Crash Reporting for Nim Game Projects

Nim is an appealing language for indie games: it reads like a high level language but compiles to C and produces a fast native binary. That dual nature shapes how crashes happen. Nim has its own error model with exceptions and defects, but underneath it is C, so a memory fault becomes a raw signal exactly as it would in any native program. To capture crashes reliably you have to handle both the Nim level failures and the C level ones, and you have to understand how Nim's memory management and its defect concept affect what reaches your handler. This post walks through all of it.

Nim's error model: exceptions and defects

Nim distinguishes between exceptions, which are recoverable error conditions you are expected to catch, and defects, which represent programming errors like an array index out of bounds or a nil access. The distinction matters for crash reporting because defects are not meant to be caught in normal flow and, depending on compiler flags, may abort the program rather than propagate as a catchable exception. So the try and except pattern that catches a normal exception may not intercept a defect, and a defect is exactly the kind of bug a crash report needs to capture.

Nim gives you getStackTrace and the stack trace carried on raised exceptions, so when you do catch a failure you can record where it came from. At your program's top level you can install an unhandled exception path, but the cleaner approach is often to wrap your main loop and capture both exceptions and the defects that surface as catchable in your configuration. Understanding which failures your build treats as catchable exceptions and which it treats as aborting defects tells you how much the Nim level handler can cover and where you must fall back to the C level.

The C backend and signals

Because Nim emits C and links as a native binary, the failures that never become Nim exceptions, a genuine segfault, a stack overflow, an abort from the C runtime, arrive as POSIX signals or Windows structured exceptions just like in a C or C++ game. Your Nim level handler cannot see these. To capture them you install signal handlers, SIGSEGV, SIGABRT, and friends, on an alternate stack, exactly as you would for a native program, and write a minimal report from the handler. This native layer is what catches the crashes that the Nim error model lets fall through.

Nim's interop makes this straightforward: you can call C functions for sigaction directly, or use a small native shim. The same async signal safety rules apply, since after a fault you are in a damaged process and must avoid allocation and complex runtime calls. Symbolication also follows the native pattern, the C backend produces a binary whose debug symbols you keep per build so addresses resolve to functions. Treating the C backend's crashes with native discipline, rather than assuming Nim's high level feel protects you, is what closes the gap the exception model leaves open.

Manual memory and memory management modes

Nim has evolved through several memory management strategies, and the one your project uses changes its crash profile. The modern ARC and ORC modes use deterministic, reference counting based management with optional cycle collection, which removes the unpredictable garbage collector pauses of older modes but introduces native style lifetime bugs if you mix in manual memory or unsafe pointer code. A use after free or a double free under ARC manifests as a native segfault, not a Nim exception, which is another reason the signal layer is essential.

Games often reach for manual memory in hot paths, raw pointers, alloc and dealloc, or interop with a C library that owns its own memory. Each of those is a place a memory fault can originate that Nim's safety does not cover. When a crash report comes in as a segfault, knowing which memory mode your build uses and where you employ manual memory narrows the search immediately. Recording the memory management mode and relevant build flags as context in the report is a small step that makes these native lifetime crashes far quicker to localize than a bare stack would.

Building a complete report

A useful Nim crash report combines what each layer can give you. From the Nim exception or defect you get a message and a getStackTrace with named frames; from the signal handler you get the native context and a backtrace that you symbolicate against the build's debug info. Tagging which layer produced the report, a caught Nim failure versus a native signal, tells you instantly whether you are looking at a logic bug Nim expressed or a memory fault that escaped to C. Add the build version, platform, and your game state, the level or scene, as context.

Because Nim binaries are small and fast, the reporting code can afford to be thorough without weighing the game down. The discipline that makes the reports trustworthy is the same as any native target: keep the debug symbols for every build so native backtraces resolve, and verify that both the Nim level and the signal level paths actually fire. A report that says only that the process received SIGSEGV with no symbols is barely better than nothing; the same report with a symbolicated stack and the memory mode tagged points you at the line.

Setting it up with Bugnet

Bugnet receives both kinds of Nim report and stores them together, so a caught defect with a getStackTrace and a native segfault with a symbolicated backtrace land in the same dashboard with build and platform context attached. From your top level handler and your signal handler you send the stack, the message, the layer tag, and custom fields like the memory management mode and current scene, turning a Nim crash from a silent exit into a contextual, readable issue. The in game report button adds a path for players to describe non crashing problems and attach state.

Nim games, like any native game, see the same crash recur across many players, and occurrence grouping folds identical stacks into one issue with a count so you triage once. The count separates a rare edge case from a common failure, and filtering by platform or build tells you whether a crash is universal or tied to one configuration. Because Nim's smaller community means fewer prebuilt integrations, having a general purpose destination that accepts your reports with the context you choose is especially valuable, it gives a less mainstream toolchain the same crash visibility a mainstream engine enjoys.

Verifying both layers

The failure mode to guard against is a setup that catches Nim exceptions and feels complete while silently missing every native segfault, which on a game with manual memory may be the majority of real crashes. So test both layers explicitly: raise an uncaught exception and confirm the Nim path reports it with a stack, then force a segfault through a deliberate nil dereference or bad pointer and confirm the signal handler reports it symbolicated. Do this on each platform you ship, since signal handling and symbol formats differ between Windows, Linux, and macOS.

Once both paths are verified and symbols are archived per build, a Nim game has crash visibility on par with any mainstream engine despite a smaller ecosystem. You see your logic defects and your native faults, grouped and contextual, and you fix the ones that hit the most players first. For an indie team that chose Nim for its speed and expressiveness, that completeness means the choice does not cost them the operational maturity of knowing why their game crashes in the field.

Nim feels high level but runs as C. Catch its exceptions and defects, but install signal handlers too, or you will miss the native segfaults that matter most.