improve debuginfo error message when build script fails

Author: lqd

src/cargo/core/compiler/custom_build.rs

@@ -332,6 +332,8 @@ fn build_work(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Job> {
     // Need a separate copy for the fresh closure.
     let targets_fresh = targets.clone();
 
+    let env_profile_name = unit.profile.name.to_uppercase();
+
     // Prepare the unit of "dirty work" which will actually run the custom build
     // command.
     //
@@ -406,15 +408,19 @@ fn build_work(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Job> {
                 true,
             )
             .with_context(|| {
-                let mut build_error_context = format!("failed to run custom build command for `{}`", pkg_descr);
+                let mut build_error_context =
+                    format!("failed to run custom build command for `{}`", pkg_descr);
 
                 // If we're opting into backtraces, mention that build dependencies' backtraces can
                 // be improved by setting a higher debuginfo level.
                 if let Ok(show_backtraces) = std::env::var("RUST_BACKTRACE") {
                     if show_backtraces != "0" {
-                        build_error_context.push_str("\n\
-                            note: To improve backtraces for build dependencies, make sure full debug info is turned on. \
-                            More details at https://doc.rust-lang.org/cargo/reference/profiles.html#build-dependencies");
+                        build_error_context.push_str(&format!(
+                            "\n\
+                            note: To improve backtraces for build dependencies, set the \
+                            CARGO_PROFILE_{env_profile_name}_BUILD_OVERRIDE_DEBUG=true environment \
+                            variable to enable debug information generation.",
+                        ));
                     }
                 }
 

tests/testsuite/build_script.rs

@@ -77,7 +77,24 @@ fn custom_build_script_failed_backtraces_message() {
 [RUNNING] `rustc --crate-name build_script_build build.rs [..]--crate-type bin [..]`
 [RUNNING] `[..]/build-script-build`
 [ERROR] failed to run custom build command for `foo v0.5.0 ([CWD])`
-note: To improve backtraces for build dependencies[..]
+note: To improve backtraces for build dependencies, set the \
+CARGO_PROFILE_DEV_BUILD_OVERRIDE_DEBUG=true environment variable [..]
+
+Caused by:
+  process didn't exit successfully: `[..]/build-script-build` (exit [..]: 101)",
+        )
+        .run();
+
+    p.cargo("check -v")
+        .env("RUST_BACKTRACE", "1")
+        .with_status(101)
+        .with_stderr(
+            "\
+[COMPILING] foo v0.5.0 ([CWD])
+[RUNNING] `[..]/build-script-build`
+[ERROR] failed to run custom build command for `foo v0.5.0 ([CWD])`
+note: To improve backtraces for build dependencies, set the \
+CARGO_PROFILE_DEV_BUILD_OVERRIDE_DEBUG=true environment variable [..]
 
 Caused by:
   process didn't exit successfully: `[..]/build-script-build` (exit [..]: 101)",