From cafa730ce5e1b13135ccbdc0befa58d693302999 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 3 Sep 2018 10:18:23 +0200
Subject: Use (native) C and C++ compilers we were built with as defaults

---
 build/root.build     |  5 +++++
 build2/buildfile     | 12 ++++++++++++
 build2/c/init.cxx    | 10 +++++++++-
 build2/cc/module.cxx | 19 ++++++++++++++-----
 build2/cxx/init.cxx  | 10 +++++++++-
 5 files changed, 49 insertions(+), 7 deletions(-)

diff --git a/build/root.build b/build/root.build
index f5ce7cb..f6be793 100644
--- a/build/root.build
+++ b/build/root.build
@@ -13,6 +13,11 @@ cxx{*}: extension = cxx
 
 cxx.poptions =+ "-I$out_root" "-I$src_root"
 
+# While we don't have any C sources to compile, we need to get the C compiler
+# path to use as native/default.
+#
+using c
+
 # Load the cli module but only if it's available. This way a distribution
 # that includes pre-generated files can be built without installing cli.
 # This is also the reason why we need to explicitly spell out individual
diff --git a/build2/buildfile b/build2/buildfile
index 396fcf4..1e3b447 100644
--- a/build2/buildfile
+++ b/build2/buildfile
@@ -17,6 +17,18 @@ hxx{version}: in{version} $src_root/manifest
 #
 obj{b context}: cxx.poptions += -DBUILD2_HOST_TRIPLET=\"$cxx.target\"
 
+# Pass native C and C++ compiler paths (not forgetting to escape backslashes
+# on Windows). These are used as defaults for BUILD2_DEFAULT_*.
+#
+if ($cxx.target == $build.host)
+{
+  c/obj{init}: cxx.poptions += \
+    -DBUILD2_NATIVE_C=\"$regex.replace($recall($c.path), '\\', '\\\\')\"
+
+  cxx/obj{init}: cxx.poptions += \
+    -DBUILD2_NATIVE_CXX=\"$regex.replace($recall($cxx.path), '\\', '\\\\')\"
+}
+
 if ($cxx.target.class != "windows")
   cxx.libs += -lpthread
 else
diff --git a/build2/c/init.cxx b/build2/c/init.cxx
index 63043d7..56b3f02 100644
--- a/build2/c/init.cxx
+++ b/build2/c/init.cxx
@@ -13,6 +13,14 @@
 
 #include <build2/c/target.hxx>
 
+#ifndef BUILD2_DEFAULT_C
+#  ifdef BUILD2_NATIVE_C
+#    define BUILD2_DEFAULT_C BUILD2_NATIVE_C
+#  else
+#    define BUILD2_DEFAULT_C ""
+#  endif
+#endif
+
 using namespace std;
 using namespace butl;
 
@@ -145,7 +153,7 @@ namespace build2
 
         "c",
         "c",
-        "gcc",
+        BUILD2_DEFAULT_C,
         ".i",
 
         hinters,
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index 858a2fd..e9d5c09 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -87,11 +87,20 @@ namespace build2
         // (optional) pattern to guess an appropriate default (e.g., for {gcc,
         // *-4.9} we will get g++-4.9).
         //
-        path d (cc_loaded
-                ? guess_default (x_lang,
-                                 cast<string> (rs["cc.id"]),
-                                 cast<string> (rs["cc.pattern"]))
-                : path (x_default));
+        path d;
+
+        if (cc_loaded)
+          d = guess_default (x_lang,
+                             cast<string> (rs["cc.id"]),
+                             cast<string> (rs["cc.pattern"]));
+        else
+        {
+          d = path (x_default);
+
+          if (d.empty ())
+            fail << "not built with default " << x_lang << " compiler" <<
+              info << "use config." << x << " to specify";
+        }
 
         // If this value was hinted, save it as commented out so that if the
         // user changes the source of the pattern, this one will get updated
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index 1f5eba3..2fa5dac 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -13,6 +13,14 @@
 
 #include <build2/cxx/target.hxx>
 
+#ifndef BUILD2_DEFAULT_CXX
+#  ifdef BUILD2_NATIVE_CXX
+#    define BUILD2_DEFAULT_CXX BUILD2_NATIVE_CXX
+#  else
+#    define BUILD2_DEFAULT_CXX ""
+#  endif
+#endif
+
 using namespace std;
 using namespace butl;
 
@@ -351,7 +359,7 @@ namespace build2
 
         "cxx",
         "c++",
-        "g++",
+        BUILD2_DEFAULT_CXX,
         ".ii",
 
         hinters,
-- 
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