ChildProcess: account for a system error when launching a process

CHANGELOG.md

@@ -10,6 +10,8 @@ New features:
 
 Bugfixes:
 
+- Account for child creation to possibly fail with system error (#66 by @Hi-Angel)
+
 Other improvements:
 
 ## [v11.1.0](https://github.com/purescript-node/purescript-node-child-process/releases/tag/v11.1.0) - 2023-11-14
@@ -76,7 +78,7 @@ Breaking changes:
   - Moved from `Node.ChildProces` to `Node.ChildProces.Types`
   - Changed the `BySignal`'s constructor's arg type from `Signal` to `String`
 - Breaking changes made to the `Handle` type (#46 by @JordanMartinez)
-  
+
   - Moved from `Node.ChildProces` to `Node.ChildProces.Types`
 - Converted `defaultOptions { override = Just 1}` pattern to `(_ { override = Just 1})`  (#46 by @JordanMartinez)
 

bower.json

@@ -16,6 +16,7 @@
     "package.json"
   ],
   "dependencies": {
+    "purescript-aff": "^7.0.0",
     "purescript-exceptions": "^6.0.0",
     "purescript-node-event-emitter": "https://github.com/purescript-node/purescript-node-event-emitter.git#^3.0.0",
     "purescript-foreign": "^7.0.0",

src/Node/ChildProcess.purs

@@ -21,7 +21,7 @@
 -- | defined in this library that doesn't exist in the Node docs.
 -- | It exists to allow the end-user to append additional values to the `safeStdio` value
 -- | used here. For example,
--- | 
+-- |
 -- | ```
 -- | spawn' file args (_ { appendStdio = Just [ fileDescriptor8, pipe, pipe ]})
 -- | ```
@@ -86,7 +86,7 @@ module Node.ChildProcess
 
 import Prelude
 
-import Data.Maybe (Maybe(..), fromMaybe)
+import Data.Maybe (Maybe(..), fromMaybe, isJust)
 import Data.Nullable (Nullable, toMaybe, toNullable)
 import Data.Posix (Pid, Gid, Uid)
 import Data.Posix.Signal (Signal)
@@ -237,7 +237,11 @@ spawnSync command args = (UnsafeCP.spawnSync command args) <#> \r ->
   , exitStatus: case toMaybe r.status, toMaybe r.signal of
       Just c, _ -> Normally c
       _, Just s -> BySignal s
-      _, _ -> unsafeCrashWith $ "Impossible: `spawnSync` child process neither exited nor was killed."
+      _, _ ->
+        if isJust $ toMaybe r.error then
+          BySysError
+        else
+          unsafeCrashWith $ "Impossible: `spawnSync` child process neither exited nor was killed."
   , error: toMaybe r.error
   }
 
@@ -282,7 +286,11 @@ spawnSync' command args buildOpts = (UnsafeCP.spawnSync' command args opts) <#>
   , exitStatus: case toMaybe r.status, toMaybe r.signal of
       Just c, _ -> Normally c
       _, Just s -> BySignal s
-      _, _ -> unsafeCrashWith $ "Impossible: `spawnSync` child process neither exited nor was killed."
+      _, _ ->
+        if isJust $ toMaybe r.error then
+          BySysError
+        else
+          unsafeCrashWith $ "Impossible: `spawnSync` child process neither exited nor was killed."
   , error: toMaybe r.error
   }
   where

src/Node/ChildProcess/Types.purs

@@ -52,7 +52,7 @@ foreign import data StdIO :: Type
 -- | Note: when used with `stdin`, piping the parent stdin to this stream
 -- | will not cause the child process to terminate when that parent stdin stream
 -- | ends via `Ctrl+D` user input. Rather, the child process will hang
--- | until the parent process calls `Stream.end` on the child process' 
+-- | until the parent process calls `Stream.end` on the child process'
 -- | `stdin` stream. Since it's impossible to know when the user
 -- | inputs `Ctrl+D`, `inherit` should be used instead.
 pipe :: StdIO
@@ -140,12 +140,14 @@ customShell = unsafeCoerce
 -- | what options were used.
 foreign import data StringOrBuffer :: Type
 
--- | Specifies how a child process exited; normally (with an exit code), or
--- | due to a signal.
+-- | Specifies how a child process exited; normally (with an exit code), due to
+-- | a signal or if it failed to even launch (e.g. if a command doesn't exist).
 data Exit
   = Normally Int
   | BySignal KillSignal
+  | BySysError
 
 instance showExit :: Show Exit where
   show (Normally x) = "Normally " <> show x
   show (BySignal sig) = "BySignal " <> (either show show $ fromKillSignal sig)
+  show BySysError = "BySysError"

test/Main.purs

@@ -72,6 +72,7 @@ spawnLs = do
     Normally 0 -> log $ "ls exited with 0"
     Normally i -> liftEffect $ throw $ "ls had non-zero exit: " <> show i
     BySignal sig -> liftEffect $ throw $ "ls exited with sig: " <> show sig
+    BySysError -> liftEffect $ throw "ls exited with system error"
 
 nonExistentExecutable :: Aff Unit
 nonExistentExecutable = do