Auto merge of #67080 - JohnTitor:rollup-2t6fm3u, r=JohnTitor

Rollup of 10 pull requests

Successful merges:

 - #66649 (VxWorks: fix issues in accessing environment variables)
 - #66764 (Tweak wording of `collect()` on bad target type)
 - #66900 (Clean up error codes)
 - #66974 ([CI] fix the `! isCI` check in src/ci/run.sh)
 - #66979 (Add long error for E0631 and update ui tests.)
 - #67017 (cleanup long error explanations)
 - #67021 (Fix docs for formatting delegations)
 - #67041 (add ExitStatusExt into prelude)
 - #67065 (Fix fetching arguments on the wasm32-wasi target)
 - #67066 (Update the revision of wasi-libc used in wasm32-wasi)

Failed merges:

r? @ghost

src/ci/docker/dist-various-2/build-wasi-toolchain.sh

@@ -12,7 +12,7 @@ export PATH=`pwd`/clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-14.04/bin:$PATH
 git clone https://github.com/CraneStation/wasi-libc
 
 cd wasi-libc
-git reset --hard a94d2d04e7722b323573da2bd04e909a5763d35b
+git reset --hard f645f498dfbbbc00a7a97874d33082d3605c3f21
 make -j$(nproc) INSTALL_DIR=/wasm32-wasi install
 
 cd ..

src/ci/run.sh

@@ -23,7 +23,7 @@ fi
 ci_dir=`cd $(dirname $0) && pwd`
 source "$ci_dir/shared.sh"
 
-if [ ! isCI ] || isCiBranch auto || isCiBranch beta; then
+if ! isCI || isCiBranch auto || isCiBranch beta; then
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set build.print-step-timings --enable-verbose-tests"
 fi
 

src/libcore/fmt/mod.rs

@@ -662,7 +662,7 @@ pub trait Display {
 ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 ///         let val = self.0;
 ///
-///         write!(f, "{:o}", val) // delegate to i32's implementation
+///         fmt::Octal::fmt(&val, f) // delegate to i32's implementation
 ///     }
 /// }
 ///
@@ -712,7 +712,7 @@ pub trait Octal {
 ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 ///         let val = self.0;
 ///
-///         write!(f, "{:b}", val) // delegate to i32's implementation
+///         fmt::Binary::fmt(&val, f) // delegate to i32's implementation
 ///     }
 /// }
 ///
@@ -771,7 +771,7 @@ pub trait Binary {
 ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 ///         let val = self.0;
 ///
-///         write!(f, "{:x}", val) // delegate to i32's implementation
+///         fmt::LowerHex::fmt(&val, f) // delegate to i32's implementation
 ///     }
 /// }
 ///
@@ -824,7 +824,7 @@ pub trait LowerHex {
 ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 ///         let val = self.0;
 ///
-///         write!(f, "{:X}", val) // delegate to i32's implementation
+///         fmt::UpperHex::fmt(&val, f) // delegate to i32's implementation
 ///     }
 /// }
 ///
@@ -869,7 +869,8 @@ pub trait UpperHex {
 ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 ///         // use `as` to convert to a `*const T`, which implements Pointer, which we can use
 ///
-///         write!(f, "{:p}", self as *const Length)
+///         let ptr = self as *const Self;
+///         fmt::Pointer::fmt(&ptr, f)
 ///     }
 /// }
 ///

src/libcore/iter/traits/collect.rs

@@ -91,9 +91,9 @@
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(
-    message="a collection of type `{Self}` cannot be built from an iterator \
+    message="a value of type `{Self}` cannot be built from an iterator \
              over elements of type `{A}`",
-    label="a collection of type `{Self}` cannot be built from `std::iter::Iterator<Item={A}>`",
+    label="value of type `{Self}` cannot be built from `std::iter::Iterator<Item={A}>`",
 )]
 pub trait FromIterator<A>: Sized {
     /// Creates a value from an iterator.

src/librustc_error_codes/error_codes.rs

@@ -347,6 +347,7 @@
 E0623: include_str!("./error_codes/E0623.md"),
 E0624: include_str!("./error_codes/E0624.md"),
 E0626: include_str!("./error_codes/E0626.md"),
+E0631: include_str!("./error_codes/E0631.md"),
 E0633: include_str!("./error_codes/E0633.md"),
 E0635: include_str!("./error_codes/E0635.md"),
 E0636: include_str!("./error_codes/E0636.md"),
@@ -580,7 +581,6 @@
     // rustc_const_unstable attribute must be paired with stable/unstable
     // attribute
     E0630,
-    E0631, // type mismatch in closure arguments
     E0632, // cannot provide explicit generic arguments when `impl Trait` is
            // used in argument position
     E0634, // type has conflicting packed representaton hints

src/librustc_error_codes/error_codes/E0092.md

@@ -1,4 +1,5 @@
-You tried to declare an undefined atomic operation function.
+An undefined atomic operation function was declared.
+
 Erroneous code example:
 
 ```compile_fail,E0092
@@ -11,8 +12,8 @@ extern "rust-intrinsic" {
 ```
 
 Please check you didn't make a mistake in the function's name. All intrinsic
-functions are defined in librustc_codegen_llvm/intrinsic.rs and in
-libcore/intrinsics.rs in the Rust source code. Example:
+functions are defined in `librustc_codegen_llvm/intrinsic.rs` and in
+`libcore/intrinsics.rs` in the Rust source code. Example:
 
 ```
 #![feature(intrinsics)]

src/librustc_error_codes/error_codes/E0093.md

@@ -1,4 +1,6 @@
-You declared an unknown intrinsic function. Erroneous code example:
+An unknown intrinsic function was declared.
+
+Erroneous code example:
 
 ```compile_fail,E0093
 #![feature(intrinsics)]
@@ -15,8 +17,8 @@ fn main() {
 ```
 
 Please check you didn't make a mistake in the function's name. All intrinsic
-functions are defined in librustc_codegen_llvm/intrinsic.rs and in
-libcore/intrinsics.rs in the Rust source code. Example:
+functions are defined in `librustc_codegen_llvm/intrinsic.rs` and in
+`libcore/intrinsics.rs` in the Rust source code. Example:
 
 ```
 #![feature(intrinsics)]

src/librustc_error_codes/error_codes/E0094.md

@@ -1,4 +1,5 @@
-You gave an invalid number of type parameters to an intrinsic function.
+An invalid number of type parameters was given to an intrinsic function.
+
 Erroneous code example:
 
 ```compile_fail,E0094

src/librustc_error_codes/error_codes/E0106.md

@@ -2,7 +2,7 @@ This error indicates that a lifetime is missing from a type. If it is an error
 inside a function signature, the problem may be with failing to adhere to the
 lifetime elision rules (see below).
 
-Here are some simple examples of where you'll run into this error:
+Erroneous code examples:
 
 ```compile_fail,E0106
 struct Foo1 { x: &bool }
@@ -27,7 +27,7 @@ function signatures which allows you to leave out lifetimes in certain cases.
 For more background on lifetime elision see [the book][book-le].
 
 The lifetime elision rules require that any function signature with an elided
-output lifetime must either have
+output lifetime must either have:
 
  - exactly one input lifetime
  - or, multiple input lifetimes, but the function must also be a method with a

src/librustc_error_codes/error_codes/E0107.md

@@ -1,4 +1,6 @@
-This error means that an incorrect number of generic arguments were provided:
+An incorrect number of generic arguments were provided.
+
+Erroneous code example:
 
 ```compile_fail,E0107
 struct Foo<T> { x: T }
@@ -9,6 +11,7 @@ struct Baz<S, T> { x: Foo<S, T> } // error: wrong number of type arguments:
                                   //        expected 1, found 2
 
 fn foo<T, U>(x: T, y: U) {}
+fn f() {}
 
 fn main() {
     let x: bool = true;
@@ -16,12 +19,26 @@ fn main() {
                                     //        expected 2, found 1
     foo::<bool, i32, i32>(x, 2, 4); // error: wrong number of type arguments:
                                     //        expected 2, found 3
+    f::<'static>();                 // error: wrong number of lifetime arguments
+                                    //        expected 0, found 1
 }
+```
 
+When using/declaring an item with generic arguments, you must provide the exact
+same number:
+
+```
+struct Foo<T> { x: T }
+
+struct Bar<T> { x: Foo<T> }               // ok!
+struct Baz<S, T> { x: Foo<S>, y: Foo<T> } // ok!
+
+fn foo<T, U>(x: T, y: U) {}
 fn f() {}
 
 fn main() {
-    f::<'static>(); // error: wrong number of lifetime arguments:
-                    //        expected 0, found 1
+    let x: bool = true;
+    foo::<bool, u32>(x, 12);              // ok!
+    f();                                  // ok!
 }
 ```

src/librustc_error_codes/error_codes/E0109.md

@@ -1,4 +1,5 @@
 You tried to provide a generic argument to a type which doesn't need it.
+
 Erroneous code example:
 
 ```compile_fail,E0109

src/librustc_error_codes/error_codes/E0116.md

@@ -1,11 +1,15 @@
-You can only define an inherent implementation for a type in the same crate
-where the type was defined. For example, an `impl` block as below is not allowed
-since `Vec` is defined in the standard library:
+An inherent implementation was defined for a type outside the current crate.
+
+Erroneous code example:
 
 ```compile_fail,E0116
 impl Vec<u8> { } // error
 ```
 
+You can only define an inherent implementation for a type in the same crate
+where the type was defined. For example, an `impl` block as above is not allowed
+since `Vec` is defined in the standard library.
+
 To fix this problem, you can do either of these things:
 
  - define a trait that has the desired associated functions/types/constants and

src/librustc_error_codes/error_codes/E0117.md

@@ -1,3 +1,11 @@
+The `Drop` trait was implemented on a non-struct type.
+
+Erroneous code example:
+
+```compile_fail,E0117
+impl Drop for u32 {}
+```
+
 This error indicates a violation of one of Rust's orphan rules for trait
 implementations. The rule prohibits any implementation of a foreign trait (a
 trait defined in another crate) where
@@ -6,12 +14,6 @@ trait defined in another crate) where
  - all of the parameters being passed to the trait (if there are any) are also
    foreign.
 
-Here's one example of this error:
-
-```compile_fail,E0117
-impl Drop for u32 {}
-```
-
 To avoid this kind of error, ensure that at least one local type is referenced
 by the `impl`:
 

src/librustc_error_codes/error_codes/E0118.md

@@ -1,5 +1,7 @@
-You're trying to write an inherent implementation for something which isn't a
-struct nor an enum. Erroneous code example:
+An inherent implementation was defined for something which isn't a struct nor
+an enum.
+
+Erroneous code example:
 
 ```compile_fail,E0118
 impl (u8, u8) { // error: no base type found for inherent implementation

src/librustc_error_codes/error_codes/E0119.md

@@ -1,5 +1,6 @@
 There are conflicting trait implementations for the same type.
-Example of erroneous code:
+
+Erroneous code example:
 
 ```compile_fail,E0119
 trait MyTrait {

src/librustc_error_codes/error_codes/E0631.md

@@ -0,0 +1,27 @@
+This error indicates a type mismatch in closure arguments.
+
+Erroneous code example:
+
+```compile_fail,E0631
+fn foo<F: Fn(i32)>(f: F) {
+}
+
+fn main() {
+    foo(|x: &str| {});
+}
+```
+
+The error occurs because `foo` accepts a closure that takes an `i32` argument,
+but in `main`, it is passed a closure with a `&str` argument.
+
+This can be resolved by changing the type annotation or removing it entirely
+if it can be inferred.
+
+```
+fn foo<F: Fn(i32)>(f: F) {
+}
+
+fn main() {
+    foo(|x: i32| {});
+}
+```

src/libstd/sys/vxworks/ext/mod.rs

@@ -18,4 +18,7 @@ pub mod prelude {
     #[doc(no_inline)]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub use super::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
+    #[doc(no_inline)]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub use super::process::ExitStatusExt;
 }

src/libstd/sys/vxworks/os.rs

@@ -11,14 +11,12 @@
 use crate::ptr;
 use crate::slice;
 use crate::str;
-use crate::sys_common::mutex::Mutex;
+use crate::sys_common::mutex::{Mutex, MutexGuard};
 use crate::sys::cvt;
 /*use sys::fd; this one is probably important */
 use crate::vec;
 
 const TMPBUF_SZ: usize = 128;
-static ENV_LOCK: Mutex = Mutex::new();
-
 
 // This is a terrible fix
 use crate::sys::os_str::Buf;
@@ -200,11 +198,18 @@ pub unsafe fn environ() -> *mut *const *const c_char {
     &mut environ
 }
 
+pub unsafe fn env_lock() -> MutexGuard<'static> {
+    // We never call `ENV_LOCK.init()`, so it is UB to attempt to
+    // acquire this mutex reentrantly!
+    static ENV_LOCK: Mutex = Mutex::new();
+    ENV_LOCK.lock()
+}
+
 /// Returns a vector of (variable, value) byte-vector pairs for all the
 /// environment variables of the current process.
 pub fn env() -> Env {
     unsafe {
-        let _guard = ENV_LOCK.lock();
+        let _guard = env_lock();
         let mut environ = *environ();
         if environ == ptr::null() {
             panic!("os::env() failure getting env string from OS: {}",
@@ -244,7 +249,7 @@ pub fn getenv(k: &OsStr) -> io::Result<Option<OsString>> {
     // always None as well
     let k = CString::new(k.as_bytes())?;
     unsafe {
-        let _guard = ENV_LOCK.lock();
+        let _guard = env_lock();
         let s = libc::getenv(k.as_ptr()) as *const libc::c_char;
         let ret = if s.is_null() {
             None
@@ -260,7 +265,7 @@ pub fn setenv(k: &OsStr, v: &OsStr) -> io::Result<()> {
     let v = CString::new(v.as_bytes())?;
 
     unsafe {
-        let _guard = ENV_LOCK.lock();
+        let _guard = env_lock();
         cvt(libc::setenv(k.as_ptr(), v.as_ptr(), 1)).map(|_| ())
     }
 }
@@ -269,7 +274,7 @@ pub fn unsetenv(n: &OsStr) -> io::Result<()> {
     let nbuf = CString::new(n.as_bytes())?;
 
     unsafe {
-        let _guard = ENV_LOCK.lock();
+        let _guard = env_lock();
         cvt(libc::unsetenv(nbuf.as_ptr())).map(|_| ())
     }
 }

src/libstd/sys/vxworks/process/process_vxworks.rs

@@ -15,6 +15,7 @@ pub fn spawn(&mut self, default: Stdio, needs_stdin: bool)
                  -> io::Result<(Process, StdioPipes)> {
         use crate::sys::{cvt_r};
         const CLOEXEC_MSG_FOOTER: &'static [u8] = b"NOEX";
+        let envp = self.capture_env();
 
         if self.saw_nul() {
             return Err(io::Error::new(ErrorKind::InvalidInput,
@@ -52,12 +53,19 @@ macro_rules! t {
                 t!(cvt(libc::chdir(cwd.as_ptr())));
             }
 
+            let c_envp = envp.as_ref().map(|c| c.as_ptr())
+                .unwrap_or_else(|| *sys::os::environ() as *const _);
+            let stack_size = thread::min_stack();
+
+            // ensure that access to the environment is synchronized
+            let _lock = sys::os::env_lock();
+
             let ret = libc::rtpSpawn(
                 self.get_argv()[0],                   // executing program
                 self.get_argv().as_ptr() as *mut *const c_char, // argv
-                *sys::os::environ() as *mut *const c_char,
+                c_envp as *mut *const c_char,
                 100 as c_int,                         // initial priority
-                thread::min_stack(),                  // initial stack size.
+                stack_size,                           // initial stack size.
                 0,                                    // options
                 0                                     // task options
             );

src/libstd/sys/wasi/args.rs

@@ -26,6 +26,7 @@ fn maybe_args() -> Option<Vec<OsString>> {
         let mut argv = Vec::with_capacity(argc);
         let mut buf = Vec::with_capacity(buf_size);
         wasi::args_get(argv.as_mut_ptr(), buf.as_mut_ptr()).ok()?;
+        argv.set_len(argc);
         let mut ret = Vec::with_capacity(argc);
         for ptr in argv {
             let s = CStr::from_ptr(ptr.cast());

src/test/ui/anonymous-higher-ranked-lifetime.stderr

@@ -121,3 +121,4 @@ LL | fn h2<F>(_: F) where F: for<'t0> Fn(&(), Box<dyn Fn(&())>, &'t0 (), fn(&(),
 
 error: aborting due to 11 previous errors
 
+For more information about this error, try `rustc --explain E0631`.

src/test/ui/closure-expected-type/expect-fn-supply-fn.nll.stderr

@@ -39,3 +39,4 @@ LL |     with_closure_expecting_fn_with_bound_region(|x: Foo<'_>, y| {
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0631`.

src/test/ui/closure-expected-type/expect-fn-supply-fn.stderr

@@ -77,4 +77,5 @@ LL |     with_closure_expecting_fn_with_bound_region(|x: Foo<'_>, y| {
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0308, E0631.
+For more information about an error, try `rustc --explain E0308`.

src/test/ui/closure-expected-type/expect-infer-var-appearing-twice.stderr

@@ -13,3 +13,4 @@ LL |     with_closure(|x: u32, y: i32| {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0631`.

src/test/ui/closures/issue-41366.stderr

@@ -19,4 +19,5 @@ LL |     (&|_|()) as &dyn for<'x> Fn(<u32 as T<'x>>::V);
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+Some errors have detailed explanations: E0271, E0631.
+For more information about an error, try `rustc --explain E0271`.

src/test/ui/issues/issue-43623.stderr

@@ -25,4 +25,5 @@ LL |     break_me::<Type, fn(_)>;
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+Some errors have detailed explanations: E0271, E0631.
+For more information about an error, try `rustc --explain E0271`.

src/test/ui/issues/issue-60283.stderr

@@ -27,4 +27,5 @@ LL |     foo((), drop)
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+Some errors have detailed explanations: E0271, E0631.
+For more information about an error, try `rustc --explain E0271`.

src/test/ui/mismatched_types/E0631.stderr

@@ -46,3 +46,4 @@ LL |     bar(f);
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0631`.

src/test/ui/mismatched_types/closure-arg-type-mismatch.stderr

@@ -45,4 +45,5 @@ LL |     baz(f);
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+Some errors have detailed explanations: E0271, E0631.
+For more information about an error, try `rustc --explain E0271`.

src/test/ui/mismatched_types/closure-mismatch.stderr

@@ -24,4 +24,5 @@ LL |     baz(|_| ());
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+Some errors have detailed explanations: E0271, E0631.
+For more information about an error, try `rustc --explain E0271`.

src/test/ui/mismatched_types/fn-variance-1.stderr

@@ -24,3 +24,4 @@ LL |     apply(&mut 3, takes_imm);
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0631`.

src/test/ui/mismatched_types/issue-36053-2.stderr

@@ -18,4 +18,5 @@ LL |     once::<&str>("str").fuse().filter(|a: &str| true).count();
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0599`.
+Some errors have detailed explanations: E0599, E0631.
+For more information about an error, try `rustc --explain E0599`.

src/test/ui/mismatched_types/unboxed-closures-vtable-mismatch.stderr

@@ -12,3 +12,4 @@ LL |     let z = call_it(3, f);
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0631`.

src/test/ui/type/type-check-defaults.rs

@@ -4,9 +4,9 @@
 
 struct Foo<T, U: FromIterator<T>>(T, U);
 struct WellFormed<Z = Foo<i32, i32>>(Z);
-//~^ ERROR a collection of type `i32` cannot be built from an iterator over elements of type `i32`
+//~^ ERROR a value of type `i32` cannot be built from an iterator over elements of type `i32`
 struct WellFormedNoBounds<Z:?Sized = Foo<i32, i32>>(Z);
-//~^ ERROR a collection of type `i32` cannot be built from an iterator over elements of type `i32`
+//~^ ERROR a value of type `i32` cannot be built from an iterator over elements of type `i32`
 
 struct Bounds<T:Copy=String>(T);
 //~^ ERROR the trait bound `std::string::String: std::marker::Copy` is not satisfied [E0277]

src/test/ui/type/type-check-defaults.stderr

@@ -1,21 +1,21 @@
-error[E0277]: a collection of type `i32` cannot be built from an iterator over elements of type `i32`
+error[E0277]: a value of type `i32` cannot be built from an iterator over elements of type `i32`
   --> $DIR/type-check-defaults.rs:6:19
    |
 LL | struct Foo<T, U: FromIterator<T>>(T, U);
    | ---------------------------------------- required by `Foo`
 LL | struct WellFormed<Z = Foo<i32, i32>>(Z);
-   |                   ^ a collection of type `i32` cannot be built from `std::iter::Iterator<Item=i32>`
+   |                   ^ value of type `i32` cannot be built from `std::iter::Iterator<Item=i32>`
    |
    = help: the trait `std::iter::FromIterator<i32>` is not implemented for `i32`
 
-error[E0277]: a collection of type `i32` cannot be built from an iterator over elements of type `i32`
+error[E0277]: a value of type `i32` cannot be built from an iterator over elements of type `i32`
   --> $DIR/type-check-defaults.rs:8:27
    |
 LL | struct Foo<T, U: FromIterator<T>>(T, U);
    | ---------------------------------------- required by `Foo`
 ...
 LL | struct WellFormedNoBounds<Z:?Sized = Foo<i32, i32>>(Z);
-   |                           ^ a collection of type `i32` cannot be built from `std::iter::Iterator<Item=i32>`
+   |                           ^ value of type `i32` cannot be built from `std::iter::Iterator<Item=i32>`
    |
    = help: the trait `std::iter::FromIterator<i32>` is not implemented for `i32`
 

src/test/ui/type/type-dependent-def-issue-49241.rs

@@ -3,5 +3,5 @@ fn main() {
     const l: usize = v.count(); //~ ERROR attempt to use a non-constant value in a constant
     let s: [u32; l] = v.into_iter().collect();
     //~^ ERROR evaluation of constant value failed
-    //~^^ ERROR a collection of type
+    //~^^ ERROR a value of type
 }

src/test/ui/type/type-dependent-def-issue-49241.stderr

@@ -10,11 +10,11 @@ error[E0080]: evaluation of constant value failed
 LL |     let s: [u32; l] = v.into_iter().collect();
    |                  ^ referenced constant has errors
 
-error[E0277]: a collection of type `[u32; _]` cannot be built from an iterator over elements of type `{integer}`
+error[E0277]: a value of type `[u32; _]` cannot be built from an iterator over elements of type `{integer}`
   --> $DIR/type-dependent-def-issue-49241.rs:4:37
    |
 LL |     let s: [u32; l] = v.into_iter().collect();
-   |                                     ^^^^^^^ a collection of type `[u32; _]` cannot be built from `std::iter::Iterator<Item={integer}>`
+   |                                     ^^^^^^^ value of type `[u32; _]` cannot be built from `std::iter::Iterator<Item={integer}>`
    |
    = help: the trait `std::iter::FromIterator<{integer}>` is not implemented for `[u32; _]`