"pod lib lint" command throws error with mixed objective-c and objective-c++ files

I try to create a simple cocoapods library with objective-c and objective-c++ files. When executing the command pod lib lint I get an error.

Pod structure:

mypod

src

// A.h
#pragma once

#import <Foundation/Foundation.h>

NSString* foo(void);
NSString* bar(void);

// A.m
#import "foo.h"
#import "bar.h"

NSString* foo() {
  return @"Foo";
}

NSString* bar() {
  int myInt = getValue();
  return [NSString stringWithFormat:@"%d",myInt];
}

// B.h
#pragma once

int getValue(void);

// B.mm
#import "bar.h"

int getValue(void)
{
  return 2;
}

mypod.podspec

Pod::Spec.new do |spec|
    spec.name                     = 'mypod'
    spec.version                  = '1.0'
    spec.homepage                 = 'mypod'
    spec.source                   = { :git => "Not Published", :tag => "Cocoapods/#{spec.name}/#{spec.version}" }
    spec.authors                  = ''
    spec.license                  = ''
    spec.summary                  = 'mypod'
    spec.ios.deployment_target    = '13.5'
    spec.source_files             = 'src/A.h', 'src/A.m', 'src/B.h', 'src/B.mm'
    spec.private_header_files     = 'src/A.h'
    spec.public_header_files      = 'src/B.h'
    spec.library = "c++"
    spec.pod_target_xcconfig      = {
    "OTHER_LDFLAGS" => "-lstdc++",
    'LANG_CXX_LANGUAGE_STANDARD' => 'c++20',
    'CLANG_CXX_LIBRARY' => 'libc++',
    'ARCHS' => 'arm64'
    }
end

Executing the command `pod lib lint --platforms=ios --verbose` on an M1 mac throws an error:

    Undefined symbols for architecture arm64:
      "_getValue", referenced from:
          _bar in foo.o
    ld: symbol(s) not found for architecture arm64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)

    ** BUILD FAILED **

Does somebody know what's the problem?

Solution

When importing the sames headers into C++ and Objective-C compilation units, you have to wrap the declarations with extern "C" guards to avoid their names being mangled when linking:

#ifdef __cplusplus
extern "C" {
#endif

int getValue(void);

#ifdef __cplusplus
}
#endif