Forbid using 0 as issue number

src/librustc_attr/builtin.rs

@@ -396,26 +396,31 @@ where
                                     issue_num = match &*issue.unwrap().as_str() {
                                         "none" => None,
                                         issue => {
+                                            let emit_diag = |msg: &str| {
+                                                struct_span_err!(
+                                                    diagnostic,
+                                                    mi.span,
+                                                    E0545,
+                                                    "`issue` must be a non-zero numeric string \
+                                                    or \"none\"",
+                                                )
+                                                .span_label(
+                                                    mi.name_value_literal().unwrap().span,
+                                                    msg,
+                                                )
+                                                .emit();
+                                            };
                                             match issue.parse() {
-                                                Ok(num) => {
-                                                    // FIXME(rossmacarthur): disallow 0
-                                                    // Disallowing this requires updates to
-                                                    // some submodules
-                                                    NonZeroU32::new(num)
+                                                Ok(num) if num == 0 => {
+                                                    emit_diag(
+                                                        "`issue` must not be \"0\", \
+                                                        use \"none\" instead",
+                                                    );
+                                                    continue 'outer;
                                                 }
+                                                Ok(num) => NonZeroU32::new(num),
                                                 Err(err) => {
-                                                    struct_span_err!(
-                                                        diagnostic,
-                                                        mi.span,
-                                                        E0545,
-                                                        "`issue` must be a numeric string \
-                                                        or \"none\"",
-                                                    )
-                                                    .span_label(
-                                                        mi.name_value_literal().unwrap().span,
-                                                        &err.to_string(),
-                                                    )
-                                                    .emit();
+                                                    emit_diag(&err.to_string());
                                                     continue 'outer;
                                                 }
                                             }

src/test/ui/feature-gate/unstable-attribute-allow-issue-0.rs

@@ -4,10 +4,10 @@
 #![stable(feature = "stable_test_feature", since = "1.0.0")]
 
 #[unstable(feature = "unstable_test_feature", issue = "0")]
-fn unstable_issue_0() {}
+fn unstable_issue_0() {} //~^ ERROR `issue` must be a non-zero numeric string or "none"
 
 #[unstable(feature = "unstable_test_feature", issue = "none")]
 fn unstable_issue_none() {}
 
 #[unstable(feature = "unstable_test_feature", issue = "something")]
-fn unstable_issue_not_allowed() {} //~^ ERROR `issue` must be a numeric string or "none"
+fn unstable_issue_not_allowed() {} //~^ ERROR `issue` must be a non-zero numeric string or "none"

src/test/ui/feature-gate/unstable-attribute-allow-issue-0.stderr

@@ -1,10 +1,18 @@
-error[E0545]: `issue` must be a numeric string or "none"
+error[E0545]: `issue` must be a non-zero numeric string or "none"
+  --> $DIR/unstable-attribute-allow-issue-0.rs:6:47
+   |
+LL | #[unstable(feature = "unstable_test_feature", issue = "0")]
+   |                                               ^^^^^^^^---
+   |                                                       |
+   |                                                       `issue` must not be "0", use "none" instead
+
+error[E0545]: `issue` must be a non-zero numeric string or "none"
   --> $DIR/unstable-attribute-allow-issue-0.rs:12:47
    |
 LL | #[unstable(feature = "unstable_test_feature", issue = "something")]
    |                                               ^^^^^^^^-----------
    |                                                       |
    |                                                       invalid digit found in string
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 

src/test/ui/stability-attribute/stability-attribute-sanity-2.rs

@@ -10,7 +10,8 @@ fn f1() { }
 #[stable(feature = "a", sinse = "1.0.0")] //~ ERROR unknown meta item 'sinse'
 fn f2() { }
 
-#[unstable(feature = "a", issue = "no")] //~ ERROR `issue` must be a numeric string or "none"
+#[unstable(feature = "a", issue = "no")]
+//~^ ERROR `issue` must be a non-zero numeric string or "none"
 fn f3() { }
 
 fn main() { }

src/test/ui/stability-attribute/stability-attribute-sanity-2.stderr

@@ -10,7 +10,7 @@ error[E0541]: unknown meta item 'sinse'
 LL | #[stable(feature = "a", sinse = "1.0.0")]
    |                         ^^^^^^^^^^^^^^^ expected one of `since`, `note`
 
-error[E0545]: `issue` must be a numeric string or "none"
+error[E0545]: `issue` must be a non-zero numeric string or "none"
   --> $DIR/stability-attribute-sanity-2.rs:13:27
    |
 LL | #[unstable(feature = "a", issue = "no")]