test(code_gen): add incremental compilation test

crates/mun_codegen/Cargo.toml

@@ -27,6 +27,7 @@ features = ["llvm7-0"]
 
 [dev-dependencies]
 insta = "0.12.0"
+parking_lot = "0.10"
 
 [build-dependencies]
 semver = "0.9.0"

crates/mun_codegen/src/mock.rs

@@ -1,5 +1,6 @@
 use crate::{IrDatabase, OptimizationLevel};
 use hir::{FileId, RelativePathBuf, SourceDatabase, SourceRoot, SourceRootId};
+use parking_lot::Mutex;
 use std::sync::Arc;
 
 /// A mock implementation of the IR database. It can be used to set up a simple test case.
@@ -12,12 +13,20 @@ use std::sync::Arc;
 #[derive(Default, Debug)]
 pub(crate) struct MockDatabase {
     runtime: salsa::Runtime<MockDatabase>,
+    events: Mutex<Option<Vec<salsa::Event<MockDatabase>>>>,
 }
 
 impl salsa::Database for MockDatabase {
     fn salsa_runtime(&self) -> &salsa::Runtime<MockDatabase> {
         &self.runtime
     }
+
+    fn salsa_event(&self, event: impl Fn() -> salsa::Event<MockDatabase>) {
+        let mut events = self.events.lock();
+        if let Some(events) = &mut *events {
+            events.push(event());
+        }
+    }
 }
 
 impl MockDatabase {
@@ -43,4 +52,25 @@ impl MockDatabase {
         db.set_context(Arc::new(context));
         (db, file_id)
     }
+
+    pub fn log(&self, f: impl FnOnce()) -> Vec<salsa::Event<MockDatabase>> {
+        *self.events.lock() = Some(Vec::new());
+        f();
+        self.events.lock().take().unwrap()
+    }
+
+    pub fn log_executed(&self, f: impl FnOnce()) -> Vec<String> {
+        let events = self.log(f);
+        events
+            .into_iter()
+            .filter_map(|e| match e.kind {
+                // This pretty horrible, but `Debug` is the only way to inspect
+                // QueryDescriptor at the moment.
+                salsa::EventKind::WillExecute { database_key } => {
+                    Some(format!("{:?}", database_key))
+                }
+                _ => None,
+            })
+            .collect()
+    }
 }

crates/mun_codegen/src/test.rs

@@ -479,6 +479,51 @@ fn extern_fn() {
     )
 }
 
+#[test]
+fn incremental_compilation() {
+    let (mut db, file_id) = MockDatabase::with_single_file(
+        r#"
+        struct Foo(int);
+
+        pub fn foo(foo: Foo):int {
+            foo.0
+        }
+        "#,
+    );
+    db.set_optimization_lvl(OptimizationLevel::Default);
+    db.set_target(Target::host_target().unwrap());
+
+    {
+        let events = db.log_executed(|| {
+            db.file_ir(file_id);
+        });
+        assert!(
+            format!("{:?}", events).contains("group_ir"),
+            "{:#?}",
+            events
+        );
+        assert!(format!("{:?}", events).contains("file_ir"), "{:#?}", events);
+    }
+
+    db.set_optimization_lvl(OptimizationLevel::Aggressive);
+
+    {
+        let events = db.log_executed(|| {
+            db.file_ir(file_id);
+        });
+        println!("events: {:?}", events);
+        assert!(
+            !format!("{:?}", events).contains("group_ir"),
+            "{:#?}",
+            events
+        );
+        assert!(format!("{:?}", events).contains("file_ir"), "{:#?}", events);
+    }
+
+    // TODO: Try to disconnect `group_ir` and `file_ir`
+    // TODO: Add support for multiple files in a group
+}
+
 fn test_snapshot(text: &str) {
     test_snapshot_with_optimization(text, OptimizationLevel::Default);
 }