Fix issue with old rubygems not detecting musl linux properly (#40)

* Fix issue with old rubygems not detecting musl linux properly

Old versions of rubygems (for instance 3.0.3) don't properly detect
alternative libc implementations on Linux; in particular for our case,
they don't detect musl.

(For reference, Rubies older than 2.7 may have shipped with an affected
 version of rubygems).

In such cases, we fall back to use RbConfig::CONFIG['arch'] instead.

Why not use `RbConfig::CONFIG['arch']` always? Because
`Gem::Platform.local.to_s` does some normalization we want
in other situations -- for instance, it turns `x86_64-linux-gnu` to
`x86_64-linux`. So for now we only add this workaround in a specific
situation where we actually know it is wrong.

See also rubygems/rubygems#2922 and
rubygems/rubygems#4082

Fixes DataDog/dd-trace-rb#2222

* Bump libdatadog minor version in preparation for release

I'm planning to release 0.7.0.1.1 with the musl fix. This will be
automatically picked up by customers using the currently-released
version of dd-trace-rb (1.3.0).

* Fix file open permissions / directory creation

Otherwise this breaks in Linux due to the rest of the spec flow.

* Remove redundant directory creation in spec

ruby/lib/libdatadog.rb

@@ -11,6 +11,23 @@ def self.available_binaries
   def self.pkgconfig_folder(pkgconfig_file_name = "ddprof_ffi_with_rpath.pc")
     current_platform = Gem::Platform.local.to_s
 
+    if RbConfig::CONFIG["arch"].include?("-musl") && !current_platform.include?("-musl")
+      # Fix/workaround for https://github.com/DataDog/dd-trace-rb/issues/2222
+      #
+      # Old versions of rubygems (for instance 3.0.3) don't properly detect alternative libc implementations on Linux;
+      # in particular for our case, they don't detect musl. (For reference, Rubies older than 2.7 may have shipped with
+      # an affected version of rubygems).
+      # In such cases, we fall back to use RbConfig::CONFIG['arch'] instead.
+      #
+      # Why not use RbConfig::CONFIG['arch'] always? Because Gem::Platform.local.to_s does some normalization we want
+      # in other situations -- for instance, it turns `x86_64-linux-gnu` to `x86_64-linux`. So for now we only add this
+      # workaround in a specific situation where we actually know it is wrong.
+      #
+      # See also https://github.com/rubygems/rubygems/pull/2922 and https://github.com/rubygems/rubygems/pull/4082
+
+      current_platform = RbConfig::CONFIG["arch"]
+    end
+
     return unless available_binaries.include?(current_platform)
 
     pkgconfig_file = Dir.glob("#{vendor_directory}/#{current_platform}/**/#{pkgconfig_file_name}").first

ruby/lib/libdatadog/version.rb

@@ -5,7 +5,7 @@ module Libdatadog
   LIB_VERSION = "0.7.0"
 
   GEM_MAJOR_VERSION = "1"
-  GEM_MINOR_VERSION = "0"
+  GEM_MINOR_VERSION = "1"
   GEM_PRERELEASE_VERSION = "" # remember to include dot prefix, if needed!
   private_constant :GEM_MAJOR_VERSION, :GEM_MINOR_VERSION, :GEM_PRERELEASE_VERSION
 

ruby/spec/libdatadog_spec.rb

@@ -66,15 +66,41 @@
         let(:pkgconfig_folder) { "#{temporary_directory}/#{Gem::Platform.local}/some/folder/containing/the/pkgconfig/file" }
 
         before do
-          FileUtils.mkdir_p(pkgconfig_folder)
-          File.open("#{pkgconfig_folder}/ddprof_ffi_with_rpath.pc", "w") {}
+          create_dummy_pkgconfig_file(pkgconfig_folder)
+        end
+
+        def create_dummy_pkgconfig_file(pkgconfig_folder)
+          begin
+            FileUtils.mkdir_p(pkgconfig_folder)
+          rescue Errno::EEXIST
+            # No problem, a few specs try to create the same folder
+          end
+
+          File.open("#{pkgconfig_folder}/ddprof_ffi_with_rpath.pc", "w+") {}
         end
 
         describe ".pkgconfig_folder" do
           it "returns the folder containing the pkgconfig file" do
             expect(Libdatadog.pkgconfig_folder).to eq pkgconfig_folder
           end
         end
+
+        context "when `RbConfig::CONFIG[\"arch\"]` indicates we're on musl libc, but `Gem::Platform.local.to_s` does not detect it" do
+          # Fix for https://github.com/DataDog/dd-trace-rb/issues/2222
+
+          before do
+            allow(RbConfig::CONFIG).to receive(:[]).with("arch").and_return("x86_64-linux-musl")
+            allow(Gem::Platform).to receive(:local).and_return("x86_64-linux")
+
+            ["x86_64-linux", "x86_64-linux-musl"].each do |arch|
+              create_dummy_pkgconfig_file("#{temporary_directory}/#{arch}/some/folder/containing/the/pkgconfig/file")
+            end
+          end
+
+          it "returns the folder containing the pkgconfig file for the musl variant" do
+            expect(Libdatadog.pkgconfig_folder).to eq "#{temporary_directory}/x86_64-linux-musl/some/folder/containing/the/pkgconfig/file"
+          end
+        end
       end
 
       context "but not for the current platform" do