Resolve the always-present Windows linker's warnings (crystal-lang#9307)

* Resolve the always-present Windows linker's warnings

Currently when building on Windows, the version of MSVC linker is always printed first, then the list of all inputs, then a warning for every object file because it ends with .o, not .obj.

So, use the .obj extension and disable the default outputs. So errors are still printed, but normally the output is empty.

* Also switch the file extension for llvm_ext.obj

.github/workflows/win.yml

@@ -16,12 +16,13 @@ jobs:
       - name: Cross-compile Crystal
         run: |
           LLVM_TARGETS=X86 bin/crystal build --cross-compile --target x86_64-pc-windows-msvc src/compiler/crystal.cr -Dwithout_playground
+          mv crystal.o crystal.obj || true  # TODO: Remove this after 0.35.0
 
       - name: Upload Crystal object file
         uses: actions/upload-artifact@v1
         with:
           name: objs
-          path: crystal.o
+          path: crystal.obj
 
   windows-job:
     needs: linux-job
@@ -146,10 +147,10 @@ jobs:
           name: objs
       - name: Build LLVM extensions
         run: |
-          cl /MT /c src\llvm\ext\llvm_ext.cc -I llvm\include /Fosrc\llvm\ext\llvm_ext.o
+          cl /MT /c src\llvm\ext\llvm_ext.cc -I llvm\include /Fosrc\llvm\ext\llvm_ext.obj
       - name: Link Crystal executable
         run: |
-          Invoke-Expression "cl objs\crystal.o /Fecrystal-cross src\llvm\ext\llvm_ext.o $(llvm\bin\llvm-config.exe --libs) libs\pcre.lib libs\gc.lib advapi32.lib libcmt.lib legacy_stdio_definitions.lib /F10000000"
+          Invoke-Expression "cl objs\crystal.obj /Fecrystal-cross src\llvm\ext\llvm_ext.obj $(llvm\bin\llvm-config.exe --libs) libs\pcre.lib libs\gc.lib advapi32.lib libcmt.lib legacy_stdio_definitions.lib /F10000000"
 
       - name: Re-build Crystal
         run: |

.gitignore

@@ -12,6 +12,7 @@ all_spec
 /tmp
 /docs/
 /src/llvm/ext/llvm_ext.o
+/src/llvm/ext/llvm_ext.obj
 /src/llvm/ext/llvm_ext.dwo
 /src/ext/*.o
 /src/ext/libcrystal.a

src/compiler/crystal/codegen/link.cr

@@ -86,6 +86,10 @@ module Crystal
   end
 
   class Program
+    def object_extension
+      has_flag?("windows") ? ".obj" : ".o"
+    end
+
     def lib_flags
       has_flag?("windows") ? lib_flags_windows : lib_flags_posix
     end

src/compiler/crystal/compiler.cr

@@ -274,7 +274,7 @@ module Crystal
       units = llvm_modules.map do |type_name, info|
         llvm_mod = info.mod
         llvm_mod.target = target_triple
-        CompilationUnit.new(self, type_name, llvm_mod, output_dir, bc_flags_changed)
+        CompilationUnit.new(self, program, type_name, llvm_mod, output_dir, bc_flags_changed)
       end
 
       if @cross_compile
@@ -304,7 +304,7 @@ module Crystal
     private def cross_compile(program, units, output_filename)
       unit = units.first
       llvm_mod = unit.llvm_mod
-      object_name = "#{output_filename}.o"
+      object_name = output_filename + program.object_extension
 
       optimize llvm_mod if @release
 
@@ -327,7 +327,7 @@ module Crystal
         # Execute and expand `subcommands`.
         lib_flags = lib_flags.gsub(/`(.*?)`/) { `#{$1}` } if expand
 
-        args = %(#{object_names.join(" ")} "/Fe#{output_filename}" #{lib_flags} #{@link_flags})
+        args = %(/nologo #{object_names.join(" ")} "/Fe#{output_filename}" #{lib_flags} #{@link_flags})
         cmd = "#{CL} #{args}"
 
         if cmd.to_utf16.size > 32000
@@ -597,9 +597,10 @@ module Crystal
       getter original_name
       getter llvm_mod
       getter? reused_previous_compilation = false
+      @object_extension : String
 
-      def initialize(@compiler : Compiler, @name : String, @llvm_mod : LLVM::Module,
-                     @output_dir : String, @bc_flags_changed : Bool)
+      def initialize(@compiler : Compiler, program : Program, @name : String,
+                     @llvm_mod : LLVM::Module, @output_dir : String, @bc_flags_changed : Bool)
         @name = "_main" if @name == ""
         @original_name = @name
         @name = String.build do |str|
@@ -621,6 +622,8 @@ module Crystal
           # 17 chars from name + 1 (dash) + 32 (md5) = 50
           @name = "#{@name[0..16]}-#{Digest::MD5.hexdigest(@name)}"
         end
+
+        @object_extension = program.object_extension
       end
 
       def compile
@@ -721,7 +724,7 @@ module Crystal
           llvm_mod.print_to_file "#{output_filename}.ll"
         end
         if emit_target.obj?
-          FileUtils.cp(object_name, "#{output_filename}.o")
+          FileUtils.cp(object_name, output_filename + @object_extension)
         end
       end
 
@@ -730,7 +733,7 @@ module Crystal
       end
 
       def object_filename
-        "#{@name}.o"
+        @name + @object_extension
       end
 
       def temporary_object_name

src/llvm/lib_llvm_ext.cr

@@ -1,5 +1,9 @@
 require "./lib_llvm"
-@[Link(ldflags: "#{__DIR__}/ext/llvm_ext.o")]
+{% if flag?(:win32) %}
+  @[Link(ldflags: "#{__DIR__}/ext/llvm_ext.obj")]
+{% else %}
+  @[Link(ldflags: "#{__DIR__}/ext/llvm_ext.o")]
+{% end %}
 lib LibLLVMExt
   alias Char = LibC::Char
   alias Int = LibC::Int