Add :gcc5 and :gcc6 as valid GCC choices for future-proofing (#139)

`platform_matches()` will consider `:gcc4`, `:gcc5` and `:gcc6` as all
matching at this point, as we only really care about libgfortran version.
The latest compatible release should be the one that gets downloaded
in the event of an ambiguity.

src/PlatformNames.jl

@@ -10,15 +10,15 @@ end
 # We need to track our compiler ABI compatibility.
 struct CompilerABI
     # Major GCC version that we're locked into.
-    # Can be [:gcc4, :gcc7, :gcc8, :gcc_any]
+    # Can be [:gcc4, :gcc5, :gcc6, :gcc7, :gcc8, :gcc_any]
     gcc_version::Symbol
 
     # Whether we're using cxx11abi strings
     # Can be [:cxx03, :cxx11, :cxx_any]
     cxx_abi::Symbol
 
     function CompilerABI(gcc_version::Symbol = :gcc_any, cxx_abi::Symbol = :cxx_any)
-        if !in(gcc_version, [:gcc4, :gcc7, :gcc8, :gcc_any])
+        if !in(gcc_version, [:gcc4, :gcc5, :gcc6, :gcc7, :gcc8, :gcc_any])
             throw(ArgumentError("Unsupported GCC major version '$gcc_version'"))
         end
 
@@ -389,6 +389,8 @@ function platform_key_abi(machine::AbstractString)
     gcc_version_mapping = Dict(
         :gcc_any => "",
         :gcc4 => "-gcc4",
+        :gcc5 => "-gcc5",
+        :gcc6 => "-gcc6",
         :gcc7 => "-gcc7",
         :gcc8 => "-gcc8",
     )
@@ -703,9 +705,21 @@ function platforms_match(a::Platform, b::Platform)
     function flexible_constraints(a, b)
         ac = compiler_abi(a)
         bc = compiler_abi(b)
+
+        # Map from GCC version to libgfortran SO version
+        gfmap = Dict(
+            :gcc4 => 3,
+            :gcc5 => 3,
+            :gcc6 => 3,
+            :gcc7 => 4,
+            :gcc8 => 5,
+        )
+
+        # We consider two GCC versions to match if their libgfortran
+        # versions match; e.g. :gcc4 and :gcc5 match.
         gcc_match = (ac.gcc_version == :gcc_any
                   || bc.gcc_version == :gcc_any
-                  || ac.gcc_version == bc.gcc_version)
+                  || gfmap[ac.gcc_version] == gfmap[bc.gcc_version])
         cxx_match = (ac.cxx_abi == :cxx_any
                   || bc.cxx_abi == :cxx_any
                   || ac.cxx_abi == bc.cxx_abi)

test/runtests.jl

@@ -271,6 +271,20 @@ end
         @test !BinaryProvider.platforms_match(Linux(:x86_64), UnknownPlatform())
         @test !BinaryProvider.platforms_match(Linux(:x86_64, compiler_abi=CompilerABI(:gcc7)), Linux(:x86_64, compiler_abi=CompilerABI(:gcc8)))
         @test !BinaryProvider.platforms_match(Linux(:x86_64, compiler_abi=CompilerABI(:gcc7, :cxx11)), Linux(:x86_64, compiler_abi=CompilerABI(:gcc7, :cxx03)))
+
+        # Test that :gcc4 matches with :gcc5 and :gcc6, as we only care aobut libgfortran version
+        @test BinaryProvider.platforms_match(
+            Linux(:x86_64; compiler_abi=CompilerABI(:gcc4)),
+            Linux(:x86_64; compiler_abi=CompilerABI(:gcc5)),
+        )
+        @test BinaryProvider.platforms_match(
+            Linux(:x86_64; compiler_abi=CompilerABI(:gcc4)),
+            Linux(:x86_64; compiler_abi=CompilerABI(:gcc6)),
+        )
+        @test BinaryProvider.platforms_match(
+            Linux(:x86_64; compiler_abi=CompilerABI(:gcc5)),
+            Linux(:x86_64; compiler_abi=CompilerABI(:gcc6)),
+        )
     end
 
     @testset "DL name/version parsing" begin
@@ -789,21 +803,37 @@ end
 
 @testset "choose_download" begin
     platforms = Dict(
+        # Typical binning test
         Linux(:x86_64, compiler_abi=CompilerABI(:gcc4)) => "linux4",
         Linux(:x86_64, compiler_abi=CompilerABI(:gcc7)) => "linux7",
         Linux(:x86_64, compiler_abi=CompilerABI(:gcc8)) => "linux8",
+
+        # Ambiguity test
+        Linux(:aarch64, compiler_abi=CompilerABI(:gcc4)) => "linux4",
+        Linux(:aarch64, compiler_abi=CompilerABI(:gcc5)) => "linux5",
+
         MacOS(:x86_64, compiler_abi=CompilerABI(:gcc4)) => "mac4",
         Windows(:x86_64, compiler_abi=CompilerABI(:gcc_any, :cxx11)) => "win",
     )
 
     @test choose_download(platforms, Linux(:x86_64)) == "linux8"
     @test choose_download(platforms, Linux(:x86_64, compiler_abi=CompilerABI(:gcc7))) == "linux7"
-
+
+    # Ambiguity test
+    @test choose_download(platforms, Linux(:aarch64)) == "linux5"
+    @test choose_download(platforms, Linux(:aarch64; compiler_abi=CompilerABI(:gcc4))) == "linux5"
+    @test choose_download(platforms, Linux(:aarch64; compiler_abi=CompilerABI(:gcc5))) == "linux5"
+    @test choose_download(platforms, Linux(:aarch64; compiler_abi=CompilerABI(:gcc6))) == "linux5"
+    @test choose_download(platforms, Linux(:aarch64; compiler_abi=CompilerABI(:gcc7))) == nothing
+
     @test choose_download(platforms, MacOS(:x86_64)) == "mac4"
     @test choose_download(platforms, MacOS(:x86_64, compiler_abi=CompilerABI(:gcc7))) == nothing
 
     @test choose_download(platforms, Windows(:x86_64, compiler_abi=CompilerABI(:gcc_any, :cxx11))) == "win"
     @test choose_download(platforms, Windows(:x86_64, compiler_abi=CompilerABI(:gcc_any, :cxx03))) == nothing
+
+    # Poor little guy
+    @test choose_download(platforms, FreeBSD(:x86_64)) == nothing
 end
 
 # Use `build_libfoo_tarball.jl` in the BinaryBuilder.jl repository to generate more of these