Add support for dynamic dependencies in ad hoc Buildscript recipes

Specifically, add the new `depdb dyndep` builtin that can be used to extract
dynamic dependencies from a program run or a file. For example:

obje{hello.o}: cxx{hello}
{{
  s = $path($<[0])

  depdb dyndep $cxx.poptions $cc.poptions --what=header --default-prereq-type=h -- $cxx.path $cxx.poptions $cc.poptions $cxx.mode -M -MG $s

  diag c++ ($<[0])

  o = $path($>)
  $cxx.path $cxx.poptions $cc.poptions $cc.coptions $cxx.coptions $cxx.mode -o $o -c $s
}}

Currently only the `make` dependency format is supported.

1 files changed, 49 insertions, 0 deletions

diff --git a/libbuild2/build/script/types-parsers.hxx b/libbuild2/build/script/types-parsers.hxx
new file mode 100644
index 0000000..a42dab7
--- /dev/null
+++ b/libbuild2/build/script/types-parsers.hxx
@@ -0,0 +1,49 @@
+// file      : libbuild2/build/script/types-parsers.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+// CLI parsers, included into the generated source files.
+//
+
+#ifndef LIBBUILD2_BUILD_SCRIPT_TYPES_PARSERS_HXX
+#define LIBBUILD2_BUILD_SCRIPT_TYPES_PARSERS_HXX
+
+#include <libbuild2/types.hxx>
+
+namespace build2
+{
+  namespace build
+  {
+    namespace script
+    {
+      namespace cli
+      {
+        class scanner;
+
+        template <typename T>
+        struct parser;
+
+        template <>
+        struct parser<path>
+        {
+          static void
+          parse (path&, bool&, scanner&);
+
+          static void
+          merge (path& b, const path& a) {b = a;}
+        };
+
+        template <>
+        struct parser<dir_path>
+        {
+          static void
+          parse (dir_path&, bool&, scanner&);
+
+          static void
+          merge (dir_path& b, const dir_path& a) {b = a;}
+        };
+      }
+    }
+  }
+}
+
+#endif // LIBBUILD2_BUILD_SCRIPT_TYPES_PARSERS_HXX