Miri: unleash all feature gates

src/librustc_interface/interface.rs

@@ -193,7 +193,7 @@ pub fn run_compiler_in_existing_thread_pool<R>(
 
     let r = {
         let _sess_abort_error = OnDrop(|| {
-            compiler.sess.diagnostic().print_error_count(registry);
+            compiler.sess.finish_diagnostics(registry);
         });
 
         f(&compiler)

src/librustc_mir/transform/check_consts/validation.rs

@@ -248,12 +248,12 @@ impl Validator<'mir, 'tcx> {
             return;
         }
 
-        // If an operation is supported in miri (and is not already controlled by a feature gate) it
-        // can be turned on with `-Zunleash-the-miri-inside-of-you`.
-        let is_unleashable = O::IS_SUPPORTED_IN_MIRI && O::feature_gate().is_none();
+        // If an operation is supported in miri it can be turned on with
+        // `-Zunleash-the-miri-inside-of-you`.
+        let is_unleashable = O::IS_SUPPORTED_IN_MIRI;
 
         if is_unleashable && self.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
-            self.tcx.sess.span_warn(span, "skipping const checks");
+            self.tcx.sess.miri_unleashed_feature(span, O::feature_gate());
             return;
         }
 

src/librustc_session/session.rs

@@ -18,10 +18,11 @@ use rustc_data_structures::sync::{
 use rustc_errors::annotate_snippet_emitter_writer::AnnotateSnippetEmitterWriter;
 use rustc_errors::emitter::{Emitter, EmitterWriter, HumanReadableErrorType};
 use rustc_errors::json::JsonEmitter;
+use rustc_errors::registry::Registry;
 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticId, ErrorReported};
 use rustc_span::edition::Edition;
 use rustc_span::source_map::{self, FileLoader, MultiSpan, RealFileLoader, SourceMap, Span};
-use rustc_span::SourceFileHashAlgorithm;
+use rustc_span::{SourceFileHashAlgorithm, Symbol};
 use rustc_target::spec::{PanicStrategy, RelocModel, RelroLevel, Target, TargetTriple, TlsModel};
 
 use std::cell::{self, RefCell};
@@ -142,6 +143,12 @@ pub struct Session {
     /// and immediately printing the backtrace to stderr.
     pub ctfe_backtrace: Lock<CtfeBacktrace>,
 
+    /// This tracks where `-Zunleash-the-miri-inside-of-you` was used to get around a
+    /// const check, optionally with the relevant feature gate.  We use this to
+    /// warn about unleashing, but with a single diagnostic instead of dozens that
+    /// drown everything else in noise.
+    miri_unleashed_features: Lock<Vec<(Span, Option<Symbol>)>>,
+
     /// Base directory containing the `src/` for the Rust standard library, and
     /// potentially `rustc` as well, if we can can find it. Right now it's always
     /// `$sysroot/lib/rustlib/src/rust` (i.e. the `rustup` `rust-src` component).
@@ -189,6 +196,44 @@ impl From<&'static lint::Lint> for DiagnosticMessageId {
 }
 
 impl Session {
+    pub fn miri_unleashed_feature(&self, span: Span, feature_gate: Option<Symbol>) {
+        self.miri_unleashed_features.lock().push((span, feature_gate));
+    }
+
+    fn check_miri_unleashed_features(&self) {
+        let unleashed_features = self.miri_unleashed_features.lock();
+        if !unleashed_features.is_empty() {
+            let mut must_err = false;
+            // Create a diagnostic pointing at where things got unleashed.
+            let mut diag = self.struct_warn("skipping const checks");
+            for &(span, feature_gate) in unleashed_features.iter() {
+                // FIXME: `span_label` doesn't do anything, so we use "help" as a hack.
+                if let Some(feature_gate) = feature_gate {
+                    diag.span_help(span, &format!("skipping check for `{}` feature", feature_gate));
+                    // The unleash flag must *not* be used to just "hack around" feature gates.
+                    must_err = true;
+                } else {
+                    diag.span_help(span, "skipping check that does not even have a feature gate");
+                }
+            }
+            diag.emit();
+            // If we should err, make sure we did.
+            if must_err && !self.has_errors() {
+                // We have skipped a feature gate, and not run into other errors... reject.
+                self.err(
+                    "`-Zunleash-the-miri-inside-of-you` may not be used to circumvent feature \
+                     gates, except when testing error paths in the CTFE engine",
+                );
+            }
+        }
+    }
+
+    /// Invoked all the way at the end to finish off diagnostics printing.
+    pub fn finish_diagnostics(&self, registry: &Registry) {
+        self.check_miri_unleashed_features();
+        self.diagnostic().print_error_count(registry);
+    }
+
     pub fn local_crate_disambiguator(&self) -> CrateDisambiguator {
         *self.crate_disambiguator.get()
     }
@@ -1139,6 +1184,7 @@ pub fn build_session_with_source_map(
         confused_type_with_std_module: Lock::new(Default::default()),
         system_library_path: OneThread::new(RefCell::new(Default::default())),
         ctfe_backtrace,
+        miri_unleashed_features: Lock::new(Default::default()),
         real_rust_source_base_dir,
     };
 

src/test/ui/consts/const-eval/const_fn_ptr.rs

@@ -9,15 +9,15 @@ const X: fn(usize) -> usize = double;
 const X_CONST: fn(usize) -> usize = double_const;
 
 const fn bar(x: usize) -> usize {
-    X(x) //~ WARNING skipping const checks
+    X(x)
 }
 
 const fn bar_const(x: usize) -> usize {
-    X_CONST(x) //~ WARNING skipping const checks
+    X_CONST(x)
 }
 
 const fn foo(x: fn(usize) -> usize, y: usize)  -> usize {
-    x(y) //~ WARNING skipping const checks
+    x(y)
 }
 
 fn main() {

src/test/ui/consts/const-eval/const_fn_ptr.stderr

@@ -1,20 +1,20 @@
 warning: skipping const checks
+   |
+help: skipping check that does not even have a feature gate
   --> $DIR/const_fn_ptr.rs:12:5
    |
 LL |     X(x)
    |     ^^^^
-
-warning: skipping const checks
+help: skipping check that does not even have a feature gate
   --> $DIR/const_fn_ptr.rs:16:5
    |
 LL |     X_CONST(x)
    |     ^^^^^^^^^^
-
-warning: skipping const checks
+help: skipping check that does not even have a feature gate
   --> $DIR/const_fn_ptr.rs:20:5
    |
 LL |     x(y)
    |     ^^^^
 
-warning: 3 warnings emitted
+warning: 1 warning emitted
 

src/test/ui/consts/const-eval/const_fn_ptr_fail.rs

@@ -8,7 +8,6 @@ const X: fn(usize) -> usize = double;
 
 const fn bar(x: usize) -> usize {
     X(x) // FIXME: this should error someday
-    //~^ WARN: skipping const checks
 }
 
 fn main() {}

src/test/ui/consts/const-eval/const_fn_ptr_fail.stderr

@@ -1,4 +1,6 @@
 warning: skipping const checks
+   |
+help: skipping check that does not even have a feature gate
   --> $DIR/const_fn_ptr_fail.rs:10:5
    |
 LL |     X(x) // FIXME: this should error someday

src/test/ui/consts/const-eval/const_fn_ptr_fail2.rs

@@ -10,7 +10,7 @@ fn double(x: usize) -> usize {
 const X: fn(usize) -> usize = double;
 
 const fn bar(x: fn(usize) -> usize, y: usize) -> usize {
-    x(y) //~ WARN skipping const checks
+    x(y)
 }
 
 const Y: usize = bar(X, 2); // FIXME: should fail to typeck someday

src/test/ui/consts/const-eval/const_fn_ptr_fail2.stderr

@@ -1,9 +1,3 @@
-warning: skipping const checks
-  --> $DIR/const_fn_ptr_fail2.rs:13:5
-   |
-LL |     x(y)
-   |     ^^^^
-
 error[E0080]: evaluation of constant expression failed
   --> $DIR/const_fn_ptr_fail2.rs:20:5
    |
@@ -24,6 +18,14 @@ LL |     assert_eq!(Z, 4);
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
+warning: skipping const checks
+   |
+help: skipping check that does not even have a feature gate
+  --> $DIR/const_fn_ptr_fail2.rs:13:5
+   |
+LL |     x(y)
+   |     ^^^^
+
 error: aborting due to 2 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/const-points-to-static.rs

@@ -3,8 +3,9 @@
 #![allow(dead_code)]
 
 const TEST: &u8 = &MY_STATIC;
-//~^ skipping const checks
-//~| it is undefined behavior to use this value
+//~^ ERROR it is undefined behavior to use this value
+//~| NOTE  encountered a reference pointing to a static variable
+//~| NOTE
 
 static MY_STATIC: u8 = 4;
 

src/test/ui/consts/const-points-to-static.stderr

@@ -1,9 +1,3 @@
-warning: skipping const checks
-  --> $DIR/const-points-to-static.rs:5:20
-   |
-LL | const TEST: &u8 = &MY_STATIC;
-   |                    ^^^^^^^^^
-
 error[E0080]: it is undefined behavior to use this value
   --> $DIR/const-points-to-static.rs:5:1
    |
@@ -12,6 +6,14 @@ LL | const TEST: &u8 = &MY_STATIC;
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
 
+warning: skipping const checks
+   |
+help: skipping check that does not even have a feature gate
+  --> $DIR/const-points-to-static.rs:5:20
+   |
+LL | const TEST: &u8 = &MY_STATIC;
+   |                    ^^^^^^^^^
+
 error: aborting due to previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/const-prop-read-static-in-const.rs

@@ -3,7 +3,6 @@
 #![allow(dead_code)]
 
 const TEST: u8 = MY_STATIC; //~ ERROR any use of this value will cause an error
-//~^ skipping const checks
 
 static MY_STATIC: u8 = 4;
 

src/test/ui/consts/const-prop-read-static-in-const.stderr

@@ -1,9 +1,3 @@
-warning: skipping const checks
-  --> $DIR/const-prop-read-static-in-const.rs:5:18
-   |
-LL | const TEST: u8 = MY_STATIC;
-   |                  ^^^^^^^^^
-
 error: any use of this value will cause an error
   --> $DIR/const-prop-read-static-in-const.rs:5:18
    |
@@ -14,5 +8,13 @@ LL | const TEST: u8 = MY_STATIC;
    |
    = note: `#[deny(const_err)]` on by default
 
+warning: skipping const checks
+   |
+help: skipping check that does not even have a feature gate
+  --> $DIR/const-prop-read-static-in-const.rs:5:18
+   |
+LL | const TEST: u8 = MY_STATIC;
+   |                  ^^^^^^^^^
+
 error: aborting due to previous error; 1 warning emitted
 

src/test/ui/consts/miri_unleashed/abi-mismatch.rs

@@ -8,14 +8,12 @@ const extern "C" fn c_fn() {}
 
 const fn call_rust_fn(my_fn: extern "Rust" fn()) {
     my_fn();
-    //~^ WARN skipping const checks
-    //~| ERROR could not evaluate static initializer
+    //~^ ERROR could not evaluate static initializer
     //~| NOTE calling a function with ABI C using caller ABI Rust
     //~| NOTE inside `call_rust_fn`
 }
 
 static VAL: () = call_rust_fn(unsafe { std::mem::transmute(c_fn as extern "C" fn()) });
-//~^ WARN skipping const checks
-//~| NOTE inside `VAL`
+//~^ NOTE inside `VAL`
 
 fn main() {}

src/test/ui/consts/miri_unleashed/abi-mismatch.stderr

@@ -1,27 +1,28 @@
-warning: skipping const checks
+error[E0080]: could not evaluate static initializer
   --> $DIR/abi-mismatch.rs:10:5
    |
 LL |     my_fn();
    |     ^^^^^^^
+   |     |
+   |     calling a function with ABI C using caller ABI Rust
+   |     inside `call_rust_fn` at $DIR/abi-mismatch.rs:10:5
+...
+LL | static VAL: () = call_rust_fn(unsafe { std::mem::transmute(c_fn as extern "C" fn()) });
+   |                  --------------------------------------------------------------------- inside `VAL` at $DIR/abi-mismatch.rs:16:18
 
 warning: skipping const checks
-  --> $DIR/abi-mismatch.rs:17:40
    |
-LL | static VAL: () = call_rust_fn(unsafe { std::mem::transmute(c_fn as extern "C" fn()) });
-   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error[E0080]: could not evaluate static initializer
+help: skipping check that does not even have a feature gate
   --> $DIR/abi-mismatch.rs:10:5
    |
 LL |     my_fn();
    |     ^^^^^^^
-   |     |
-   |     calling a function with ABI C using caller ABI Rust
-   |     inside `call_rust_fn` at $DIR/abi-mismatch.rs:10:5
-...
+help: skipping check that does not even have a feature gate
+  --> $DIR/abi-mismatch.rs:16:40
+   |
 LL | static VAL: () = call_rust_fn(unsafe { std::mem::transmute(c_fn as extern "C" fn()) });
-   |                  --------------------------------------------------------------------- inside `VAL` at $DIR/abi-mismatch.rs:17:18
+   |                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error; 2 warnings emitted
+error: aborting due to previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/miri_unleashed/assoc_const.rs

@@ -11,7 +11,7 @@ trait Foo<T> {
 }
 
 trait Bar<T, U: Foo<T>> {
-    const F: u32 = (U::X, 42).1; //~ WARN skipping const checks
+    const F: u32 = (U::X, 42).1;
 }
 
 impl Foo<u32> for () {

src/test/ui/consts/miri_unleashed/assoc_const.stderr

@@ -1,15 +1,17 @@
-warning: skipping const checks
-  --> $DIR/assoc_const.rs:14:20
-   |
-LL |     const F: u32 = (U::X, 42).1;
-   |                    ^^^^^^^^^^
-
 error[E0080]: erroneous constant used
   --> $DIR/assoc_const.rs:31:13
    |
 LL |     let y = <String as Bar<Vec<u32>, String>>::F;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ referenced constant has errors
 
+warning: skipping const checks
+   |
+help: skipping check that does not even have a feature gate
+  --> $DIR/assoc_const.rs:14:20
+   |
+LL |     const F: u32 = (U::X, 42).1;
+   |                    ^^^^^^^^^^
+
 error: aborting due to previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/miri_unleashed/box.rs

@@ -1,5 +1,5 @@
 // compile-flags: -Zunleash-the-miri-inside-of-you
-#![feature(const_mut_refs, box_syntax)]
+#![feature(box_syntax)]
 #![allow(const_err)]
 
 use std::mem::ManuallyDrop;
@@ -8,7 +8,6 @@ fn main() {}
 
 static TEST_BAD: &mut i32 = {
     &mut *(box 0)
-    //~^ WARN skipping const check
-    //~| ERROR could not evaluate static initializer
+    //~^ ERROR could not evaluate static initializer
     //~| NOTE heap allocations
 };