Clarify that repeat count must be positive

Author: syvb

compiler/rustc_builtin_macros/src/concat_bytes.rs

@@ -154,7 +154,7 @@ pub fn expand_concat_bytes(
                         }
                     }
                 } else {
-                    cx.span_err(count.value.span, "repeat count is not a number");
+                    cx.span_err(count.value.span, "repeat count is not a positive number");
                 }
             }
             ast::ExprKind::Lit(ref lit) => match lit.kind {

src/test/ui/macros/concat-bytes-error.rs

@@ -39,12 +39,12 @@ fn main() {
     ]);
     concat_bytes!(5u16); //~ ERROR cannot concatenate numeric literals
     concat_bytes!([5u16]); //~ ERROR numeric literal is not a `u8`
-    concat_bytes!([3; ()]); //~ ERROR repeat count is not a number
-    concat_bytes!([3; -2]); //~ ERROR repeat count is not a number
-    concat_bytes!([pie; -2]); //~ ERROR repeat count is not a number
+    concat_bytes!([3; ()]); //~ ERROR repeat count is not a positive number
+    concat_bytes!([3; -2]); //~ ERROR repeat count is not a positive number
+    concat_bytes!([pie; -2]); //~ ERROR repeat count is not a positive number
     concat_bytes!([pie; 2]); //~ ERROR expected a byte literal
     concat_bytes!([2.2; 0]); //~ ERROR cannot concatenate float literals
-    concat_bytes!([5.5; ()]); //~ ERROR repeat count is not a number
+    concat_bytes!([5.5; ()]); //~ ERROR repeat count is not a positive number
     concat_bytes!([[1, 2, 3]; 3]); //~ ERROR cannot concatenate doubly nested array
     concat_bytes!([[42; 2]; 3]); //~ ERROR cannot concatenate doubly nested array
 }

src/test/ui/macros/concat-bytes-error.stderr

@@ -127,19 +127,19 @@ error: numeric literal is not a `u8`
 LL |     concat_bytes!([5u16]);
    |                    ^^^^
 
-error: repeat count is not a number
+error: repeat count is not a positive number
   --> $DIR/concat-bytes-error.rs:42:23
    |
 LL |     concat_bytes!([3; ()]);
    |                       ^^
 
-error: repeat count is not a number
+error: repeat count is not a positive number
   --> $DIR/concat-bytes-error.rs:43:23
    |
 LL |     concat_bytes!([3; -2]);
    |                       ^^
 
-error: repeat count is not a number
+error: repeat count is not a positive number
   --> $DIR/concat-bytes-error.rs:44:25
    |
 LL |     concat_bytes!([pie; -2]);
@@ -159,7 +159,7 @@ error: cannot concatenate float literals
 LL |     concat_bytes!([2.2; 0]);
    |                    ^^^
 
-error: repeat count is not a number
+error: repeat count is not a positive number
   --> $DIR/concat-bytes-error.rs:47:25
    |
 LL |     concat_bytes!([5.5; ()]);