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]>

1 files changed, 24 insertions, 0 deletions

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
+"###
+    );
+}