Add support for specifying minimum required build2 version

The syntax is:

using build@0.1.0-a1

The idea is that we will later also use it for modules and 'build' is
a special, the "build system itself" module.

Also fix a problem with peeking and lexer mode switching.

1 files changed, 78 insertions, 0 deletions

diff --git a/build/utility.cxx b/build/utility.cxx
index d394186..7ee679b 100644
--- a/build/utility.cxx
+++ b/build/utility.cxx
@@ -4,6 +4,8 @@
 
 #include <build/utility>
 
+#include <cstdlib> // strtol()
+
 using namespace std;
 
 namespace build
@@ -12,5 +14,81 @@ namespace build
   const path empty_path;
   const dir_path empty_dir_path;
 
+  unsigned int
+  to_version (const string& s)
+  {
+    // See tests/version.
+    //
+
+    auto parse = [&s] (size_t& p, const char* m, long min = 0, long max = 99)
+      -> unsigned int
+    {
+      if (s[p] == '-' || s[p] == '+') // stoi() allows these.
+        throw invalid_argument (m);
+
+      const char* b (s.c_str () + p);
+      char* e;
+      long r (strtol (b, &e, 10));
+
+      if (b == e || r < min || r > max)
+        throw invalid_argument (m);
+
+      p = e - s.c_str ();
+      return static_cast<unsigned int> (r);
+    };
+
+    auto bail = [] (const char* m) {throw invalid_argument (m);};
+
+    unsigned int ma, mi, bf, ab;
+
+    size_t p (0), n (s.size ());
+    ma = parse (p, "invalid major version");
+
+    if (p >= n || s[p] != '.')
+      bail ("'.' expected after major version");
+
+    mi = parse (++p, "invalid minor version");
+
+    if (p >= n || s[p] != '.')
+      bail ("'.' expected after minor version");
+
+    bf = parse (++p, "invalid bugfix version");
+
+    if (p < n)
+    {
+      if (s[p] != '-')
+        bail ("'-' expected after bugfix version");
+
+      char k (s[++p]);
+
+      if (k != 'a' && k != 'b')
+        bail ("'a' or 'b' expected in release component");
+
+      ab = parse (++p, "invalid release component", 1, 49);
+
+      if (p != n)
+        bail ("junk after release component");
+
+      if (k == 'b')
+        ab += 50;
+    }
+
+    //                  AABBCCDD
+    unsigned int r (ma * 1000000U +
+                    mi *   10000U +
+                    bf *     100U);
+
+    if (ab != 0)
+    {
+      if (r == 0)
+        bail ("0.0.0 version with release component");
+
+      r -= 100;
+      r += ab;
+    }
+
+    return r;
+  }
+
   bool exception_unwinding_dtor = false;
 }