internal: Make use of salsa's new NEVER_CHANGE durability

crates/base-db/src/change.rs

@@ -10,14 +10,14 @@ use vfs::FileId;
 
 use crate::{
     CrateGraphBuilder, CratesIdMap, LibraryRoots, LocalRoots, SourceDatabase, SourceRoot,
-    SourceRootId,
+    SourceRootId, SourceRootKind,
 };
 
 /// Encapsulate a bunch of raw `.set` calls on the database.
 #[derive(Default)]
 pub struct FileChange {
-    pub roots: Option<Vec<SourceRoot>>,
-    pub files_changed: Vec<(FileId, Option<String>)>,
+    pub roots: Option<Vec<(SourceRootId, SourceRoot)>>,
+    pub files_changed: Vec<(FileId, Option<String>, SourceRootKind)>,
     pub crate_graph: Option<CrateGraphBuilder>,
 }
 
@@ -38,12 +38,12 @@ impl fmt::Debug for FileChange {
 }
 
 impl FileChange {
-    pub fn set_roots(&mut self, roots: Vec<SourceRoot>) {
+    pub fn set_roots(&mut self, roots: Vec<(SourceRootId, SourceRoot)>) {
         self.roots = Some(roots);
     }
 
-    pub fn change_file(&mut self, file_id: FileId, new_text: Option<String>) {
-        self.files_changed.push((file_id, new_text))
+    pub fn change_file(&mut self, file_id: FileId, new_text: Option<String>, kind: SourceRootKind) {
+        self.files_changed.push((file_id, new_text, kind))
     }
 
     pub fn set_crate_graph(&mut self, graph: CrateGraphBuilder) {
@@ -55,13 +55,18 @@ impl FileChange {
         if let Some(roots) = self.roots {
             let mut local_roots = FxHashSet::default();
             let mut library_roots = FxHashSet::default();
-            for (idx, root) in roots.into_iter().enumerate() {
-                let root_id = SourceRootId(idx as u32);
+            for (root_id, root) in roots {
                 if root.is_library {
                     library_roots.insert(root_id);
                 } else {
                     local_roots.insert(root_id);
                 }
+                // Library source roots (and their file mappings) are stored with `NEVER_CHANGE`
+                // durability and are assumed immutable, so we emit them only once. Repartitioning
+                // re-produces them on every structural change; re-setting them would panic.
+                if root.is_library && db.is_source_root_initialized(root_id) {
+                    continue;
+                }
                 let durability = source_root_durability(&root);
                 for file_id in root.iter() {
                     db.set_file_source_root_with_durability(file_id, root_id, durability);
@@ -73,11 +78,8 @@ impl FileChange {
             LibraryRoots::get(db).set_roots(db).to(library_roots);
         }
 
-        for (file_id, text) in self.files_changed {
-            let source_root_id = db.file_source_root(file_id);
-            let source_root = db.source_root(source_root_id.source_root_id(db));
-
-            let durability = file_text_durability(&source_root.source_root(db));
+        for (file_id, text, kind) in self.files_changed {
+            let durability = kind.file_text_durability();
             // XXX: can't actually remove the file, just reset the text
             let text = text.unwrap_or_default();
             db.set_file_text_with_durability(file_id, &text, durability)
@@ -91,9 +93,5 @@ impl FileChange {
 }
 
 fn source_root_durability(source_root: &SourceRoot) -> Durability {
-    if source_root.is_library { Durability::MEDIUM } else { Durability::LOW }
-}
-
-fn file_text_durability(source_root: &SourceRoot) -> Durability {
-    if source_root.is_library { Durability::HIGH } else { Durability::LOW }
+    if source_root.is_library { Durability::NEVER_CHANGE } else { Durability::MEDIUM }
 }

crates/base-db/src/input.rs

@@ -124,6 +124,27 @@ impl SourceRoot {
     }
 }
 
+/// Whether a file or source root belongs to immutable library sources (sysroot,
+/// crates.io) or to the mutable local workspace.
+///
+/// Library sources are assumed to never change over the lifetime of the program,
+/// which lets us store their file text with [`salsa::Durability::NEVER_CHANGE`].
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
+pub enum SourceRootKind {
+    Local,
+    Library,
+}
+
+impl SourceRootKind {
+    /// Durability to use for the text of files belonging to a source root of this kind.
+    pub fn file_text_durability(self) -> Durability {
+        match self {
+            SourceRootKind::Local => Durability::LOW,
+            SourceRootKind::Library => Durability::NEVER_CHANGE,
+        }
+    }
+}
+
 #[derive(Default, Clone)]
 pub struct CrateGraphBuilder {
     arena: Arena<CrateBuilder>,
@@ -447,7 +468,7 @@ impl BuiltDependency {
 
 pub type CratesIdMap = FxHashMap<CrateBuilderId, Crate>;
 
-#[salsa_macros::input]
+#[salsa::input]
 #[derive(Debug, PartialOrd, Ord)]
 pub struct Crate {
     #[returns(ref)]

crates/base-db/src/lib.rs

@@ -29,7 +29,7 @@ pub use crate::{
         BuiltCrateData, BuiltDependency, Crate, CrateBuilder, CrateBuilderId, CrateDataBuilder,
         CrateDisplayName, CrateGraphBuilder, CrateName, CrateOrigin, CratesIdMap, CratesMap,
         DependencyBuilder, Env, ExtraCrateData, LangCrateOrigin, ProcMacroLoadingError,
-        ProcMacroPaths, ReleaseChannel, SourceRoot, SourceRootId, UniqueCrateData,
+        ProcMacroPaths, ReleaseChannel, SourceRoot, SourceRootId, SourceRootKind, UniqueCrateData,
     },
 };
 use dashmap::{DashMap, mapref::entry::Entry};
@@ -151,6 +151,11 @@ impl Files {
         *source_root
     }
 
+    /// Whether a source root with the given id has already been set.
+    pub fn is_source_root_initialized(&self, source_root_id: SourceRootId) -> bool {
+        self.source_roots.contains_key(&source_root_id)
+    }
+
     pub fn set_source_root_with_durability(
         &self,
         db: &mut dyn SourceDatabase,
@@ -236,19 +241,19 @@ pub struct LocalRoots {
     pub roots: FxHashSet<SourceRootId>,
 }
 
-#[salsa_macros::input(debug)]
+#[salsa::input(debug)]
 pub struct FileText {
     #[returns(ref)]
     pub text: Arc<str>,
     pub file_id: vfs::FileId,
 }
 
-#[salsa_macros::input(debug)]
+#[salsa::input(debug)]
 pub struct FileSourceRootInput {
     pub source_root_id: SourceRootId,
 }
 
-#[salsa_macros::input(debug)]
+#[salsa::input(debug)]
 pub struct SourceRootInput {
     pub source_root: Arc<SourceRoot>,
 }
@@ -270,6 +275,11 @@ pub trait SourceDatabase: salsa::Database {
     /// Contents of the source root.
     fn source_root(&self, id: SourceRootId) -> SourceRootInput;
 
+    /// Whether a source root with the given id has already been set.
+    ///
+    /// Unlike [`SourceDatabase::source_root`], this does not panic for unknown ids.
+    fn is_source_root_initialized(&self, id: SourceRootId) -> bool;
+
     fn file_source_root(&self, id: vfs::FileId) -> FileSourceRootInput;
 
     fn set_file_source_root_with_durability(

crates/hir-def/src/test_db.rs

@@ -111,6 +111,10 @@ impl SourceDatabase for TestDB {
         self.files.source_root(source_root_id)
     }
 
+    fn is_source_root_initialized(&self, source_root_id: SourceRootId) -> bool {
+        self.files.is_source_root_initialized(source_root_id)
+    }
+
     fn set_source_root_with_durability(
         &mut self,
         source_root_id: SourceRootId,

crates/hir-expand/src/change.rs

@@ -1,6 +1,8 @@
 //! Defines a unit of change that can applied to the database to get the next
 //! state. Changes are transactional.
-use base_db::{CrateGraphBuilder, FileChange, SourceRoot, salsa::Durability};
+use base_db::{
+    CrateGraphBuilder, FileChange, SourceRoot, SourceRootId, SourceRootKind, salsa::Durability,
+};
 use span::FileId;
 use triomphe::Arc;
 
@@ -25,8 +27,8 @@ impl ChangeWithProcMacros {
         }
     }
 
-    pub fn change_file(&mut self, file_id: FileId, new_text: Option<String>) {
-        self.source_change.change_file(file_id, new_text)
+    pub fn change_file(&mut self, file_id: FileId, new_text: Option<String>, kind: SourceRootKind) {
+        self.source_change.change_file(file_id, new_text, kind)
     }
 
     pub fn set_crate_graph(&mut self, graph: CrateGraphBuilder) {
@@ -37,7 +39,7 @@ impl ChangeWithProcMacros {
         self.proc_macros = Some(proc_macros);
     }
 
-    pub fn set_roots(&mut self, roots: Vec<SourceRoot>) {
+    pub fn set_roots(&mut self, roots: Vec<(SourceRootId, SourceRoot)>) {
         self.source_change.set_roots(roots)
     }
 }

crates/hir-ty/src/test_db.rs

@@ -101,6 +101,10 @@ impl SourceDatabase for TestDB {
         self.files.source_root(source_root_id)
     }
 
+    fn is_source_root_initialized(&self, source_root_id: SourceRootId) -> bool {
+        self.files.is_source_root_initialized(source_root_id)
+    }
+
     fn set_source_root_with_durability(
         &mut self,
         source_root_id: SourceRootId,

crates/ide-db/src/lib.rs

@@ -149,6 +149,10 @@ impl SourceDatabase for RootDatabase {
         self.files.source_root(source_root_id)
     }
 
+    fn is_source_root_initialized(&self, source_root_id: SourceRootId) -> bool {
+        self.files.is_source_root_initialized(source_root_id)
+    }
+
     fn set_source_root_with_durability(
         &mut self,
         source_root_id: SourceRootId,

crates/ide/src/lib.rs

@@ -136,7 +136,7 @@ pub use ide_completion::{
 pub use ide_db::{
     FileId, FilePosition, FileRange, RootDatabase, Severity, SymbolKind,
     assists::ExprFillDefaultMode,
-    base_db::{Crate, CrateGraphBuilder, FileChange, SourceRoot, SourceRootId},
+    base_db::{Crate, CrateGraphBuilder, FileChange, SourceRoot, SourceRootId, SourceRootKind},
     documentation::Documentation,
     label::Label,
     line_index::{LineCol, LineIndex},
@@ -263,7 +263,7 @@ impl Analysis {
         let source_root = SourceRoot::new_local(file_set);
 
         let mut change = ChangeWithProcMacros::default();
-        change.set_roots(vec![source_root]);
+        change.set_roots(vec![(SourceRootId(0), source_root)]);
         let mut crate_graph = CrateGraphBuilder::default();
         // FIXME: cfg options
         // Default to enable test for single file.
@@ -288,7 +288,7 @@ impl Analysis {
                 toolchain: None,
             }),
         );
-        change.change_file(file_id, Some(text));
+        change.change_file(file_id, Some(text), SourceRootKind::Local);
         change.set_crate_graph(crate_graph);
 
         host.apply_change(change);