Make sure no exceptions leave ignoreException()

I noticed that occasional Ctrl-C leaves *.lock files around.
`nix-daemon`'s journal logs contained crashes like:

    nix-daemon[30416]: terminate called after throwing an instance of 'nix::SysError'
    nix-daemon[30416]:   what():  error: writing to file: Broken pipe

And core dump backtraces pointed at `teriminate()` call from
destructors:

    ...
    _Unwind_Resume ()
    nix::ignoreException() ()
    nix::LocalDerivationGoal::~LocalDerivationGoal()
    ...

    void ignoreException()
    {
        try {
            throw;
        } catch (std::exception & e) {
            printError("error (ignored): %1%", e.what());
        }
    }

The crashes happen when client side closes early and printError() throws
an IO error.

The change wraps `ignoreException()` into blanket `try { ... } catch (...) {}`.

Closes: https://github.com/NixOS/nix/issues/6046

1 files changed, 8 insertions, 4 deletions

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index cd359cfee..8b317f6a8 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1358,11 +1358,15 @@ std::string shellEscape(const std::string_view s)
 
 void ignoreException()
 {
+    /* Make sure no exceptions leave this function.
+       printError() also throws when remote is closed. */
     try {
-        throw;
-    } catch (std::exception & e) {
-        printError("error (ignored): %1%", e.what());
-    }
+        try {
+            throw;
+        } catch (std::exception & e) {
+            printError("error (ignored): %1%", e.what());
+        }
+    } catch (...) { }
 }
 
 bool shouldANSI()