Upgrade stable branch to Rust 1.86.0

[zhassan-aws]

Advance the stable branch to fe0d9d2 and use the 1.86.0 channel.

Additional Details:

• The 1.86.0 release was branched from main on 2025-02-14 (see https://releases.rs/docs/1.86.0/)
• The latest commit on main with a close toolchain is fe0d9d2 which upgraded the toolchain to 2025-02-12. The next commit upgrades the toolchain to 2025-02-21, which doesn't compile without reverting some of the changes done in that commit.
• Based on the previous point, I picked fe0d9d2, and made an additional change to make it compatible with the 1.86.0 release:

diff --git a/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs b/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
index 860619668c9..0c2a81c3082 100644
--- a/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
+++ b/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
@@ -667,7 +667,7 @@ fn codegen_rvalue_aggregate(
                 assert!(operands.len() == 2);
                 let typ = self.codegen_ty_stable(res_ty);
                 let layout = self.layout_of_stable(res_ty);
-                assert!(layout.ty.is_unsafe_ptr());
+                assert!(layout.ty.is_raw_ptr());
                 let data = self.codegen_operand_stable(&operands[0]);
                 match pointee_ty.kind() {
                     TyKind::RigidTy(RigidTy::Slice(inner_ty)) => {

(the same change was made in the next commit that upgraded the toolchain to 2025-02-21)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[zhassan-aws]

Only review the last commit in this PR. The others are merged as is from main.

[carolynzech]

It may be cleaner to do this via rebase rather than have a merge commit, but I'll leave that up to you.

Also, for posterity, would you mind updating the PR description with something like:
"Kani went from the 2/12 toolchain to 2/21, while 1.86.0 branched off of the 2/14 toolchain. So, this PR operates off of the 2/12 version of Kani, with a small change in 860140a to make it compatible with the 2/14 stable version."
Just so that future contributors know the steps we take to go about updating the stable branch.

[zhassan-aws]

After this PR, the diff w.r.t to the corresponding commit in main is reduced than for 1.85.1 (and is expected to be reduced further in the future):

diff --git a/.cargo/config.toml b/.cargo/config.toml
index 9bb4e080834..f0df939ef50 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -20,6 +20,8 @@ KANI_SYSROOT ={value = "target/kani", relative = true}
 KANI_BUILD_LIBS ={value = "target/build-libs", relative = true}
 # Build Kani library without `build-std`.
 KANI_LEGACY_LIBS ={value = "target/legacy-libs", relative = true}
+# This is only required for stable but is a no-op for nightly channels
+RUSTC_BOOTSTRAP = "1"
 
 [target.'cfg(all())']
 rustflags = [ # Global lints/warnings. Need to use underscore instead of -.
diff --git a/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs b/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
index 860619668c9..0c2a81c3082 100644
--- a/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
+++ b/kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs
@@ -667,7 +667,7 @@ fn codegen_rvalue_aggregate(
                 assert!(operands.len() == 2);
                 let typ = self.codegen_ty_stable(res_ty);
                 let layout = self.layout_of_stable(res_ty);
-                assert!(layout.ty.is_unsafe_ptr());
+                assert!(layout.ty.is_raw_ptr());
                 let data = self.codegen_operand_stable(&operands[0]);
                 match pointee_ty.kind() {
                     TyKind::RigidTy(RigidTy::Slice(inner_ty)) => {
diff --git a/kani-compiler/src/main.rs b/kani-compiler/src/main.rs
index c8a56d3ef06..106ad662b3a 100644
--- a/kani-compiler/src/main.rs
+++ b/kani-compiler/src/main.rs
@@ -16,6 +16,8 @@
 #![feature(f128)]
 #![feature(f16)]
 #![feature(non_exhaustive_omitted_patterns_lint)]
+#![feature(cfg_version)]
+#![cfg_attr(not(version("1.86")), feature(float_next_up_down))]
 #![feature(try_blocks)]
 extern crate rustc_abi;
 extern crate rustc_ast;
diff --git a/kani-driver/src/call_cargo.rs b/kani-driver/src/call_cargo.rs
index 4c39b03183b..9097713a001 100644
--- a/kani-driver/src/call_cargo.rs
+++ b/kani-driver/src/call_cargo.rs
@@ -206,6 +206,8 @@ pub fn cargo_build(&mut self, keep_going: bool) -> Result<CargoOutputs> {
                     // Use CARGO_ENCODED_RUSTFLAGS instead of RUSTFLAGS is preferred. See
                     // https://doc.rust-lang.org/cargo/reference/environment-variables.html
                     .env("CARGO_ENCODED_RUSTFLAGS", rustc_args.join(OsStr::new("\x1f")))
+                    // This is only required for stable but is a no-op for nightly channels
+                    .env("RUSTC_BOOTSTRAP", "1")
                     .env("CARGO_TERM_PROGRESS_WHEN", "never");
 
                 match self.run_build_target(cmd, verification_target.target()) {
diff --git a/kani-driver/src/call_single_file.rs b/kani-driver/src/call_single_file.rs
index 9a09ce6163f..f21f8334578 100644
--- a/kani-driver/src/call_single_file.rs
+++ b/kani-driver/src/call_single_file.rs
@@ -84,6 +84,8 @@ pub fn compile_single_rust_file(
         let mut cmd = Command::new(&self.kani_compiler);
         let kani_compiler_args = to_rustc_arg(kani_args);
         cmd.arg(kani_compiler_args).args(rustc_args);
+        // This is only required for stable but is a no-op for nightly channels
+        cmd.env("RUSTC_BOOTSTRAP", "1");
 
         if self.args.common_args.quiet {
             self.run_suppress(cmd)?;
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 2286133bf40..4e330c13244 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-02-12"
+channel = "1.86.0"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]
diff --git a/rustfmt.toml b/rustfmt.toml
index 44cbfe4a3dc..f8ff0d0fd10 100644
--- a/rustfmt.toml
+++ b/rustfmt.toml
@@ -6,13 +6,3 @@ edition = "2021"
 style_edition = "2024"
 use_small_heuristics = "Max"
 merge_derives = false
-
-ignore = [
-    "**/build/",
-    "**/target/",
-
-    # Do not format submodules
-    # For some reason, this is not working without the directory wildcard.
-    "**/firecracker",
-    "**/tests/perf/s2n-quic/",
-]
diff --git a/scripts/kani-fmt.sh b/scripts/kani-fmt.sh
index 5eca1582cc4..6a136f244ff 100755
--- a/scripts/kani-fmt.sh
+++ b/scripts/kani-fmt.sh
@@ -19,19 +19,25 @@ error=0
 cargo fmt "$@" || error=1
 
 # Check test source files.
-# Note that this will respect the ignore section of rustfmt.toml. If you need to
-# skip any file / directory, add it there.
 TESTS=("tests" "docs/src/tutorial")
+# Add ignore patterns for code we don't want to format.
+IGNORE=("*/perf/s2n-quic/*")
+
+# Arguments for the find command for excluding the IGNORE paths
+IGNORE_ARGS=()
+for ignore in "${IGNORE[@]}"; do
+    IGNORE_ARGS+=(-not -path "$ignore")
+done
 
 for suite in "${TESTS[@]}"; do
     # Find uses breakline to split between files. This ensures that we can
     # handle files with space in their path.
     set -f; IFS=$'\n'
-    files=($(find "${suite}" -name "*.rs"))
+    files=($(find "${suite}" -name "*.rs" ${IGNORE_ARGS[@]}))
     set +f; unset IFS
     # Note: We set the configuration file here because some submodules have
     # their own configuration file.
-    rustfmt --unstable-features "$@" --config-path rustfmt.toml "${files[@]}" || error=1
+    rustfmt --config-path rustfmt.toml "${files[@]}" || error=1
 done
 
 exit $error
diff --git a/tests/cargo-ui/verbose-cmds/expected b/tests/cargo-ui/verbose-cmds/expected
index f883ef972cb..b47b60d51ff 100644
--- a/tests/cargo-ui/verbose-cmds/expected
+++ b/tests/cargo-ui/verbose-cmds/expected
@@ -1,5 +1,5 @@
 CARGO_ENCODED_RUSTFLAGS=
-cargo +nightly
+cargo +
 Running: `goto-cc
 Running: `goto-instrument
 Checking harness dummy_harness...
diff --git a/tests/expected/function-contract/valid_ptr.expected b/tests/expected/function-contract/valid_ptr.expected
index 38f31a63d5c..0c43cd901cc 100644
--- a/tests/expected/function-contract/valid_ptr.expected
+++ b/tests/expected/function-contract/valid_ptr.expected
@@ -4,9 +4,7 @@ Failed Checks: |result| kani::mem::can_dereference(result.0)
 VERIFICATION:- FAILED
 
 Checking harness pre_condition::harness_invalid_ptr...
-Failed Checks: assertion failed: unsafe { read_ptr(ptr) } == -20
 Failed Checks: Kani does not support reasoning about pointer to unallocated memory
-Failed Checks: dereference failure: pointer outside object bounds
 VERIFICATION:- FAILED
 
 Checking harness pre_condition::harness_stack_ptr...

[zhassan-aws]

It may be cleaner to do this via rebase rather than have a merge commit, but I'll leave that up to you.

I've been deliberating this, and it seemed to me that doing a rebase would make us lose the commits for the previous releases since history will be rewritten. Using a merge commit, we would be able to maintain commits for previous stable releases (and perhaps we should even tag them). What do you think?

Also, for posterity, would you mind updating the PR description with something like

Will do. Done

[carolynzech]

I've been deliberating this, and it seemed to me that doing a rebase would make us lose the commits for the previous releases since history will be rewritten. Using a merge commit, we would be able to maintain commits for previous stable releases (and perhaps we should even tag them). What do you think?

Yeah, you're right, let's keep it as is.

[zhassan-aws]

The release bundle local toolchain test is failing because it's trying to download the bundle's nightly toolchain. We will probably need to create a separate workflow for testing the stable release bundle.

Merging this PR since the release bundle is not a required check anyway.