[experiment] Eagerly expand cfg and cfg_attr in all attribute inputs

Author: petrochenkov

compiler/rustc_builtin_macros/src/cfg_eval.rs

@@ -2,7 +2,6 @@ use crate::util::check_builtin_macro_attribute;
 
 use rustc_ast as ast;
 use rustc_expand::base::{Annotatable, ExtCtxt};
-use rustc_expand::config::cfg_eval;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 
@@ -13,5 +12,5 @@ crate fn expand(
     annotatable: Annotatable,
 ) -> Vec<Annotatable> {
     check_builtin_macro_attribute(ecx, meta_item, sym::cfg_eval);
-    cfg_eval(ecx, annotatable)
+    vec![annotatable]
 }

compiler/rustc_builtin_macros/src/derive.rs

@@ -1,7 +1,6 @@
 use rustc_ast::{self as ast, attr, token, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
 use rustc_errors::{struct_span_err, Applicability};
 use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
-use rustc_expand::config::cfg_eval;
 use rustc_feature::AttributeTemplate;
 use rustc_parse::validate_attr;
 use rustc_session::Session;
@@ -58,7 +57,7 @@ impl MultiItemModifier for Expander {
             });
 
         match result {
-            Ok(()) => ExpandResult::Ready(cfg_eval(ecx, item)),
+            Ok(()) => ExpandResult::Ready(vec![item]),
             Err(Indeterminate) => ExpandResult::Retry(item),
         }
     }

compiler/rustc_expand/src/config.rs

@@ -547,16 +547,15 @@ fn is_cfg(sess: &Session, attr: &Attribute) -> bool {
     sess.check_name(attr, sym::cfg)
 }
 
-pub fn cfg_eval(ecx: &ExtCtxt<'_>, annotatable: Annotatable) -> Vec<Annotatable> {
+pub(crate) fn cfg_eval(ecx: &ExtCtxt<'_>, annotatable: Annotatable) -> Annotatable {
     let mut visitor = CfgEval {
         cfg: &mut StripUnconfigured {
             sess: ecx.sess,
             features: ecx.ecfg.features,
             config_tokens: true,
         },
     };
-    let annotatable = visitor.configure_annotatable(annotatable);
-    vec![annotatable]
+    visitor.configure_annotatable(annotatable)
 }
 
 struct CfgEval<'a, 'b> {

compiler/rustc_expand/src/expand.rs

@@ -1,5 +1,5 @@
 use crate::base::*;
-use crate::config::StripUnconfigured;
+use crate::config::{cfg_eval, StripUnconfigured};
 use crate::configure;
 use crate::hygiene::SyntaxContext;
 use crate::mbe::macro_rules::annotate_err_with_kind;
@@ -731,6 +731,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                 (item_inner.ident.name.is_empty() || !matches!(mod_kind, ast::ModKind::Loaded(_, Inline::Yes, _)));
                         }
                     }
+                    let item = cfg_eval(self.cx, item);
                     let tokens = if fake_tokens {
                         rustc_parse::fake_token_stream(
                             &self.cx.sess.parse_sess,
@@ -753,6 +754,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 SyntaxExtensionKind::LegacyAttr(expander) => {
                     match validate_attr::parse_meta(&self.cx.sess.parse_sess, &attr) {
                         Ok(meta) => {
+                            let item = cfg_eval(self.cx, item);
                             let items = match expander.expand(self.cx, span, &meta, item) {
                                 ExpandResult::Ready(items) => items,
                                 ExpandResult::Retry(item) => {

src/test/ui/proc-macro/attribute-after-derive.stdout

@@ -1,4 +1,4 @@
-PRINT-ATTR INPUT (DISPLAY): #[derive(Print)] struct AttributeDerive { #[cfg(FALSE)] field : u8, }
+PRINT-ATTR INPUT (DISPLAY): #[derive(Print)] struct AttributeDerive { }
 PRINT-ATTR INPUT (DEBUG): TokenStream [
     Punct {
         ch: '#',
@@ -35,51 +35,7 @@ PRINT-ATTR INPUT (DEBUG): TokenStream [
     },
     Group {
         delimiter: Brace,
-        stream: TokenStream [
-            Punct {
-                ch: '#',
-                spacing: Alone,
-                span: $DIR/attribute-after-derive.rs:19:5: 19:6 (#0),
-            },
-            Group {
-                delimiter: Bracket,
-                stream: TokenStream [
-                    Ident {
-                        ident: "cfg",
-                        span: $DIR/attribute-after-derive.rs:19:7: 19:10 (#0),
-                    },
-                    Group {
-                        delimiter: Parenthesis,
-                        stream: TokenStream [
-                            Ident {
-                                ident: "FALSE",
-                                span: $DIR/attribute-after-derive.rs:19:11: 19:16 (#0),
-                            },
-                        ],
-                        span: $DIR/attribute-after-derive.rs:19:10: 19:17 (#0),
-                    },
-                ],
-                span: $DIR/attribute-after-derive.rs:19:6: 19:18 (#0),
-            },
-            Ident {
-                ident: "field",
-                span: $DIR/attribute-after-derive.rs:20:5: 20:10 (#0),
-            },
-            Punct {
-                ch: ':',
-                spacing: Alone,
-                span: $DIR/attribute-after-derive.rs:20:10: 20:11 (#0),
-            },
-            Ident {
-                ident: "u8",
-                span: $DIR/attribute-after-derive.rs:20:12: 20:14 (#0),
-            },
-            Punct {
-                ch: ',',
-                spacing: Alone,
-                span: $DIR/attribute-after-derive.rs:20:14: 20:15 (#0),
-            },
-        ],
+        stream: TokenStream [],
         span: $DIR/attribute-after-derive.rs:18:24: 21:2 (#0),
     },
 ]

src/test/ui/proc-macro/auxiliary/attr-cfg.rs

@@ -11,11 +11,10 @@ use proc_macro::TokenStream;
 pub fn attr_cfg(args: TokenStream, input: TokenStream) -> TokenStream {
     let input_str = input.to_string();
 
-    assert_eq!(input_str, "fn outer() -> u8
-{
-    #[cfg(foo)] fn inner() -> u8 { 1 } #[cfg(bar)] fn inner() -> u8 { 2 }
-    inner()
-}");
+    assert!(
+        input_str == "fn outer() -> u8 { #[cfg(foo)] fn inner() -> u8 { 1 } inner() }"
+            || input_str == "fn outer() -> u8 { #[cfg(bar)] fn inner() -> u8 { 2 } inner() }"
+    );
 
     input
 }