Rollup merge of #127022 - adwinwhite:attrs, r=celinval

Support fetching `Attribute` of items.

Fixes [https://github.com/rust-lang/project-stable-mir/issues/83](https://github.com/rust-lang/project-stable-mir/issues/83)

`rustc_ast::ast::Attribute` doesn't impl `Hash` and `Eq`. Thus it cannot be directly used as key of `IndexMap` in `rustc_smir::rustc_smir::Tables` and we cannot define stable `Attribute` as index to `rustc_ast::ast::Attribute` like `Span` and many other stable definitions.

Since an string (or tokens) and its span contain all info about an attribute, I defined a simple `Attribute` struct on stable side.

I choose to fetch attributes via `tcx::get_attrs_by_path()` due to `get_attrs()` is marked as deprecated and `get_attrs_by_name()` cannot handle name of multiple segments like `rustfmt::skip`.

r? `@celinval`

compiler/rustc_smir/Cargo.toml

@@ -6,6 +6,8 @@ edition = "2021"
 [dependencies]
 # tidy-alphabetical-start
 rustc_abi = { path = "../rustc_abi" }
+rustc_ast = { path = "../rustc_ast" }
+rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_middle = { path = "../rustc_middle" }

compiler/rustc_smir/src/rustc_smir/context.rs

@@ -228,6 +228,46 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         }
     }
 
+    fn get_attrs_by_path(
+        &self,
+        def_id: stable_mir::DefId,
+        attr: &[stable_mir::Symbol],
+    ) -> Vec<stable_mir::crate_def::Attribute> {
+        let mut tables = self.0.borrow_mut();
+        let tcx = tables.tcx;
+        let did = tables[def_id];
+        let attr_name: Vec<_> =
+            attr.iter().map(|seg| rustc_span::symbol::Symbol::intern(&seg)).collect();
+        tcx.get_attrs_by_path(did, &attr_name)
+            .map(|attribute| {
+                let attr_str = rustc_ast_pretty::pprust::attribute_to_string(attribute);
+                let span = attribute.span;
+                stable_mir::crate_def::Attribute::new(attr_str, span.stable(&mut *tables))
+            })
+            .collect()
+    }
+
+    fn get_all_attrs(&self, def_id: stable_mir::DefId) -> Vec<stable_mir::crate_def::Attribute> {
+        let mut tables = self.0.borrow_mut();
+        let tcx = tables.tcx;
+        let did = tables[def_id];
+        let filter_fn = move |a: &&rustc_ast::ast::Attribute| {
+            matches!(a.kind, rustc_ast::ast::AttrKind::Normal(_))
+        };
+        let attrs_iter = if let Some(did) = did.as_local() {
+            tcx.hir().attrs(tcx.local_def_id_to_hir_id(did)).iter().filter(filter_fn)
+        } else {
+            tcx.item_attrs(did).iter().filter(filter_fn)
+        };
+        attrs_iter
+            .map(|attribute| {
+                let attr_str = rustc_ast_pretty::pprust::attribute_to_string(attribute);
+                let span = attribute.span;
+                stable_mir::crate_def::Attribute::new(attr_str, span.stable(&mut *tables))
+            })
+            .collect()
+    }
+
     fn span_to_string(&self, span: stable_mir::ty::Span) -> String {
         let tables = self.0.borrow();
         tables.tcx.sess.source_map().span_to_diagnostic_string(tables[span])

compiler/stable_mir/src/compiler_interface.rs

@@ -6,6 +6,7 @@
 use std::cell::Cell;
 
 use crate::abi::{FnAbi, Layout, LayoutShape};
+use crate::crate_def::Attribute;
 use crate::mir::alloc::{AllocId, GlobalAlloc};
 use crate::mir::mono::{Instance, InstanceDef, StaticDef};
 use crate::mir::{BinOp, Body, Place, UnOp};
@@ -55,6 +56,15 @@ pub trait Context {
     /// Returns the name of given `DefId`
     fn def_name(&self, def_id: DefId, trimmed: bool) -> Symbol;
 
+    /// Return attributes with the given attribute name.
+    ///
+    /// Single segmented name like `#[inline]` is specified as `&["inline".to_string()]`.
+    /// Multi-segmented name like `#[rustfmt::skip]` is specified as `&["rustfmt".to_string(), "skip".to_string()]`.
+    fn get_attrs_by_path(&self, def_id: DefId, attr: &[Symbol]) -> Vec<Attribute>;
+
+    /// Get all attributes of a definition.
+    fn get_all_attrs(&self, def_id: DefId) -> Vec<Attribute>;
+
     /// Returns printable, human readable form of `Span`
     fn span_to_string(&self, span: Span) -> String;
 

compiler/stable_mir/src/crate_def.rs

@@ -50,6 +50,21 @@ pub trait CrateDef {
         let def_id = self.def_id();
         with(|cx| cx.span_of_an_item(def_id))
     }
+
+    /// Return attributes with the given attribute name.
+    ///
+    /// Single segmented name like `#[inline]` is specified as `&["inline".to_string()]`.
+    /// Multi-segmented name like `#[rustfmt::skip]` is specified as `&["rustfmt".to_string(), "skip".to_string()]`.
+    fn attrs_by_path(&self, attr: &[Symbol]) -> Vec<Attribute> {
+        let def_id = self.def_id();
+        with(|cx| cx.get_attrs_by_path(def_id, attr))
+    }
+
+    /// Return all attributes of this definition.
+    fn all_attrs(&self) -> Vec<Attribute> {
+        let def_id = self.def_id();
+        with(|cx| cx.get_all_attrs(def_id))
+    }
 }
 
 /// A trait that can be used to retrieve a definition's type.
@@ -69,6 +84,28 @@ pub trait CrateDefType: CrateDef {
     }
 }
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Attribute {
+    value: String,
+    span: Span,
+}
+
+impl Attribute {
+    pub fn new(value: String, span: Span) -> Attribute {
+        Attribute { value, span }
+    }
+
+    /// Get the span of this attribute.
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    /// Get the string representation of this attribute.
+    pub fn as_str(&self) -> &str {
+        &self.value
+    }
+}
+
 macro_rules! crate_def {
     ( $(#[$attr:meta])*
       $vis:vis $name:ident $(;)?