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-rw-r--r--libbuild2/cxx/init.cxx80
1 files changed, 56 insertions, 24 deletions
diff --git a/libbuild2/cxx/init.cxx b/libbuild2/cxx/init.cxx
index 6a449c7..d4e3151 100644
--- a/libbuild2/cxx/init.cxx
+++ b/libbuild2/cxx/init.cxx
@@ -58,7 +58,36 @@ namespace build2
uint64_t mi (ci.version.minor);
uint64_t p (ci.version.patch);
- // Features.
+ // Besides various `c++NN` we have two special values: `latest` and
+ // `experimental`.
+ //
+ // The semantics of the `latest` value is the latest available standard
+ // that is not necessarily complete or final but is practically usable.
+ // In other words, a project that uses this value and does not rely on
+ // any unstable/bleeding edge parts of the standard (or takes care to
+ // deal with them, for example, using feature test macros), can
+ // reasonably expect to work. In particular, this is the value we use by
+ // default in projects created by bdep-new(1) as well as to build the
+ // build2 toolchain itself.
+ //
+ // The `experimental` value, as the name suggests, is the latest
+ // available standard that is not necessarily usable in real projects.
+ // By definition, `experimental` >= `latest`.
+ //
+ // In addition to the `experimental` value itself we have a number of
+ // feature flags that can be used to enable or disable certain major
+ // parts (such as modules, concepts, etc) in this mode. They are also
+ // used to signal back to the project whether a particular feature is
+ // available. A feature flag set by the user has a tri-state semantics:
+ //
+ // - false - disabled
+ // - unspecified - enabled if practically usable
+ // - true - enabled even if practically unusable
+ //
+ bool latest (v != nullptr && *v == "latest");
+ bool experimental (v != nullptr && *v == "experimental");
+
+ // Feature flags.
//
auto enter = [&rs] (const char* v) -> const variable&
{
@@ -66,19 +95,11 @@ namespace build2
v, variable_visibility::project);
};
- // NOTE: see also module sidebuild subproject if changing anything about
- // modules here.
-
//bool concepts (false); auto& v_c (enter ("cxx.features.concepts"));
bool modules (false); auto& v_m (enter ("cxx.features.modules"));
- // Translate "latest" and "experimental" to the compiler/version-
- // appropriate option(s). Experimental is normally like latest with
- // extra stuff enabled via additional flags. Otherwise translate the
- // standard value.
- //
- bool experimental ( v != nullptr && *v == "experimental");
- bool latest (experimental || (v != nullptr && *v == "latest"));
+ // NOTE: see also module sidebuild subproject if changing anything about
+ // modules here.
string o;
@@ -91,6 +112,10 @@ namespace build2
// to c++14 but can be set to c++latest. And from 15.3 it can be
// c++17.
//
+ bool v16_0 ( mj > 19 || (mj == 19 && mi >= 20));
+ bool v15_3 (v16_0 || (mj == 19 && mi >= 11));
+ bool v14_3 (v15_3 || (mj == 19 && (mi > 0 || (mi == 0 && p >= 24215))));
+
// The question is also whether we should verify that the requested
// standard is provided by this VC version. And if so, from which
// version should we say VC supports 11, 14, and 17? We should
@@ -100,9 +125,21 @@ namespace build2
//
// For now we are not going to bother doing this for C++03.
//
- if (latest)
+ if (experimental)
{
- if (mj > 19 || (mj == 19 && (mi > 0 || (mi == 0 && p >= 24215))))
+ if (v14_3)
+ o = "/std:c++latest";
+ }
+ else if (latest)
+ {
+ // We used to map `latest` to `c++latest` but starting from 16.1,
+ // VC seem to have adopted the "move fast and break things" motto
+ // for this mode. So starting from 16 we only enable it in
+ // `experimental`.
+ //
+ if (v16_0)
+ o = "/std:c++17";
+ else if (v14_3)
o = "/std:c++latest";
}
else if (v == nullptr)
@@ -131,12 +168,12 @@ namespace build2
fail << "C++" << *v << " is not supported by " << ci.signature <<
info << "required by " << project (rs) << '@' << rs;
- if (mj > 19 || (mj == 19 && mi >= 11)) // 15.3
+ if (v15_3)
{
if (*v == "14") o = "/std:c++14";
else if (*v == "17") o = "/std:c++17";
}
- else if (mj == 19 && (mi > 0 || (mi == 0 && p >= 24215))) // 14.3
+ else if (v14_3)
{
if (*v == "14") o = "/std:c++14";
else if (*v == "17") o = "/std:c++latest";
@@ -150,7 +187,7 @@ namespace build2
}
case compiler_class::gcc:
{
- if (latest)
+ if (latest || experimental)
{
switch (ct)
{
@@ -247,8 +284,8 @@ namespace build2
{
// Starting with 15.5 (19.12) Visual Studio-created projects
// default to the strict mode. However, this flag currently tends
- // to trigger too many compiler bugs. So for now we leave it
- // to the experimenters to enjoy.
+ // to trigger too many compiler bugs. So for now we leave it to
+ // the experimenters to enjoy.
//
if (mj > 19 || (mj == 19 && mi >= 12))
r.push_back ("/permissive-");
@@ -259,12 +296,7 @@ namespace build2
break;
}
- // Unless disabled by the user, try to enable C++ modules. Here we use
- // a tri-state:
- //
- // - false - disabled
- // - unspecified - enabled if practically usable
- // - true - enabled even if practically unusable
+ // Unless disabled by the user, try to enable C++ modules.
//
lookup l;
if (!(l = rs[v_m]) || cast<bool> (l))