Merge pull request #5958 from xu-cheng/compiler

CompilerSelector: prefer the gcc version offered by the gcc formula

Library/Homebrew/compilers.rb

@@ -102,11 +102,19 @@ class CompilerSelector
 
   private
 
+  def gnu_gcc_versions
+    # prioritize gcc version provided by gcc formula.
+    v = Formulary.factory("gcc").version.to_s.slice(/\d/)
+    GNU_GCC_VERSIONS - [v] + [v] # move the version to the end of the list
+  rescue FormulaUnavailableError
+    GNU_GCC_VERSIONS
+  end
+
   def find_compiler
     compilers.each do |compiler|
       case compiler
       when :gnu
-        GNU_GCC_VERSIONS.reverse_each do |v|
+        gnu_gcc_versions.reverse_each do |v|
           name = "gcc-#{v}"
           version = compiler_version(name)
           yield Compiler.new(name, version) unless version.null?

Library/Homebrew/test/compiler_selector_spec.rb

@@ -39,6 +39,12 @@ describe CompilerSelector do
       expect(subject.compiler).to eq("gcc-7")
     end
 
+    it "returns gcc-6 if gcc formula offers gcc-6" do
+      software_spec.fails_with(:clang)
+      allow(Formulary).to receive(:factory).with("gcc").and_return(double(version: "6.0"))
+      expect(subject.compiler).to eq("gcc-6")
+    end
+
     it "raises an error when gcc or llvm is missing" do
       software_spec.fails_with(:clang)
       software_spec.fails_with(gcc: "7")