dolt/go/cmd/dolt/fileno_check_darwin.go: Fix setrlimit(RLIMIT_NOFILE,…

… ...) on Darwin.

It turns out rlim_max from getrlimit(RLIMIT_NOFILE, ...) is not a valid value
for rlim_cur in setrlimit(RLIMIT_NOFILE, ...) on Darwin. Golang used to silently
fix this for us, but it stopped doing it. See
golang/go#30401.

Take reasonable steps to work around it for now.

go/cmd/dolt/fileno_check_darwin.go

@@ -13,12 +13,20 @@ var yellow = color.New(color.FgYellow).SprintFunc()
 
 const warningThreshold = 4096
 
+// Darwin setrlimit fails with EINVAL if
+// lim.Cur > OPEN_MAX (from sys/syslimits.h), regardless of lim.Max.
+// Just choose a reasonable number here.
+const darwinMaxFiles = 8192
+
 func warnIfMaxFilesTooLow() {
 	var lim unix.Rlimit
 	if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &lim); err != nil {
 		return
 	}
 	lim.Cur = lim.Max
+	if lim.Cur > darwinMaxFiles {
+		lim.Cur = darwinMaxFiles
+	}
 	if err := unix.Setrlimit(unix.RLIMIT_NOFILE, &lim); err != nil {
 		return
 	}
@@ -30,6 +38,5 @@ func warnIfMaxFilesTooLow() {
 		cli.Printf("%s\n", yellow(fmt.Sprintf("Only %d file descriptors are available for this process, which is less than the recommended amount, %d.", lim.Cur, warningThreshold)))
 		cli.Printf("%s\n", yellow("You may experience I/O errors by continuing to run dolt in this configuration."))
 		cli.Printf("\n")
-
 	}
 }