Rollup merge of #143245 - tgross35:metavariable-expr-organization, r=petrochenkov

mbe: Add tests and restructure metavariable expressions

Add tests that show better diagnostics, and factor `concat` handling to a separate function. Each commit message has further details.

This performs the nonfunctional perparation for further changes such as https://github.com/rust-lang/rust/pull/142950 and https://github.com/rust-lang/rust/pull/142975 .

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/ui/macros/metavar-expressions/required-feature.rs b/tests/ui/macros/metavar-expressions/required-feature.rs
new file mode 100644
index 00000000000..77c165e3855
--- /dev/null
+++ b/tests/ui/macros/metavar-expressions/required-feature.rs
@@ -0,0 +1,43 @@
+macro_rules! count {
+    ( $( $e:stmt ),* ) => {
+        ${ count($e) }
+        //~^ ERROR meta-variable expressions are unstable
+    };
+}
+
+macro_rules! dollar_dollar {
+    () => {
+        macro_rules! bar {
+            ( $$( $$any:tt )* ) => { $$( $$any )* };
+            //~^ ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+            //~| ERROR meta-variable expressions are unstable
+        }
+    };
+}
+
+macro_rules! index {
+    ( $( $e:stmt ),* ) => {
+        $( ${ignore($e)} ${index()} )*
+        //~^ ERROR meta-variable expressions are unstable
+        //~| ERROR meta-variable expressions are unstable
+    };
+}
+
+macro_rules! ignore {
+    ( $( $i:stmt ),* ) => {{
+        0 $( + 1 ${ignore($i)} )*
+        //~^ ERROR meta-variable expressions are unstable
+    }};
+}
+
+macro_rules! len {
+    ( $( $e:stmt ),* ) => {
+        $( ${ignore($e)} ${len()} )*
+        //~^ ERROR meta-variable expressions are unstable
+        //~| ERROR meta-variable expressions are unstable
+    };
+}
+
+fn main() {}