prompt: case-insensitive sorting for subscriptions

cli/azd/pkg/prompt/prompter.go

@@ -11,7 +11,6 @@ import (
 	"os"
 	"slices"
 	"strconv"
-	"strings"
 
 	"github.com/Azure/azure-sdk-for-go/sdk/azcore/to"
 	"github.com/MakeNowJust/heredoc/v2"
@@ -22,6 +21,7 @@ import (
 	"github.com/azure/azure-dev/cli/azd/pkg/cloud"
 	"github.com/azure/azure-dev/cli/azd/pkg/environment"
 	"github.com/azure/azure-dev/cli/azd/pkg/input"
+	"github.com/azure/azure-dev/cli/azd/pkg/stringutil"
 )
 
 type LocationFilterPredicate func(loc account.Location) bool
@@ -157,7 +157,7 @@ func (p *DefaultPrompter) PromptResourceGroupFrom(
 	}
 
 	slices.SortFunc(groups, func(a, b *azapi.Resource) int {
-		return strings.Compare(a.Name, b.Name)
+		return stringutil.CompareLower(a.Name, b.Name)
 	})
 
 	canCreateNeResourceGroup := !options.DisableCreateNew
@@ -218,6 +218,10 @@ func (p *DefaultPrompter) getSubscriptionOptions(ctx context.Context) ([]string,
 		return nil, nil, nil, fmt.Errorf("listing accounts: %w", err)
 	}
 
+	slices.SortFunc(subscriptionInfos, func(a, b account.Subscription) int {
+		return stringutil.CompareLower(a.Name, b.Name)
+	})
+
 	// The default value is based on AZURE_SUBSCRIPTION_ID, falling back to whatever default subscription in
 	// set in azd's config.
 	defaultSubscriptionId := os.Getenv(environment.SubscriptionIdEnvVarName)

cli/azd/pkg/stringutil/stringutil.go

@@ -0,0 +1,43 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package stringutil
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// CompareLower returns an integer comparing two strings in a case-insensitive manner.
+// The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
+//
+// This comparison does not obey locale-specific rules.
+// To compare strings based on case-insensitive, locale-specific ordering, see [golang.org/x/text/collate].
+func CompareLower(a, b string) int {
+	for {
+		rb, nb := utf8.DecodeRuneInString(b)
+		if nb == 0 {
+			// len(a) > len(b), a > b.
+			return 1
+		}
+
+		ra, na := utf8.DecodeRuneInString(a)
+		if na == 0 {
+			// len(b) > len(a), b > a.
+			return -1
+		}
+
+		rb = unicode.ToLower(rb)
+		ra = unicode.ToLower(ra)
+
+		if ra > rb {
+			return 1
+		} else if ra < rb {
+			return -1
+		}
+
+		// Trim slices to the next rune.
+		a = a[na:]
+		b = b[nb:]
+	}
+}

cli/azd/pkg/stringutil/stringutil_test.go

@@ -0,0 +1,47 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package stringutil
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestCompareLowerSort(t *testing.T) {
+	unordered := []string{
+		"Zebra",
+		"apple",
+		"applesauce",
+		"Banana",
+		"CHERRY",
+		"date",
+		"",
+		"Apple",
+		"café",
+		"cafe",
+		"APPLE",
+	}
+
+	expected := []string{
+		"",
+		"apple",
+		"Apple",
+		"APPLE",
+		"applesauce",
+		"Banana",
+		"cafe",
+		"café",
+		"CHERRY",
+		"date",
+		"Zebra",
+	}
+
+	slices.SortFunc(unordered, func(a, b string) int {
+		return CompareLower(a, b)
+	})
+
+	if !slices.Equal(unordered, expected) {
+		t.Errorf("incorrect sort order:\ngot:  %q\nwant: %q", unordered, expected)
+	}
+}