cbindgen-0.14.0 "crashes" while building firefox

[Ponce]

slackware64-current, gcc-9.3.0, rust-1.42.0, firefox-76.0b2 (or 75.0)

as the shell script used on Slackware to build firefox downloads and install the latest cbindgen silently in ~/.cargo/bin/ since a few days builds of the latest firefox were failing.
examining the output I noticed it was because of cbingen, so I tried building firefox with fixed cbindgen versions: with 0.14.0 it fails with this error (I set in the environment RUST_BACKTRACE=full, as hinted)

 1:32.94 xpcom/ds/nsGkAtomList.h.stub
 1:33.07 b''
 1:33.10 b"WARN: Skip wgpu-core::MAX - (not `pub`).\nWARN: Skip wgpu-core::EMPTY - (not `pub`).\nWARN: Skip wgpu-core::BITS_PER_BYTE - (not `pub`).\nWARN: Skip wgpu-core::BIND_BUFFER_ALIGNMENT - (Unhandled const definition)\nWARN: Skip wgpu-core::CLEANUP_WAIT_MS - (not `pub`).\nWARN: Skip wgpu-core::VARIANT - (not `pub`).\nWARN: Skip wgpu-core::VARIANT - (not `pub`).\nWARN: Skip wgpu-core::VARIANT - (not `pub`).\nWARN: Skip wgpu-core::VARIANT - (not `pub`).\nWARN: Skip wgpu-core::BACKEND_BITS - (not `pub`).\nWARN: Skip wgpu-core::EPOCH_MASK - (not `pub`).\nWARN: Skip wgpu-core::ERROR - (Unhandled const definition)\nWARN: Skip wgpu-core::FRAME_TIMEOUT_MS - (not `pub`).\nWARN: Skip wgpu-core::DUMMY_SELECTOR - (Cannot have a zero sized const definition.)\nWARN: Skip wgpu-types::VULKAN - (Unsupported expression. Cast(ExprCast { attrs: [], expr: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Backend), arguments: None }, Colon2, PathSegment { ident: Ident(Vulkan), arguments: None }] } }), as_token: As, ty: Path(TypePath { qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(u32), arguments: None }] } }) }))\nWARN: Skip wgpu-types::GL - (Unsupported expression. Cast(ExprCast { attrs: [], expr: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Backend), arguments: None }, Colon2, PathSegment { ident: Ident(Gl), arguments: None }] } }), as_token: As, ty: Path(TypePath { qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(u32), arguments: None }] } }) }))\nWARN: Skip wgpu-types::METAL - (Unsupported expression. Cast(ExprCast { attrs: [], expr: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Backend), arguments: None }, Colon2, PathSegment { ident: Ident(Metal), arguments: None }] } }), as_token: As, ty: Path(TypePath { qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(u32), arguments: None }] } }) }))\nWARN: Skip wgpu-types::DX12 - (Unsupported expression. Cast(ExprCast { attrs: [], expr: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Backend), arguments: None }, Colon2, PathSegment { ident: Ident(Dx12), arguments: None }] } }), as_token: As, ty: Path(TypePath { qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(u32), arguments: None }] } }) }))\nWARN: Skip wgpu-types::DX11 - (Unsupported expression. Cast(ExprCast { attrs: [], expr: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Backend), arguments: None }, Colon2, PathSegment { ident: Ident(Dx11), arguments: None }] } }), as_token: As, ty: Path(TypePath { qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(u32), arguments: None }] } }) }))\nWARN: Skip wgpu-types::BROWSER_WEBGPU - (Unsupported expression. Cast(ExprCast { attrs: [], expr: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Backend), arguments: None }, Colon2, PathSegment { ident: Ident(BrowserWebGpu), arguments: None }] } }), as_token: As, ty: Path(TypePath { qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(u32), arguments: None }] } }) }))\nWARN: Skip wgpu-types::PRIMARY - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(VULKAN), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::SECONDARY - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(GL), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::READ_ALL - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(MAP_READ), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::WRITE_ALL - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(MAP_WRITE), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::ORDERED - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(READ_ALL), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::READ_ALL - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(COPY_SRC), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::WRITE_ALL - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(COPY_DST), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::ORDERED - (Unsupported expression. Field(ExprField { attrs: [], base: Path(ExprPath { attrs: [], qself: None, path: Path { leading_colon: None, segments: [PathSegment { ident: Ident(Self), arguments: None }, Colon2, PathSegment { ident: Ident(READ_ALL), arguments: None }] } }), dot_token: Dot, member: Named(Ident(bits)) }))\nWARN: Skip wgpu-types::REPLACE - (Unsupported path expression. [PathSegment { ident: Ident(BlendFactor), arguments: None }, Colon2, PathSegment { ident: Ident(One), arguments: None }])\nWARN: Skip wgpu-types::IGNORE - (Unsupported path expression. [PathSegment { ident: Ident(CompareFunction), arguments: None }, Colon2, PathSegment { ident: Ident(Always), arguments: None }])\nthread 'main' panicked at 'Unable to mangle generic parameter Ptr(Primitive(UInt8)) for 'Result'', src/bindgen/mangle.rs:52:17\nstack backtrace:\n   0:     0x563827cc8c93 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hb1dbfc7419c3ffbf\n   1:     0x563827ce9f6d - core::fmt::write::h7be4cf574d82590c\n   2:     0x563827cc8625 - std::io::Write::write_fmt::h4153108fd7e5952c\n   3:     0x563827cbc160 - std::panicking::default_hook::{{closure}}::h605411d7e5327846\n   4:     0x563827cbbe78 - std::panicking::default_hook::hafddd3c4bf5674d5\n   5:     0x563827cbc87c - std::panicking::rust_panic_with_hook::hcd919988461ee8aa\n   6:     0x563827cbc390 - rust_begin_unwind\n   7:     0x563827cbc30b - std::panicking::begin_panic_fmt::hf346097d32db72ce\n   8:     0x563827ac4dac - cbindgen::bindgen::mangle::internal_mangle_name::hb6899f364edc591d\n   9:     0x563827b11484 - <cbindgen::bindgen::ir::opaque::OpaqueItem as cbindgen::bindgen::ir::item::Item>::instantiate_monomorph::h6f28d167dd0d4209\n  10:     0x563827ac3fb4 - cbindgen::bindgen::ir::ty::Type::add_monomorphs::h476674f0df57c4fd\n  11:     0x563827b2bfae - cbindgen::bindgen::library::Library::generate::h4bb717dec9c0795e\n  12:     0x563827a4b63b - cbindgen::bindgen::builder::Builder::generate::h33bcee20302b3894\n  13:     0x563827a54b78 - cbindgen::main::hec7f96b44236a916\n  14:     0x563827a46353 - std::rt::lang_start::{{closure}}::hb549067eeb018666\n  15:     0x563827cbc283 - std::panicking::try::do_call::h1693beeec7d06c75\n  16:     0x563827ccee67 - __rust_maybe_catch_panic\n  17:     0x563827cbf857 - std::rt::lang_start_internal::hfbcfc7b0accd3206\n  18:     0x563827a55802 - main\n  19:     0x7fc504386e5b - __libc_start_main\n  20:     0x56382795a1ca - _start\n  21:                0x0 - <unknown>\n"
 1:33.10 xpcom/base/ErrorNamesInternal.h.stub
 1:33.10 gmake[4]: *** [backend.mk:12: .deps/wgpu_ffi_generated.h.stub] Error 101
 1:33.10 gmake[3]: *** [/tmp/firefox-76.0/config/recurse.mk:101: dom/webgpu/ffi/export] Error 2
 1:33.10 gmake[3]: *** Waiting for unfinished jobs....
 1:33.13 intl/locale/unic_langid_ffi_generated.h.stub
 1:33.21 /tmp/firefox-76.0/xpcom/ds/StaticAtoms.py:2578: SyntaxWarning: "is" with a literal. Did you mean "=="?
 1:33.21   if atom.atom_type is "PseudoElementAtom":
 1:33.21 /tmp/firefox-76.0/xpcom/ds/StaticAtoms.py:2582: SyntaxWarning: "is" with a literal. Did you mean "=="?
 1:33.21   elif atom.atom_type is "NonInheritingAnonBoxAtom" or atom.atom_type is "InheritingAnonBoxAtom":
 1:33.21 /tmp/firefox-76.0/xpcom/ds/StaticAtoms.py:2582: SyntaxWarning: "is" with a literal. Did you mean "=="?
 1:33.21   elif atom.atom_type is "NonInheritingAnonBoxAtom" or atom.atom_type is "InheritingAnonBoxAtom":
 1:33.22 xpcom/ds/nsGkAtomConsts.h.stub
 1:33.23 dom/media/audioipc_server_ffi_generated.h.stub
 1:33.29 xpcom/base/error_list.rs.stub
 1:33.49 xpcom/base/gk_rust_utils_ffi_generated.h.stub
 2:22.09 gmake[2]: *** [/tmp/firefox-76.0/config/recurse.mk:34: export] Error 2
 2:22.09 gmake[1]: *** [/tmp/firefox-76.0/config/rules.mk:394: default] Error 2
 2:22.09 gmake: *** [client.mk:125: build] Error 2
 2:22.12 0 compiler warnings present.

while with 0.13.2 everything goes fine.

let me know if I can test something else.

[Ponce]

I tried a manual bisect and it seems to go fine reverting this commit

ec1631f

[emilio]

Yeah. The workaround they were using for that stopped working. Anyhow #508 should fix the root cause.