Don't create archive without object files

[maxgerhardt]

What kind of issue is this?

• [X ] PlatformIO Core.
  If you’ve found a bug, please provide an information below.

You can erase any parts of this template not applicable to your Issue.

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Configuration

Operating system: Mac OS
PlatformIO Version (platformio --version): 5.2.0b1

Description of problem

A user in this thread has run into the problem that when a header-only library is used in lib_deps, specifically rlogiacco/CircularBuffer, the program fails to compile at the stage where PlatformIO attempts to create a .a archive file for the library.

Steps to Reproduce

1. Use platformio.ini and code from below
2. Compile

Actual Results

Dependency Graph
|-- <CircularBuffer> 1.3.3 (/Users/ali/Documents/PlatformIO/Projects/esp_template/.pio/libdeps/native/CircularBuffer)
Building in debug mode
Retrieved `.pioenvs/native/src/native/main.o' from cache
ar rc .pioenvs/native/libcaf/libCircularBuffer.a
ar: no archive members specified
usage:  ar -d [-TLsv] archive file ...
        ar -m [-TLsv] archive file ...
        ar -m [-abiTLsv] position archive file ...
        ar -p [-TLsv] archive [file ...]
        ar -q [-cTLsv] archive file ...
        ar -r [-cuTLsv] archive file ...
        ar -r [-abciuTLsv] position archive file ...
        ar -t [-TLsv] archive [file ...]
        ar -x [-ouTLsv] archive [file ...]
*** [.pioenvs/native/libcaf/libCircularBuffer.a] Error 1

Expected Results

PlatformIO does not attempt to invoke the archiver if no object files are present as sources.

If problems with PlatformIO Build System:

The content of platformio.ini:

[env:native]
platform = native
build_type = debug
build_flags = -std=gnu++11
lib_compat_mode = off
lib_deps =
    rlogiacco/CircularBuffer @ ^1.3.3

Source file to reproduce issue:

#include <stdio.h>
#include <CircularBuffer.h>

int main(void){
  printf("main ran\n");
  return 0;
}

Additional info

The problem also seems to be specific to the toolchain version and/or OS being used, since the user says the problem occurs on Mac but not on Windows.

Adding

lib_archive = no

to forcibly prevent PlatformIO from linking the library is a workaround (but should be automatically detected).