Auto merge of #60224 - Centril:rollup-lfuhhsk, r=Centril

Rollup of 5 pull requests

Successful merges:

 - #56278 (Future-proof MIR for dedicated debuginfo.)
 - #59739 (Stabilize futures_api)
 - #59822 (Fix dark css rule)
 - #60186 (Temporarily accept [i|u][32|size] suffixes on a tuple index and warn)
 - #60190 (Don't generate unnecessary rmeta files.)

Failed merges:

r? @ghost

2 files changed, 45 insertions, 7 deletions

diff --git a/src/libsyntax/attr/builtin.rs b/src/libsyntax/attr/builtin.rs
index 74c952b076c..db821f4e536 100644
--- a/src/libsyntax/attr/builtin.rs
+++ b/src/libsyntax/attr/builtin.rs
@@ -114,6 +114,8 @@ pub struct Stability {
     pub const_stability: Option<Symbol>,
     /// whether the function has a `#[rustc_promotable]` attribute
     pub promotable: bool,
+    /// whether the function has a `#[rustc_allow_const_fn_ptr]` attribute
+    pub allow_const_fn_ptr: bool,
 }
 
 /// The available stability levels.
@@ -178,6 +180,7 @@ fn find_stability_generic<'a, I>(sess: &ParseSess,
     let mut rustc_depr: Option<RustcDeprecation> = None;
     let mut rustc_const_unstable: Option<Symbol> = None;
     let mut promotable = false;
+    let mut allow_const_fn_ptr = false;
     let diagnostic = &sess.span_diagnostic;
 
     'outer: for attr in attrs_iter {
@@ -187,6 +190,7 @@ fn find_stability_generic<'a, I>(sess: &ParseSess,
             "unstable",
             "stable",
             "rustc_promotable",
+            "rustc_allow_const_fn_ptr",
         ].iter().any(|&s| attr.path == s) {
             continue // not a stability level
         }
@@ -198,6 +202,9 @@ fn find_stability_generic<'a, I>(sess: &ParseSess,
         if attr.path == "rustc_promotable" {
             promotable = true;
         }
+        if attr.path == "rustc_allow_const_fn_ptr" {
+            allow_const_fn_ptr = true;
+        }
         // attributes with data
         else if let Some(MetaItem { node: MetaItemKind::List(ref metas), .. }) = meta {
             let meta = meta.as_ref().unwrap();
@@ -354,6 +361,7 @@ fn find_stability_generic<'a, I>(sess: &ParseSess,
                                 rustc_depr: None,
                                 const_stability: None,
                                 promotable: false,
+                                allow_const_fn_ptr: false,
                             })
                         }
                         (None, _, _) => {
@@ -418,6 +426,7 @@ fn find_stability_generic<'a, I>(sess: &ParseSess,
                                 rustc_depr: None,
                                 const_stability: None,
                                 promotable: false,
+                                allow_const_fn_ptr: false,
                             })
                         }
                         (None, _) => {
@@ -458,13 +467,14 @@ fn find_stability_generic<'a, I>(sess: &ParseSess,
     }
 
     // Merge the const-unstable info into the stability info
-    if promotable {
+    if promotable || allow_const_fn_ptr {
         if let Some(ref mut stab) = stab {
-            stab.promotable = true;
+            stab.promotable = promotable;
+            stab.allow_const_fn_ptr = allow_const_fn_ptr;
         } else {
             span_err!(diagnostic, item_sp, E0717,
-                      "rustc_promotable attribute must be paired with \
-                       either stable or unstable attribute");
+                      "rustc_promotable and rustc_allow_const_fn_ptr attributes \
+                      must be paired with either stable or unstable attribute");
         }
     }
 
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 53dab510ac3..75d687be280 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1145,9 +1145,34 @@ impl<'a> Parser<'a> {
                 if text.is_empty() {
                     self.span_bug(sp, "found empty literal suffix in Some")
                 }
-                self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
-                    .span_label(sp, format!("invalid suffix `{}`", text))
-                    .emit();
+                let mut err = if kind == "a tuple index" &&
+                    ["i32", "u32", "isize", "usize"].contains(&text.to_string().as_str())
+                {
+                    // #59553: warn instead of reject out of hand to allow the fix to percolate
+                    // through the ecosystem when people fix their macros
+                    let mut err = self.struct_span_warn(
+                        sp,
+                        &format!("suffixes on {} are invalid", kind),
+                    );
+                    err.note(&format!(
+                        "`{}` is *temporarily* accepted on tuple index fields as it was \
+                         incorrectly accepted on stable for a few releases",
+                        text,
+                    ));
+                    err.help(
+                        "on proc macros, you'll want to use `syn::Index::from` or \
+                         `proc_macro::Literal::*_unsuffixed` for code that will desugar \
+                         to tuple field access",
+                    );
+                    err.note(
+                        "for more context, see https://github.com/rust-lang/rust/issues/60210",
+                    );
+                    err
+                } else {
+                    self.struct_span_err(sp, &format!("suffixes on {} are invalid", kind))
+                };
+                err.span_label(sp, format!("invalid suffix `{}`", text));
+                err.emit();
             }
         }
     }
@@ -1455,6 +1480,9 @@ impl<'a> Parser<'a> {
     fn struct_span_err<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
         self.sess.span_diagnostic.struct_span_err(sp, m)
     }
+    fn struct_span_warn<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> DiagnosticBuilder<'a> {
+        self.sess.span_diagnostic.struct_span_warn(sp, m)
+    }
     crate fn span_bug<S: Into<MultiSpan>>(&self, sp: S, m: &str) -> ! {
         self.sess.span_diagnostic.span_bug(sp, m)
     }