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, 33 insertions, 0 deletions

diff --git a/tests/ui/macros/metavar-expressions/concat-trace-errors.rs b/tests/ui/macros/metavar-expressions/concat-trace-errors.rs
new file mode 100644
index 00000000000..45407f5e86d
--- /dev/null
+++ b/tests/ui/macros/metavar-expressions/concat-trace-errors.rs
@@ -0,0 +1,33 @@
+// Our diagnostics should be able to point to a specific input that caused an invalid
+// identifier.
+
+#![feature(macro_metavar_expr_concat)]
+
+// See what we can do without expanding anything
+macro_rules! pre_expansion {
+    ($a:ident) => {
+        ${concat("hi", " bye ")};
+        ${concat("hi", "-", "bye")};
+        ${concat($a, "-")};
+    }
+}
+
+macro_rules! post_expansion {
+    ($a:literal) => {
+        const _: () = ${concat("hi", $a, "bye")};
+        //~^ ERROR is not generating a valid identifier
+    }
+}
+
+post_expansion!("!");
+
+macro_rules! post_expansion_many {
+    ($a:ident, $b:ident, $c:ident, $d:literal, $e:ident) => {
+        const _: () = ${concat($a, $b, $c, $d, $e)};
+        //~^ ERROR is not generating a valid identifier
+    }
+}
+
+post_expansion_many!(a, b, c, ".d", e);
+
+fn main() {}