panic: frontmatter without EOF \n

---
-

note for the repro there must not be a "\n" at the end of the file; save as code.rs, then truncate -s -1 code.rs

RUSTFLAGS="" ~/.rustup/toolchains/master/bin/rust-analyzer highlight < code.rs

thread 'main' (1114745) panicked at /rustc/d62fb1c8a007f6967376a52da8315ae51b64a70c/library/core/src/str/mod.rs:861:21:
end byte index 2 is out of bounds for string of length 1
stack backtrace:
   0:     0x7f10ed64bed6 - <<std[cf0678d25afc9ccf]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[9662e8fc1527f23c]::fmt::Display>::fmt
   1:     0x7f10edc0f0c8 - core[9662e8fc1527f23c]::fmt::write
   2:     0x7f10ed66113c - <std[cf0678d25afc9ccf]::sys::stdio::unix::Stderr as core[9662e8fc1527f23c]::io::write::Write>::write_fmt
   3:     0x7f10ed61e04a - std[cf0678d25afc9ccf]::panicking::default_hook::{closure#0}
   4:     0x7f10ed63e5f3 - std[cf0678d25afc9ccf]::panicking::default_hook
   5:     0x7f10ed63ea5b - std[cf0678d25afc9ccf]::panicking::panic_with_hook
   6:     0x7f10ed61e102 - std[cf0678d25afc9ccf]::panicking::panic_handler::{closure#0}
   7:     0x7f10ed616a89 - std[cf0678d25afc9ccf]::sys::backtrace::__rust_end_short_backtrace::<std[cf0678d25afc9ccf]::panicking::panic_handler::{closure#0}, !>
   8:     0x7f10ed61fa5d - __rustc[c7d2cd00dee8f709]::rust_begin_unwind
   9:     0x7f10ea360bac - core[9662e8fc1527f23c]::panicking::panic_fmt
  10:     0x7f10ebf95e46 - core[9662e8fc1527f23c]::str::slice_error_fail_rt
  11:     0x7f10ebd93f3a - core[9662e8fc1527f23c]::str::slice_error_fail
  12:     0x5618991013c9 - <parser[ca50523a01af9e94]::lexed_str::LexedStr>::new
  13:     0x561899787e33 - <syntax[88d6ea7446ced16c]::ast::generated::nodes::SourceFile>::parse
  14:     0x56189802409b - <<base_db[1ece6b420f9ff01c]::editioned_file_id::EditionedFileId>::parse::_::parse_Configuration_ as salsa[65a99894a6a39c25]::function::Configuration>::execute
  15:     0x5618980132e8 - <salsa[65a99894a6a39c25]::function::IngredientImpl<<base_db[1ece6b420f9ff01c]::editioned_file_id::EditionedFileId>::parse::_::parse_Configuration_>>::execute
  16:     0x56189801102b - <base_db[1ece6b420f9ff01c]::editioned_file_id::EditionedFileId>::parse
  17:     0x561898439628 - <hir_expand[b9ae3878f9b984c5]::HirFileId>::parse_or_expand
  18:     0x5618984200cb - <salsa[65a99894a6a39c25]::function::IngredientImpl<<hir_expand[b9ae3878f9b984c5]::HirFileId>::ast_id_map::_::ast_id_map__Configuration_>>::execute
  19:     0x56189840d5f6 - salsa[65a99894a6a39c25]::attach::attach::<&span[d2036d0eb69be145]::ast_id::AstIdMap, dyn base_db[1ece6b420f9ff01c]::SourceDatabase, <hir_expand[b9ae3878f9b984c5]::HirFileId>::ast_id_map::ast_id_map_::{closure#0}>::{closure#0}
  20:     0x561898319796 - <hir_def[36b966b8558e1ecf]::item_tree::_::file_item_tree_query_Configuration_ as salsa[65a99894a6a39c25]::function::Configuration>::execute
  21:     0x56189820683c - <salsa[65a99894a6a39c25]::function::IngredientImpl<hir_def[36b966b8558e1ecf]::item_tree::_::file_item_tree_query_Configuration_>>::execute
  22:     0x5618982d107e - hir_def[36b966b8558e1ecf]::item_tree::file_item_tree
  23:     0x5618982db8f4 - hir_def[36b966b8558e1ecf]::nameres::collector::collect_defs
  24:     0x561898317fc8 - <hir_def[36b966b8558e1ecf]::nameres::_::crate_local_def_map_Configuration_ as salsa[65a99894a6a39c25]::function::Configuration>::execute
  25:     0x561898205e05 - <salsa[65a99894a6a39c25]::function::IngredientImpl<hir_def[36b966b8558e1ecf]::nameres::_::crate_local_def_map_Configuration_>>::execute
  26:     0x561898203581 - <salsa[65a99894a6a39c25]::function::IngredientImpl<hir_def[36b966b8558e1ecf]::nameres::_::crate_local_def_map_Configuration_>>::fetch
  27:     0x5618981598a1 - <salsa[65a99894a6a39c25]::attach::Attached>::attach::<dyn base_db[1ece6b420f9ff01c]::SourceDatabase, &hir_def[36b966b8558e1ecf]::nameres::DefMapPair, hir_def[36b966b8558e1ecf]::nameres::crate_local_def_map::{closure#0}>
  28:     0x561898115357 - <hir[c107f094967a75ab]::semantics::source_to_def::SourceToDefCtx>::file_to_def
  29:     0x5618980f2454 - <hir[c107f094967a75ab]::semantics::SemanticsImpl>::file_to_module_defs
  30:     0x5618980ffae6 - <hir[c107f094967a75ab]::semantics::SemanticsImpl>::attach_first_edition_opt
  31:     0x561898a91d5c - ide[37737ece80204ca3]::syntax_highlighting::html::highlight_as_html_with_config
  32:     0x5618989f8dec - <ide[37737ece80204ca3]::Analysis>::highlight_as_html
  33:     0x561899447872 - <rust_analyzer[c9a7b5a74bd4f6b9]::cli::flags::Highlight>::run
  34:     0x5618996e7034 - rust_analyzer[e3769bb504499c95]::main
  35:     0x56189967d713 - std[cf0678d25afc9ccf]::sys::backtrace::__rust_begin_short_backtrace::<fn() -> core[9662e8fc1527f23c]::result::Result<std[cf0678d25afc9ccf]::process::ExitCode, anyhow[6279a09abd95b935]::Error>, core[9662e8fc1527f23c]::result::Result<std[cf0678d25afc9ccf]::process::ExitCode, anyhow[6279a09abd95b935]::Error>>
  36:     0x5618996e0082 - std[cf0678d25afc9ccf]::rt::lang_start::<core[9662e8fc1527f23c]::result::Result<std[cf0678d25afc9ccf]::process::ExitCode, anyhow[6279a09abd95b935]::Error>>::{closure#0}
  37:     0x7f10eed6af99 - std[cf0678d25afc9ccf]::rt::lang_start_internal
  38:     0x561899700148 - main
  39:     0x7f10e8627741 - <unknown>
  40:     0x7f10e8627879 - __libc_start_main
  41:     0x561897ff16e9 - <unknown>
  42:                0x0 - <unknown>

rust-analyzer 1.99.0-nightly (d62fb1c 2026-07-16)

Reproduce the issue with the provided rust-analyzer highlight < code.rs command and the EOF-less frontmatter input. Start at parser::lexed_str::LexedStr::new, then follow syntax::ast::generated::nodes::SourceFile::parse into the highlighting entry point. Done means this input no longer panics during highlighting.