[feature] Autodetect <target-os> from compiler triplet

src/tools/clang-darwin.jam

@@ -50,6 +50,12 @@ rule init ( version ? :  command * : options * )
         : version $(version) ] ;
 
     common.handle-options clang-darwin : $(condition) : $(command) : $(options) ;
+
+    if $(command)
+    {
+        clang.set-target-os-default clang-darwin : $(condition) : $(command-string) : $(options) ;
+    }
+
     clang.init-flags clang-darwin : $(condition) : $(version) :
         [ feature.get-values <triplet> : $(options) ] ;
 

src/tools/clang-linux.jam

@@ -74,6 +74,12 @@ rule init ( version ? :  command * : options * ) {
     : version $(version) ] ;
 
   common.handle-options clang-linux : $(condition) : $(command) : $(options) ;
+
+  if $(command)
+  {
+      clang.set-target-os-default clang-linux : $(condition) : $(command-string) : $(options) ;
+  }
+
   clang.init-flags clang-linux : $(condition) : $(version) :
       [ feature.get-values <triple> : $(options) ] ;
 

src/tools/clang.jam

@@ -35,6 +35,37 @@ rule init ( * : * )
 }
 
 
+rule set-target-os-default ( toolset : condition * : command-string : options * )
+{
+    # Autodetect target-os from the compiler's own triple, unless the
+    # toolset was already told what to target
+    if ! [ feature.get-values <target-os> : $(options) ]
+    {
+        local machine = [ MATCH "^([^ ]+)" :
+            [ SHELL "$(command-string) -dumpmachine" ] ] ;
+        local target-os ;
+        switch $(machine:L)
+        {
+            case *android* : target-os ?= android ;
+            case *mingw*   : target-os ?= windows ;
+            case *cygwin*  : target-os ?= cygwin ;
+            case *linux*   : target-os ?= linux ;
+            case *tvos*    : target-os ?= appletv ;
+            case *watchos* : target-os ?= iphone ;
+            case *ios*     : target-os ?= iphone ;
+            case *darwin*  : target-os ?= darwin ;
+            case *freebsd* : target-os ?= freebsd ;
+            case *solaris* : target-os ?= solaris ;
+            case *qnx*     : target-os ?= qnxnto ;
+        }
+        if $(target-os)
+        {
+            local conditionx = [ regex.replace $(condition) "/" "," ] ;
+            toolset.add-defaults $(conditionx)\:<target-os>$(target-os) ;
+        }
+    }
+}
+
 local rule cxxstd-flags ( toolset : condition * : options * )
 {
     toolset.flags $(toolset).compile.c++ OPTIONS $(condition) : $(options) : unchecked ;

src/tools/gcc.jam

@@ -199,11 +199,16 @@ rule init ( version ? : command * : options * : requirement * )
         }
         switch $(machine:L)
         {
-            case *mingw*  : target-os ?= windows ;
-            case *cygwin* : target-os ?= cygwin ;
-            case *linux*  : target-os ?= linux ;
-            case *aix*    : target-os ?= aix ;
-            case *hpux*   : target-os ?= hpux ;
+            case *mingw*   : target-os ?= windows ;
+            case *cygwin*  : target-os ?= cygwin ;
+            case *android* : target-os ?= android ;
+            case *linux*   : target-os ?= linux ;
+            case *aix*     : target-os ?= aix ;
+            case *hpux*    : target-os ?= hpux ;
+            case *darwin*  : target-os ?= darwin ;
+            case *freebsd* : target-os ?= freebsd ;
+            case *solaris* : target-os ?= solaris ;
+            case *qnx*     : target-os ?= qnxnto ;
             # TODO: finish this list.
         }
     }

test/test_all.py

@@ -486,6 +486,7 @@ def reorder_tests(tests, first_test):
     "toolset_intel_darwin",
     "toolset_msvc",
     "toolset_requirements",
+    "toolset_target_os_autodetect",
     "transitive_skip",
     "unit_test",
     "unused",

test/toolset_target_os_autodetect.py

@@ -0,0 +1,120 @@
+#!/usr/bin/env python3
+#
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.txt or copy at
+# https://www.bfgroup.xyz/b2/LICENSE.txt)
+
+# Test for autodetecting <target-os> from the compiler's own
+# `-dumpmachine` triple when target-os is not given explicitly, covering
+# the gcc, clang-linux and clang-darwin toolsets.
+
+import BoostBuild
+import sys
+import textwrap
+
+MOCK_COMPILER_TEMPLATE = '''#!/usr/bin/env python3
+import sys
+
+args = sys.argv[1:]
+
+if args == ["-dumpmachine"]:
+    print("@TRIPLE@")
+    sys.exit(0)
+
+if args == ["-print-prog-name=ar"]:
+    print("ar")
+    sys.exit(0)
+
+if "-c" in args and "-o" in args:
+    if "-DOS_AUTODETECTED_OK" not in args:
+        sys.exit(1)
+    with open(args[args.index("-o") + 1], "w") as f:
+        f.write("mock object\\n")
+    sys.exit(0)
+
+sys.exit(1)
+'''
+
+
+def test_target_os_gcc_autodetect():
+    t = BoostBuild.Tester(pass_toolset=0)
+
+    t.write("fake-compiler.py", MOCK_COMPILER_TEMPLATE.replace("@TRIPLE@", "arm-linux-androideabi"))
+    t.write("project-config.jam", textwrap.dedent('''
+        import os ;
+        path-constant HERE : . ;
+        local PYTHON = [ os.environ PYTHON_CMD ] ;
+        using gcc : autodetect : $(PYTHON) $(HERE)/fake-compiler.py ;
+        '''))
+    t.write("Jamroot.jam", textwrap.dedent('''
+        obj test : test.cpp :
+        <target-os>android:<define>OS_AUTODETECTED_OK ;
+        '''))
+    t.write("test.cpp", "int f() { return 0; }")
+
+    t.run_build_system(["-sPYTHON_CMD=" + sys.executable, "toolset=gcc-autodetect", "test"])
+    t.cleanup()
+
+def test_target_os_clang_linux_autodetect():
+    t = BoostBuild.Tester(pass_toolset=0)
+
+    t.write("fake-compiler.py", MOCK_COMPILER_TEMPLATE.replace("@TRIPLE@", "aarch64-linux-android21"))
+    t.write("project-config.jam", textwrap.dedent('''
+        import os ;
+        path-constant HERE : . ;
+        local PYTHON = [ os.environ PYTHON_CMD ] ;
+        using clang-linux : autodetect : $(PYTHON) $(HERE)/fake-compiler.py ;
+        '''))
+    t.write("Jamroot.jam", textwrap.dedent('''
+        obj test : test.cpp :
+        <target-os>android:<define>OS_AUTODETECTED_OK ;
+        '''))
+    t.write("test.cpp", "int f() { return 0; }")
+
+    t.run_build_system(["-sPYTHON_CMD=" + sys.executable, "toolset=clang-linux-autodetect", "test"])
+    t.cleanup()
+
+def test_target_os_clang_darwin_autodetect():
+    t = BoostBuild.Tester(pass_toolset=0)
+
+    t.write("fake-compiler.py", MOCK_COMPILER_TEMPLATE.replace("@TRIPLE@", "x86_64-pc-solaris2.11"))
+    t.write("project-config.jam", textwrap.dedent('''
+        import os ;
+        path-constant HERE : . ;
+        local PYTHON = [ os.environ PYTHON_CMD ] ;
+        using clang-darwin : autodetect : $(PYTHON) $(HERE)/fake-compiler.py ;
+        '''))
+    t.write("Jamroot.jam", textwrap.dedent('''
+        obj test : test.cpp :
+        <target-os>solaris:<define>OS_AUTODETECTED_OK ;
+        '''))
+    t.write("test.cpp", "int f() { return 0; }")
+
+    t.run_build_system(["-sPYTHON_CMD=" + sys.executable, "toolset=clang-darwin-autodetect", "test"])
+    t.cleanup()
+
+
+def test_target_os_clang_darwin_autodetect_linux():
+    t = BoostBuild.Tester(pass_toolset=0)
+
+    t.write("fake-compiler.py", MOCK_COMPILER_TEMPLATE.replace("@TRIPLE@", "armv7-unknown-linux-gnueabihf"))
+    t.write("project-config.jam", textwrap.dedent('''
+        import os ;
+        path-constant HERE : . ;
+        local PYTHON = [ os.environ PYTHON_CMD ] ;
+        using clang-darwin : autodetect : $(PYTHON) $(HERE)/fake-compiler.py ;
+        '''))
+    t.write("Jamroot.jam", textwrap.dedent('''
+        obj test : test.cpp :
+        <target-os>linux:<define>OS_AUTODETECTED_OK ;
+        '''))
+    t.write("test.cpp", "int f() { return 0; }")
+
+    t.run_build_system(["-sPYTHON_CMD=" + sys.executable, "toolset=clang-darwin-autodetect", "test"])
+    t.cleanup()
+
+
+test_target_os_gcc_autodetect()
+test_target_os_clang_linux_autodetect()
+test_target_os_clang_darwin_autodetect()
+test_target_os_clang_darwin_autodetect_linux()