Stop compilation on missing const_generics feature.

src/librustc_ast_passes/feature_gate.rs

@@ -2,7 +2,7 @@ use rustc_ast::ast::{self, AssocTyConstraint, AssocTyConstraintKind, NodeId};
 use rustc_ast::ast::{GenericParam, GenericParamKind, PatKind, RangeEnd, VariantData};
 use rustc_ast::attr;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
-use rustc_errors::{struct_span_err, Handler};
+use rustc_errors::{struct_span_err, FatalError, Handler};
 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP};
 use rustc_feature::{Features, GateIssue, UnstableFeatures};
 use rustc_session::parse::{feature_err, feature_err_issue, ParseSess};
@@ -13,19 +13,22 @@ use rustc_span::Span;
 use log::debug;
 
 macro_rules! gate_feature_fn {
-    ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
+    ($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr $(, $fatal: expr $(,)?)?) => {{
         let (cx, has_feature, span, name, explain) = (&*$cx, $has_feature, $span, $name, $explain);
         let has_feature: bool = has_feature(&$cx.features);
         debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
         if !has_feature && !span.allows_unstable($name) {
             feature_err_issue(cx.parse_sess, name, span, GateIssue::Language, explain).emit();
+            $(
+                $fatal.raise();
+            )?
         }
     }};
 }
 
 macro_rules! gate_feature_post {
-    ($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
-        gate_feature_fn!($cx, |x: &Features| x.$feature, $span, sym::$feature, $explain)
+    ($cx: expr, $feature: ident, $span: expr, $explain: expr $(, $fatal: expr $(,)?)?) => {
+        gate_feature_fn!($cx, |x: &Features| x.$feature, $span, sym::$feature, $explain $(, $fatal)?)
     };
 }
 
@@ -517,12 +520,18 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
     fn visit_generic_param(&mut self, param: &'a GenericParam) {
         match param.kind {
-            GenericParamKind::Const { .. } => gate_feature_post!(
-                &self,
-                const_generics,
-                param.ident.span,
-                "const generics are unstable"
-            ),
+            GenericParamKind::Const { .. } => {
+                // FIXME(const_generics): we currently stop compilation prematurely in case a
+                // generic param is found in locations where the `const_generics`
+                // feature is required.
+                gate_feature_post!(
+                    &self,
+                    const_generics,
+                    param.ident.span,
+                    "const generics are unstable",
+                    FatalError,
+                );
+            }
             _ => {}
         }
         visit::walk_generic_param(self, param)

src/test/ui/const-generics/const-param-type-depends-on-type-param-ungated.rs

@@ -1,6 +1,9 @@
+#![feature(const_generics)]
+//~^ WARNING the feature `const_generics` is incomplete and may cause the compiler to crash
+
 use std::marker::PhantomData;
 
-struct B<T, const N: T>(PhantomData<[T; N]>); //~ ERROR const generics are unstable
+struct B<T, const N: T>(PhantomData<[T; N]>);
 //~^ ERROR the types of const generic parameters must derive `PartialEq` and `Eq`
 
 fn main() {}

src/test/ui/const-generics/const-param-type-depends-on-type-param-ungated.stderr

@@ -1,19 +1,17 @@
-error[E0658]: const generics are unstable
-  --> $DIR/const-param-type-depends-on-type-param-ungated.rs:3:19
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/const-param-type-depends-on-type-param-ungated.rs:1:12
    |
-LL | struct B<T, const N: T>(PhantomData<[T; N]>);
-   |                   ^
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
    |
-   = note: see issue #44580 </~https://github.com/rust-lang/rust/issues/44580> for more information
-   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+   = note: `#[warn(incomplete_features)]` on by default
 
 error[E0741]: the types of const generic parameters must derive `PartialEq` and `Eq`
-  --> $DIR/const-param-type-depends-on-type-param-ungated.rs:3:22
+  --> $DIR/const-param-type-depends-on-type-param-ungated.rs:6:22
    |
 LL | struct B<T, const N: T>(PhantomData<[T; N]>);
    |                      ^ `T` doesn't derive both `PartialEq` and `Eq`
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0658, E0741.
-For more information about an error, try `rustc --explain E0658`.
+For more information about this error, try `rustc --explain E0741`.

src/test/ui/const-generics/issues/issue-69913.rs

@@ -0,0 +1,5 @@
+fn foo<const A: usize, const B: usize>(bar: [usize; A + B]) {
+    //~^ ERROR const generics are unstable
+}
+
+fn main() { }

src/test/ui/const-generics/issues/issue-69913.stderr

@@ -0,0 +1,12 @@
+error[E0658]: const generics are unstable
+  --> $DIR/issue-69913.rs:1:14
+   |
+LL | fn foo<const A: usize, const B: usize>(bar: [usize; A + B]) {
+   |              ^
+   |
+   = note: see issue #44580 </~https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-const_generics-fn.rs

@@ -0,0 +1,5 @@
+// gate-test-const_generics
+
+fn foo<const X: ()>() {} //~ ERROR const generics are unstable
+
+fn main() {}

src/test/ui/feature-gates/feature-gate-const_generics-fn.stderr

@@ -0,0 +1,12 @@
+error[E0658]: const generics are unstable
+  --> $DIR/feature-gate-const_generics-fn.rs:3:14
+   |
+LL | fn foo<const X: ()>() {}
+   |              ^
+   |
+   = note: see issue #44580 </~https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-const_generics-ptr.rs

@@ -1,9 +1,10 @@
+#![feature(const_generics)]
+//~^ WARNING the feature `const_generics` is incomplete and may cause the compiler to crash
+
 struct ConstFn<const F: fn()>;
-//~^ ERROR const generics are unstable
-//~^^ ERROR using function pointers as const generic parameters is unstable
+//~^ ERROR using function pointers as const generic parameters is unstable
 
 struct ConstPtr<const P: *const u32>;
-//~^ ERROR const generics are unstable
-//~^^ ERROR using raw pointers as const generic parameters is unstable
+//~^ ERROR using raw pointers as const generic parameters is unstable
 
 fn main() {}

src/test/ui/feature-gates/feature-gate-const_generics-ptr.stderr

@@ -1,23 +1,13 @@
-error[E0658]: const generics are unstable
-  --> $DIR/feature-gate-const_generics-ptr.rs:1:22
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/feature-gate-const_generics-ptr.rs:1:12
    |
-LL | struct ConstFn<const F: fn()>;
-   |                      ^
-   |
-   = note: see issue #44580 </~https://github.com/rust-lang/rust/issues/44580> for more information
-   = help: add `#![feature(const_generics)]` to the crate attributes to enable
-
-error[E0658]: const generics are unstable
-  --> $DIR/feature-gate-const_generics-ptr.rs:5:23
-   |
-LL | struct ConstPtr<const P: *const u32>;
-   |                       ^
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
    |
-   = note: see issue #44580 </~https://github.com/rust-lang/rust/issues/44580> for more information
-   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+   = note: `#[warn(incomplete_features)]` on by default
 
 error[E0658]: using function pointers as const generic parameters is unstable
-  --> $DIR/feature-gate-const_generics-ptr.rs:1:25
+  --> $DIR/feature-gate-const_generics-ptr.rs:4:25
    |
 LL | struct ConstFn<const F: fn()>;
    |                         ^^^^
@@ -26,14 +16,14 @@ LL | struct ConstFn<const F: fn()>;
    = help: add `#![feature(const_compare_raw_pointers)]` to the crate attributes to enable
 
 error[E0658]: using raw pointers as const generic parameters is unstable
-  --> $DIR/feature-gate-const_generics-ptr.rs:5:26
+  --> $DIR/feature-gate-const_generics-ptr.rs:7:26
    |
 LL | struct ConstPtr<const P: *const u32>;
    |                          ^^^^^^^^^^
    |
    = note: see issue #53020 </~https://github.com/rust-lang/rust/issues/53020> for more information
    = help: add `#![feature(const_compare_raw_pointers)]` to the crate attributes to enable
 
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-const_generics.rs → src/test/ui/feature-gates/feature-gate-const_generics-struct.rs

@@ -1,4 +1,4 @@
-fn foo<const X: ()>() {} //~ ERROR const generics are unstable
+// gate-test-const_generics
 
 struct Foo<const X: usize>([(); X]); //~ ERROR const generics are unstable
 

src/test/ui/feature-gates/feature-gate-const_generics-struct.stderr

@@ -0,0 +1,12 @@
+error[E0658]: const generics are unstable
+  --> $DIR/feature-gate-const_generics-struct.rs:3:18
+   |
+LL | struct Foo<const X: usize>([(); X]);
+   |                  ^
+   |
+   = note: see issue #44580 </~https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: add `#![feature(const_generics)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.