Emit diagnostics for unresolved imports and extern crates

crates/hir_def/src/diagnostics.rs

@@ -28,3 +28,45 @@ impl Diagnostic for UnresolvedModule {
         self
     }
 }
+
+#[derive(Debug)]
+pub struct UnresolvedExternCrate {
+    pub file: HirFileId,
+    pub item: AstPtr<ast::ExternCrate>,
+}
+
+impl Diagnostic for UnresolvedExternCrate {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("unresolved-extern-crate")
+    }
+    fn message(&self) -> String {
+        "unresolved extern crate".to_string()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.item.clone().into())
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct UnresolvedImport {
+    pub file: HirFileId,
+    pub node: AstPtr<ast::UseTree>,
+}
+
+impl Diagnostic for UnresolvedImport {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("unresolved-import")
+    }
+    fn message(&self) -> String {
+        "unresolved import".to_string()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.node.clone().into())
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}

crates/hir_def/src/item_tree.rs

@@ -291,7 +291,6 @@ pub enum AttrOwner {
 
     Variant(Idx<Variant>),
     Field(Idx<Field>),
-    // FIXME: Store variant and field attrs, and stop reparsing them in `attrs_query`.
 }
 
 macro_rules! from_attrs {
@@ -483,6 +482,11 @@ pub struct Import {
     /// AST ID of the `use` or `extern crate` item this import was derived from. Note that many
     /// `Import`s can map to the same `use` item.
     pub ast_id: FileAstId<ast::Use>,
+    /// Index of this `Import` when the containing `Use` is visited via `ModPath::expand_use_item`.
+    ///
+    /// This can be used to get the `UseTree` this `Import` corresponds to and allows emitting
+    /// precise diagnostics.
+    pub index: usize,
 }
 
 #[derive(Debug, Clone, Eq, PartialEq)]

crates/hir_def/src/item_tree/lower.rs

@@ -482,14 +482,15 @@ impl Ctx {
         ModPath::expand_use_item(
             InFile::new(self.file, use_item.clone()),
             &self.hygiene,
-            |path, _tree, is_glob, alias| {
+            |path, _use_tree, is_glob, alias| {
                 imports.push(id(tree.imports.alloc(Import {
                     path,
                     alias,
                     visibility,
                     is_glob,
                     is_prelude,
                     ast_id,
+                    index: imports.len(),
                 })));
             },
         );

crates/hir_def/src/item_tree/tests.rs

@@ -228,9 +228,9 @@ fn smoke() {
 
             top-level items:
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_on_use"))] }, input: None }]) }]
-            Import { path: ModPath { kind: Plain, segments: [Name(Text("a"))] }, alias: None, visibility: RawVisibilityId("pub(self)"), is_glob: false, is_prelude: false, ast_id: FileAstId::<syntax::ast::generated::nodes::Use>(0) }
+            Import { path: ModPath { kind: Plain, segments: [Name(Text("a"))] }, alias: None, visibility: RawVisibilityId("pub(self)"), is_glob: false, is_prelude: false, ast_id: FileAstId::<syntax::ast::generated::nodes::Use>(0), index: 0 }
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_on_use"))] }, input: None }]) }]
-            Import { path: ModPath { kind: Plain, segments: [Name(Text("b"))] }, alias: None, visibility: RawVisibilityId("pub(self)"), is_glob: true, is_prelude: false, ast_id: FileAstId::<syntax::ast::generated::nodes::Use>(0) }
+            Import { path: ModPath { kind: Plain, segments: [Name(Text("b"))] }, alias: None, visibility: RawVisibilityId("pub(self)"), is_glob: true, is_prelude: false, ast_id: FileAstId::<syntax::ast::generated::nodes::Use>(0), index: 1 }
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("ext_crate"))] }, input: None }]) }]
             ExternCrate { path: ModPath { kind: Plain, segments: [Name(Text("krate"))] }, alias: None, visibility: RawVisibilityId("pub(self)"), is_macro_use: false, ast_id: FileAstId::<syntax::ast::generated::nodes::ExternCrate>(1) }
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("on_trait"))] }, input: None }]) }]

crates/hir_def/src/nameres.rs

@@ -288,38 +288,107 @@ pub enum ModuleSource {
 
 mod diagnostics {
     use hir_expand::diagnostics::DiagnosticSink;
+    use hir_expand::hygiene::Hygiene;
+    use hir_expand::InFile;
     use syntax::{ast, AstPtr};
 
-    use crate::{db::DefDatabase, diagnostics::UnresolvedModule, nameres::LocalModuleId, AstId};
+    use crate::path::ModPath;
+    use crate::{db::DefDatabase, diagnostics::*, nameres::LocalModuleId, AstId};
 
     #[derive(Debug, PartialEq, Eq)]
-    pub(super) enum DefDiagnostic {
-        UnresolvedModule {
-            module: LocalModuleId,
-            declaration: AstId<ast::Module>,
-            candidate: String,
-        },
+    enum DiagnosticKind {
+        UnresolvedModule { declaration: AstId<ast::Module>, candidate: String },
+
+        UnresolvedExternCrate { ast: AstId<ast::ExternCrate> },
+
+        UnresolvedImport { ast: AstId<ast::Use>, index: usize },
+    }
+
+    #[derive(Debug, PartialEq, Eq)]
+    pub(super) struct DefDiagnostic {
+        in_module: LocalModuleId,
+        kind: DiagnosticKind,
     }
 
     impl DefDiagnostic {
+        pub(super) fn unresolved_module(
+            container: LocalModuleId,
+            declaration: AstId<ast::Module>,
+            candidate: String,
+        ) -> Self {
+            Self {
+                in_module: container,
+                kind: DiagnosticKind::UnresolvedModule { declaration, candidate },
+            }
+        }
+
+        pub(super) fn unresolved_extern_crate(
+            container: LocalModuleId,
+            declaration: AstId<ast::ExternCrate>,
+        ) -> Self {
+            Self {
+                in_module: container,
+                kind: DiagnosticKind::UnresolvedExternCrate { ast: declaration },
+            }
+        }
+
+        pub(super) fn unresolved_import(
+            container: LocalModuleId,
+            ast: AstId<ast::Use>,
+            index: usize,
+        ) -> Self {
+            Self { in_module: container, kind: DiagnosticKind::UnresolvedImport { ast, index } }
+        }
+
         pub(super) fn add_to(
             &self,
             db: &dyn DefDatabase,
             target_module: LocalModuleId,
             sink: &mut DiagnosticSink,
         ) {
-            match self {
-                DefDiagnostic::UnresolvedModule { module, declaration, candidate } => {
-                    if *module != target_module {
-                        return;
-                    }
+            if self.in_module != target_module {
+                return;
+            }
+
+            match &self.kind {
+                DiagnosticKind::UnresolvedModule { declaration, candidate } => {
                     let decl = declaration.to_node(db.upcast());
                     sink.push(UnresolvedModule {
                         file: declaration.file_id,
                         decl: AstPtr::new(&decl),
                         candidate: candidate.clone(),
                     })
                 }
+
+                DiagnosticKind::UnresolvedExternCrate { ast } => {
+                    let item = ast.to_node(db.upcast());
+                    sink.push(UnresolvedExternCrate {
+                        file: ast.file_id,
+                        item: AstPtr::new(&item),
+                    });
+                }
+
+                DiagnosticKind::UnresolvedImport { ast, index } => {
+                    let use_item = ast.to_node(db.upcast());
+                    let hygiene = Hygiene::new(db.upcast(), ast.file_id);
+                    let mut cur = 0;
+                    let mut tree = None;
+                    ModPath::expand_use_item(
+                        InFile::new(ast.file_id, use_item),
+                        &hygiene,
+                        |_mod_path, use_tree, _is_glob, _alias| {
+                            if cur == *index {
+                                tree = Some(use_tree.clone());
+                            }
+
+                            cur += 1;
+                        },
+                    );
+
+                    if let Some(tree) = tree {
+                        sink.push(UnresolvedImport { file: ast.file_id, node: AstPtr::new(&tree) });
+                    }
+                }
             }
         }
     }