Add a test for $:ident in proc macro input

Author: petrochenkov

src/test/ui/proc-macro/input-interpolated.rs

@@ -0,0 +1,25 @@
+// Check what token streams proc macros see when interpolated tokens are passed to them as input.
+
+// check-pass
+// aux-build:test-macros.rs
+
+#[macro_use]
+extern crate test_macros;
+
+macro_rules! pass_ident {
+    ($i:ident) => {
+        fn f() {
+            print_bang!($i);
+        }
+
+        #[print_attr]
+        const $i: u8 = 0;
+
+        #[derive(Print)]
+        struct $i {}
+    };
+}
+
+pass_ident!(A);
+
+fn main() {}

src/test/ui/proc-macro/input-interpolated.stdout

@@ -0,0 +1,69 @@
+PRINT-BANG INPUT (DISPLAY): A
+PRINT-BANG RE-COLLECTED (DISPLAY):  A 
+PRINT-BANG INPUT (DEBUG): TokenStream [
+    Group {
+        delimiter: None,
+        stream: TokenStream [
+            Ident {
+                ident: "A",
+                span: #0 bytes(402..403),
+            },
+        ],
+        span: #3 bytes(269..271),
+    },
+]
+PRINT-ATTR INPUT (DISPLAY): const A: u8 = 0;
+PRINT-ATTR RE-COLLECTED (DISPLAY): const A : u8 = 0 ;
+PRINT-ATTR INPUT (DEBUG): TokenStream [
+    Ident {
+        ident: "const",
+        span: #0 bytes(0..0),
+    },
+    Ident {
+        ident: "A",
+        span: #0 bytes(0..0),
+    },
+    Punct {
+        ch: ':',
+        spacing: Alone,
+        span: #0 bytes(0..0),
+    },
+    Ident {
+        ident: "u8",
+        span: #0 bytes(0..0),
+    },
+    Punct {
+        ch: '=',
+        spacing: Alone,
+        span: #0 bytes(0..0),
+    },
+    Literal {
+        kind: Integer,
+        symbol: "0",
+        suffix: None,
+        span: #0 bytes(0..0),
+    },
+    Punct {
+        ch: ';',
+        spacing: Alone,
+        span: #0 bytes(0..0),
+    },
+]
+PRINT-DERIVE INPUT (DISPLAY): struct A {
+}
+PRINT-DERIVE RE-COLLECTED (DISPLAY): struct A { }
+PRINT-DERIVE INPUT (DEBUG): TokenStream [
+    Ident {
+        ident: "struct",
+        span: #0 bytes(0..0),
+    },
+    Ident {
+        ident: "A",
+        span: #0 bytes(0..0),
+    },
+    Group {
+        delimiter: Brace,
+        stream: TokenStream [],
+        span: #0 bytes(0..0),
+    },
+]