fix out-of-bounds read in genversion at a tagged commit

+ merge the two git describe parsers

src/vernum.hpp

@@ -85,6 +85,13 @@ class VerNum {
     return vernum;
   }
 
+  constexpr ValT operator[](const unsigned char seg) const
+  {
+    if(seg >= MAX_SEGS)
+      throw reascript_error { "out of range segment" };
+    return (m_value >> ((MAX_SEGS - seg - 1) * SEG_BITS)) & SEG_MASK;
+  }
+
 private:
   ValT m_value;
 };

tests/vernum_test.cpp

@@ -28,3 +28,18 @@ TEST(VerNumTest, FormatString) {
   EXPECT_EQ(VerNum { "1.2.3.4" }.toString(), "1.2.3.4");
   EXPECT_EQ(VerNum { "016.032.064.128" }.toString(), "16.32.64.128");
 }
+
+static void expectSegments(const VerNum &ver,
+  const std::array<decltype(ver[0]), 4> &segs)
+{
+  for(size_t i {}; i < segs.size(); ++i)
+    EXPECT_EQ(ver[i], segs[i]);
+}
+
+TEST(VerNumTest, SegmentAccess) {
+ expectSegments("0",     { 0, 0, 0, 0 });
+ expectSegments("1",     { 1, 0, 0, 0 });
+ expectSegments("1.2",   { 1, 2, 0, 0 });
+ expectSegments("1.2.3", { 1, 2, 3, 0 });
+ expectSegments("016.032.064.128", { 16, 32, 64, 128 });
+}

tools/genversion.cpp.in

@@ -15,51 +15,24 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <algorithm>
-#include <array>
 #include <iostream>
-#include <string_view>
 
-using Segments = std::array<std::string_view, 4>;
-
-static Segments explode(std::string_view version)
-{
-  Segments segments;
-  for(std::string_view &segment : segments) {
-    const auto sep { std::find_if_not(version.begin(), version.end(),
-      [](char c) { return std::isdigit(c); }) };
-
-    // reached the end (version is empty) or segment is empty (consecutive dots)
-    if(sep == version.begin()) {
-      segment = "0";
-      continue;
-    }
-
-    // FIXME: C++20
-    // segment = { version.begin(), segEnd };
-    segment = { version.data(), static_cast<size_t>(sep - version.begin()) };
-
-    if(*sep == '.')
-      version.remove_prefix(segment.size() + 1);
-    else
-      version = {};
-  }
-
-  return segments;
-}
+#include "../api/compstr.hpp"
+#include "../src/vernum.hpp"
 
 int main()
 {
   // replaced by the output of `git describe`, eg. "v0.8.6.1-8-g19dcefc"
-  std::string_view version { "@VCS_TAG@" };
-
-  if(!version.empty() && version.front() == 'v')
-    version.remove_prefix(1);
-
-  const Segments segments { explode(version) };
-  std::cout << "#define REAIMGUI_VERSION \""     << version   << "\"\n"
-            << "#define REAIMGUI_VERSION_MAJOR " << segments[0] << '\n'
-            << "#define REAIMGUI_VERSION_MINOR " << segments[1] << '\n'
-            << "#define REAIMGUI_VERSION_PATCH " << segments[2] << '\n'
-            << "#define REAIMGUI_VERSION_TWEAK " << segments[3] << '\n';
+  static constexpr const char gitDescribe[] { "@VCS_TAG@" };
+  constexpr VerNum version { CompStr::version<&gitDescribe> };
+
+  const char *tagVersion { gitDescribe };
+  if(*tagVersion == 'v')
+    ++tagVersion;
+
+  std::cout << "#define REAIMGUI_VERSION \""     << tagVersion << "\"\n"
+            << "#define REAIMGUI_VERSION_MAJOR " << version[0] << '\n'
+            << "#define REAIMGUI_VERSION_MINOR " << version[1] << '\n'
+            << "#define REAIMGUI_VERSION_PATCH " << version[2] << '\n'
+            << "#define REAIMGUI_VERSION_TWEAK " << version[3] << '\n';
 }

tools/meson.build

@@ -16,7 +16,8 @@ endif
 genversion_src = vcs_tag(
   command: [find_program('git'), 'describe', '--match=v*', '--dirty=+'],
   input: 'genversion.cpp.in', output: 'genversion.cpp', fallback: '0.0-nogit')
-genversion = executable('genversion', genversion_src, native: native)
+genversion = executable('genversion', genversion_src, native: native,
+  dependencies: [compat_dep])
 version = custom_target('version.hpp',
   command: [genversion], capture: true, output: 'version.hpp')