Auto merge of #67575 - Centril:rollup-feikoir, r=Centril

Rollup of 7 pull requests

Successful merges:

 - #67337 (Ensure that evaluating or validating a constant never reads from a static)
 - #67543 (Add regression tests for fixed ICEs)
 - #67547 (Cleanup err codes)
 - #67551 (Add long error code explanation message for E0627)
 - #67561 (remove `description` from `Error` impls in docs)
 - #67569 (Clean up unsafety in char::encode_utf8)
 - #67572 (Use the chocolatey CDN directly to avoid the flaky API)

Failed merges:

r? @ghost

src/ci/scripts/install-msys2.sh

@@ -12,10 +12,14 @@ IFS=$'\n\t'
 source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
 
 if isWindows; then
-    for RETRY_COUNT in 1 2 3 4 5 6 7 8 9 10; do
-        choco install msys2 \
-            --params="/InstallDir:$(ciCheckoutPath)/msys2 /NoPath" -y --no-progress \
-            && mkdir -p "$(ciCheckoutPath)/msys2/home/${USERNAME}" \
-            && ciCommandAddPath "$(ciCheckoutPath)/msys2/usr/bin" && break
-    done
+    # Pre-followed the api/v2 URL to the CDN since the API can be a bit flakey
+    curl -sSL https://packages.chocolatey.org/msys2.20190524.0.0.20191030.nupkg > \
+        msys2.nupkg
+    curl -sSL https://packages.chocolatey.org/chocolatey-core.extension.1.3.5.1.nupkg > \
+        chocolatey-core.extension.nupkg
+    choco install -s . msys2 \
+        --params="/InstallDir:$(ciCheckoutPath)/msys2 /NoPath" -y --no-progress
+    rm msys2.nupkg chocolatey-core.extension.nupkg
+    mkdir -p "$(ciCheckoutPath)/msys2/home/${USERNAME}"
+    ciCommandAddPath "$(ciCheckoutPath)/msys2/usr/bin"
 fi

src/libcore/char/methods.rs

@@ -434,36 +434,35 @@ impl char {
     #[inline]
     pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
         let code = self as u32;
-        // SAFETY: each arm checks the size of the slice and only uses `get_unchecked` unsafe ops
-        unsafe {
-            let len = if code < MAX_ONE_B && !dst.is_empty() {
-                *dst.get_unchecked_mut(0) = code as u8;
-                1
-            } else if code < MAX_TWO_B && dst.len() >= 2 {
-                *dst.get_unchecked_mut(0) = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
-                *dst.get_unchecked_mut(1) = (code & 0x3F) as u8 | TAG_CONT;
-                2
-            } else if code < MAX_THREE_B && dst.len() >= 3 {
-                *dst.get_unchecked_mut(0) = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
-                *dst.get_unchecked_mut(1) = (code >> 6 & 0x3F) as u8 | TAG_CONT;
-                *dst.get_unchecked_mut(2) = (code & 0x3F) as u8 | TAG_CONT;
-                3
-            } else if dst.len() >= 4 {
-                *dst.get_unchecked_mut(0) = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
-                *dst.get_unchecked_mut(1) = (code >> 12 & 0x3F) as u8 | TAG_CONT;
-                *dst.get_unchecked_mut(2) = (code >> 6 & 0x3F) as u8 | TAG_CONT;
-                *dst.get_unchecked_mut(3) = (code & 0x3F) as u8 | TAG_CONT;
-                4
-            } else {
-                panic!(
-                    "encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
-                    from_u32_unchecked(code).len_utf8(),
-                    code,
-                    dst.len(),
-                )
-            };
-            from_utf8_unchecked_mut(dst.get_unchecked_mut(..len))
-        }
+        let len = self.len_utf8();
+        match (len, &mut dst[..]) {
+            (1, [a, ..]) => {
+                *a = code as u8;
+            }
+            (2, [a, b, ..]) => {
+                *a = (code >> 6 & 0x1F) as u8 | TAG_TWO_B;
+                *b = (code & 0x3F) as u8 | TAG_CONT;
+            }
+            (3, [a, b, c, ..]) => {
+                *a = (code >> 12 & 0x0F) as u8 | TAG_THREE_B;
+                *b = (code >> 6 & 0x3F) as u8 | TAG_CONT;
+                *c = (code & 0x3F) as u8 | TAG_CONT;
+            }
+            (4, [a, b, c, d, ..]) => {
+                *a = (code >> 18 & 0x07) as u8 | TAG_FOUR_B;
+                *b = (code >> 12 & 0x3F) as u8 | TAG_CONT;
+                *c = (code >> 6 & 0x3F) as u8 | TAG_CONT;
+                *d = (code & 0x3F) as u8 | TAG_CONT;
+            }
+            _ => panic!(
+                "encode_utf8: need {} bytes to encode U+{:X}, but the buffer has {}",
+                len,
+                code,
+                dst.len(),
+            ),
+        };
+        // SAFETY: We just wrote UTF-8 content in, so converting to str is fine.
+        unsafe { from_utf8_unchecked_mut(&mut dst[..len]) }
     }
 
     /// Encodes this character as UTF-16 into the provided `u16` buffer,

src/libcore/lib.rs

@@ -129,6 +129,7 @@
 #![feature(associated_type_bounds)]
 #![feature(const_type_id)]
 #![feature(const_caller_location)]
+#![feature(slice_patterns)]
 
 #[prelude_import]
 #[allow(unused)]

src/librustc/traits/error_reporting.rs

@@ -2373,7 +2373,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let span = self.tcx.def_span(generator_did);
 
         // Do not ICE on closure typeck (#66868).
-        if let None = self.tcx.hir().as_local_hir_id(generator_did) {
+        if self.tcx.hir().as_local_hir_id(generator_did).is_none() {
             return false;
         }
 

src/librustc_error_codes/error_codes.rs

@@ -346,6 +346,7 @@ E0622: include_str!("./error_codes/E0622.md"),
 E0623: include_str!("./error_codes/E0623.md"),
 E0624: include_str!("./error_codes/E0624.md"),
 E0626: include_str!("./error_codes/E0626.md"),
+E0627: include_str!("./error_codes/E0627.md"),
 E0631: include_str!("./error_codes/E0631.md"),
 E0633: include_str!("./error_codes/E0633.md"),
 E0635: include_str!("./error_codes/E0635.md"),
@@ -574,7 +575,6 @@ E0745: include_str!("./error_codes/E0745.md"),
 //  E0612, // merged into E0609
 //  E0613, // Removed (merged with E0609)
     E0625, // thread-local statics cannot be accessed at compile-time
-    E0627, // yield statement outside of generator literal
     E0628, // generators cannot have explicit parameters
     E0629, // missing 'feature' (rustc_const_unstable)
     // rustc_const_unstable attribute must be paired with stable/unstable

src/librustc_error_codes/error_codes/E0124.md

@@ -1,5 +1,6 @@
-You declared two fields of a struct with the same name. Erroneous code
-example:
+A struct was declared with two fields having the same name.
+
+Erroneous code example:
 
 ```compile_fail,E0124
 struct Foo {

src/librustc_error_codes/error_codes/E0128.md

@@ -1,4 +1,5 @@
-Type parameter defaults can only use parameters that occur before them.
+A type parameter with default value is using forward declared identifier.
+
 Erroneous code example:
 
 ```compile_fail,E0128
@@ -7,11 +8,11 @@ struct Foo<T = U, U = ()> {
     field2: U,
 }
 // error: type parameters with a default cannot use forward declared
-// identifiers
+//        identifiers
 ```
 
-Since type parameters are evaluated in-order, you may be able to fix this issue
-by doing:
+Type parameter defaults can only use parameters that occur before them. Since
+type parameters are evaluated in-order, this issue could be fixed by doing:
 
 ```
 struct Foo<U = (), T = U> {

src/librustc_error_codes/error_codes/E0627.md

@@ -0,0 +1,30 @@
+A yield expression was used outside of the generator literal.
+
+Erroneous code example:
+
+```compile_fail,E0627
+#![feature(generators, generator_trait)]
+
+fn fake_generator() -> &'static str {
+    yield 1;
+    return "foo"
+}
+
+fn main() {
+    let mut generator = fake_generator;
+}
+```
+
+The error occurs because keyword `yield` can only be used inside the generator
+literal. This can be fixed by constructing the generator correctly.
+
+```
+#![feature(generators, generator_trait)]
+
+fn main() {
+    let mut generator = || {
+        yield 1;
+        return "foo"
+    };
+}
+```

src/librustc_mir/borrow_check/mod.rs

@@ -1424,7 +1424,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
     }
 
     /// Reports an error if this is a borrow of local data.
-    /// This is called for all Yield statements on movable generators
+    /// This is called for all Yield expressions on movable generators
     fn check_for_local_borrow(&mut self, borrow: &BorrowData<'tcx>, yield_span: Span) {
         debug!("check_for_local_borrow({:?})", borrow);
 

src/librustc_mir/borrow_check/path_utils.rs

@@ -131,7 +131,7 @@ pub(super) fn is_active<'tcx>(
 }
 
 /// Determines if a given borrow is borrowing local data
-/// This is called for all Yield statements on movable generators
+/// This is called for all Yield expressions on movable generators
 pub(super) fn borrow_of_local_data(place: &Place<'_>) -> bool {
     match place.base {
         PlaceBase::Static(_) => false,

src/librustc_mir/const_eval.rs

@@ -45,9 +45,15 @@ fn mk_eval_cx<'mir, 'tcx>(
     tcx: TyCtxt<'tcx>,
     span: Span,
     param_env: ty::ParamEnv<'tcx>,
+    can_access_statics: bool,
 ) -> CompileTimeEvalContext<'mir, 'tcx> {
     debug!("mk_eval_cx: {:?}", param_env);
-    InterpCx::new(tcx.at(span), param_env, CompileTimeInterpreter::new(), Default::default())
+    InterpCx::new(
+        tcx.at(span),
+        param_env,
+        CompileTimeInterpreter::new(),
+        MemoryExtra { can_access_statics },
+    )
 }
 
 fn op_to_const<'tcx>(
@@ -176,6 +182,7 @@ fn eval_body_using_ecx<'mir, 'tcx>(
 #[derive(Clone, Debug)]
 pub enum ConstEvalError {
     NeedsRfc(String),
+    ConstAccessesStatic,
 }
 
 impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
@@ -195,6 +202,7 @@ impl fmt::Display for ConstEvalError {
                     msg
                 )
             }
+            ConstAccessesStatic => write!(f, "constant accesses static"),
         }
     }
 }
@@ -204,6 +212,7 @@ impl Error for ConstEvalError {
         use self::ConstEvalError::*;
         match *self {
             NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
+            ConstAccessesStatic => "constant accesses static",
         }
     }
 
@@ -224,6 +233,12 @@ pub struct CompileTimeInterpreter<'mir, 'tcx> {
     pub(super) loop_detector: snapshot::InfiniteLoopDetector<'mir, 'tcx>,
 }
 
+#[derive(Copy, Clone, Debug)]
+pub struct MemoryExtra {
+    /// Whether this machine may read from statics
+    can_access_statics: bool,
+}
+
 impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
     fn new() -> Self {
         CompileTimeInterpreter {
@@ -311,7 +326,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
     type ExtraFnVal = !;
 
     type FrameExtra = ();
-    type MemoryExtra = ();
+    type MemoryExtra = MemoryExtra;
     type AllocExtra = ();
 
     type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
@@ -473,7 +488,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
 
     #[inline(always)]
     fn init_allocation_extra<'b>(
-        _memory_extra: &(),
+        _memory_extra: &MemoryExtra,
         _id: AllocId,
         alloc: Cow<'b, Allocation>,
         _kind: Option<MemoryKind<!>>,
@@ -484,7 +499,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
 
     #[inline(always)]
     fn tag_static_base_pointer(
-        _memory_extra: &(),
+        _memory_extra: &MemoryExtra,
         _id: AllocId,
     ) -> Self::PointerTag {
         ()
@@ -527,6 +542,17 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
     fn stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
         Ok(())
     }
+
+    fn before_access_static(
+        memory_extra: &MemoryExtra,
+        _allocation: &Allocation,
+    ) -> InterpResult<'tcx> {
+        if memory_extra.can_access_statics {
+            Ok(())
+        } else {
+            Err(ConstEvalError::ConstAccessesStatic.into())
+        }
+    }
 }
 
 /// Extracts a field of a (variant of a) const.
@@ -540,7 +566,7 @@ pub fn const_field<'tcx>(
     value: &'tcx ty::Const<'tcx>,
 ) -> &'tcx ty::Const<'tcx> {
     trace!("const_field: {:?}, {:?}", field, value);
-    let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
+    let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
     // get the operand again
     let op = ecx.eval_const_to_op(value, None).unwrap();
     // downcast
@@ -560,7 +586,7 @@ pub fn const_caller_location<'tcx>(
     (file, line, col): (Symbol, u32, u32),
 ) -> &'tcx ty::Const<'tcx> {
     trace!("const_caller_location: {}:{}:{}", file, line, col);
-    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, ty::ParamEnv::reveal_all());
+    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, ty::ParamEnv::reveal_all(), false);
 
     let loc_ty = tcx.caller_location_ty();
     let loc_place = ecx.alloc_caller_location(file, line, col);
@@ -581,7 +607,7 @@ pub fn const_variant_index<'tcx>(
     val: &'tcx ty::Const<'tcx>,
 ) -> VariantIdx {
     trace!("const_variant_index: {:?}", val);
-    let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
+    let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
     let op = ecx.eval_const_to_op(val, None).unwrap();
     ecx.read_discriminant(op).unwrap().1
 }
@@ -610,7 +636,9 @@ fn validate_and_turn_into_const<'tcx>(
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
     let cid = key.value;
-    let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env);
+    let def_id = cid.instance.def.def_id();
+    let is_static = tcx.is_static(def_id);
+    let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
     let val = (|| {
         let mplace = ecx.raw_const_to_mplace(constant)?;
         let mut ref_tracking = RefTracking::new(mplace);
@@ -624,8 +652,7 @@ fn validate_and_turn_into_const<'tcx>(
         // Now that we validated, turn this into a proper constant.
         // Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
         // whether they become immediates.
-        let def_id = cid.instance.def.def_id();
-        if tcx.is_static(def_id) || cid.promoted.is_some() {
+        if is_static || cid.promoted.is_some() {
             let ptr = mplace.ptr.to_ptr()?;
             Ok(tcx.mk_const(ty::Const {
                 val: ty::ConstKind::Value(ConstValue::ByRef {
@@ -732,12 +759,14 @@ pub fn const_eval_raw_provider<'tcx>(
         return Err(ErrorHandled::Reported);
     }
 
+    let is_static = tcx.is_static(def_id);
+
     let span = tcx.def_span(cid.instance.def_id());
     let mut ecx = InterpCx::new(
         tcx.at(span),
         key.param_env,
         CompileTimeInterpreter::new(),
-        Default::default()
+        MemoryExtra { can_access_statics: is_static },
     );
 
     let res = ecx.load_mir(cid.instance.def, cid.promoted);
@@ -751,7 +780,7 @@ pub fn const_eval_raw_provider<'tcx>(
     }).map_err(|error| {
         let err = error_to_const_error(&ecx, error);
         // errors in statics are always emitted as fatal errors
-        if tcx.is_static(def_id) {
+        if is_static {
             // Ensure that if the above error was either `TooGeneric` or `Reported`
             // an error must be reported.
             let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");