Add exception_guard

3 files changed, 48 insertions, 1 deletions

diff --git a/bpkg/diagnostics.cxx b/bpkg/diagnostics.cxx
index 39ad1d2..697bd28 100644
--- a/bpkg/diagnostics.cxx
+++ b/bpkg/diagnostics.cxx
@@ -6,6 +6,8 @@
 
 #include <iostream>
 
+#include <bpkg/utility>
+
 using namespace std;
 
 namespace bpkg
@@ -62,7 +64,7 @@ namespace bpkg
     // this ugly special check which we will be able to get rid of
     // once C++17 uncaught_exceptions() becomes available.
     //
-    if (!empty_ && (!uncaught_exception () /*|| exception_unwinding_dtor*/))
+    if (!empty_ && (!uncaught_exception () || exception_unwinding_dtor))
     {
       *diag_stream << os_.str () << endl;
 
diff --git a/bpkg/utility b/bpkg/utility
index a5bafec..ea7dfa6 100644
--- a/bpkg/utility
+++ b/bpkg/utility
@@ -5,6 +5,9 @@
 #ifndef BPKG_UTILITY
 #define BPKG_UTILITY
 
+#include <utility>   // move()
+#include <exception> // uncaught_exception ()
+
 #include <bpkg/types>
 
 namespace bpkg
@@ -39,6 +42,46 @@ namespace bpkg
 
   inline void
   run (const cstrings& args) {run (args.data ());}
+
+  // Call a function if there is an exception.
+  //
+
+  // True means we are in the body of a destructor that is being
+  // called as part of the exception stack unwindining. Used to
+  // compensate for the deficiencies of uncaught_exception() until
+  // C++17 uncaught_exceptions() becomes available.
+  //
+  // @@ MT: will have to be TLS.
+  //
+  extern bool exception_unwinding_dtor;
+
+  template <typename F>
+  struct exception_guard;
+
+  template <typename F>
+  inline exception_guard<F>
+  make_exception_guard (F f)
+  {
+    return exception_guard<F> (std::move (f));
+  }
+
+  template <typename F>
+  struct exception_guard
+  {
+    exception_guard (F f): f_ (std::move (f)) {}
+    ~exception_guard ()
+    {
+      if (std::uncaught_exception ())
+      {
+        exception_unwinding_dtor = true;
+        f_ ();
+        exception_unwinding_dtor = false;
+      }
+    }
+
+  private:
+    F f_;
+  };
 }
 
 #endif // BPKG_UTILITY
diff --git a/bpkg/utility.cxx b/bpkg/utility.cxx
index f1e9a5a..632791c 100644
--- a/bpkg/utility.cxx
+++ b/bpkg/utility.cxx
@@ -132,4 +132,6 @@ namespace bpkg
       throw failed ();
     }
   }
+
+  bool exception_unwinding_dtor = false;
 }