Change toolchain from nightly to stable

As of Rust 1.68, the uefi crates work on stable. Remove the
`channel = "nightly"` setting from `rust-toolchain.toml` and
`template/rust-toolchain.toml`.

Related changes:
* The CI job to compile with the MSRV has been changed from `nightly-2022-11-22`
  to `1.68`. So for now the MSRV job isn't checking anything that isn't already
  checked by other jobs, but once 1.69 comes out it will.
* The CI job to test the latest crates.io release still needs the nightly
  toolchain until we do a new release.
* Some of the uefi-macros compiler ui tests have been modified so that the error
  output matches the errors produced by stable compiler, which are currently
  slightly different in a few cases from the nightly compiler. In particular,
  the precise spans we output for errors in the guid macros don't work on
  stable, because proc-macro's Literal::subspan method is currently unstable.

.github/workflows/msrv_toolchain.toml

@@ -1,4 +1,3 @@
 [toolchain]
-# Oldest nightly that currently works with `cargo xtask build`.
-channel = "nightly-2022-11-22"
+channel = "1.68"
 targets = ["aarch64-unknown-uefi", "i686-unknown-uefi", "x86_64-unknown-uefi"]

.github/workflows/rust.yml

@@ -108,6 +108,10 @@ jobs:
     - name: Checkout sources
       uses: actions/checkout@v3
 
+    # TODO: for now our latest release (0.19.1) requires nightly.
+    - name: Set nightly toolchain
+      run: cp .github/workflows/nightly_toolchain.toml rust-toolchain.toml
+
     - name: Build
       run: cargo xtask test-latest-release
 
@@ -143,6 +147,8 @@ jobs:
     - name: Build
       run: cargo xtask build
 
+  # This job requires the nightly channel, but keep it as a separate job from
+  # `nightly_channel` because it takes a while to run.
   build_feature_permutations:
     name: Check that the build works for all feature combinations
     runs-on: ubuntu-latest
@@ -150,6 +156,9 @@ jobs:
     - name: Checkout sources
       uses: actions/checkout@v3
 
+    - name: Set nightly toolchain so that `unstable` can be included
+      run: cp .github/workflows/nightly_toolchain.toml rust-toolchain.toml
+
     - name: Build
       run: cargo xtask build --feature-permutations
 

rust-toolchain.toml

@@ -1,3 +1,2 @@
 [toolchain]
-channel = "nightly"
 targets = ["aarch64-unknown-uefi", "i686-unknown-uefi", "x86_64-unknown-uefi"]

template/rust-toolchain.toml

@@ -1,3 +1,2 @@
 [toolchain]
-channel = "nightly"
 targets = ["aarch64-unknown-uefi", "i686-unknown-uefi", "x86_64-unknown-uefi"]

uefi-macros/tests/ui/entry_bad_abi.stderr

@@ -2,4 +2,4 @@ error: Entry method must have no ABI modifier
  --> tests/ui/entry_bad_abi.rs:8:1
   |
 8 | extern "C" fn main(_handle: Handle, _st: SystemTable<Boot>) -> Status {
-  | ^^^^^^^^^^
+  | ^^^^^^

uefi-macros/tests/ui/entry_bad_return_type.stderr

@@ -2,7 +2,7 @@ error[E0308]: mismatched types
  --> tests/ui/entry_bad_return_type.rs:8:1
   |
 8 | fn main(_handle: Handle, _st: SystemTable<Boot>) -> bool {
-  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Status`, found `bool`
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `Status`, found `bool`
   |
   = note: expected fn pointer `extern "efiapi" fn(uefi::Handle, uefi::table::SystemTable<_>) -> Status`
              found fn pointer `extern "efiapi" fn(uefi::Handle, uefi::table::SystemTable<_>) -> bool`

uefi-macros/tests/ui/guid_bad_hex_group2.stderr

@@ -1,5 +1,5 @@
 error: GUID component "Gaaa" is not a hexadecimal number
- --> tests/ui/guid_bad_hex_group2.rs:5:44
+ --> tests/ui/guid_bad_hex_group2.rs:5:34
   |
 5 | const BadHexGroup2: Guid = guid!("aaaaaaaa-Gaaa-aaaa-aaaa-aaaaaaaaaaaa");
-  |                                            ^^^^
+  |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

uefi-macros/tests/ui/guid_bad_hex_group5.stderr

@@ -1,5 +1,5 @@
 error: GUID component "aaaaaaaaaaaG" is not a hexadecimal number
- --> tests/ui/guid_bad_hex_group5.rs:5:59
+ --> tests/ui/guid_bad_hex_group5.rs:5:34
   |
 5 | const BadHexGroup5: Guid = guid!("aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaG");
-  |                                                           ^^^^^^^^^^^^
+  |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

xtask/src/main.rs

@@ -50,7 +50,7 @@ fn build(opt: &BuildOpt) -> Result<()> {
 
     let cargo = Cargo {
         action: CargoAction::Build,
-        features: Feature::more_code(true, true),
+        features: Feature::more_code(false, true),
         packages: Package::all_except_xtask(),
         release: opt.build_mode.release,
         target: Some(*opt.target),
@@ -64,8 +64,7 @@ fn clippy(opt: &ClippyOpt) -> Result<()> {
     // Run clippy on all the UEFI packages.
     let cargo = Cargo {
         action: CargoAction::Clippy,
-        // for all possible features
-        features: Feature::more_code(true, true),
+        features: Feature::more_code(false, true),
         packages: Package::all_except_xtask(),
         release: false,
         target: Some(*opt.target),