`Path::strip_prefix` may panic when a path consists only of a prefix component

[dlon]

This code panics on Windows:

fn main() {
    std::path::Path::new("C:").strip_prefix("C:");
}

According to the documentation for strip_prefix, it should either succeed or return Err(StripPrefixError). Instead, it panics due to an out-of-range index:

thread 'main' panicked at 'range start index 2 out of range for slice of length 0', library\std\src\path.rs:716:24

Meta

rustc --version --verbose:

rustc 1.58.1 (db9d1b20b 2022-01-20)
binary: rustc
commit-hash: db9d1b20bba1968c1ec1fc49616d4742c1725b4b
commit-date: 2022-01-20
host: x86_64-pc-windows-msvc
release: 1.58.1
LLVM version: 13.0.0

The bug is also present in nightly.

Backtrace

thread 'main' panicked at 'range start index 2 out of range for slice of length 0', library\std\src\path.rs:716:24
stack backtrace:
   0: std::panicking::begin_panic_handler
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\panicking.rs:498
   1: core::panicking::panic_fmt
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\core\src\panicking.rs:107
   2: core::slice::index::slice_start_index_len_fail
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\core\src\slice\index.rs:34
   3: core::slice::index::impl$5::index
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\library\core\src\slice\index.rs:324
   4: core::slice::index::impl$0::index
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\library\core\src\slice\index.rs:15
   5: std::path::Components::include_cur_dir
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\path.rs:722
   6: std::path::Components::len_before_body
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\path.rs:657
   7: std::path::Components::trim_right
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\path.rs:774
   8: std::path::Components::as_path
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\path.rs:693
   9: std::path::impl$62::_strip_prefix::closure$0
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\path.rs:2242
  10: core::option::Option::map
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\library\core\src\option.rs:846
  11: std::path::Path::_strip_prefix
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\/library\std\src\path.rs:2241
  12: std::path::Path::strip_prefix<str>
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\library\std\src\path.rs:2237
  13: test_path_panic::main
             at .\src\main.rs:2
  14: core::ops::function::FnOnce::call_once<void (*)(),tuple$<> >
             at /rustc/db9d1b20bba1968c1ec1fc49616d4742c1725b4b\library\core\src\ops\function.rs:227
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
error: process didn't exit successfully: `target\debug\test-path-panic.exe` (exit code: 101)

[ChrisDenton]

I can confirm this. The problem originates in Components. A minimal example:

fn main() {
    let path = std::path::Path::new("C:");
    let mut iter = path.components();
    iter.next();
    iter.as_path(); // panics at 'range start index 2 out of range for slice of length 0'
}

[name1e5s]

It seems that the prefix_len() in include_cur_dir causes the issue, I'll try to fix.

[name1e5s]

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