Switch to Snappy compression for metadata

Cargo.lock

@@ -3344,7 +3344,6 @@ name = "rustc_codegen_llvm"
 version = "0.0.0"
 dependencies = [
  "bitflags",
- "flate2",
  "libc",
  "measureme",
  "rustc-demangle",
@@ -3365,6 +3364,7 @@ dependencies = [
  "rustc_span",
  "rustc_target",
  "smallvec 1.4.2",
+ "snap",
  "tracing",
 ]
 
@@ -3689,7 +3689,6 @@ dependencies = [
 name = "rustc_metadata"
 version = "0.0.0"
 dependencies = [
- "flate2",
  "libc",
  "memmap",
  "rustc_ast",
@@ -3707,6 +3706,7 @@ dependencies = [
  "rustc_span",
  "rustc_target",
  "smallvec 1.4.2",
+ "snap",
  "stable_deref_trait",
  "tracing",
  "winapi 0.3.9",
@@ -4377,6 +4377,12 @@ version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fbee7696b84bbf3d89a1c2eccff0850e3047ed46bfcd2e92c29a2d074d57e252"
 
+[[package]]
+name = "snap"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da73c8f77aebc0e40c300b93f0a5f1bece7a248a36eee287d4e095f35c7b7d6e"
+
 [[package]]
 name = "socket2"
 version = "0.3.12"

src/librustc_codegen_llvm/Cargo.toml

@@ -12,9 +12,9 @@ doctest = false
 
 [dependencies]
 bitflags = "1.0"
-flate2 = "1.0"
 libc = "0.2"
 measureme = "0.7.1"
+snap = "1"
 tracing = "0.1"
 rustc_middle = { path = "../librustc_middle" }
 rustc-demangle = "0.1"

src/librustc_codegen_llvm/base.rs

@@ -45,15 +45,12 @@ pub fn write_compressed_metadata<'tcx>(
     metadata: &EncodedMetadata,
     llvm_module: &mut ModuleLlvm,
 ) {
-    use flate2::write::DeflateEncoder;
-    use flate2::Compression;
+    use snap::write::FrameEncoder;
     use std::io::Write;
 
     let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
     let mut compressed = tcx.metadata_encoding_version();
-    DeflateEncoder::new(&mut compressed, Compression::fast())
-        .write_all(&metadata.raw_data)
-        .unwrap();
+    FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();
 
     let llmeta = common::bytes_in_context(metadata_llcx, &compressed);
     let llconst = common::struct_in_context(metadata_llcx, &[llmeta], false);

src/librustc_metadata/Cargo.toml

@@ -10,8 +10,8 @@ path = "lib.rs"
 doctest = false
 
 [dependencies]
-flate2 = "1.0"
 libc = "0.2"
+snap = "1"
 tracing = "0.1"
 memmap = "0.7"
 smallvec = { version = "1.0", features = ["union", "may_dangle"] }

src/librustc_metadata/locator.rs

@@ -229,7 +229,7 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 use rustc_target::spec::{Target, TargetTriple};
 
-use flate2::read::DeflateDecoder;
+use snap::read::FrameDecoder;
 use std::io::{Read, Result as IoResult, Write};
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
@@ -766,7 +766,7 @@ fn get_metadata_section(
             let compressed_bytes = &buf[header_len..];
             debug!("inflating {} bytes of compressed metadata", compressed_bytes.len());
             let mut inflated = Vec::new();
-            match DeflateDecoder::new(compressed_bytes).read_to_end(&mut inflated) {
+            match FrameDecoder::new(compressed_bytes).read_to_end(&mut inflated) {
                 Ok(_) => rustc_erase_owner!(OwningRef::new(inflated).map_owner_box()),
                 Err(_) => {
                     return Err(format!("failed to decompress metadata: {}", filename.display()));

src/tools/tidy/src/deps.rs

@@ -42,6 +42,7 @@ const EXCEPTIONS: &[(&str, &str)] = &[
     ("crossbeam-queue", "MIT/Apache-2.0 AND BSD-2-Clause"), // rls via rayon
     ("arrayref", "BSD-2-Clause"),       // cargo-miri/directories/.../rust-argon2 (redox)
     ("instant", "BSD-3-Clause"),        // rustc_driver/tracing-subscriber/parking_lot
+    ("snap", "BSD-3-Clause"),           // rustc
     // FIXME: this dependency violates the documentation comment above:
     ("fortanix-sgx-abi", "MPL-2.0"), // libstd but only for `sgx` target
 ];
@@ -159,6 +160,7 @@ const PERMITTED_DEPENDENCIES: &[&str] = &[
     "serde_derive",
     "sha-1",
     "smallvec",
+    "snap",
     "stable_deref_trait",
     "stacker",
     "syn",