fix: don't panic when a lifetime is passed to an ident metavariable

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

@@ -106,6 +106,22 @@ fn f2() { /* error: expected ident */ }
     )
 }
 
+#[test]
+fn lifetime_bound_to_ident_fragment() {
+    check(
+        r#"
+macro_rules! m { ($t:ident) => { $t } }
+
+fn f() { m!('a); }
+"#,
+        expect![[r#"
+macro_rules! m { ($t:ident) => { $t } }
+
+fn f() { /* error: expected ident */missing; }
+"#]],
+    )
+}
+
 #[test]
 fn expansion_does_not_parse_as_expression() {
     check(

crates/mbe/src/expander/matcher.rs

@@ -842,11 +842,14 @@ fn match_meta_var<'t>(
                 _ => unreachable!(),
             }
             .err();
-            let tt_result = input.from_savepoint(savepoint);
-            return ValueResult {
-                value: Fragment::Tokens { tree: tt_result, origin: TokensOrigin::Raw },
-                err,
+            let value = match err {
+                Some(_) => Fragment::Empty,
+                None => Fragment::Tokens {
+                    tree: input.from_savepoint(savepoint),
+                    origin: TokensOrigin::Raw,
+                },
             };
+            return ValueResult { value, err };
         }
         MetaVarKind::Ty => (parser::PrefixEntryPoint::Ty, TokensOrigin::Ast),
         MetaVarKind::Pat => (parser::PrefixEntryPoint::PatTop, TokensOrigin::Ast),

crates/mbe/src/tests.rs

@@ -468,9 +468,8 @@ fn minus_belongs_to_literal() {
             }
 
             SUBTREE $$ 1:Root[0000, 0]@0..6#ROOT2024 1:Root[0000, 0]@0..6#ROOT2024
-              PUNCH   - [joint] 1:Root[0000, 0]@1..2#ROOT2024
-              PUNCH   - [alone] 1:Root[0000, 0]@2..3#ROOT2024
+              IDENT   missing 0:Root[0000, 0]@72..75#ROOT2024
 
-            --"#]],
+            missing"#]],
     );
 }