Merge #1034

1034: HIR diagnostics API r=matklad a=matklad

This PR introduces diagnostics API for HIR, so we can now start issuing errors and warnings! Here are requirements that this solution aims to fulfill:

* structured diagnostics: rather than immediately rendering error to string, we provide a well-typed blob of data with error-description. These data is used by IDE to provide fixes
* open set diagnostics: there's no single enum with all possible diagnostics, which hopefully should result in better modularity

The `Diagnostic` trait describes "a diagnostic", which can be downcast to a specific diagnostic kind. Diagnostics are expressed in terms of macro-expanded syntax tree: they store pointers to syntax nodes. Diagnostics are self-contained: you don't need any context, besides `db`, to fully understand the meaning of a diagnostic. 

Because diagnostics are tied to the source, we can't store them in salsa. So subsystems like type-checking produce subsystem-local diagnostic (which is a closed `enum`), which is expressed in therms of subsystem IR. A separate step converts these proto-diagnostics into `Diagnostic`, by merging them with source-maps.

Note that this PR stresses type-system quite a bit: we now type-check every function in open files to compute errors!

Discussion on Zulip: https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0/topic/Diagnostics.20API

Co-authored-by: Aleksey Kladov <[email protected]>

2 files changed, 53 insertions, 36 deletions

diff --git a/crates/ra_hir/src/nameres/collector.rs b/crates/ra_hir/src/nameres/collector.rs
index c5b73cfbe..8830b4624 100644
--- a/crates/ra_hir/src/nameres/collector.rs
+++ b/crates/ra_hir/src/nameres/collector.rs
@@ -6,14 +6,17 @@ use ra_db::FileId;
 
 use crate::{
     Function, Module, Struct, Enum, Const, Static, Trait, TypeAlias,
-    DefDatabase, HirFileId, Name, Path, Problem, Crate,
+    DefDatabase, HirFileId, Name, Path, Crate,
     KnownName,
-    nameres::{Resolution, PerNs, ModuleDef, ReachedFixedPoint, ResolveMode, raw},
+    nameres::{
+        Resolution, PerNs, ModuleDef, ReachedFixedPoint, ResolveMode,
+        CrateDefMap, CrateModuleId, ModuleData, CrateMacroId,
+        diagnostics::DefDiagnostic,
+        raw,
+    },
     ids::{AstItemDef, LocationCtx, MacroCallLoc, SourceItemId, MacroCallId},
 };
 
-use super::{CrateDefMap, CrateModuleId, ModuleData, CrateMacroId};
-
 pub(super) fn collect_defs(db: &impl DefDatabase, mut def_map: CrateDefMap) -> CrateDefMap {
     // populate external prelude
     for dep in def_map.krate.dependencies(db) {
@@ -405,25 +408,27 @@ where
             raw::ModuleData::Declaration { name, source_item_id } => {
                 let source_item_id = source_item_id.with_file_id(self.file_id);
                 let is_root = self.def_collector.def_map.modules[self.module_id].parent.is_none();
-                let (file_ids, problem) =
-                    resolve_submodule(self.def_collector.db, self.file_id, name, is_root);
-
-                if let Some(problem) = problem {
-                    self.def_collector.def_map.problems.add(source_item_id, problem)
-                }
-
-                if let Some(&file_id) = file_ids.first() {
-                    let module_id =
-                        self.push_child_module(name.clone(), source_item_id, Some(file_id));
-                    let raw_items = self.def_collector.db.raw_items(file_id);
-                    ModCollector {
-                        def_collector: &mut *self.def_collector,
-                        module_id,
-                        file_id: file_id.into(),
-                        raw_items: &raw_items,
+                match resolve_submodule(self.def_collector.db, self.file_id, name, is_root) {
+                    Ok(file_id) => {
+                        let module_id =
+                            self.push_child_module(name.clone(), source_item_id, Some(file_id));
+                        let raw_items = self.def_collector.db.raw_items(file_id);
+                        ModCollector {
+                            def_collector: &mut *self.def_collector,
+                            module_id,
+                            file_id: file_id.into(),
+                            raw_items: &raw_items,
+                        }
+                        .collect(raw_items.items())
                     }
-                    .collect(raw_items.items())
-                }
+                    Err(candidate) => self.def_collector.def_map.diagnostics.push(
+                        DefDiagnostic::UnresolvedModule {
+                            module: self.module_id,
+                            declaration: source_item_id,
+                            candidate,
+                        },
+                    ),
+                };
             }
         }
     }
@@ -524,7 +529,7 @@ fn resolve_submodule(
     file_id: HirFileId,
     name: &Name,
     is_root: bool,
-) -> (Vec<FileId>, Option<Problem>) {
+) -> Result<FileId, RelativePathBuf> {
     // FIXME: handle submodules of inline modules properly
     let file_id = file_id.original_file(db);
     let source_root_id = db.file_source_root(file_id);
@@ -545,17 +550,10 @@ fn resolve_submodule(
         candidates.push(file_dir_mod.clone());
     };
     let sr = db.source_root(source_root_id);
-    let points_to = candidates
-        .into_iter()
-        .filter_map(|path| sr.files.get(&path))
-        .map(|&it| it)
-        .collect::<Vec<_>>();
-    let problem = if points_to.is_empty() {
-        Some(Problem::UnresolvedModule {
-            candidate: if is_dir_owner { file_mod } else { file_dir_mod },
-        })
-    } else {
-        None
-    };
-    (points_to, problem)
+    let mut points_to = candidates.into_iter().filter_map(|path| sr.files.get(&path)).map(|&it| it);
+    // FIXME: handle ambiguity
+    match points_to.next() {
+        Some(file_id) => Ok(file_id),
+        None => Err(if is_dir_owner { file_mod } else { file_dir_mod }),
+    }
 }
diff --git a/crates/ra_hir/src/nameres/tests.rs b/crates/ra_hir/src/nameres/tests.rs
index ac9b88520..572bd1bf7 100644
--- a/crates/ra_hir/src/nameres/tests.rs
+++ b/crates/ra_hir/src/nameres/tests.rs
@@ -552,3 +552,22 @@ foo: v
 "###
     );
 }
+
+#[test]
+fn unresolved_module_diagnostics() {
+    let diagnostics = MockDatabase::with_files(
+        r"
+        //- /lib.rs
+        mod foo;
+        mod bar;
+        mod baz {}
+        //- /foo.rs
+        ",
+    )
+    .diagnostics();
+
+    assert_snapshot_matches!(diagnostics, @r###"
+"mod bar;": unresolved module
+"###
+    );
+}