Rollup merge of #64858 - skinny121:str-const-generics, r=varkor

Add support for relating slices in `super_relate_consts`

This allows passing strings as generic arguments.

Fixes #63773
Fixes #60813

r? @varkor

src/librustc/mir/interpret/mod.rs

@@ -101,7 +101,7 @@ pub use self::error::{
     InvalidProgramInfo, ResourceExhaustionInfo, UndefinedBehaviorInfo,
 };
 
-pub use self::value::{Scalar, ScalarMaybeUndef, RawConst, ConstValue};
+pub use self::value::{Scalar, ScalarMaybeUndef, RawConst, ConstValue, get_slice_bytes};
 
 pub use self::allocation::{Allocation, AllocationExtra, Relocations, UndefMask};
 

src/librustc/mir/interpret/value.rs

@@ -611,3 +611,18 @@ impl_stable_hash_for!(enum crate::mir::interpret::ScalarMaybeUndef {
     Scalar(v),
     Undef
 });
+
+/// Gets the bytes of a constant slice value.
+pub fn get_slice_bytes<'tcx>(cx: &impl HasDataLayout, val: ConstValue<'tcx>) -> &'tcx [u8] {
+    if let ConstValue::Slice { data, start, end } = val {
+        let len = end - start;
+        data.get_bytes(
+            cx,
+            // invent a pointer, only the offset is relevant anyway
+            Pointer::new(AllocId(0), Size::from_bytes(start as u64)),
+            Size::from_bytes(len as u64),
+        ).unwrap_or_else(|err| bug!("const slice is invalid: {:?}", err))
+    } else {
+        bug!("expected const slice, but found another const value");
+    }
+}

src/librustc/ty/relate.rs

@@ -8,7 +8,7 @@ use crate::hir::def_id::DefId;
 use crate::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
 use crate::ty::{self, Ty, TyCtxt, TypeFoldable};
 use crate::ty::error::{ExpectedFound, TypeError};
-use crate::mir::interpret::{ConstValue, Scalar};
+use crate::mir::interpret::{ConstValue, get_slice_bytes, Scalar};
 use std::rc::Rc;
 use std::iter;
 use rustc_target::spec::abi;
@@ -584,7 +584,20 @@ pub fn super_relate_consts<R: TypeRelation<'tcx>>(
         // FIXME(const_generics): we should either handle `Scalar::Ptr` or add a comment
         // saying that we're not handling it intentionally.
 
-        // FIXME(const_generics): handle `ConstValue::ByRef` and `ConstValue::Slice`.
+        (a_val @ ConstValue::Slice { .. }, b_val @ ConstValue::Slice { .. }) => {
+            let a_bytes = get_slice_bytes(&tcx, a_val);
+            let b_bytes = get_slice_bytes(&tcx, b_val);
+            if a_bytes == b_bytes {
+                Ok(tcx.mk_const(ty::Const {
+                    val: a_val,
+                    ty: a.ty,
+                }))
+            } else {
+                Err(TypeError::ConstMismatch(expected_found(relation, &a, &b)))
+            }
+        }
+
+        // FIXME(const_generics): handle `ConstValue::ByRef`.
 
         // FIXME(const_generics): this is wrong, as it is a projection
         (ConstValue::Unevaluated(a_def_id, a_substs),

src/librustc_mir/hair/pattern/mod.rs

@@ -13,12 +13,12 @@ use crate::hair::constant::*;
 use rustc::lint;
 use rustc::mir::{Field, BorrowKind, Mutability};
 use rustc::mir::{UserTypeProjection};
-use rustc::mir::interpret::{GlobalId, ConstValue, sign_extend, AllocId, Pointer};
+use rustc::mir::interpret::{GlobalId, ConstValue, get_slice_bytes, sign_extend};
 use rustc::traits::{ObligationCause, PredicateObligation};
 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty, UserType, DefIdTree};
 use rustc::ty::{CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations};
 use rustc::ty::subst::{SubstsRef, GenericArg};
-use rustc::ty::layout::{VariantIdx, Size};
+use rustc::ty::layout::VariantIdx;
 use rustc::hir::{self, RangeEnd};
 use rustc::hir::def::{CtorOf, Res, DefKind, CtorKind};
 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
@@ -1526,27 +1526,10 @@ pub fn compare_const_vals<'tcx>(
 
     if let ty::Str = ty.kind {
         match (a.val, b.val) {
-            (
-                ConstValue::Slice { data: alloc_a, start: offset_a, end: end_a },
-                ConstValue::Slice { data: alloc_b, start: offset_b, end: end_b },
-            ) => {
-                let len_a = end_a - offset_a;
-                let len_b = end_b - offset_b;
-                let a = alloc_a.get_bytes(
-                    &tcx,
-                    // invent a pointer, only the offset is relevant anyway
-                    Pointer::new(AllocId(0), Size::from_bytes(offset_a as u64)),
-                    Size::from_bytes(len_a as u64),
-                );
-                let b = alloc_b.get_bytes(
-                    &tcx,
-                    // invent a pointer, only the offset is relevant anyway
-                    Pointer::new(AllocId(0), Size::from_bytes(offset_b as u64)),
-                    Size::from_bytes(len_b as u64),
-                );
-                if let (Ok(a), Ok(b)) = (a, b) {
-                    return from_bool(a == b);
-                }
+            (ConstValue::Slice { .. }, ConstValue::Slice { .. }) => {
+                let a_bytes = get_slice_bytes(&tcx, a.val);
+                let b_bytes = get_slice_bytes(&tcx, b.val);
+                return from_bool(a_bytes == b_bytes);
             }
             _ => (),
         }

src/test/ui/const-generics/slice-const-param-mismatch.rs

@@ -0,0 +1,14 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct ConstString<const T: &'static str>;
+struct ConstBytes<const T: &'static [u8]>;
+
+pub fn main() {
+    let _: ConstString<"Hello"> = ConstString::<"Hello">;
+    let _: ConstString<"Hello"> = ConstString::<"World">; //~ ERROR mismatched types
+    let _: ConstString<"ℇ㇈↦"> = ConstString::<"ℇ㇈↦">;
+    let _: ConstString<"ℇ㇈↦"> = ConstString::<"ℇ㇈↥">; //~ ERROR mismatched types
+    let _: ConstBytes<b"AAA"> = ConstBytes::<{&[0x41, 0x41, 0x41]}>;
+    let _: ConstBytes<b"AAA"> = ConstBytes::<b"BBB">; //~ ERROR mismatched types
+}

src/test/ui/const-generics/slice-const-param-mismatch.stderr

@@ -0,0 +1,38 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/slice-const-param-mismatch.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0308]: mismatched types
+  --> $DIR/slice-const-param-mismatch.rs:9:35
+   |
+LL |     let _: ConstString<"Hello"> = ConstString::<"World">;
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^ expected `"Hello"`, found `"World"`
+   |
+   = note: expected type `ConstString<>`
+              found type `ConstString<>`
+
+error[E0308]: mismatched types
+  --> $DIR/slice-const-param-mismatch.rs:11:33
+   |
+LL |     let _: ConstString<"ℇ㇈↦"> = ConstString::<"ℇ㇈↥">;
+   |                                  ^^^^^^^^^^^^^^^^^^^^^ expected `"ℇ㇈↦"`, found `"ℇ㇈↥"`
+   |
+   = note: expected type `ConstString<>`
+              found type `ConstString<>`
+
+error[E0308]: mismatched types
+  --> $DIR/slice-const-param-mismatch.rs:13:33
+   |
+LL |     let _: ConstBytes<b"AAA"> = ConstBytes::<b"BBB">;
+   |                                 ^^^^^^^^^^^^^^^^^^^^ expected `b"AAA"`, found `b"BBB"`
+   |
+   = note: expected type `ConstBytes<>`
+              found type `ConstBytes<>`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/const-generics/slice-const-param.rs

@@ -0,0 +1,19 @@
+// run-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+pub fn function_with_str<const STRING: &'static str>() -> &'static str {
+    STRING
+}
+
+pub fn function_with_bytes<const BYTES: &'static [u8]>() -> &'static [u8] {
+    BYTES
+}
+
+pub fn main() {
+    assert_eq!(function_with_str::<"Rust">(), "Rust");
+    assert_eq!(function_with_str::<"ℇ㇈↦">(), "ℇ㇈↦");
+    assert_eq!(function_with_bytes::<b"AAAA">(), &[0x41, 0x41, 0x41, 0x41]);
+    assert_eq!(function_with_bytes::<{&[0x41, 0x41, 0x41, 0x41]}>(), b"AAAA");
+}

src/test/ui/const-generics/slice-const-param.stderr

@@ -0,0 +1,8 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/slice-const-param.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+