Split ignoreException to avoid suppressing CTRL-C

This splits `ignoreException` into `ignoreExceptionExceptInterrupt`
(which ignores all exceptions except `Interrupt`, which indicates a
SIGINT/CTRL-C) and `ignoreExceptionInDestructor` (which ignores all
exceptions, so that destructors do not throw exceptions).

This prevents many cases where Nix ignores CTRL-C entirely.
See: https://github.com/NixOS/nix/issues/7245

Upstream-PR: https://github.com/NixOS/nix/pull/11618
Change-Id: Ie7d2467eedbe840d1b9fa2e88a4e88e4ab26a87b

src/libutil/current-process.cc

@@ -49,7 +49,7 @@ unsigned int getMaxCPU()
         auto period = cpuMaxParts[1];
         if (quota != "max")
                 return std::ceil(std::stoi(quota) / std::stof(period));
-    } catch (Error &) { ignoreException(lvlDebug); }
+    } catch (Error &) { ignoreExceptionInDestructor(lvlDebug); }
     #endif
 
     return 0;

src/libutil/error.cc

@@ -4,6 +4,7 @@
 #include "position.hh"
 #include "terminal.hh"
 #include "strings.hh"
+#include "signals.hh"
 
 #include <iostream>
 #include <optional>
@@ -416,7 +417,7 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
     return out;
 }
 
-void ignoreException(Verbosity lvl)
+void ignoreExceptionInDestructor(Verbosity lvl)
 {
     /* Make sure no exceptions leave this function.
        printError() also throws when remote is closed. */
@@ -429,4 +430,15 @@ void ignoreException(Verbosity lvl)
     } catch (...) { }
 }
 
+void ignoreExceptionExceptInterrupt(Verbosity lvl)
+{
+    try {
+        throw;
+    } catch (const Interrupted & e) {
+        throw;
+    } catch (std::exception & e) {
+        printMsg(lvl, "error (ignored): %1%", e.what());
+    }
+}
+
 }

src/libutil/error.hh

@@ -204,7 +204,22 @@ public:
 /**
  * Exception handling in destructors: print an error message, then
  * ignore the exception.
+ *
+ * If you're not in a destructor, you usually want to use `ignoreExceptionExceptInterrupt()`.
+ *
+ * This function might also be used in callbacks whose caller may not handle exceptions,
+ * but ideally we propagate the exception using an exception_ptr in such cases.
+ * See e.g. `PackBuilderContext`
  */
-void ignoreException(Verbosity lvl = lvlError);
+void ignoreExceptionInDestructor(Verbosity lvl = lvlError);
+
+/**
+ * Not destructor-safe.
+ * Print an error message, then ignore the exception.
+ * If the exception is an `Interrupted` exception, rethrow it.
+ *
+ * This may be used in a few places where Interrupt can't happen, but that's ok.
+ */
+void ignoreExceptionExceptInterrupt(Verbosity lvl = lvlError);
 
 }

src/libutil/file-descriptor.cc

@@ -146,7 +146,7 @@ AutoCloseFD::~AutoCloseFD()
     try {
         close();
     } catch (...) {
-        ignoreException();
+        ignoreExceptionInDestructor();
     }
 }
 

src/libutil/file-system.cc

@@ -522,7 +522,7 @@ AutoDelete::~AutoDelete()
             }
         }
     } catch (...) {
-        ignoreException();
+        ignoreExceptionInDestructor();
     }
 }
 

src/libutil/logging.cc

@@ -352,7 +352,7 @@ Activity::~Activity()
     try {
         logger.stopActivity(id);
     } catch (...) {
-        ignoreException();
+        ignoreExceptionInDestructor();
     }
 }
 

src/libutil/serialise.cc

@@ -83,7 +83,7 @@ void BufferedSink::flush()
 
 FdSink::~FdSink()
 {
-    try { flush(); } catch (...) { ignoreException(); }
+    try { flush(); } catch (...) { ignoreExceptionInDestructor(); }
 }
 
 

src/libutil/serialise.hh

@@ -549,7 +549,7 @@ struct FramedSource : Source
                 }
             }
         } catch (...) {
-            ignoreException();
+            ignoreExceptionInDestructor();
         }
     }
 
@@ -595,7 +595,7 @@ struct FramedSink : nix::BufferedSink
             to << 0;
             to.flush();
         } catch (...) {
-            ignoreException();
+            ignoreExceptionInDestructor();
         }
     }
 

src/libutil/signals.cc

@@ -78,7 +78,7 @@ void triggerInterrupt()
             try {
                 callback();
             } catch (...) {
-                ignoreException();
+                ignoreExceptionInDestructor();
             }
         }
     }

src/libutil/thread-pool.cc

@@ -109,9 +109,8 @@ void ThreadPool::doWork(bool mainThread)
                         try {
                             std::rethrow_exception(exc);
                         } catch (std::exception & e) {
-                            if (!dynamic_cast<Interrupted*>(&e) &&
-                                !dynamic_cast<ThreadPoolShutDown*>(&e))
-                                ignoreException();
+                            if (!dynamic_cast<ThreadPoolShutDown*>(&e))
+                                ignoreExceptionExceptInterrupt();
                         } catch (...) {
                         }
                     }