Driver cleanups

[nnethercote]

Minor improvements I found while looking at this code.

r? @jieyouxu

[nnethercote]

@bors rollup

[rust-log-analyzer]

The job x86_64-gnu-llvm-18 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

#16 exporting to docker image format
#16 sending tarball 28.1s done
#16 DONE 34.2s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-18]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-18', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-18/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
---- [ui] tests/ui-fulldeps/stable-mir/check_def_ty.rs stdout ----

error: test run failed!
status: exit status: 101
command: cd "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/stable-mir/check_def_ty" && RUSTC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" RUST_TEST_THREADS="16" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/stable-mir/check_def_ty/a"
--- stderr -------------------------------
warning: the feature `core_intrinsics` is internal to the compiler or standard library
##[warning] --> defs_ty_input.rs:3:20
  |
---

warning: constant `CONST_U32` is never used
##[warning] --> defs_ty_input.rs:5:15
  |
5 |         const CONST_U32: u32 = 0u32;

warning: function `extern_fn` is never used
##[warning]  --> defs_ty_input.rs:14:16
   |
   |
14 |             fn extern_fn(x: i32) -> i32;

warning: static `EXT_STATIC` is never used
##[warning]  --> defs_ty_input.rs:15:20
   |
---
--- stderr -------------------------------
warning: variable does not need to be mutable
##[warning]  --> alloc_input.rs:16:56
   |
16 |         pub unsafe extern "C" fn variadic_fn(n: usize, mut args: ...) -> usize {
   |                                                        |
   |                                                        help: remove this `mut`
   |
   = note: `#[warn(unused_mut)]` on by default
---

warning: static `C_STR` is never used
##[warning] --> alloc_input.rs:8:12
  |
8 |     static C_STR: &std::ffi::CStr = c"cstr";
  |
  = note: `#[warn(dead_code)]` on by default

warning: function `check_type_id` is never used
---

warning: unused variable: `vtable_sz`
##[warning] --> binop_input.rs:5:17
  |
5 |             let vtable_sz = unsafe { vtable_size(0 as *const ()) };
  |                 ^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_vtable_sz`
  = note: `#[warn(unused_variables)]` on by default

thread 'rustc' panicked at compiler/rustc_interface/src/queries.rs:37:25:
already borrowed: BorrowMutError
already borrowed: BorrowMutError
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
warning: 2 warnings emitted
------------------------------------------


---- [ui] tests/ui-fulldeps/obtain-borrowck.rs stdout ----
Saved the actual run.stdout to "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/obtain-borrowck/obtain-borrowck.run.stdout"

- Bodies retrieved for:
- ::X::provided
- ::foo
- ::foo
- ::main
- ::main::{constant#0}
- ::{impl#0}::new
- ::{impl#1}::provided
- ::{impl#1}::required


The actual run.stdout differed from the expected run.stdout.
The actual run.stdout differed from the expected run.stdout.
Saved the actual run.stderr to "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/obtain-borrowck/obtain-borrowck.run.stderr"
thread 'rustc' panicked at compiler/rustc_interface/src/queries.rs:37:25:
already borrowed: BorrowMutError
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace




The actual run.stderr differed from the expected run.stderr.

error: 2 errors occurred comparing run output.
status: exit status: 101
command: cd "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/obtain-borrowck" && RUSTC="/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" RUST_TEST_THREADS="16" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui-fulldeps/obtain-borrowck/a" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--edition=2021" "/checkout/tests/ui-fulldeps/auxiliary/obtain-borrowck-input.rs"
--- stderr -------------------------------
thread 'rustc' panicked at compiler/rustc_interface/src/queries.rs:37:25:
already borrowed: BorrowMutError
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[jieyouxu]

I suspect the queries.global_ctxt()? was indeed for abiding with dynamic borrowck rules

[bjorn3]

This PR looks fine to me. Just FYI: I've got a whole bunch of driver refactorings myself that may conflict with whatever cleanups you want to do to the driver. Part of them are in #132410 and the rest are in a branch somewhere waiting for this PR to be merged.

[jieyouxu]

@bjorn3 what would you like to do, coalesce this PR into #132410?

[bjorn3]

I'm fine with this PR being merged separately. It contains some changes that are not in my PR and it may take a while before my PR gets reviewed.

[jieyouxu]

Thanks, this also LGTM otherwise too, feel free to r=me after PR CI is green.

[petrochenkov]

This change was attempted before and reverted - #107740.

[jieyouxu]

Huh, we should add a comment to point this out linking to #107740 and why.

[bjorn3]

FWIW #132410 changes after_analysis to pass in TyCtxt directly, avoiding the double locking issue.

[petrochenkov]

The naming (input_fragment, fragment_with_placeholders, expanded_fragment) was important to me when I (re)wrote this code.
Otherwise it's not clear what is actually happening with the fragment during the mutations.

[jieyouxu]

I guess we should also leave a comment explaining the difference between these fragment phases?

[jieyouxu]

(Unassigning myself as petrochenkov knows about this part better.)