Fatal error "Is a directory" when dep-info contains subdirectory paths from `proc_macro::tracked::path()`

[mmastrac]

sccache crashes with a fatal error when compiling a crate whose dep-info includes subdirectory paths registered via the unstable, nightly-only proc_macro::tracked::path() API. The same build is successful when run via cargo +nightly build.

Error

  sccache: encountered fatal error
  sccache: error: failed to read from file `/private/tmp/dir-simple/data`: Is a directory (os error 21)
  sccache: caused by: failed to read from file `/private/tmp/dir-simple/data`: Is a directory (os error 21)                                                                         
  error: could not compile `sccache-repro` (lib)

Environment

• sccache 0.14.0
• rustc 1.94.0-nightly (22c74ba91 2026-01-15)

Minimal reproduction

The repro uses a fork of include_dir. The only difference from the crates.io 0.7.4 release is that the unstable API names are updated to match current nightly.

Note that I was unable to reproduce it with a single directory level.

Setup

Cargo.toml:

  [package]
  name = "sccache-repro"
  version = "0.1.0"     
  edition = "2021"                                                                                                                                                                  
  [dependencies]                                                                                                                                                                    
  include_dir = { git = "https://github.com/vercel-labs/include_dir", branch = "turbopack", features = ["nightly"] }

src/lib.rs:

  use include_dir::{include_dir, Dir};
  pub static DATA: Dir<'_> = include_dir!("$CARGO_MANIFEST_DIR/data");                                                                                                              

Create fixture files:

  mkdir -p data/subdir                                                  
  echo "hello" > data/file1.txt                                                                                                                                                     
  echo "world" > data/subdir/file2.txt                                                                                                                                              

To run:

RUSTC_WRAPPER=sccache cargo +nightly build