Unnamed repository; edit this file 'description' to name the repository.
Diffstat (limited to 'crates/hir_expand/src/builtin_attr_macro.rs')
| -rw-r--r-- | crates/hir_expand/src/builtin_attr_macro.rs | 80 |
1 files changed, 36 insertions, 44 deletions
diff --git a/crates/hir_expand/src/builtin_attr_macro.rs b/crates/hir_expand/src/builtin_attr_macro.rs index 1996624598..6301da1c83 100644 --- a/crates/hir_expand/src/builtin_attr_macro.rs +++ b/crates/hir_expand/src/builtin_attr_macro.rs @@ -82,30 +82,47 @@ fn dummy_attr_expand( ExpandResult::ok(tt.clone()) } +/// We generate a very specific expansion here, as we do not actually expand the `#[derive]` attribute +/// itself in name res, but we do want to expand it to something for the IDE layer, so that the input +/// derive attributes can be downmapped, and resolved as proper paths. +/// This is basically a hack, that simplifies the hacks we need in a lot of ide layer places to +/// somewhat inconsistently resolve derive attributes. +/// +/// As such, we expand `#[derive(Foo, bar::Bar)]` into +/// ``` +/// #[Foo] +/// #[bar::Bar] +/// (); +/// ``` +/// which allows fallback path resolution in hir::Semantics to properly identify our derives. +/// Since we do not expand the attribute in nameres though, we keep the original item. +/// +/// The ideal expansion here would be for the `#[derive]` to re-emit the annotated item and somehow +/// use the input paths in its output as well. +/// But that would bring two problems with it, for one every derive would duplicate the item token tree +/// wasting a lot of memory, and it would also require some way to use a path in a way that makes it +/// always resolve as a derive without nameres recollecting them. +/// So this hacky approach is a lot more friendly for us, though it does require a bit of support in +/// [`hir::Semantics`] to make this work. fn derive_attr_expand( db: &dyn AstDatabase, id: MacroCallId, tt: &tt::Subtree, ) -> ExpandResult<tt::Subtree> { - // we generate a very specific expansion here, as we do not actually expand the `#[derive]` attribute - // itself in name res, but we do want to expand it to something for the IDE layer, so that the input - // derive attributes can be downmapped, and resolved - // This is basically a hack, to get rid of hacks in the IDE layer that slowly accumulate more and more - // in various places. - - // we transform the token tree of `#[derive(Foo, bar::Bar)]` into - // ``` - // #[Foo] - // #[bar::Bar] - // (); - // ``` - // which allows fallback path resolution in hir::Semantics to properly identify our derives let loc = db.lookup_intern_macro_call(id); let derives = match &loc.kind { MacroCallKind::Attr { attr_args, .. } => &attr_args.0, _ => return ExpandResult::ok(tt.clone()), }; + let mk_leaf = |char| { + tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { + char, + spacing: tt::Spacing::Alone, + id: tt::TokenId::unspecified(), + })) + }; + let mut token_trees = Vec::new(); for (comma, group) in &derives .token_trees @@ -119,38 +136,13 @@ fn derive_attr_expand( if comma { continue; } - let wrap = |leaf| tt::TokenTree::Leaf(tt::Leaf::Punct(leaf)); - token_trees.push(wrap(tt::Punct { - char: '#', - spacing: tt::Spacing::Alone, - id: tt::TokenId::unspecified(), - })); - token_trees.push(wrap(tt::Punct { - char: '[', - spacing: tt::Spacing::Alone, - id: tt::TokenId::unspecified(), - })); + token_trees.push(mk_leaf('#')); + token_trees.push(mk_leaf('[')); token_trees.extend(group.cloned().map(tt::TokenTree::Leaf)); - token_trees.push(wrap(tt::Punct { - char: ']', - spacing: tt::Spacing::Alone, - id: tt::TokenId::unspecified(), - })); - token_trees.push(wrap(tt::Punct { - char: '(', - spacing: tt::Spacing::Alone, - id: tt::TokenId::unspecified(), - })); - token_trees.push(wrap(tt::Punct { - char: ')', - spacing: tt::Spacing::Alone, - id: tt::TokenId::unspecified(), - })); - token_trees.push(wrap(tt::Punct { - char: ';', - spacing: tt::Spacing::Alone, - id: tt::TokenId::unspecified(), - })); + token_trees.push(mk_leaf(']')); } + token_trees.push(mk_leaf('(')); + token_trees.push(mk_leaf(')')); + token_trees.push(mk_leaf(';')); ExpandResult::ok(tt::Subtree { delimiter: tt.delimiter, token_trees }) } |