Surface the failing command's name from the build error dump

[kornelski]

Because Cargo's formatting of build errors is very noisy users struggle to understand what is causing the build to fail.

Here's a recent case where the failure reason was simple, but the user could not see it through all the noise.

---

    Compiling openssl-sys v0.9.103 (~/openssl-sys/openssl-sys)
+The following warnings were emitted during compilation:
+
+warning: openssl-sys@0.9.103: configuring OpenSSL build: Command 'perl' not found. Is perl installed?
+
 error: failed to run custom build command for `openssl-sys v0.9.103 (~/openssl-sys/openssl-sys)`
 note: To improve backtraces for build dependencies, set the CARGO_PROFILE_DEV_BUILD_OVERRIDE_DEBUG=true environment variable to enable debug information generation.
 
 Caused by:
   process didn't exit successfully: `~/openssl-sys/target/debug/build/openssl-sys-60b6752181d583d2/build-script-main` (exit status: 101)
 
 [...]

   --- stderr
-   thread 'main' panicked at ~/openssl-src-rs/src/lib.rs:578:14:
+   thread 'main' panicked at ~/openssl-sys/build/find_vendored.rs:18:39:
 
 
 
   Error configuring OpenSSL build:
-      Command: cd "~/openssl-sys/target/debug/build/openssl-sys-8f90d3753aa6037e/out/openssl-build/build/src" && env -u CROSS_COMPILE AR="ar" CC="cc" RANLIB="ranlib" "perl" "./Configure" "--prefix=~/openssl-sys/target/debug/build/openssl-sys-8f90d3753aa6037e/out/openssl-build/install" "--openssldir=/usr/local/ssl" "no-dso" "no-shared" "no-ssl3" "no-tests" "no-comp" "no-zlib" "no-zlib-dynamic" "--libdir=lib" "no-md2" "no-rc5" "no-weak-ssl-ciphers" "no-camellia" "no-idea" "no-seed" "darwin64-arm64-cc" "-nologo" "-MD" "-O2" "-Z7" "-Brepro" "-mmacosx-version-min=11.0"
-      Failed to execute: No such file or directory (os error 2)
+      Command 'perl' not found. Is perl installed?
+      Command failed: cd "~/openssl-sys/target/debug/build/openssl-sys-3ae48db4843d8fdf/out/openssl-build/build/src" && env -u CROSS_COMPILE AR="ar" CC="cc" RANLIB="ranlib" "perl" "./Configure" "--prefix=~/openssl-sys/target/debug/build/openssl-sys-3ae48db4843d8fdf/out/openssl-build/install" "--openssldir=/usr/local/ssl" "no-shared" "no-ssl3" "no-tests" "no-comp" "no-zlib" "no-zlib-dynamic" "--libdir=lib" "no-md2" "no-rc5" "no-weak-ssl-ciphers" "no-camellia" "no-idea" "no-seed" "darwin64-arm64-cc" "-nologo" "-MD" "-O2" "-Z7" "-Brepro" "-mmacosx-version-min=11.0"

• Cleverness of the Debug impl of Command obscures the command name that has been run. This change prints the command name alone.
• NotFound error is handled with a dedicated message.
• Uses cargo:warning to also print the message above the stdout and stderr dumps.

[kornelski]

I've also added try_build, so that I can make openssl-sys report the error without a noisy backtrace.

[bjorn3]

Instead of using panic, maybe using eprintln!() + std::process::exit(1) would work? openssl-src is probably not called in any context where recovering from an unexpected build error is necessary, and you added try_build for cases where build errors are expected to happen.

[kornelski]

Exiting directly without a panic would be cleaner, but I'm leaving that to the caller of try_build – I'm adding such exits to openssl-sys.

[alexcrichton]

Thanks for the PR! If try_build is being introduced could this result-ify all the unwraps/expects? The existence of try_build and build implies that one never panics while the other might, so I'd prefer to head off confusion.

Also I agree with @bjorn3 that if the goal is a "clean exit" for the build method, could that be updated to print+exit instead of a formatted panic?

[kornelski]

I've updated it with a clean exit, and converted other panics into errors.

[alexcrichton]

Thanks for this!