Fix a splat legacy demangling display bug by teor2345 · Pull Request #160050 · rust-lang/rust

teor2345 · 2026-07-28T06:25:45Z

Tracking issue: #153629

This PR fixes a splat legacy demangling display bug, where the comma is in the wrong place in the argument list.

It also does a cleanup from @folkertdev's PR #159643 review:

move rustfmt::skip to main() and deduplicate it: Add support for splatted function pointers #159643 (comment)

@rustbot label +F-splat +C-bug +A-name-mangling

rustbot · 2026-07-28T06:25:51Z

rustbot has assigned @camelid.
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rustbot · 2026-07-28T18:47:18Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

teor2345 · 2026-07-29T01:16:24Z

@rustbot ready

camelid · 2026-07-29T15:34:11Z

+            // there are arguments before the splat.
+            // FIXME(splat): if splatting becomes part of the type, we can remove this hack
+            if index > 0 {
+                write!(self, ",")?;


There should be a space after the comma too.

Suggested change

write!(self, ",")?;

write!(self, ", ")?;

View changes since the review

Spacing unfortunately depends on the pretty-printing context, so I think I'll need to modify the trait definition and implementers. But it should be less code overall, which is nice.

rust/compiler/rustc_middle/src/ty/print/pretty.rs

Lines 292 to 300 in b5be620

/// Prints comma-separated elements.

fn comma_sep<T>(&mut self, mut elems: impl Iterator<Item = T>) -> Result<(), PrintError>

where

T: Print<Self>,

{

if let Some(first) = elems.next() {

first.print(self)?;

for elem in elems {

self.write_str(", ")?;

rust/compiler/rustc_symbol_mangling/src/legacy.rs

Lines 490 to 498 in b5be620

// Identical to `PrettyPrinter::comma_sep` except there is no space after each comma.

fn comma_sep<T>(&mut self, mut elems: impl Iterator<Item = T>) -> Result<(), PrintError>

where

T: Print<Self>,

{

if let Some(first) = elems.next() {

first.print(self)?;

for elem in elems {

self.write_str(",")?;

I ended up adding a comma_sep_has_space method, refactoring the near-duplicate comma_sep methods, and adding comments where we might want to do a similar fix in future.

(We don't currently have non-mangling pretty-printing tests for splat, and that's ok, it's an incomplete feature.)

@rustbot ready

rustbot · 2026-07-31T03:28:47Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

rust-log-analyzer · 2026-07-31T06:47:11Z

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

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


256 LL |     #[rustc_dump_symbol_name]
257    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
258 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
260   --> $DIR/splat-mangling.rs:153:5
261    |
262 LL |     #[rustc_dump_symbol_name]

274 LL |     #[rustc_dump_symbol_name]
275    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
276 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
278   --> $DIR/splat-mangling.rs:162:5
279    |
280 LL |     #[rustc_dump_symbol_name]

292 LL |     #[rustc_dump_symbol_name]
293    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
294 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
296   --> $DIR/splat-mangling.rs:171:5
297    |
298 LL |     #[rustc_dump_symbol_name]

310 LL |     #[rustc_dump_symbol_name]
311    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
312 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
314   --> $DIR/splat-mangling.rs:180:5
315    |
316 LL |     #[rustc_dump_symbol_name]

Note: some mismatched output was normalized before being compared
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:153:5
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:162:5
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:171:5
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:180:5
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args splat/splat-mangling.rs`

error in revision `default`: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/splat/splat-mangling.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "-Zcodegen-backend=gcc" "--target=x86_64-unknown-linux-gnu" "--cfg" "default" "--check-cfg" "cfg(test,FALSE,default,legacy,v0)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/splat/splat-mangling.default" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0"
stdout: none
--- stderr -------------------------------
error: symbol-name(_RMNvCsiksvdpJ6Jnj_14splat_mangling4mainINtB0_4TypeFwThmEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:23:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn(#[splat] (u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:23:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn(#[splat] (u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:23:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB2_4TypeFThmEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:32:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn((u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:32:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn((u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:32:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs0_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeFwTThmEEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:41:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn(#[splat] ((u8, u32),))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:41:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn(#[splat] ((u8, u32),))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:41:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs1_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeFTThmEEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:50:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn(((u8, u32),))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:50:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn(((u8, u32),))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:50:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs2_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypePFwTmaEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:59:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<*const fn(#[splat] (u32, i8))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:59:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<*const fn(#[splat] (u32, i8))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:59:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs3_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypePFTmaEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:68:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<*const fn((u32, i8))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:68:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<*const fn((u32, i8))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:68:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs4_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeFwTmaEdEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:78:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn(#[splat] (u32, i8), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:78:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn(#[splat] (u32, i8), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:78:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs5_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeFTmaEdEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:87:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn((u32, i8), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:87:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn((u32, i8), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:87:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs6_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeOFmawTdEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:97:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<*mut fn(u32, i8, #[splat] (f64,))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:97:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<*mut fn(u32, i8, #[splat] (f64,))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:97:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs7_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeOFmaTdEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:106:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<*mut fn(u32, i8, (f64,))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:106:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<*mut fn(u32, i8, (f64,))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:106:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs8_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeRFmwTafjEdEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:116:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<&fn(u32, #[splat] (i8, f32, usize), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:116:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<&fn(u32, #[splat] (i8, f32, usize), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:116:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs9_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeRFmTafjEdEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:125:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<&fn(u32, (i8, f32, usize), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:125:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<&fn(u32, (i8, f32, usize), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:125:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMsa_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeQFmwudEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:134:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<&mut fn(u32, #[splat] (), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:134:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<&mut fn(u32, #[splat] (), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:134:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMsb_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeQFmudEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:143:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<&mut fn(u32, (), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:143:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<&mut fn(u32, (), f64)>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:143:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMsc_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeINtNtCsmKzDxHvwyd_5alloc5boxed3BoxFmwTFwuEuaEdEuEE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:153:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:153:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<alloc::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:153:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMsd_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeINtNtCsmKzDxHvwyd_5alloc5boxed3BoxFmTFwuEuaEdEuEE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:162:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:162:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<alloc::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:162:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMse_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeINtNtCsmKzDxHvwyd_5alloc5boxed3BoxFmwTFuEuaEdEuEE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:171:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:171:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<alloc::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:171:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMsf_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeINtNtCsmKzDxHvwyd_5alloc5boxed3BoxFmTFuEuaEdEuEE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:180:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:180:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<alloc::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:180:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 54 previous errors
------------------------------------------

---- [ui] tests/ui/splat/splat-mangling.rs#default stdout end ----
---- [ui] tests/ui/splat/splat-mangling.rs#v0 stdout ----
Saved the actual stderr to `/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/splat/splat-mangling.v0/splat-mangling.v0.stderr`
diff of stderr:

256 LL |     #[rustc_dump_symbol_name]
257    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
258 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
260   --> $DIR/splat-mangling.rs:153:5
261    |
262 LL |     #[rustc_dump_symbol_name]

274 LL |     #[rustc_dump_symbol_name]
275    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
276 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
278   --> $DIR/splat-mangling.rs:162:5
279    |
280 LL |     #[rustc_dump_symbol_name]

292 LL |     #[rustc_dump_symbol_name]
293    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
294 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
296   --> $DIR/splat-mangling.rs:171:5
297    |
298 LL |     #[rustc_dump_symbol_name]

310 LL |     #[rustc_dump_symbol_name]
311    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
312 
- error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[CRATE_HASH]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
314   --> $DIR/splat-mangling.rs:180:5
315    |
316 LL |     #[rustc_dump_symbol_name]

Note: some mismatched output was normalized before being compared
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:153:5
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:162:5
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:171:5
- error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)
-   --> /checkout/tests/ui/splat/splat-mangling.rs:180:5
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(#[splat] ()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, #[splat] (fn(()), i8), f64)>>>)
+ error: demangling(<splat_mangling[CRATE_HASH]::main::Type<alloc[4462ec5c505d9a3]::boxed::Box<fn(u32, (fn(()), i8), f64)>>>)


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args splat/splat-mangling.rs`

error in revision `v0`: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/splat/splat-mangling.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "-Zcodegen-backend=gcc" "--target=x86_64-unknown-linux-gnu" "--cfg" "v0" "--check-cfg" "cfg(test,FALSE,default,legacy,v0)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/splat/splat-mangling.v0" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0" "-Z" "unstable-options" "-Csymbol-mangling-version=v0"
stdout: none
--- stderr -------------------------------
error: symbol-name(_RMNvCsiksvdpJ6Jnj_14splat_mangling4mainINtB0_4TypeFwThmEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:23:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn(#[splat] (u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:23:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn(#[splat] (u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:23:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB2_4TypeFThmEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:32:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn((u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:32:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling-alt(<splat_mangling::main::Type<fn((u8, u32))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:32:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: symbol-name(_RMs0_NvCsiksvdpJ6Jnj_14splat_mangling4mainINtB3_4TypeFwTThmEEEuE)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:41:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

error: demangling(<splat_mangling[d580343ed36ed69b]::main::Type<fn(#[splat] ((u8, u32),))>>)
##[error]  --> /checkout/tests/ui/splat/splat-mangling.rs:41:5
   |
LL |     #[rustc_dump_symbol_name]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^

Important

For more information how to resolve CI failures of this job, visit this link.

teor2345 · 2026-07-31T09:15:39Z

Failed due to a 15 digit crate hash in v0 demangling, which might be a bug to fix in demangling. This failure isn't splat related, it might happen on 1/16 of PRs (or changes to this test) anyway.

Asked for advice here:
https://rust-lang.zulipchat.com/#narrow/channel/386786-rustc-codegen-gcc/topic/crate.20hash.20drops.20leading.20zeroes/with/613817866

teor2345 · 2026-07-31T12:22:59Z

This is blocked on rust-lang/rustc-demangle#94 getting merged, publishing a release, and then rustc updating to that release.

This PR can still be reviewed if someone wants, once we rebase on the rust-lang/rustc-demangle#94 version bump, CI will pass without any code changes here.

teor2345 · 2026-08-29T18:56:47Z

It looks like we're stalled on the rustc-demangle side here, so I might redesign these tests so they're not blocked on it.

rustbot assigned camelid Jul 28, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 28, 2026

rustbot added A-name-mangling Area: Name mangling / decoration aka symbol mangling C-bug Category: This is a bug. F-splat `#![feature(splat)]` https://github.com/rust-lang/rust/issues/153629 labels Jul 28, 2026

camelid requested changes Jul 28, 2026

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Comment thread compiler/rustc_middle/src/ty/print/pretty.rs Outdated

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teor2345 force-pushed the splat-legacy-demangle branch from 980ae5d to 1099c87 Compare July 29, 2026 05:42

camelid reviewed Jul 29, 2026

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teor2345 force-pushed the splat-legacy-demangle branch from 1099c87 to 149a65c Compare July 30, 2026 00:52

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teor2345 added 2 commits July 31, 2026 13:15

Refactor pretty print comma_sep flag

ceafeb6

Fix a splat legacy demangling bug, add extra tests

aa91a46

teor2345 force-pushed the splat-legacy-demangle branch from 149a65c to 9f6099c Compare July 31, 2026 03:28

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Rename splat attribute to rustc_splat rust-lang/rustc-demangle#93

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Move rustfmt::skip to main in one test

511d292

teor2345 force-pushed the splat-legacy-demangle branch from 8db7925 to 511d292 Compare July 31, 2026 05:30

teor2345 mentioned this pull request Jul 31, 2026

Demangle using fixed-length disambiguators rust-lang/rustc-demangle#94

Open

camelid added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 31, 2026

teor2345 mentioned this pull request Aug 18, 2026

Nightly support for function overloading in FFI bindings rust-lang/goals#643

Open

	/// Prints comma-separated elements.
	fn comma_sep<T>(&mut self, mut elems: impl Iterator<Item = T>) -> Result<(), PrintError>
	where
	T: Print<Self>,
	{
	if let Some(first) = elems.next() {
	first.print(self)?;
	for elem in elems {
	self.write_str(", ")?;

	// Identical to `PrettyPrinter::comma_sep` except there is no space after each comma.
	fn comma_sep<T>(&mut self, mut elems: impl Iterator<Item = T>) -> Result<(), PrintError>
	where
	T: Print<Self>,
	{
	if let Some(first) = elems.next() {
	first.print(self)?;
	for elem in elems {
	self.write_str(",")?;

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