internal: start new diagnostics API

At the moment, this moves only a single diagnostic, but the idea is
reafactor the rest to use the same pattern. We are going to have a
single file per diagnostic. This file will define diagnostics code,
rendering range and fixes, if any. It'll also have all of the tests.
This is similar to how we deal with assists.

After we refactor all diagnostics to follow this pattern, we'll probably
move them to a new `ide_diagnostics` crate.

Not that we intentionally want to test all diagnostics on this layer,
despite the fact that they are generally emitted in the guts on the
compiler. Diagnostics care to much about the end presentation
details/fixes to be worth-while "unit" testing. So, we'll unit-test only
the primary output of compilation process (types and name res tables),
and will use integrated UI tests for diagnostics.

1 files changed, 18 insertions, 14 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index bd923cba8..ff6c68dbc 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -80,18 +80,18 @@ use tt::{Ident, Leaf, Literal, TokenTree};
 
 use crate::{
     db::{DefDatabase, HirDatabase},
-    diagnostics::{
-        BreakOutsideOfLoop, InactiveCode, InternalBailedOut, MacroError, MismatchedArgCount,
-        MissingFields, MissingMatchArms, MissingOkOrSomeInTailExpr, MissingPatFields,
-        MissingUnsafe, NoSuchField, RemoveThisSemicolon, ReplaceFilterMapNextWithFindMap,
-        UnimplementedBuiltinMacro, UnresolvedExternCrate, UnresolvedImport, UnresolvedMacroCall,
-        UnresolvedModule, UnresolvedProcMacro,
-    },
     diagnostics_sink::DiagnosticSink,
 };
 
 pub use crate::{
     attrs::{HasAttrs, Namespace},
+    diagnostics::{
+        AnyDiagnostic, BreakOutsideOfLoop, InactiveCode, InternalBailedOut, MacroError,
+        MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkOrSomeInTailExpr,
+        MissingPatFields, MissingUnsafe, NoSuchField, RemoveThisSemicolon,
+        ReplaceFilterMapNextWithFindMap, UnimplementedBuiltinMacro, UnresolvedExternCrate,
+        UnresolvedImport, UnresolvedMacroCall, UnresolvedModule, UnresolvedProcMacro,
+    },
     has_source::HasSource,
     semantics::{PathResolution, Semantics, SemanticsScope},
 };
@@ -460,10 +460,11 @@ impl Module {
         db: &dyn HirDatabase,
         sink: &mut DiagnosticSink,
         internal_diagnostics: bool,
-    ) {
+    ) -> Vec<AnyDiagnostic> {
         let _p = profile::span("Module::diagnostics").detail(|| {
             format!("{:?}", self.name(db).map_or("<unknown>".into(), |name| name.to_string()))
         });
+        let mut acc: Vec<AnyDiagnostic> = Vec::new();
         let def_map = self.id.def_map(db.upcast());
         for diag in def_map.diagnostics() {
             if diag.in_module != self.id.local_id {
@@ -473,11 +474,13 @@ impl Module {
             match &diag.kind {
                 DefDiagnosticKind::UnresolvedModule { ast: declaration, candidate } => {
                     let decl = declaration.to_node(db.upcast());
-                    sink.push(UnresolvedModule {
-                        file: declaration.file_id,
-                        decl: AstPtr::new(&decl),
-                        candidate: candidate.clone(),
-                    })
+                    acc.push(
+                        UnresolvedModule {
+                            decl: InFile::new(declaration.file_id, AstPtr::new(&decl)),
+                            candidate: candidate.clone(),
+                        }
+                        .into(),
+                    )
                 }
                 DefDiagnosticKind::UnresolvedExternCrate { ast } => {
                     let item = ast.to_node(db.upcast());
@@ -610,7 +613,7 @@ impl Module {
                 crate::ModuleDef::Module(m) => {
                     // Only add diagnostics from inline modules
                     if def_map[m.id.local_id].origin.is_inline() {
-                        m.diagnostics(db, sink, internal_diagnostics)
+                        acc.extend(m.diagnostics(db, sink, internal_diagnostics))
                     }
                 }
                 _ => {
@@ -626,6 +629,7 @@ impl Module {
                 }
             }
         }
+        acc
     }
 
     pub fn declarations(self, db: &dyn HirDatabase) -> Vec<ModuleDef> {