Run find in a cross-platform manner

Managed to finally get my hands on a relevant log entry and saw:

```
{"level":"error","github_event_type":"pull_request","github_delivery_id":"<omitted>","error":"Failed to `find` latest docs version to generate cobradocs preview for vitessio/vitess#14789: exit status 1\nstderr: find: unknown predicate `-sE'\n\nstdout: ","time":"2024-01-24T13:13:22Z","message":"Unexpected error handling webhook"}
```

So, we need to remove `-sE` on unix, but not on darwin.

`-E` _before_ the path is replaced by `-regextype posix-extended` _after_
the path.

There is no replacement for `-s` on non-darwin unix, so we now need to
pipe to `sort` to sort in dictionary order.

Signed-off-by: Andrew Mason <[email protected]>

go/pull_request.go

@@ -546,14 +546,21 @@ func (h *PullRequestHandler) createCobraDocsPreviewPR(
 	if docsVersion == "main" {
 		// We need to replace "main" with whatever the highest version under
 		// content/en/docs is.
-		find, err := shell.NewContext(ctx,
-			"find",
-			"-sE",
-			"content/en/docs",
+		//
+		// MacOS does not support -regextype flag, but Unix (non-darwin) does
+		// not support the -E equivalent. Similarly, Unix does not support the
+		// lexicographic sort opt (-s), so we rely on sort's dictionary sort
+		// (-d) instead.
+		//
+		// Unix version: find content/en/docs -regextype posix-extended -maxdepth 1 -type d -regex ... | sort -d
+		// MacOS version: find -E content/en/docs -maxdepth 1 -type d -regex ... | sort -d
+		args := shell.FindRegexpExtended("content/en/docs",
+			"-maxdepth", "1",
 			"-type", "d",
-			"-depth", "1",
-			"-regex", `.*/[0-9]+.[0-9]+`,
-		).InDir(website.LocalDir).Output()
+			"-regex", `.*/[0-9]+.[0-9]+`, "|",
+			"sort", "-d",
+		)
+		find, err := shell.NewContext(ctx, "bash", "-c", strings.Join(args, " ")).InDir(website.LocalDir).Output()
 		if err != nil {
 			return nil, errors.Wrapf(err, "Failed to `find` latest docs version to %s for %s", op, pr.GetHTMLURL())
 		}

go/shell/shell.go

@@ -25,6 +25,11 @@ import (
 
 type cmd exec.Cmd
 
+var (
+	globalRegexpOpt string
+	regexpTypeOpt   []string
+)
+
 // New returns a new command can be run.
 func New(name string, arg ...string) *cmd {
 	return NewContext(context.Background(), name, arg...)
@@ -35,6 +40,21 @@ func NewContext(ctx context.Context, name string, arg ...string) *cmd {
 	return (*cmd)(exec.CommandContext(ctx, name, arg...))
 }
 
+// FindRegexpExtended returns a slice of arguments for doing a `find` command
+// using extended regular expressions in a cross-platform-friendly manner.
+func FindRegexpExtended(path string, expressions ...string) (args []string) {
+	args = []string{path}
+	if globalRegexpOpt != "" {
+		args = []string{globalRegexpOpt, path}
+	}
+
+	if len(regexpTypeOpt) > 0 {
+		args = append(args, regexpTypeOpt...)
+	}
+
+	return append(args, expressions...)
+}
+
 // InDir updates the working directory of the command and returns it.
 //
 // Must be called before running the command.

go/shell/shell_darwin.go

@@ -0,0 +1,7 @@
+//go:build darwin
+
+package shell
+
+func init() {
+	globalRegexpOpt = "-E"
+}

go/shell/shell_unix.go

@@ -0,0 +1,11 @@
+//go:build unix && !darwin
+
+package shell
+
+func init() {
+	regexpTypeOpt = []string{
+		// This is not a typo. It is "regexp" in goland and "regex" in POSIX land. ¯\_(ツ)_/¯
+		"-regextype",
+		"posix-extended",
+	}
+}