Auto merge of #47413 - GuillaumeGomez:unstable-error-code, r=estebank

Add error code for unstable feature errors

Fixes #47397.

3 files changed, 36 insertions, 1 deletions

diff --git a/src/libsyntax/diagnostic_list.rs b/src/libsyntax/diagnostic_list.rs
index c3cf4747835..d841281e485 100644
--- a/src/libsyntax/diagnostic_list.rs
+++ b/src/libsyntax/diagnostic_list.rs
@@ -317,6 +317,31 @@ fn main() {
 ```
 "##,
 
+E0658: r##"
+An unstable feature was used.
+
+Erroneous code example:
+
+```compile_fail,E658
+let x = ::std::u128::MAX; // error: use of unstable library feature 'i128'
+```
+
+If you're using a stable or a beta version of rustc, you won't be able to use
+any unstable features. In order to do so, please switch to a nightly version of
+rustc (by using rustup).
+
+If you're using a nightly version of rustc, just add the corresponding feature
+to be able to use it:
+
+```
+#![feature(i128)]
+
+fn main() {
+    let x = ::std::u128::MAX; // ok!
+}
+```
+"##,
+
 }
 
 register_diagnostics! {
diff --git a/src/libsyntax/diagnostics/macros.rs b/src/libsyntax/diagnostics/macros.rs
index c01836b6194..61f3e7046f1 100644
--- a/src/libsyntax/diagnostics/macros.rs
+++ b/src/libsyntax/diagnostics/macros.rs
@@ -106,6 +106,14 @@ macro_rules! struct_span_err {
 }
 
 #[macro_export]
+macro_rules! stringify_error_code {
+    ($code:ident) => ({
+        __diagnostic_used!($code);
+        $crate::errors::DiagnosticId::Error(stringify!($code).to_owned())
+    })
+}
+
+#[macro_export]
 macro_rules! type_error_struct {
     ($session:expr, $span:expr, $typ:expr, $code:ident, $($message:tt)*) => ({
         if $typ.references_error() {
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index c3bf5dbff5c..196fadcc997 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -1179,7 +1179,9 @@ fn leveled_feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue
     };
 
     let mut err = match level {
-        GateStrength::Hard => diag.struct_span_err(span, &explanation),
+        GateStrength::Hard => {
+            diag.struct_span_err_with_code(span, &explanation, stringify_error_code!(E0658))
+        }
         GateStrength::Soft => diag.struct_span_warn(span, &explanation),
     };