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, 76 insertions, 3 deletions

diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index cff7e7481..5fd602a9e 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -36,7 +36,9 @@ use crate::{
     path::{GenericArgs, GenericArg},
     adt::VariantDef,
     resolve::{Resolver, Resolution},
-    nameres::Namespace
+    nameres::Namespace,
+    ty::infer::diagnostics::InferenceDiagnostic,
+    diagnostics::DiagnosticSink,
 };
 use super::{Ty, TypableDef, Substs, primitive, op, FnSig, ApplicationTy, TypeCtor};
 
@@ -96,6 +98,7 @@ pub struct InferenceResult {
     field_resolutions: FxHashMap<ExprId, StructField>,
     /// For each associated item record what it resolves to
     assoc_resolutions: FxHashMap<ExprOrPatId, ImplItem>,
+    diagnostics: Vec<InferenceDiagnostic>,
     pub(super) type_of_expr: ArenaMap<ExprId, Ty>,
     pub(super) type_of_pat: ArenaMap<PatId, Ty>,
 }
@@ -113,6 +116,14 @@ impl InferenceResult {
     pub fn assoc_resolutions_for_pat(&self, id: PatId) -> Option<ImplItem> {
         self.assoc_resolutions.get(&id.into()).map(|it| *it)
     }
+    pub(crate) fn add_diagnostics(
+        &self,
+        db: &impl HirDatabase,
+        owner: Function,
+        sink: &mut DiagnosticSink,
+    ) {
+        self.diagnostics.iter().for_each(|it| it.add_to(db, owner, sink))
+    }
 }
 
 impl Index<ExprId> for InferenceResult {
@@ -143,6 +154,7 @@ struct InferenceContext<'a, D: HirDatabase> {
     assoc_resolutions: FxHashMap<ExprOrPatId, ImplItem>,
     type_of_expr: ArenaMap<ExprId, Ty>,
     type_of_pat: ArenaMap<PatId, Ty>,
+    diagnostics: Vec<InferenceDiagnostic>,
     /// The return type of the function being inferred.
     return_ty: Ty,
 }
@@ -155,6 +167,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             assoc_resolutions: FxHashMap::default(),
             type_of_expr: ArenaMap::default(),
             type_of_pat: ArenaMap::default(),
+            diagnostics: Vec::default(),
             var_unification_table: InPlaceUnificationTable::new(),
             return_ty: Ty::Unknown, // set in collect_fn_signature
             db,
@@ -181,6 +194,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             assoc_resolutions: self.assoc_resolutions,
             type_of_expr: expr_types,
             type_of_pat: pat_types,
+            diagnostics: self.diagnostics,
         }
     }
 
@@ -915,9 +929,18 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             Expr::StructLit { path, fields, spread } => {
                 let (ty, def_id) = self.resolve_variant(path.as_ref());
                 let substs = ty.substs().unwrap_or_else(Substs::empty);
-                for field in fields {
+                for (field_idx, field) in fields.into_iter().enumerate() {
                     let field_ty = def_id
-                        .and_then(|it| it.field(self.db, &field.name))
+                        .and_then(|it| match it.field(self.db, &field.name) {
+                            Some(field) => Some(field),
+                            None => {
+                                self.diagnostics.push(InferenceDiagnostic::NoSuchField {
+                                    expr: tgt_expr,
+                                    field: field_idx,
+                                });
+                                None
+                            }
+                        })
                         .map_or(Ty::Unknown, |field| field.ty(self.db))
                         .subst(&substs);
                     self.infer_expr(field.expr, &Expectation::has_type(field_ty));
@@ -1244,3 +1267,29 @@ impl Expectation {
         Expectation { ty: Ty::Unknown }
     }
 }
+
+mod diagnostics {
+    use crate::{expr::ExprId, diagnostics::{DiagnosticSink, NoSuchField}, HirDatabase, Function};
+
+    #[derive(Debug, PartialEq, Eq, Clone)]
+    pub(super) enum InferenceDiagnostic {
+        NoSuchField { expr: ExprId, field: usize },
+    }
+
+    impl InferenceDiagnostic {
+        pub(super) fn add_to(
+            &self,
+            db: &impl HirDatabase,
+            owner: Function,
+            sink: &mut DiagnosticSink,
+        ) {
+            match self {
+                InferenceDiagnostic::NoSuchField { expr, field } => {
+                    let (file, _) = owner.source(db);
+                    let field = owner.body_source_map(db).field_syntax(*expr, *field);
+                    sink.push(NoSuchField { file, field })
+                }
+            }
+        }
+    }
+}
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 5d8ad4aa7..3aedba243 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -2319,3 +2319,27 @@ fn typing_whitespace_inside_a_function_should_not_invalidate_types() {
         assert!(!format!("{:?}", events).contains("infer"), "{:#?}", events)
     }
 }
+
+#[test]
+fn no_such_field_diagnostics() {
+    let diagnostics = MockDatabase::with_files(
+        r"
+        //- /lib.rs
+        struct S { foo: i32, bar: () }
+        impl S {
+            fn new() -> S {
+                S {
+                    foo: 92,
+                    baz: 62,
+                }
+            }
+        }
+        ",
+    )
+    .diagnostics();
+
+    assert_snapshot_matches!(diagnostics, @r###"
+"baz: 62": no such field
+"###
+    );
+}