sourceCpp compile error stderr cannot be caught/suppressed

[andrjohns]

When writing a try() function to check for compile errors from sourceCpp the compilation error is always printed to the console, regardless of whichever combinations of try(), suppressMessages(), suppressWarnings() or sink are used.

Reprex:

dcode <- "//[[Rcpp::export]]\n int fun(int x) { const int y; return x; }"
status <- suppressWarnings(suppressMessages(
  output <- capture.output(
    try(Rcpp::sourceCpp(code = dcode, verbose=FALSE, echo=FALSE),
                 silent = TRUE))
))

^{Created on 2023-03-24 with reprex v2.0.2}

Standard output and standard error

fileeed07e197428.cpp:2:29: error: default initialization of an object of const type 'const int'
 int fun(int x) { const int y; return x; }
                            ^
                              = 0
1 error generated.
make: *** [fileeed07e197428.o] Error 1

[eddelbuettel]

Hm, I think that's the way it is and likely will be -- Rcpp::sourceCpp() and friends call functions calling commands like R CMD COMPILE and R CMD SHLIB so the output suppression you desire happens at the operating system command level and R's own output suppressers (working on R's own output streams) have nothing for them.

Not really an Rcpp issue.

[andrjohns]

sourceCpp calls system(), and this can be handled with system():

cat("int fun(int x) { const int y; return x; }", file="foo.cpp")
system("R CMD SHLIB foo.cpp", ignore.stderr = TRUE, ignore.stdout = TRUE)

Could verbose/showOutput/echo be passed to these?

[eddelbuettel]

If you believe strongly that this is warranted, maybe you could sketch a change proposal in this issue, and ideally test it? One of us may take a look.

[andrjohns]

Another perspective, it also means that the verbose flag is only respected if the compilation succeeds. Since the following:

gooddcode <- "//[[Rcpp::export]]\n int fun(int x) { return x; }"
Rcpp::sourceCpp(code = gooddcode, verbose=FALSE, rebuild = TRUE)

Does not print the compilation call, but it does get printed if the compilation fails

[Enchufa2]

I think it's a reasonable request. I'll take a look, I have some experience with this kind of stuff with bspm.

[eddelbuettel]

We could also think about a new helper package that revisits the issue from a different angle but leaves the existing functions evalCpp(), cppFunction(), and sourceCpp() --- which were after all all meant for quick interactive work -- alone.

We now have system2() which if memory serves wasn't around when the existing helpers were written.

Just a suggestion.

[eddelbuettel]

@andrjohns Can you do us a favour and build of the branch @Enchufa2 submitted as part of his PR #1259 ? It now uses system2() and should be able to accomodate you.

[eddelbuettel]

@andrjohns I am going to merge this now, assuming it will indeed address the issue you pointed out to us. Should it still be an issue for you please feel free to reopen this and append any additional detail you can think of.

[andrjohns]

Thanks @Enchufa2 for sorting this so quickly and sorry for not testing earlier! It looks like this has almost fixed it - both stderr and stdout still always print to the console on failure, but they can now be captured by capture.output():

> dcode <- "//[[Rcpp::export]]\n int fun(int x) { const int y; return x; }"
> status <- suppressWarnings(suppressMessages(
+         try(Rcpp::sourceCpp(code = dcode, verbose=FALSE, echo=FALSE, showOutput = FALSE),
+             silent = TRUE)
+ ))
clang++ -arch arm64 -std=gnu++14 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG   -I"/Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/library/Rcpp/include" -I"/private/var/folders/1d/rjvd0h_n0yq20j13h4gdfytw0000gn/T/RtmpKtrHhf/sourceCpp-aarch64-apple-darwin20-1.0.10.4" -I/opt/R/arm64/include   -fPIC  -falign-functions=64 -Wall -g -O2  -Wno-unknown-warning-option -Wno-enum-compare -Wno-ignored-attributes -Wno-unused-local-typedef -Wno-sign-compare -Wno-unneeded-internal-declaration -Wno-unused-function -Wno-unused-but-set-variable -Wno-unused-variable -Wno-infinite-recursion -Wno-unknown-pragmas -Wno-unused-lambda-capture -Wno-deprecated-declarations -Wno-deprecated-builtins -Wno-unused-but-set-variables -ftemplate-backtrace-limit=0 -I/opt/homebrew/opt/libomp/include -c file4234702a2e8.cpp -o file4234702a2e8.o
file4234702a2e8.cpp:2:29: error: default initialization of an object of const type 'const int'
 int fun(int x) { const int y; return x; }
                            ^
                              = 0
1 error generated.
make: *** [file4234702a2e8.o] Error 1

Shows nothing:

dcode <- "//[[Rcpp::export]]\n int fun(int x) { const int y; return x; }"
status <- suppressWarnings(suppressMessages(
    output <- capture.output(
        try(Rcpp::sourceCpp(code = dcode, verbose=FALSE, echo=FALSE),
            silent = TRUE))
))

It would be great if the output could be suppressed by verbose=FALSE, but that's also easy enough to workaround now if not

[eddelbuettel]

Can you look into a PR accomplishing what you desire exactly as you desire? We would be happy to review.