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, 85 insertions, 0 deletions

diff --git a/libbuild2/make-parser.hxx b/libbuild2/make-parser.hxx
new file mode 100644
index 0000000..fac2215
--- /dev/null
+++ b/libbuild2/make-parser.hxx
@@ -0,0 +1,85 @@
+// file      : libbuild2/make-parser.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_MAKE_PARSER_HXX
+#define LIBBUILD2_MAKE_PARSER_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+  // Make dependency declaration parser.
+  //
+  // The format is line-based (but with potential line continuations) so we
+  // parse one line at a time. This allows the caller to bail out early (for
+  // example, on encountering a non-existent generated file).
+  //
+  class LIBBUILD2_SYMEXPORT make_parser
+  {
+  public:
+    enum {begin, targets, prereqs, end} state = begin;
+
+    // Parse next target/prerequisite on a line starting from the specified
+    // position. Update the position to point to the start of the following
+    // target/prerequisite or l.size() if there is nothing left on this
+    // line. May return an empty string for a valid if unlikely dependency
+    // declarations (see below) or if passing leading blank lines (both of
+    // which should normally be just skipped). Issue diagnostics and throw
+    // failed if the declaration is invalid.
+    //
+    // If strict is false, then allow unescaped `:` in prerequisites.
+    //
+    // Note that the (p != l.size) should be in the do-while rather than in a
+    // while loop. In other words, except for the leading blank lines, the
+    // parser needs to see the blank line to correctly identify the end of the
+    // declaration. See make-parser.test.cxx for a recommended usage.
+    //
+    // To parse more than one declaration, reset the state to begin after
+    // reaching end.
+    //
+    enum class type {target, prereq};
+
+    pair<type, string>
+    next (const string&, size_t&, const location&, bool strict);
+
+    // Lower-level stateless API.
+    //
+  public:
+    // Parse next target/prerequisite on a line starting from the specified
+    // position. Return the target/prerequisite as well as an indication of
+    // whether the end of the dependency declaration was reached. Update the
+    // position to point to the start of the following target/prerequisite,
+    // `:`, or l.size() if there is nothing left on this line.
+    //
+    // Note that some broken tools (notably MinGW GCC) do not escape `:`
+    // properly. To tolerate such cases the caller may specify that what's
+    // being parsed is the prerequisite list in which case unescaped `:` will
+    // be treated literally.
+    //
+    // Note also that this function may return an empty string (with
+    // end=false) for a valid if unlikely dependency declaration, for example
+    // (using | to represent backslash):
+    //
+    // foo:|
+    // |
+    // bar
+    //
+    // It would also return an empty string (with end=true) if passed and
+    // empty or whitespace-only line.
+    //
+    // Note also that in the make language line continuations introduce a
+    // whitespace rather than just being remove. For example, the following
+    // declaration has two prerequisites:
+    //
+    // foo: bar|
+    // baz
+    //
+    static pair<string, bool>
+    next (const string&, size_t&, optional<bool> prereq = nullopt);
+  };
+}
+
+#endif // LIBBUILD2_MAKE_PARSER_HXX