Use correct edition when parsing :pat matchers

As described in issue rust-lang#85708, we currently do not properly decode
`SyntaxContext::root()` and `ExpnId::root()` from foreign crates. As a
result, when we decode a span from a foreign crate with
`SyntaxContext::root()`, we end up up considering it to have the edition
of the *current* crate, instead of the foreign crate where it was
originally created.

A full fix for this issue will be a fairly significant undertaking.
Fortunately, it's possible to implement a partial fix, which gives us
the correct edition-dependent behavior for `:pat` matchers when the
macro is loaded from another crate. Since we have the edition of the
macro's defining crate available, we can 'recover' from seeing a
`SyntaxContext::root()` and use the edition of the macro's defining
crate.

Any solution to issue rust-lang#85708 must reproduce the behavior of this
targeted fix - properly preserving a foreign `SyntaxContext::root()`
means (among other things) preserving its edition, which by definition
is the edition of the foreign crate itself. Therefore, this fix moves us
closer to the correct overall solution, and does not expose any new
incorrect behavior to macros.

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -467,6 +467,7 @@ pub fn compile_declarative_macro(
                             &sess.parse_sess,
                             def.id,
                             features,
+                            edition,
                         )
                         .pop()
                         .unwrap();
@@ -492,6 +493,7 @@ pub fn compile_declarative_macro(
                             &sess.parse_sess,
                             def.id,
                             features,
+                            edition,
                         )
                         .pop()
                         .unwrap();

compiler/rustc_expand/src/mbe/quoted.rs

@@ -9,7 +9,8 @@ use rustc_feature::Features;
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::{kw, Ident};
 
-use rustc_span::Span;
+use rustc_span::edition::Edition;
+use rustc_span::{Span, SyntaxContext};
 
 use rustc_data_structures::sync::Lrc;
 
@@ -32,6 +33,7 @@ const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
 /// - `sess`: the parsing session. Any errors will be emitted to this session.
 /// - `node_id`: the NodeId of the macro we are parsing.
 /// - `features`: language features so we can do feature gating.
+/// - `edition`: the edition of the crate defining the macro
 ///
 /// # Returns
 ///
@@ -42,6 +44,7 @@ pub(super) fn parse(
     sess: &ParseSess,
     node_id: NodeId,
     features: &Features,
+    edition: Edition,
 ) -> Vec<TokenTree> {
     // Will contain the final collection of `self::TokenTree`
     let mut result = Vec::new();
@@ -52,7 +55,7 @@ pub(super) fn parse(
     while let Some(tree) = trees.next() {
         // Given the parsed tree, if there is a metavar and we are expecting matchers, actually
         // parse out the matcher (i.e., in `$id:ident` this would parse the `:` and `ident`).
-        let tree = parse_tree(tree, &mut trees, expect_matchers, sess, node_id, features);
+        let tree = parse_tree(tree, &mut trees, expect_matchers, sess, node_id, features, edition);
         match tree {
             TokenTree::MetaVar(start_sp, ident) if expect_matchers => {
                 let span = match trees.next() {
@@ -64,7 +67,19 @@ pub(super) fn parse(
 
                                     let kind =
                                         token::NonterminalKind::from_symbol(frag.name, || {
-                                            span.edition()
+                                            // FIXME(#85708) - once we properly decode a foreign
+                                            // crate's `SyntaxContext::root`, then we can replace
+                                            // this with just `span.edition()`. A
+                                            // `SyntaxContext::root()` from the current crate will
+                                            // have the edition of the current crate, and a
+                                            // `SyntaxxContext::root()` from a foreign crate will
+                                            // have the edition of that crate (which we manually
+                                            // retrieve via the `edition` parameter).
+                                            if span.ctxt() == SyntaxContext::root() {
+                                                edition
+                                            } else {
+                                                span.edition()
+                                            }
                                         })
                                         .unwrap_or_else(
                                             || {
@@ -117,13 +132,15 @@ pub(super) fn parse(
 /// - `expect_matchers`: same as for `parse` (see above).
 /// - `sess`: the parsing session. Any errors will be emitted to this session.
 /// - `features`: language features so we can do feature gating.
+/// - `edition` - the edition of the crate defining the macro
 fn parse_tree(
     tree: tokenstream::TokenTree,
     outer_trees: &mut impl Iterator<Item = tokenstream::TokenTree>,
     expect_matchers: bool,
     sess: &ParseSess,
     node_id: NodeId,
     features: &Features,
+    edition: Edition,
 ) -> TokenTree {
     // Depending on what `tree` is, we could be parsing different parts of a macro
     match tree {
@@ -151,7 +168,7 @@ fn parse_tree(
                         sess.span_diagnostic.span_err(span.entire(), &msg);
                     }
                     // Parse the contents of the sequence itself
-                    let sequence = parse(tts, expect_matchers, sess, node_id, features);
+                    let sequence = parse(tts, expect_matchers, sess, node_id, features, edition);
                     // Get the Kleene operator and optional separator
                     let (separator, kleene) =
                         parse_sep_and_kleene_op(&mut trees, span.entire(), sess);
@@ -204,7 +221,7 @@ fn parse_tree(
             span,
             Lrc::new(Delimited {
                 delim,
-                tts: parse(tts, expect_matchers, sess, node_id, features),
+                tts: parse(tts, expect_matchers, sess, node_id, features, edition),
             }),
         ),
     }

src/test/ui/macros/auxiliary/foreign-crate-macro-pat.rs

@@ -0,0 +1,11 @@
+// edition:2018
+
+#[macro_export]
+macro_rules! custom_matches {
+    ($expression:expr, $( $pattern:pat )|+ $( if $guard: expr )? $(,)?) => {
+        match $expression {
+            $( $pattern )|+ $( if $guard )? => true,
+            _ => false
+        }
+    }
+}

src/test/ui/macros/cross-crate-pat-span.rs

@@ -0,0 +1,12 @@
+// edition:2021
+// check-pass
+// aux-build: foreign-crate-macro-pat.rs
+//
+// Tests that the edition of the foreign crate is used
+// when determining the behavior of the `:pat` matcher.
+
+extern crate foreign_crate_macro_pat;
+
+fn main() {
+    let _b = foreign_crate_macro_pat::custom_matches!(b'3', b'0' ..= b'9');
+}

src/test/ui/macros/issue-84429-matches-edition.rs

@@ -0,0 +1,9 @@
+// edition:2021
+// check-pass
+//
+// Regression test for issue #84429
+// Tests that we can properly invoke `matches!` from a 2021-edition crate.
+
+fn main() {
+    let _b = matches!(b'3', b'0' ..= b'9');
+}