pkg: sort input packages in a consistent order when generating

This resolves a minor quirk where adding pkg/encoding/toml
would initially put it at the very end of the register.go import list.
It could be fixed by a second run of `go generate`, but it's also easy
to fix the generator so that it doesn't have this quirk.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I2798ed976918587c6c276f438f9dec6a87c1a9e3
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1201473
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

pkg/gen.go

@@ -30,6 +30,7 @@ package main
 
 import (
 	"bytes"
+	"cmp"
 	_ "embed"
 	"flag"
 	"fmt"
@@ -41,6 +42,7 @@ import (
 	"math/big"
 	"os"
 	"path/filepath"
+	"slices"
 	"sort"
 	"strings"
 	"text/template"
@@ -100,6 +102,13 @@ func main() {
 	if packages.PrintErrors(pkgs) > 0 {
 		os.Exit(1)
 	}
+	// Sort the Go packages by import path; otherwise adding a new builtin package
+	// puts it at the very end of the list the first time it is getting added to register.go,
+	// as it's not imported by the root package yet. Sorting ensures consistent output.
+	slices.SortFunc(pkgs, func(a, b *packages.Package) int {
+		return cmp.Compare(a.PkgPath, b.PkgPath)
+	})
+
 	regBuf := new(bytes.Buffer)
 	fmt.Fprintf(regBuf, "// Code generated by cuelang.org/go/pkg/gen. DO NOT EDIT.\n\n")
 	fmt.Fprintf(regBuf, "package pkg\n\n")