Change `exit()` to `Fatal()`; make it possible to throw on `Fatal()`. (#5087)

This patch makes binaryen easier to call from other applications by making more errors recoverable instead of early-exiting.

The main thing it does is change three calls to exit on I/O errors into calls to Fatal(), which is an existing custom abstraction for handling unrecoverable errors. Currently Fatal's destructor calls _Exit(1).

My intent is to make it possible for Fatal to not exit, but to throw, allowing an embedding application to catch the exception.

Because the previous early exits were exiting with error code EXIT_FAILURE, I also changed Fatal to exit with EXIT_FAILURE. The test suite continues to pass so I assume this is ok.

Next I changed Fatal to buffer its error message until the destructor instead of immediately printing it to stderr. This is for ease of patching Fatal to throw instead.

Finally, I also included the patch I need to make Fatal throw when THROW_ON_FATAL is defined at compile time. I can carry this patch out of tree, but it is a small patch, so perhaps you will be willing to take it. I am happy to remove it.

Fixes #4938

1 files changed, 3 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index eafb64471..2298928bb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,9 @@ Current Trunk
 - `TypeBuilderSetSubType` now takes a supertype as the second argument.
 - `call_ref` can now take a signature type immediate in the text format. The
   type immediate will become mandatory in the future.
+- If `THROW_ON_FATAL` is defined at compile-time, then fatal errors will throw a
+  `std::runtime_error` instead of terminating the process. This may be used by
+  embedders of Binaryen to recover from errors.
 
 v110
 ----