fix Macro error: expected Expr #19168

crates/hir-def/src/macro_expansion_tests/mbe/regression.rs

@@ -108,6 +108,42 @@ fn main() {
     );
 }
 
+#[test]
+fn ty_fragment_followed_by_expr() {
+    check(
+        r#"
+macro_rules! a {
+    ($t:tt) => {};
+}
+
+macro_rules! b {
+    ($t:ty) => {
+        a!($t);
+    };
+}
+
+fn main() {
+    b!(&'static str);
+}
+"#,
+        expect![[r#"
+macro_rules! a {
+    ($t:tt) => {};
+}
+
+macro_rules! b {
+    ($t:ty) => {
+        a!($t);
+    };
+}
+
+fn main() {
+    a!(&'static str);;
+}
+"#]],
+    );
+}
+
 #[test]
 fn test_winapi_struct() {
     // from https://github.com/retep998/winapi-rs/blob/a7ef2bca086aae76cf6c4ce4c2552988ed9798ad/src/macros.rs#L366

crates/mbe/src/expander.rs

@@ -128,7 +128,10 @@ enum Fragment<'a> {
     #[default]
     Empty,
     /// token fragments are just copy-pasted into the output
-    Tokens(tt::TokenTreesView<'a, Span>),
+    Tokens {
+        tree: tt::TokenTreesView<'a, Span>,
+        origin: TokensOrigin,
+    },
     /// Expr ast fragments are surrounded with `()` on transcription to preserve precedence.
     /// Note that this impl is different from the one currently in `rustc` --
     /// `rustc` doesn't translate fragments into token trees at all.
@@ -156,10 +159,16 @@ impl Fragment<'_> {
     fn is_empty(&self) -> bool {
         match self {
             Fragment::Empty => true,
-            Fragment::Tokens(it) => it.len() == 0,
+            Fragment::Tokens { tree, .. } => tree.len() == 0,
             Fragment::Expr(it) => it.len() == 0,
             Fragment::Path(it) => it.len() == 0,
             Fragment::TokensOwned(it) => it.0.is_empty(),
         }
     }
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum TokensOrigin {
+    Raw,
+    Ast,
+}

crates/mbe/src/expander/matcher.rs

@@ -71,7 +71,7 @@ use tt::{
 
 use crate::{
     ExpandError, ExpandErrorKind, MetaTemplate, ValueResult,
-    expander::{Binding, Bindings, ExpandResult, Fragment},
+    expander::{Binding, Bindings, ExpandResult, Fragment, TokensOrigin},
     expect_fragment,
     parser::{ExprKind, MetaVarKind, Op, RepeatKind, Separator},
 };
@@ -842,18 +842,23 @@ fn match_meta_var<'t>(
             }
             .err();
             let tt_result = input.from_savepoint(savepoint);
-            return ValueResult { value: Fragment::Tokens(tt_result), err };
+            return ValueResult {
+                value: Fragment::Tokens { tree: tt_result, origin: TokensOrigin::Raw },
+                err,
+            };
         }
-        MetaVarKind::Ty => parser::PrefixEntryPoint::Ty,
-        MetaVarKind::Pat => parser::PrefixEntryPoint::PatTop,
-        MetaVarKind::PatParam => parser::PrefixEntryPoint::Pat,
-        MetaVarKind::Stmt => parser::PrefixEntryPoint::Stmt,
-        MetaVarKind::Block => parser::PrefixEntryPoint::Block,
-        MetaVarKind::Meta => parser::PrefixEntryPoint::MetaItem,
-        MetaVarKind::Item => parser::PrefixEntryPoint::Item,
-        MetaVarKind::Vis => parser::PrefixEntryPoint::Vis,
+        MetaVarKind::Ty => (parser::PrefixEntryPoint::Ty, TokensOrigin::Ast),
+        MetaVarKind::Pat => (parser::PrefixEntryPoint::PatTop, TokensOrigin::Ast),
+        MetaVarKind::PatParam => (parser::PrefixEntryPoint::Pat, TokensOrigin::Ast),
+        MetaVarKind::Stmt => (parser::PrefixEntryPoint::Stmt, TokensOrigin::Ast),
+        MetaVarKind::Block => (parser::PrefixEntryPoint::Block, TokensOrigin::Ast),
+        MetaVarKind::Meta => (parser::PrefixEntryPoint::MetaItem, TokensOrigin::Ast),
+        MetaVarKind::Item => (parser::PrefixEntryPoint::Item, TokensOrigin::Ast),
+        MetaVarKind::Vis => (parser::PrefixEntryPoint::Vis, TokensOrigin::Ast),
     };
-    expect_fragment(db, input, fragment, delim_span).map(Fragment::Tokens)
+    let (entry_point, origin) = fragment;
+    expect_fragment(db, input, entry_point, delim_span)
+        .map(|tree| Fragment::Tokens { tree, origin })
 }
 
 fn collect_vars(collector_fun: &mut impl FnMut(Symbol), pattern: &MetaTemplate) {

crates/mbe/src/expander/transcriber.rs

@@ -5,6 +5,7 @@ use intern::{Symbol, sym};
 use span::{Edition, Span};
 use tt::{Delimiter, TopSubtreeBuilder, iter::TtElement};
 
+use super::TokensOrigin;
 use crate::{
     ExpandError, ExpandErrorKind, ExpandResult, MetaTemplate,
     expander::{Binding, Bindings, Fragment},
@@ -313,7 +314,7 @@ fn expand_subtree(
                                 }
                             };
                             let values = match &var_value {
-                                Fragment::Tokens(tokens) => {
+                                Fragment::Tokens { tree: tokens, .. } => {
                                     let mut iter = tokens.iter();
                                     (iter.next(), iter.next())
                                 }
@@ -393,7 +394,13 @@ fn expand_var(
                 // rustc spacing is not like ours. Ours is like proc macros', it dictates how puncts will actually be joined.
                 // rustc uses them mostly for pretty printing. So we have to deviate a bit from what rustc does here.
                 // Basically, a metavariable can never be joined with whatever after it.
-                Fragment::Tokens(tt) => builder.extend_with_tt_alone(tt.strip_invisible()),
+                Fragment::Tokens { tree, origin } => {
+                    let view = match origin {
+                        TokensOrigin::Raw => tree.strip_invisible(),
+                        TokensOrigin::Ast => tree,
+                    };
+                    builder.extend_with_tt_alone(view);
+                }
                 Fragment::TokensOwned(tt) => {
                     builder.extend_with_tt_alone(tt.view().strip_invisible())
                 }