Test \\?\

.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+# .github/workflows/ci.yml
+
+name: CI
+on: [push]
+jobs:
+  repro:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+
+      - run: pwd
+      - run: echo ${{github.workspace}}
+      - run: echo \\?\${{github.workspace}}
+
+      - run: cargo check --verbose && cargo clean
+
+      - run: cargo check --manifest-path \\?\${{github.workspace}}\Cargo.toml --verbose
+        if: always()
+
+      - run: cargo check --verbose
+        working-directory: \\?\${{github.workspace}}
+        if: always()

.gitignore

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+/target
+Cargo.lock

Cargo.toml

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+# Cargo.toml
+
+[package]
+name = "repro"
+version = "0.0.0"
+homepage = "https://github.com/rust-lang/cargo/pull/13914"

build.rs

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+// build.rs
+
+fn main() {
+    let out_dir = std::env::var_os("OUT_DIR").unwrap();
+    let repro = std::path::Path::new(&out_dir).join("repro.rs");
+    std::fs::write(repro, "").unwrap();
+}

src/lib.rs

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+// src/lib.rs
+
+include!(concat!(env!("OUT_DIR"), "/repro.rs"));