Only enable modularized build if forced

The two boolean command line variables that control this are:

force_modules
force_std_modules

32 files changed, 49 insertions, 185 deletions

diff --git a/build/root.build b/build/root.build
index 5129a40..839e423 100644
--- a/build/root.build
+++ b/build/root.build
@@ -2,15 +2,14 @@
 # copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
 # license   : MIT; see accompanying LICENSE file
 
-using cxx.guess
-
-if ($force_modules != true && $cxx.id == 'clang')
-  cxx.features.modules = false
-
 cxx.std = experimental
+cxx.features.modules = ($force_modules == true)
 
 using cxx
 
+if ($force_modules == true && !$cxx.features.modules)
+  fail 'c++ compiler does not support modules'
+
 mxx{*}: extension = mxx
 hxx{*}: extension = hxx
 ixx{*}: extension = ixx
diff --git a/libbutl/buildfile b/libbutl/buildfile
index ccf8908..d3ec87b 100644
--- a/libbutl/buildfile
+++ b/libbutl/buildfile
@@ -4,8 +4,11 @@
 
 int_libs =
 
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
+if ($force_std_modules == true)
 {
+  #@@ MOD is it really an interface dependency? I guess if we re-export
+  #       then it is? Or maybe it is special?
+  #
   import int_libs += libstd-modules%liba{std-modules}
   cxx.poptions += -D__cpp_lib_modules
 }
diff --git a/tests/base64/buildfile b/tests/base64/buildfile
index 535b9dc..bb27f11 100644
--- a/tests/base64/buildfile
+++ b/tests/base64/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/build/root.build b/tests/build/root.build
index 6c98ba9..85724d4 100644
--- a/tests/build/root.build
+++ b/tests/build/root.build
@@ -2,15 +2,22 @@
 # copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
 # license   : MIT; see accompanying LICENSE file
 
-using cxx.guess
-
-if ($force_modules != true && $cxx.id == 'clang')
-  cxx.features.modules = false
-
 cxx.std = experimental
+cxx.features.modules = ($force_modules == true)
 
 using cxx
 
+if ($force_modules == true && !$cxx.features.modules)
+  fail 'c++ compiler does not support modules'
+
+if ($force_std_modules == true)
+{
+  import stdmod_lib = libstd-modules%liba{std-modules}
+  cxx.poptions += -D__cpp_lib_modules
+}
+else
+  stdmod_lib =
+
 hxx{*}: extension = hxx
 cxx{*}: extension = cxx
 
diff --git a/tests/cpfile/buildfile b/tests/cpfile/buildfile
index 41275fa..3482fe7 100644
--- a/tests/cpfile/buildfile
+++ b/tests/cpfile/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/curl/buildfile b/tests/curl/buildfile
index dae375b..9040203 100644
--- a/tests/curl/buildfile
+++ b/tests/curl/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/dir-iterator/buildfile b/tests/dir-iterator/buildfile
index 7f83e4f..361100d 100644
--- a/tests/dir-iterator/buildfile
+++ b/tests/dir-iterator/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/fdstream/buildfile b/tests/fdstream/buildfile
index 6028f3f..c036673 100644
--- a/tests/fdstream/buildfile
+++ b/tests/fdstream/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/link/buildfile b/tests/link/buildfile
index 17e3eac..1180505 100644
--- a/tests/link/buildfile
+++ b/tests/link/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/manifest-parser/buildfile b/tests/manifest-parser/buildfile
index 2a89e29..fafb3d8 100644
--- a/tests/manifest-parser/buildfile
+++ b/tests/manifest-parser/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/manifest-roundtrip/buildfile b/tests/manifest-roundtrip/buildfile
index 5cd296f..19678d8 100644
--- a/tests/manifest-roundtrip/buildfile
+++ b/tests/manifest-roundtrip/buildfile
@@ -3,12 +3,7 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
 exe{driver}: test.roundtrip = manifest
diff --git a/tests/manifest-serializer/buildfile b/tests/manifest-serializer/buildfile
index df633ae..3111d6e 100644
--- a/tests/manifest-serializer/buildfile
+++ b/tests/manifest-serializer/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/mventry/buildfile b/tests/mventry/buildfile
index d9af3a2..3e58110 100644
--- a/tests/mventry/buildfile
+++ b/tests/mventry/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/openssl/buildfile b/tests/openssl/buildfile
index 08b0878..f78d532 100644
--- a/tests/openssl/buildfile
+++ b/tests/openssl/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/pager/buildfile b/tests/pager/buildfile
index d7d0123..67b14fa 100644
--- a/tests/pager/buildfile
+++ b/tests/pager/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/path-entry/buildfile b/tests/path-entry/buildfile
index e6515ae..635246c 100644
--- a/tests/path-entry/buildfile
+++ b/tests/path-entry/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/path/buildfile b/tests/path/buildfile
index aa39b2d..d48fcbe 100644
--- a/tests/path/buildfile
+++ b/tests/path/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/prefix-map/buildfile b/tests/prefix-map/buildfile
index 140fda9..f24743c 100644
--- a/tests/prefix-map/buildfile
+++ b/tests/prefix-map/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/process-run/buildfile b/tests/process-run/buildfile
index 5200af7..0802c8e 100644
--- a/tests/process-run/buildfile
+++ b/tests/process-run/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/process/buildfile b/tests/process/buildfile
index 2ecc915..c0fc49d 100644
--- a/tests/process/buildfile
+++ b/tests/process/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/progress/buildfile b/tests/progress/buildfile
index d8cb6d6..e7031ee 100644
--- a/tests/progress/buildfile
+++ b/tests/progress/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/regex/buildfile b/tests/regex/buildfile
index ae7e2c3..07bcd6f 100644
--- a/tests/regex/buildfile
+++ b/tests/regex/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/sendmail/buildfile b/tests/sendmail/buildfile
index a854e89..773efe0 100644
--- a/tests/sendmail/buildfile
+++ b/tests/sendmail/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/sha256/buildfile b/tests/sha256/buildfile
index fb490d0..1d6cece 100644
--- a/tests/sha256/buildfile
+++ b/tests/sha256/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/small-vector/buildfile b/tests/small-vector/buildfile
index 16d61f8..3d4d1b4 100644
--- a/tests/small-vector/buildfile
+++ b/tests/small-vector/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/standard-version/buildfile b/tests/standard-version/buildfile
index eb30733..57fd517 100644
--- a/tests/standard-version/buildfile
+++ b/tests/standard-version/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/strcase/buildfile b/tests/strcase/buildfile
index efe8442..0c34da7 100644
--- a/tests/strcase/buildfile
+++ b/tests/strcase/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/string-parser/buildfile b/tests/string-parser/buildfile
index 4613df1..b279250 100644
--- a/tests/string-parser/buildfile
+++ b/tests/string-parser/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/tab-parser/buildfile b/tests/tab-parser/buildfile
index eb30733..57fd517 100644
--- a/tests/tab-parser/buildfile
+++ b/tests/tab-parser/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}
diff --git a/tests/target-triplet/buildfile b/tests/target-triplet/buildfile
index 7dec846..a2cc548 100644
--- a/tests/target-triplet/buildfile
+++ b/tests/target-triplet/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/timestamp/buildfile b/tests/timestamp/buildfile
index c554fc3..a0aecb8 100644
--- a/tests/timestamp/buildfile
+++ b/tests/timestamp/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs
diff --git a/tests/wildcard/buildfile b/tests/wildcard/buildfile
index 90e8b58..4ec6488 100644
--- a/tests/wildcard/buildfile
+++ b/tests/wildcard/buildfile
@@ -3,11 +3,6 @@
 # license   : MIT; see accompanying LICENSE file
 
 import libs = libbutl%lib{butl}
-
-if ($cxx.features.modules && ($force_std_modules == true || $cxx.id != 'msvc'))
-{
-  import libs += libstd-modules%liba{std-modules}
-  cxx.poptions += -D__cpp_lib_modules
-}
+libs += $stdmod_lib
 
 exe{driver}: {hxx cxx}{*} $libs test{testscript}