Don't treat rustc exit on signal as internal error.

src/cargo/core/compiler/mod.rs

@@ -5,13 +5,14 @@ use std::io::{self, Write};
 use std::path::{self, Path, PathBuf};
 use std::sync::Arc;
 
+use failure::Error;
 use same_file::is_same_file;
 use serde_json;
 
 use core::manifest::TargetSourcePath;
 use core::profiles::{Lto, Profile};
 use core::{PackageId, Target};
-use util::errors::{CargoResult, CargoResultExt, Internal};
+use util::errors::{CargoResult, CargoResultExt, Internal, ProcessError};
 use util::paths;
 use util::{self, machine_message, Freshness, ProcessBuilder, process};
 use util::{internal, join_paths, profile};
@@ -275,6 +276,19 @@ fn rustc<'a, 'cfg>(
             }
         }
 
+        fn internal_if_simple_exit_code(err: Error) -> Error {
+            // If a signal on unix (code == None) or an abnormal termination
+            // on Windows (codes like 0xC0000409), don't hide the error details.
+            match err
+                .downcast_ref::<ProcessError>()
+                .as_ref()
+                .and_then(|perr| perr.exit.and_then(|e| e.code()))
+            {
+                Some(n) if n < 128 => Internal::new(err).into(),
+                _ => err,
+            }
+        }
+
         state.running(&rustc);
         if json_messages {
             exec.exec_json(
@@ -284,13 +298,14 @@ fn rustc<'a, 'cfg>(
                 mode,
                 &mut assert_is_empty,
                 &mut |line| json_stderr(line, &package_id, &target),
-            ).map_err(Internal::new)
+            )
+            .map_err(internal_if_simple_exit_code)
             .chain_err(|| format!("Could not compile `{}`.", name))?;
         } else if build_plan {
             state.build_plan(buildkey, rustc.clone(), outputs.clone());
         } else {
             exec.exec_and_capture_output(rustc, &package_id, &target, mode, state)
-                .map_err(Internal::new)
+                .map_err(internal_if_simple_exit_code)
                 .chain_err(|| format!("Could not compile `{}`.", name))?;
         }
 

tests/testsuite/build.rs

@@ -4373,3 +4373,65 @@ fn target_filters_workspace_not_found() {
         .with_stderr("[ERROR] no library targets found in packages: a, b")
         .run();
 }
+
+#[cfg(unix)]
+#[test]
+fn signal_display() {
+    // Cause the compiler to crash with a signal.
+    let foo = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+            [dependencies]
+            pm = { path = "pm" }
+        "#,
+        )
+        .file(
+            "src/lib.rs",
+            r#"
+            #[macro_use]
+            extern crate pm;
+
+            #[derive(Foo)]
+            pub struct S;
+        "#,
+        )
+        .file(
+            "pm/Cargo.toml",
+            r#"
+            [package]
+            name = "pm"
+            version = "0.1.0"
+            [lib]
+            proc-macro = true
+        "#,
+        )
+        .file(
+            "pm/src/lib.rs",
+            r#"
+            extern crate proc_macro;
+            use proc_macro::TokenStream;
+
+            #[proc_macro_derive(Foo)]
+            pub fn derive(_input: TokenStream) -> TokenStream {
+                std::process::abort()
+            }
+        "#,
+        )
+        .build();
+
+    foo.cargo("build")
+        .with_stderr("\
+[COMPILING] pm [..]
+[COMPILING] foo [..]
+[ERROR] Could not compile `foo`.
+
+Caused by:
+  process didn't exit successfully: `rustc [..]` (signal: 6, SIGABRT: process abort signal)
+")
+        .with_status(101)
+        .run();
+}