3 files changed, 19 insertions, 8 deletions

diff --git a/crates/rust-analyzer/src/cli/load_cargo.rs b/crates/rust-analyzer/src/cli/load_cargo.rs
index d51f4a93a..e5ab6c73b 100644
--- a/crates/rust-analyzer/src/cli/load_cargo.rs
+++ b/crates/rust-analyzer/src/cli/load_cargo.rs
@@ -73,7 +73,7 @@ fn load(
             }
             vfs::loader::Message::Loaded { files } => {
                 for (path, contents) in files {
-                    vfs.set_file_contents(path.into(), contents)
+                    vfs.set_file_contents(path.into(), contents);
                 }
             }
         }
diff --git a/crates/rust-analyzer/src/main_loop.rs b/crates/rust-analyzer/src/main_loop.rs
index 95be2ebd3..d7f8374af 100644
--- a/crates/rust-analyzer/src/main_loop.rs
+++ b/crates/rust-analyzer/src/main_loop.rs
@@ -255,7 +255,7 @@ impl GlobalState {
                             for (path, contents) in files {
                                 let path = VfsPath::from(path);
                                 if !self.mem_docs.contains_key(&path) {
-                                    vfs.set_file_contents(path, contents)
+                                    vfs.set_file_contents(path, contents);
                                 }
                             }
                         }
@@ -503,11 +503,21 @@ impl GlobalState {
                     {
                         log::error!("duplicate DidOpenTextDocument: {}", path)
                     }
-                    this.vfs
+                    let changed = this
+                        .vfs
                         .write()
                         .0
                         .set_file_contents(path, Some(params.text_document.text.into_bytes()));
-                    this.maybe_update_diagnostics();
+
+                    // If the VFS contents are unchanged, update diagnostics, since `handle_event`
+                    // won't see any changes. This avoids missing diagnostics when opening a file.
+                    //
+                    // If the file *was* changed, `handle_event` will already recompute and send
+                    // diagnostics. We can't do it here, since the *current* file contents might be
+                    // unset in salsa, since the VFS change hasn't been applied to the database yet.
+                    if !changed {
+                        this.maybe_update_diagnostics();
+                    }
                 }
                 Ok(())
             })?
diff --git a/crates/vfs/src/lib.rs b/crates/vfs/src/lib.rs
index cdf6f1fd0..a2c6a3400 100644
--- a/crates/vfs/src/lib.rs
+++ b/crates/vfs/src/lib.rs
@@ -99,18 +99,19 @@ impl Vfs {
                 (file_id, path)
             })
     }
-    pub fn set_file_contents(&mut self, path: VfsPath, contents: Option<Vec<u8>>) {
+    pub fn set_file_contents(&mut self, path: VfsPath, contents: Option<Vec<u8>>) -> bool {
         let file_id = self.alloc_file_id(path);
         let change_kind = match (&self.get(file_id), &contents) {
-            (None, None) => return,
+            (None, None) => return false,
             (None, Some(_)) => ChangeKind::Create,
             (Some(_), None) => ChangeKind::Delete,
-            (Some(old), Some(new)) if old == new => return,
+            (Some(old), Some(new)) if old == new => return false,
             (Some(_), Some(_)) => ChangeKind::Modify,
         };
 
         *self.get_mut(file_id) = contents;
-        self.changes.push(ChangedFile { file_id, change_kind })
+        self.changes.push(ChangedFile { file_id, change_kind });
+        true
     }
     pub fn has_changes(&self) -> bool {
         !self.changes.is_empty()