Indicate no_std support is only available on Rust >= 1.30.0.

Issue #135

Author: azriel91

.travis.yml

@@ -43,9 +43,25 @@ matrix:
     - rust: nightly
       script: *test_all
 
-    # Test everything on Rust 1.25.0 for backward compatibility
+    # Test features with std on Rust 1.25.0 for backward compatibility
     - rust: 1.25.0
-      script: *test_all
+      script:
+        - cargo build --manifest-path backtrace-sys/Cargo.toml
+        - cargo build
+        - cargo test
+        - cargo test --no-default-features --features 'libunwind std'
+        - cargo test --no-default-features --features 'libunwind dladdr std'
+        - cargo test --no-default-features --features 'libunwind libbacktrace std'
+        - cargo test --no-default-features --features 'unix-backtrace std'
+        - cargo test --no-default-features --features 'unix-backtrace dladdr std'
+        - cargo test --no-default-features --features 'unix-backtrace libbacktrace std'
+        - cargo test --no-default-features --features 'serialize-serde std'
+        - cargo test --no-default-features --features 'serialize-rustc std'
+        - cargo test --no-default-features --features 'serialize-rustc serialize-serde std'
+        - cargo test --no-default-features --features 'cpp_demangle std'
+        - cargo test --no-default-features --features 'gimli-symbolize std'
+        - cd ./cpp_smoke_test && cargo test && cd ..
+        - cargo clean && cargo build
 
     # Upload docs on nightly
     - rust: nightly

Cargo.toml

@@ -41,6 +41,9 @@ winapi = { version = "0.3.3", features = ["dbghelp", "processthreadsapi", "winnt
 [target.'cfg(all(unix, not(target_os = "fuchsia"), not(target_os = "emscripten"), not(target_os = "macos"), not(target_os = "ios")))'.dependencies]
 backtrace-sys = { path = "backtrace-sys", version = "0.1.17", optional = true }
 
+[build-dependencies]
+autocfg = "0.1"
+
 # Each feature controls the two phases of finding a backtrace: getting a
 # backtrace and then resolving instruction pointers to symbols. The default
 # feature enables all the necessary features for each platform this library

build.rs

@@ -0,0 +1,11 @@
+extern crate autocfg;
+
+fn main() {
+    let ac = autocfg::new();
+
+    // ffi types moved from `std` to `core` in Rust 1.30, so we need to adjust imports based on
+    // this.
+    //
+    // <https://github.com/rust-lang/rust/pull/53910>
+    ac.emit_rustc_version(1, 30);
+}

src/types.rs

@@ -7,8 +7,10 @@ cfg_if! {
         use std::fmt;
         use std::path::PathBuf;
         use std::prelude::v1::*;
-    } else {
+    } else if #[cfg(rustc_1_30)] {
         pub use core::ffi::c_void;
+    } else {
+        compile_error!("`backtrace` requires Rust >=1.30.0 to support `no_std`.");
     }
 }