ICE inlining failed in call to ‘always_inline’ function body not available

[matthiaskrgr]

snippet:

//@compile-flags: --edition=2024 -Zcodegen-backend=gcc -Clink-dead-code=true
//@run-rustfix

#![warn(clippy::all, clippy::pedantic)]
#![allow(clippy::let_underscore_untyped)]
#![allow(clippy::missing_docs_in_private_items)]
#![allow(clippy::map_identity)]
#![allow(clippy::redundant_closure)]
#![allow(clippy::unnecessary_wraps)]
#![feature(result_flattening)]

fn main() {
    // mapping to Option on Iterator
    fn option_id(x: i8) -> Option<i8> {
        Some(x)
    }
    let option_id_ref: fn(i8) -> Option<i8> = option_id;
    let option_id_closure = |x| Some(x);
    let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id).flatten().collect();
    let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id_ref).flatten().collect();
    let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id_closure).flatten().collect();
    let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| x.checked_add(1)).flatten().collect();

    // mapping to Iterator on Iterator
    let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();

    // mapping to Option on Option
    let _: Option<_> = (Some(Some(1))).map(|x| x).flatten();

    // mapping to Result on Result
    let _: Result<_, &str> = (Ok(Ok(1))).map(|x| x).flatten();

    issue8734();
    issue8878();
}

fn issue8734() {
    let _ = [0u8, 1, 2, 3]
        .into_iter()
        .map(|n| match n {
            1 => [n
                .saturating_add(1)
                .saturating_add(1)
                .saturating_add(1)
                .saturating_add(1)
                .saturating_add(1)
                .saturating_add(1)
                .saturating_add(1)
                .saturating_add(1)],
            n => [n],
        })
        .flatten();
}

#[allow(clippy::bind_instead_of_map)] // map + flatten will be suggested to `and_then`, but afterwards `map` is suggested again
#[rustfmt::skip] // whitespace is important for this one
fn issue8878() {
    std::collections::HashMap::<u32, u32>::new()
        .get(&0)
        .map(|_| {
// we need some newlines
// so that the span is big enough
// for a split output of the diagnostic
            Some("")
 // whitespace beforehand is important as well
        })
        .flatten();
}

Version information

rustc 1.95.0-nightly (d222ddc4d 2026-01-23)
binary: rustc
commit-hash: d222ddc4d90743dfc1e53b610be8fc9d95893d2c
commit-date: 2026-01-23
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc --edition=2024 -Zcodegen-backend=gcc -Clink-dead-code=true

Program output

warning: the feature `result_flattening` has been stable since 1.89.0 and no longer requires an attribute to enable
 --> /tmp/icemaker_global_tempdir.DCV30WOGYWbd/rustc_testrunner_tmpdir_reporting.t6FVbqkY94un/mvce.rs:9:12
  |
9 | #![feature(result_flattening)]
  |            ^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(stable_features)]` on by default

libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs1U_NtNtCs8mkrhYlWyjl_4core9core_arch4simdNtB6_5i8x163newCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: note: : called from here
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs4_NtCs8mkrhYlWyjl_4core3numh14saturating_addCs3e1qynuMko5_4mvce’: function body not available
error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-m64" "/tmp/icemaker_global_tempdir.DCV30WOGYWbd/rustc_testrunner_tmpdir_reporting.t6FVbqkY94un/rustcTWZgik/symbols.o" "<3 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/tmp/icemaker_global_tempdir.DCV30WOGYWbd/rustc_testrunner_tmpdir_reporting.t6FVbqkY94un/rustcTWZgik/raw-dylibs" "-B<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/bin/gcc-ld" "-fuse-ld=lld" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "outputfile" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: rust-lld: error: cannot open outputfile.mvce.2593c9541c790827-cgu.0.rcgu.o: No such file or directory
          rust-lld: error: cannot open outputfile.mvce.2593c9541c790827-cgu.1.rcgu.o: No such file or directory
          collect2: error: ld returned 1 exit status
          

error: aborting due to 1 previous error; 1 warning emitted

[matthiaskrgr]

smaller

fn main() {
  let option_id_closure = | x | x;
  let _ : Vec<_> = [6].into_iter().map(option_id_closure).collect();
  let _ : Vec<_> = vec ![5].into_iter().collect();
  let _ : Vec<_> = [].into_iter().map(| x | 0..x).flatten().collect();
  std::collections::HashMap::<u32, u32>::new ().get(&0);
}