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, 137 insertions, 0 deletions

diff --git a/libbuild2/make-parser.cxx b/libbuild2/make-parser.cxx
new file mode 100644
index 0000000..d076a0a
--- /dev/null
+++ b/libbuild2/make-parser.cxx
@@ -0,0 +1,137 @@
+// file      : libbuild2/make-parser.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/make-parser.hxx>
+
+#include <libbuild2/diagnostics.hxx>
+
+namespace build2
+{
+  auto make_parser::
+  next (const string& l,
+        size_t& p,
+        const location& ll,
+        bool strict) -> pair<type, string>
+  {
+    assert (state != end);
+
+    pair<string, bool> r (
+      next (l, p, !strict ? state == prereqs : optional<bool> ()));
+
+    type t (state == prereqs ? type::prereq : type::target);
+
+    // Deal with the end.
+    //
+    if (r.second)
+    {
+      if (state == begin && r.first.empty ())
+        ; // Skip leading blank line.
+      else
+      {
+        if (state != prereqs)
+          fail (ll) << "end of make dependency declaration before ':'";
+
+        state = end;
+      }
+    }
+    // Deal with the first target.
+    //
+    else if (state == begin && !r.first.empty ())
+      state = targets;
+
+    // Deal with `:`.
+    //
+    if (p != l.size () && l[p] == ':')
+    {
+      switch (state)
+      {
+      case begin:   fail (ll) << "':' before make target";      break;
+      case targets: state = prereqs;                            break;
+      case prereqs: fail (ll) << "':' after make prerequisite"; break;
+      case end:                                                 break;
+      }
+
+      if (++p == l.size ())
+        state = end; // Not a mere optimization: the caller will get next line.
+    }
+
+    return pair<type, string> (t, move (r.first));
+  }
+
+  pair<string, bool> make_parser::
+  next (const string& l, size_t& p, optional<bool> prereq)
+  {
+    size_t n (l.size ());
+
+    // Skip leading spaces.
+    //
+    for (; p != n && l[p] == ' '; p++) ;
+
+    // Lines containing multiple targets/prerequisites are customarily 80
+    // characters max.
+    //
+    string r;
+    r.reserve (n - p);
+
+    // Scan the next target/prerequisite while watching out for escape
+    // sequences.
+    //
+    // @@ Can't we do better for the (common) case where nothing is escaped?
+    //
+    for (char c, q (prereq && *prereq ? '\0' : ':');
+         p != n && (c = l[p]) != ' ' && c != q; )
+    {
+      // If we have another character, then handle the escapes.
+      //
+      if (++p != n)
+      {
+        if (c == '\\')
+        {
+          // This may or may not be an escape sequence depending on whether
+          // what follows is "escapable".
+          //
+          switch (c = l[p])
+          {
+          case '\\':
+          case ' ':
+          case ':': ++p; break;
+          default: c = '\\'; // Restore.
+          }
+        }
+        else if (c == '$')
+        {
+          // Got to be another (escaped) '$'.
+          //
+          if (l[p] == '$')
+            ++p;
+        }
+      }
+      // Note that the newline escape is not necessarily separated with space.
+      //
+      else if (c == '\\')
+      {
+        --p;
+        break;
+      }
+
+      r += c;
+    }
+
+    // Skip trailing spaces.
+    //
+    for (; p != n && l[p] == ' '; p++) ;
+
+    // Skip final '\' and determine if this is the end.
+    //
+    bool e (false);
+    if (p == n - 1)
+    {
+      if (l[p] == '\\')
+        p++;
+    }
+    else if (p == n)
+      e = true;
+
+    return pair<string, bool> (move (r), e);
+  }
+}