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, 13 insertions, 2 deletions

diff --git a/crates/ra_hir/src/expr.rs b/crates/ra_hir/src/expr.rs
index c37fd0454..a85422955 100644
--- a/crates/ra_hir/src/expr.rs
+++ b/crates/ra_hir/src/expr.rs
@@ -5,7 +5,7 @@ use rustc_hash::FxHashMap;
 
 use ra_arena::{Arena, RawId, impl_arena_id, map::ArenaMap};
 use ra_syntax::{
-    SyntaxNodePtr, AstNode,
+    SyntaxNodePtr, AstPtr, AstNode,
     ast::{self, LoopBodyOwner, ArgListOwner, NameOwner, LiteralFlavor, TypeAscriptionOwner}
 };
 
@@ -54,6 +54,7 @@ pub struct BodySourceMap {
     expr_map_back: ArenaMap<ExprId, SyntaxNodePtr>,
     pat_map: FxHashMap<SyntaxNodePtr, PatId>,
     pat_map_back: ArenaMap<PatId, SyntaxNodePtr>,
+    field_map: FxHashMap<(ExprId, usize), AstPtr<ast::NamedField>>,
 }
 
 impl Body {
@@ -138,6 +139,10 @@ impl BodySourceMap {
     pub fn node_pat(&self, node: &ast::Pat) -> Option<PatId> {
         self.pat_map.get(&SyntaxNodePtr::new(node.syntax())).cloned()
     }
+
+    pub fn field_syntax(&self, expr: ExprId, field: usize) -> AstPtr<ast::NamedField> {
+        self.field_map[&(expr, field)].clone()
+    }
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]
@@ -629,8 +634,10 @@ impl ExprCollector {
             }
             ast::ExprKind::StructLit(e) => {
                 let path = e.path().and_then(Path::from_ast);
+                let mut field_ptrs = Vec::new();
                 let fields = if let Some(nfl) = e.named_field_list() {
                     nfl.fields()
+                        .inspect(|field| field_ptrs.push(AstPtr::new(*field)))
                         .map(|field| StructLitField {
                             name: field
                                 .name_ref()
@@ -657,7 +664,11 @@ impl ExprCollector {
                     Vec::new()
                 };
                 let spread = e.spread().map(|s| self.collect_expr(s));
-                self.alloc_expr(Expr::StructLit { path, fields, spread }, syntax_ptr)
+                let res = self.alloc_expr(Expr::StructLit { path, fields, spread }, syntax_ptr);
+                for (i, ptr) in field_ptrs.into_iter().enumerate() {
+                    self.source_map.field_map.insert((res, i), ptr);
+                }
+                res
             }
             ast::ExprKind::FieldExpr(e) => {
                 let expr = self.collect_expr_opt(e.expr());