Fix nil pointer dereference in GetPersistentShell

[AvicennaJr]

Issue

The application was crashing with a "runtime error: invalid memory address or nil pointer dereference" in the shell tool. This occurred because the GetPersistentShell function was attempting to access properties of a potentially nil shellInstance. Here is the exact panic log:

Panic in agent.Run: runtime error: invalid memory address or nil pointer dereference

Time: 2025-04-26T22:48:32+03:00

Stack Trace:
goroutine 139 [running]:
runtime/debug.Stack()
        /home/avi/go/pkg/mod/golang.org/[email protected]/src/runtime/debug/stack.go:26 +0x5e
github.com/opencode-ai/opencode/internal/logging.RecoverPanic({0x1b5d7c8, 0x9}, 0xc00005df90)
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/logging/logger.go:68 +0x325
panic({0x18426c0?, 0x2fa2350?})
        /home/avi/go/pkg/mod/golang.org/[email protected]/src/runtime/panic.go:792 +0x132
github.com/opencode-ai/opencode/internal/llm/tools/shell.GetPersistentShell({0x7ffe16419c39?, 0xc003d8a7b0?})
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/llm/tools/shell/shell.go:50 +0x4f
github.com/opencode-ai/opencode/internal/llm/tools.(*bashTool).Run(0xc00185a000, {0x217ff68, 0xc003d8a7b0}, {{0xc0007ba0e4, 0x1e}, {0xc0007ba126, 0x4}, {0xc0027ee468, 0x11}})
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/llm/tools/bash.go:287 +0x812
github.com/opencode-ai/opencode/internal/llm/agent.(*agent).streamAndHandleEvents(0xc0001cd8c0, {0x217ffa0, 0xc00059e9b0}, {0xc0006885a0, 0x24}, {0xc003d1cb40?, 0x23c?, 0x1730160?})
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/llm/agent/agent.go:313 +0xcad
github.com/opencode-ai/opencode/internal/llm/agent.(*agent).processGeneration(0xc0001cd8c0, {0x217ffa0, 0xc00059e9b0}, {0xc0006885a0, 0x24}, {0x1bd16c8, 0x23c})
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/llm/agent/agent.go:221 +0x645
github.com/opencode-ai/opencode/internal/llm/agent.(*agent).Run.func1()
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/llm/agent/agent.go:175 +0x1a5
created by github.com/opencode-ai/opencode/internal/llm/agent.(*agent).Run in goroutine 1
        /home/avi/go/pkg/mod/github.com/opencode-ai/[email protected]/internal/llm/agent/agent.go:169 +0x196

Root Cause

The newPersistentShell function can return nil in error cases (when failing to create stdin pipe or when cmd.Start() fails), but GetPersistentShell wasn't checking for this possibility before accessing shellInstance.isAlive.

Solution

Added a nil check in GetPersistentShell before accessing shellInstance.isAlive to safely handle cases where shell initialization fails. This prevents the panic and ensures the code attempts to create a new shell instance when needed.

[kujtimiihoxha]

Suggested change

	if shellInstance == nil || !shellInstance.isAlive {
	if shellInstance != nil && !shellInstance.isAlive {

Is this what we should do instead ?

[AvicennaJr]

No, we want to create a shell instance when it doesn't exist (ie when its nil) or when its not alive

[kujtimiihoxha]

Ah ok, but we need to change the next line also, we are trying to get .cwd from shellInstance and that shellInstance could be nil in this case.

[AvicennaJr]

Funny thing is I was getting that nil error, but adding that nil check did do the fix. Not sure why it didn't panic on the next line 😆

Will find out the reason and modify it if needed

[AvicennaJr]

@kujtimiihoxha I've updated the line to use the provided workingDir if shellInstance is nil, otherwise it will use cwd

[kujtimiihoxha]

Thanks @AvicennaJr