From 272cd384e8d1006240ecaed5077fe2990f576dbb Mon Sep 17 00:00:00 2001 From: Ben Kimock Date: Mon, 4 Sep 2023 17:35:46 -0400 Subject: [PATCH] Fall back to an unoptimized implementation in read_binary_file if File::metadata lies --- compiler/rustc_span/src/source_map.rs | 33 +++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) diff --git a/compiler/rustc_span/src/source_map.rs b/compiler/rustc_span/src/source_map.rs index 68727a6c40e..0b575c13adf 100644 --- a/compiler/rustc_span/src/source_map.rs +++ b/compiler/rustc_span/src/source_map.rs @@ -127,10 +127,39 @@ impl FileLoader for RealFileLoader { let mut bytes = Lrc::new_uninit_slice(len as usize); let mut buf = BorrowedBuf::from(Lrc::get_mut(&mut bytes).unwrap()); - file.read_buf_exact(buf.unfilled())?; + match file.read_buf_exact(buf.unfilled()) { + Ok(()) => {} + Err(e) if e.kind() == io::ErrorKind::UnexpectedEof => { + drop(bytes); + return fs::read(path).map(Vec::into); + } + Err(e) => return Err(e), + } // SAFETY: If the read_buf_exact call returns Ok(()), then we have // read len bytes and initialized the buffer. - Ok(unsafe { bytes.assume_init() }) + let bytes = unsafe { bytes.assume_init() }; + + // At this point, we've read all the bytes that filesystem metadata reported exist. + // But we are not guaranteed to be at the end of the file, because we did not attempt to do + // a read with a non-zero-sized buffer and get Ok(0). + // So we do small read to a fixed-size buffer. If the read returns no bytes then we're + // already done, and we just return the Lrc we built above. + // If the read returns bytes however, we just fall back to reading into a Vec then turning + // that into an Lrc, losing our nice peak memory behavior. This fallback code path should + // be rarely exercised. + + let mut probe = [0u8; 32]; + let n = loop { + match file.read(&mut probe) { + Ok(0) => return Ok(bytes), + Err(e) if e.kind() == io::ErrorKind::Interrupted => continue, + Err(e) => return Err(e), + Ok(n) => break n, + } + }; + let mut bytes: Vec = bytes.iter().copied().chain(probe[..n].iter().copied()).collect(); + file.read_to_end(&mut bytes)?; + Ok(bytes.into()) } }