Add repro-check tool for verifying reproducible Rust builds

Cargo.lock

@@ -239,6 +239,21 @@ dependencies = [
  "wait-timeout",
 ]
 
+[[package]]
+name = "assert_fs"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a652f6cb1f516886fcfee5e7a5c078b9ade62cfcb889524efe5a64d682dd27a9"
+dependencies = [
+ "anstyle",
+ "doc-comment",
+ "globwalk",
+ "predicates",
+ "predicates-core",
+ "predicates-tree",
+ "tempfile",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.5.0"
@@ -544,8 +559,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "145052bdd345b87320e369255277e3fb5152762ad123a901ef5c262dd38fe8d2"
 dependencies = [
  "iana-time-zone",
+ "js-sys",
  "num-traits",
  "serde",
+ "wasm-bindgen",
  "windows-link 0.2.1",
 ]
 
@@ -1265,6 +1282,12 @@ version = "1.0.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8975ffdaa0ef3661bfe02dbdcc06c9f829dfafe6a3c474de366a8d5e44276921"
 
+[[package]]
+name = "doc-comment"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "780955b8b195a21ab8e4ac6b60dd1dbdcec1dc6c51c0617964b08c81785e12c9"
+
 [[package]]
 name = "dyn-clone"
 version = "1.0.20"
@@ -1637,6 +1660,17 @@ dependencies = [
  "regex-syntax",
 ]
 
+[[package]]
+name = "globwalk"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0bf760ebf69878d9fd8f110c89703d90ce35095324d1f1edcb595c63945ee757"
+dependencies = [
+ "bitflags",
+ "ignore",
+ "walkdir",
+]
+
 [[package]]
 name = "gsgdt"
 version = "0.1.2"
@@ -3311,6 +3345,27 @@ dependencies = [
  "walkdir",
 ]
 
+[[package]]
+name = "repro-check"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "assert_fs",
+ "chrono",
+ "clap",
+ "env_logger",
+ "hex",
+ "ignore",
+ "log",
+ "num_cpus",
+ "rayon",
+ "serde",
+ "sha2",
+ "tempfile",
+ "toml 0.8.23",
+ "walkdir",
+]
+
 [[package]]
 name = "run_make_support"
 version = "0.0.0"

Cargo.toml

@@ -33,6 +33,7 @@ members = [
   "src/tools/remote-test-client",
   "src/tools/remote-test-server",
   "src/tools/replace-version-placeholder",
+  "src/tools/repro-check",
   "src/tools/run-make-support",
   "src/tools/rust-installer",
   "src/tools/rustdoc",

src/bootstrap/src/core/build_steps/tool.rs

@@ -501,6 +501,7 @@ bootstrap_tool!(
     UnicodeTableGenerator, "src/tools/unicode-table-generator", "unicode-table-generator";
     FeaturesStatusDump, "src/tools/features-status-dump", "features-status-dump";
     OptimizedDist, "src/tools/opt-dist", "opt-dist", submodules = &["src/tools/rustc-perf"];
+    ReproCheck, "src/tools/repro-check", "repro-check";
     RunMakeSupport, "src/tools/run-make-support", "run_make_support", artifact_kind = ToolArtifactKind::Library;
 );
 

src/bootstrap/src/core/builder/mod.rs

@@ -801,6 +801,7 @@ impl<'a> Builder<'a> {
                 llvm::CrtBeginEnd,
                 tool::RustdocGUITest,
                 tool::OptimizedDist,
+                tool::ReproCheck,
                 tool::CoverageDump,
                 tool::LlvmBitcodeLinker,
                 tool::RustcPerf,

src/tools/repro-check/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "repro-check"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+anyhow = "1.0"
+clap = { version = "4.5", features = ["derive", "env"] }
+chrono = { version = "0.4", features = ["clock"] }
+env_logger = "0.11"
+hex = "0.4"
+ignore = "0.4"
+log = "0.4"
+num_cpus = "1.16"
+rayon = "1.10"
+serde = { version = "1.0", features = ["derive"] }
+sha2 = "0.10"
+toml = "0.8"
+walkdir = "2.5"
+
+[dev-dependencies]
+assert_fs = "1.1"
+tempfile = "3.12"

src/tools/repro-check/README.md

@@ -0,0 +1,47 @@
+# repro-check
+
+repro-check is a lightweight tool designed to verify the reproducibility of Rust compiler builds.
+
+It works by creating two separate copies of the Rust source tree, building stage-2 (or a full distribution)
+in each copy, and then comparing the resulting sysroots using SHA-256 checksums.
+If any discrepancies are detected, repro-check generates a detailed HTML report highlighting the differences
+and exits with a non-zero status.
+
+This tool is ideal for developers and CI systems aiming to ensure deterministic, reproducible builds of Rust.
+
+## How to build and run:
+
+```bash
+./x.py build src/tools/repro-check
+./build/<your-host-triple>/stage1-tools-bin/repro-check --help
+
+# simplest run (host target, stage 2 only)
+./build/x86_64-unknown-linux-gnu/stage1-tools-bin/repro-check
+
+# Recommended usage
+./build/x86_64-unknown-linux-gnu/stage1-tools-bin/repro-check \
+    --jobs 16 \
+    --exclude-pattern .so \
+    --path-delta 10 \
+    --html-output my-report.html
+
+# full distribution (takes a long time)
+./build/x86_64-unknown-linux-gnu/stage1-tools-bin/repro-check --full-dist
+
+# start from scratch
+./build/x86_64-unknown-linux-gnu/stage1-tools-bin/repro-check --clean
+
+All flags:
+
+--src-root <dir>         path to the rust checkout (default: current dir)
+--target <triple>        build for this target (default: host)
+--jobs <n>               parallel jobs (default: number of CPUs)
+--html-output <file>     report file (default: repro_report.html)
+--exclude-pattern <pat>  ignore files ending with <pat> (can be repeated)
+--path-delta <n>         make the second build’s path longer by n segments (default 10)
+--full-dist              build a complete distribution instead of stage 2
+--clean                  delete the workspace first
+--skip-copy              reuse an existing workspace (don’t copy source)
+--verbose                print more details
+
+- Tests: Run `cargo test` in src/tools/repro-check.

src/tools/repro-check/src/build.rs

@@ -0,0 +1,82 @@
+use std::env;
+use std::path::Path;
+use std::process::{Command, Stdio};
+
+use anyhow::{Context, Result};
+use log::{info, warn};
+
+// Runs x.py in the given environment root. Handles the build or dist command,
+// stage limiting, and job config.
+pub fn run_xpy(env_root: &Path, jobs: u32, target: Option<&str>, full_dist: bool) -> Result<()> {
+    let x_py = env_root.join("x.py");
+
+    let python = env::var("BOOTSTRAP_PYTHON").unwrap_or_else(|_| {
+        if cfg!(windows) { "python".to_string() } else { "python3".to_string() }
+    });
+
+    let mut cmd = Command::new(&python);
+    cmd.arg(&x_py);
+
+    let build_cmd = if full_dist { "dist" } else { "build" };
+    cmd.arg(build_cmd);
+
+    if !full_dist {
+        cmd.arg("--stage").arg("2");
+        cmd.arg("compiler");
+    }
+
+    if let Some(t) = target {
+        cmd.arg("--target").arg(t);
+    }
+
+    cmd.arg("-j").arg(jobs.to_string());
+    cmd.arg("--config").arg("bootstrap.toml");
+    cmd.current_dir(env_root);
+    cmd.stdout(Stdio::inherit());
+    cmd.stderr(Stdio::inherit());
+
+    info!("Kicking off: {} {}", python, x_py.display());
+
+    let status = cmd.status().with_context(|| format!("Couldn't run x.py in {:?}", env_root))?;
+    if !status.success() {
+        return Err(anyhow::anyhow!("Build bombed in {:?}", env_root));
+    }
+
+    Ok(())
+}
+
+// Figures out the host triple by asking rustc, or guessing if that fails.
+pub fn detect_host(src_root: &Path) -> Result<String> {
+    let output = Command::new("rustc")
+        .arg("-vV")
+        .output()
+        .context("Couldn't query rustc for version info")?;
+
+    if !output.status.success() {
+        warn!("rustc -vV didn't work; falling back to a guess.");
+    }
+
+    let out_str = String::from_utf8_lossy(&output.stdout);
+    for line in out_str.lines() {
+        if line.starts_with("host: ") {
+            return Ok(line.trim_start_matches("host: ").trim().to_string());
+        }
+    }
+
+    let arch = if cfg!(target_arch = "x86_64") {
+        "x86_64"
+    } else if cfg!(target_arch = "aarch64") {
+        "aarch64"
+    } else {
+        "unknown"
+    };
+    let os = if cfg!(target_os = "windows") {
+        "windows"
+    } else if cfg!(target_os = "macos") {
+        "apple-darwin"
+    } else {
+        "linux-gnu"
+    };
+    info!("Detected host from src root {:?}: {arch}-unknown-{os}", src_root);
+    Ok(format!("{arch}-unknown-{os}"))
+}