+    ///
+    /// Candidates must either exactly equal `module_path` or end with `.{module_path}`.
+    /// Among matches, prefer the one with the fewest leading path segments before the suffix,
+    /// then use lexicographic `full_module_name` ordering as a stable tie-break.
     fn fuzzy_find_module(&self, module_path: &str, last_name: &str) -> Option<&ModuleInfo> {
         let file_ids = self.module_name_to_file_ids.get(last_name)?;
         let suffix_with_boundary = format!(".{}", module_path);
-
-        // find the first matched module
-        for file_id in file_ids {
-            let module_info = self.file_module_map.get(file_id)?;
-            if module_info.full_module_name == module_path
-                || module_info
-                    .full_module_name
-                    .ends_with(&suffix_with_boundary)
-            {
-                return Some(module_info);
-            }
-        }
-
-        None
+        file_ids
+            .iter()
+            .filter_map(|file_id| {
+                let module_info = self.file_module_map.get(file_id)?;
+                let full_module_name = module_info.full_module_name.as_str();
+                let leading_segment_count = if full_module_name == module_path {
+                    Some(0)
+                } else {
+                    full_module_name
+                        .strip_suffix(&suffix_with_boundary)
+                        .map(|prefix| {
+                            prefix
+                                .split('.')
+                                .filter(|segment| !segment.is_empty())
+                                .count()
+                        })
+                }?;
+
+                Some((leading_segment_count, module_info))
+            })
+            .min_by(|(left_count, left_info), (right_count, right_info)| {
+                left_count
+                    .cmp(right_count)
+                    .then_with(|| left_info.full_module_name.cmp(&right_info.full_module_name))
+            })
+            .map(|(_, module_info)| module_info)
     }
 
     /// Find a module node by module path.
diff --git a/crates/emmylua_code_analysis/src/db_index/module/test.rs b/crates/emmylua_code_analysis/src/db_index/module/test.rs
index 490216ff9..0fc2d535d 100644
--- a/crates/emmylua_code_analysis/src/db_index/module/test.rs
+++ b/crates/emmylua_code_analysis/src/db_index/module/test.rs
@@ -187,4 +187,27 @@ mod tests {
         let module_info = m.find_module("event").unwrap();
         assert_eq!(module_info.full_module_name, "nvim-cmp.lua.cmp.utils.event");
     }
+
+    #[test]
+    fn test_require_fuzzy_match_prefers_shortest_prefix_independent_of_insert_order() {
+        const PLUGIN_ENTRY: &str = "C:/Users/username/Documents/plugin/treesitter-context.lua";
+        const LUA_ENTRY: &str = "C:/Users/username/Documents/lua/treesitter-context.lua";
+
+        // Validate both insertion orders to ensure lookup does not depend on indexing order.
+        for paths in [[PLUGIN_ENTRY, LUA_ENTRY], [LUA_ENTRY, PLUGIN_ENTRY]] {
+            let mut m = LuaModuleIndex::new();
+            m.update_config(Arc::new(Emmyrc::default()));
+            m.add_workspace_root(
+                Path::new("C:/Users/username/Documents").into(),
+                WorkspaceId::MAIN,
+            );
+
+            for (file_id, path) in [FileId { id: 1 }, FileId { id: 2 }].into_iter().zip(paths) {
+                m.add_module_by_path(file_id, path);
+            }
+
+            let module_info = m.find_module("treesitter-context").unwrap();
+            assert_eq!(module_info.full_module_name, "lua.treesitter-context");
+        }
+    }
 }