Auto merge of #35051 - japaric:backtrace, r=alexcrichton

rustbuild: make backtraces (RUST_BACKTRACE) optional

but keep them enabled by default to maintain the status quo.

When disabled shaves ~56KB off every x86_64-unknown-linux-gnu
binary.

To disable backtraces you have to use a config.toml (see
src/bootstrap/config.toml.example for details) when building rustc/std:

$ python bootstrap.py --config=config.toml

---

r? @alexcrichton
cc rust-lang/rfcs#1417

5 files changed, 25 insertions, 10 deletions

diff --git a/src/libstd/Cargo.toml b/src/libstd/Cargo.toml
index eded6e24f3e..b442d21b72b 100644
--- a/src/libstd/Cargo.toml
+++ b/src/libstd/Cargo.toml
@@ -27,5 +27,6 @@ build_helper = { path = "../build_helper" }
 gcc = "0.3"
 
 [features]
+backtrace = []
 jemalloc = ["alloc_jemalloc"]
 debug-jemalloc = ["alloc_jemalloc/debug"]
diff --git a/src/libstd/build.rs b/src/libstd/build.rs
index 9c408366f8b..9018e48d06b 100644
--- a/src/libstd/build.rs
+++ b/src/libstd/build.rs
@@ -25,7 +25,8 @@ fn main() {
 
     let target = env::var("TARGET").unwrap();
     let host = env::var("HOST").unwrap();
-    if !target.contains("apple") && !target.contains("msvc") && !target.contains("emscripten"){
+    if cfg!(feature = "backtrace") && !target.contains("apple") && !target.contains("msvc") &&
+        !target.contains("emscripten") {
         build_libbacktrace(&host, &target);
     }
 
diff --git a/src/libstd/panicking.rs b/src/libstd/panicking.rs
index d73e9542d21..57a4c3df70a 100644
--- a/src/libstd/panicking.rs
+++ b/src/libstd/panicking.rs
@@ -28,9 +28,7 @@ use intrinsics;
 use mem;
 use raw;
 use sys_common::rwlock::RWLock;
-use sync::atomic::{AtomicBool, Ordering};
 use sys::stdio::Stderr;
-use sys_common::backtrace;
 use sys_common::thread_info;
 use sys_common::util;
 use thread;
@@ -71,7 +69,6 @@ enum Hook {
 
 static HOOK_LOCK: RWLock = RWLock::new();
 static mut HOOK: Hook = Hook::Default;
-static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
 
 /// Registers a custom panic hook, replacing any that was previously registered.
 ///
@@ -183,11 +180,17 @@ impl<'a> Location<'a> {
 }
 
 fn default_hook(info: &PanicInfo) {
-    let panics = PANIC_COUNT.with(|c| c.get());
+    #[cfg(any(not(cargobuild), feature = "backtrace"))]
+    use sys_common::backtrace;
 
     // If this is a double panic, make sure that we print a backtrace
     // for this panic. Otherwise only print it if logging is enabled.
-    let log_backtrace = panics >= 2 || backtrace::log_enabled();
+    #[cfg(any(not(cargobuild), feature = "backtrace"))]
+    let log_backtrace = {
+        let panics = PANIC_COUNT.with(|c| c.get());
+
+        panics >= 2 || backtrace::log_enabled()
+    };
 
     let file = info.location.file;
     let line = info.location.line;
@@ -207,10 +210,17 @@ fn default_hook(info: &PanicInfo) {
         let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}",
                          name, msg, file, line);
 
-        if log_backtrace {
-            let _ = backtrace::write(err);
-        } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
-            let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
+        #[cfg(any(not(cargobuild), feature = "backtrace"))]
+        {
+            use sync::atomic::{AtomicBool, Ordering};
+
+            static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
+
+            if log_backtrace {
+                let _ = backtrace::write(err);
+            } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
+                let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
+            }
         }
     };
 
diff --git a/src/libstd/sys/common/mod.rs b/src/libstd/sys/common/mod.rs
index c9279883ae5..a1f3f477b3a 100644
--- a/src/libstd/sys/common/mod.rs
+++ b/src/libstd/sys/common/mod.rs
@@ -28,6 +28,7 @@ macro_rules! rtassert {
 
 pub mod args;
 pub mod at_exit_imp;
+#[cfg(any(not(cargobuild), feature = "backtrace"))]
 pub mod backtrace;
 pub mod condvar;
 pub mod io;
@@ -42,6 +43,7 @@ pub mod thread_local;
 pub mod util;
 pub mod wtf8;
 
+#[cfg(any(not(cargobuild), feature = "backtrace"))]
 #[cfg(any(all(unix, not(any(target_os = "macos", target_os = "ios", target_os = "emscripten"))),
           all(windows, target_env = "gnu")))]
 pub mod gnu;
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index f0fd42fc99b..1c25c8f77c1 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/src/libstd/sys/unix/mod.rs
@@ -30,6 +30,7 @@ use libc;
 pub mod weak;
 
 pub mod android;
+#[cfg(any(not(cargobuild), feature = "backtrace"))]
 pub mod backtrace;
 pub mod condvar;
 pub mod ext;