Move dylib version stuff to proc-macro-srv

crates/proc-macro-srv/Cargo.toml

@@ -13,8 +13,9 @@ doctest = false
 
 [dependencies]
 object.workspace = true
-libloading = "0.8.0"
-memmap2 = "0.5.4"
+libloading.workspace = true
+memmap2.workspace = true
+snap.workspace = true
 
 stdx.workspace = true
 tt.workspace = true

crates/proc-macro-srv/src/dylib.rs

@@ -1,5 +1,7 @@
 //! Handles dynamic library loading for proc macro
 
+mod version;
+
 use std::{fmt, fs::File, io};
 
 use libloading::Library;
@@ -7,7 +9,7 @@ use memmap2::Mmap;
 use object::Object;
 use paths::{AbsPath, Utf8Path, Utf8PathBuf};
 use proc_macro::bridge;
-use proc_macro_api::{read_dylib_info, ProcMacroKind};
+use proc_macro_api::ProcMacroKind;
 
 use crate::ProcMacroSrvSpan;
 
@@ -119,11 +121,14 @@ impl ProcMacroLibraryLibloading {
         let abs_file: &AbsPath = file
             .try_into()
             .map_err(|_| invalid_data_err(format!("expected an absolute path, got {file}")))?;
-        let version_info = read_dylib_info(abs_file)?;
+        let version_info = version::read_dylib_info(abs_file)?;
 
         let lib = load_library(file).map_err(invalid_data_err)?;
-        let proc_macros =
-            crate::proc_macros::ProcMacros::from_lib(&lib, symbol_name, version_info)?;
+        let proc_macros = crate::proc_macros::ProcMacros::from_lib(
+            &lib,
+            symbol_name,
+            &version_info.version_string,
+        )?;
         Ok(ProcMacroLibraryLibloading { _lib: lib, proc_macros })
     }
 }

crates/proc-macro-srv/src/dylib/version.rs

@@ -0,0 +1,180 @@
+//! Reading proc-macro rustc version information from binary data
+
+use std::{
+    fs::File,
+    io::{self, Read},
+};
+
+use memmap2::Mmap;
+use object::read::{File as BinaryFile, Object, ObjectSection};
+use paths::AbsPath;
+use snap::read::FrameDecoder as SnapDecoder;
+
+#[derive(Debug)]
+#[allow(dead_code)]
+pub struct RustCInfo {
+    pub version: (usize, usize, usize),
+    pub channel: String,
+    pub commit: Option<String>,
+    pub date: Option<String>,
+    // something like "rustc 1.58.1 (db9d1b20b 2022-01-20)"
+    pub version_string: String,
+}
+
+/// Read rustc dylib information
+pub fn read_dylib_info(dylib_path: &AbsPath) -> io::Result<RustCInfo> {
+    macro_rules! err {
+        ($e:literal) => {
+            io::Error::new(io::ErrorKind::InvalidData, $e)
+        };
+    }
+
+    let ver_str = read_version(dylib_path)?;
+    let mut items = ver_str.split_whitespace();
+    let tag = items.next().ok_or_else(|| err!("version format error"))?;
+    if tag != "rustc" {
+        return Err(err!("version format error (No rustc tag)"));
+    }
+
+    let version_part = items.next().ok_or_else(|| err!("no version string"))?;
+    let mut version_parts = version_part.split('-');
+    let version = version_parts.next().ok_or_else(|| err!("no version"))?;
+    let channel = version_parts.next().unwrap_or_default().to_owned();
+
+    let commit = match items.next() {
+        Some(commit) => {
+            match commit.len() {
+                0 => None,
+                _ => Some(commit[1..].to_string() /* remove ( */),
+            }
+        }
+        None => None,
+    };
+    let date = match items.next() {
+        Some(date) => {
+            match date.len() {
+                0 => None,
+                _ => Some(date[0..date.len() - 2].to_string() /* remove ) */),
+            }
+        }
+        None => None,
+    };
+
+    let version_numbers = version
+        .split('.')
+        .map(|it| it.parse::<usize>())
+        .collect::<Result<Vec<_>, _>>()
+        .map_err(|_| err!("version number error"))?;
+
+    if version_numbers.len() != 3 {
+        return Err(err!("version number format error"));
+    }
+    let version = (version_numbers[0], version_numbers[1], version_numbers[2]);
+
+    Ok(RustCInfo { version, channel, commit, date, version_string: ver_str })
+}
+
+/// This is used inside read_version() to locate the ".rustc" section
+/// from a proc macro crate's binary file.
+fn read_section<'a>(dylib_binary: &'a [u8], section_name: &str) -> io::Result<&'a [u8]> {
+    BinaryFile::parse(dylib_binary)
+        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?
+        .section_by_name(section_name)
+        .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "section read error"))?
+        .data()
+        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
+}
+
+/// Check the version of rustc that was used to compile a proc macro crate's
+/// binary file.
+///
+/// A proc macro crate binary's ".rustc" section has following byte layout:
+/// * [b'r',b'u',b's',b't',0,0,0,5] is the first 8 bytes
+/// * ff060000 734e6150 is followed, it's the snappy format magic bytes,
+///   means bytes from here(including this sequence) are compressed in
+///   snappy compression format. Version info is inside here, so decompress
+///   this.
+///
+/// The bytes you get after decompressing the snappy format portion has
+/// following layout:
+/// * [b'r',b'u',b's',b't',0,0,0,5] is the first 8 bytes(again)
+/// * [crate root bytes] next 8 bytes (4 in old versions) is to store
+///   crate root position, according to rustc's source code comment
+/// * [length byte] next 1 byte tells us how many bytes we should read next
+///   for the version string's utf8 bytes
+/// * [version string bytes encoded in utf8] <- GET THIS BOI
+/// * [some more bytes that we don't really care but about still there] :-)
+///
+/// Check this issue for more about the bytes layout:
+/// <https://github.com/rust-lang/rust-analyzer/issues/6174>
+pub fn read_version(dylib_path: &AbsPath) -> io::Result<String> {
+    let dylib_file = File::open(dylib_path)?;
+    let dylib_mmapped = unsafe { Mmap::map(&dylib_file) }?;
+
+    let dot_rustc = read_section(&dylib_mmapped, ".rustc")?;
+
+    // check if magic is valid
+    if &dot_rustc[0..4] != b"rust" {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("unknown metadata magic, expected `rust`, found `{:?}`", &dot_rustc[0..4]),
+        ));
+    }
+    let version = u32::from_be_bytes([dot_rustc[4], dot_rustc[5], dot_rustc[6], dot_rustc[7]]);
+    // Last supported version is:
+    // https://github.com/rust-lang/rust/commit/b94cfefc860715fb2adf72a6955423d384c69318
+    let (snappy_portion, bytes_before_version) = match version {
+        5 | 6 => (&dot_rustc[8..], 13),
+        7 | 8 => {
+            let len_bytes = &dot_rustc[8..12];
+            let data_len = u32::from_be_bytes(len_bytes.try_into().unwrap()) as usize;
+            (&dot_rustc[12..data_len + 12], 13)
+        }
+        9 => {
+            let len_bytes = &dot_rustc[8..16];
+            let data_len = u64::from_le_bytes(len_bytes.try_into().unwrap()) as usize;
+            (&dot_rustc[16..data_len + 12], 17)
+        }
+        _ => {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                format!("unsupported metadata version {version}"),
+            ));
+        }
+    };
+
+    let mut uncompressed: Box<dyn Read> = if &snappy_portion[0..4] == b"rust" {
+        // Not compressed.
+        Box::new(snappy_portion)
+    } else {
+        Box::new(SnapDecoder::new(snappy_portion))
+    };
+
+    // We're going to skip over the bytes before the version string, so basically:
+    // 8 bytes for [b'r',b'u',b's',b't',0,0,0,5]
+    // 4 or 8 bytes for [crate root bytes]
+    // 1 byte for length of version string
+    // so 13 or 17 bytes in total, and we should check the last of those bytes
+    // to know the length
+    let mut bytes = [0u8; 17];
+    uncompressed.read_exact(&mut bytes[..bytes_before_version])?;
+    let length = bytes[bytes_before_version - 1];
+
+    let mut version_string_utf8 = vec![0u8; length as usize];
+    uncompressed.read_exact(&mut version_string_utf8)?;
+    let version_string = String::from_utf8(version_string_utf8);
+    version_string.map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
+}
+
+#[test]
+fn test_version_check() {
+    let path = paths::AbsPathBuf::assert(crate::proc_macro_test_dylib_path());
+    let info = read_dylib_info(&path).unwrap();
+    assert_eq!(
+        info.version_string,
+        crate::RUSTC_VERSION_STRING,
+        "sysroot ABI mismatch: dylib rustc version (read from .rustc section): {:?} != proc-macro-srv version (read from 'rustc --version'): {:?}",
+        info.version_string,
+        crate::RUSTC_VERSION_STRING,
+    );
+}

crates/proc-macro-srv/src/proc_macros.rs

@@ -2,7 +2,7 @@
 
 use libloading::Library;
 use proc_macro::bridge;
-use proc_macro_api::{ProcMacroKind, RustCInfo};
+use proc_macro_api::ProcMacroKind;
 
 use crate::{dylib::LoadProcMacroDylibError, ProcMacroSrvSpan};
 
@@ -29,15 +29,15 @@ impl ProcMacros {
     pub(crate) fn from_lib(
         lib: &Library,
         symbol_name: String,
-        info: RustCInfo,
+        version_string: &str,
     ) -> Result<ProcMacros, LoadProcMacroDylibError> {
-        if info.version_string == crate::RUSTC_VERSION_STRING {
+        if version_string == crate::RUSTC_VERSION_STRING {
             let macros =
                 unsafe { lib.get::<&&[bridge::client::ProcMacro]>(symbol_name.as_bytes()) }?;
 
             return Ok(Self { exported_macros: macros.to_vec() });
         }
-        Err(LoadProcMacroDylibError::AbiMismatch(info.version_string))
+        Err(LoadProcMacroDylibError::AbiMismatch(version_string.to_owned()))
     }
 
     pub(crate) fn expand<S: ProcMacroSrvSpan>(
@@ -117,16 +117,3 @@ impl ProcMacros {
             .collect()
     }
 }
-
-#[test]
-fn test_version_check() {
-    let path = paths::AbsPathBuf::assert(crate::proc_macro_test_dylib_path());
-    let info = proc_macro_api::read_dylib_info(&path).unwrap();
-    assert_eq!(
-        info.version_string,
-        crate::RUSTC_VERSION_STRING,
-        "sysroot ABI mismatch: dylib rustc version (read from .rustc section): {:?} != proc-macro-srv version (read from 'rustc --version'): {:?}",
-        info.version_string,
-        crate::RUSTC_VERSION_STRING,
-    );
-}