Prefer glibc based Bicep when both musl and glibc are installed (#2722)

This matches the behavior of the `az` CLI, which uses this same
logic. When we orginally implemented this, `az` did not have this
special case, it was added later.

Fixes #2683

cli/azd/.vscode/cspell-azd-dictionary.txt

@@ -94,6 +94,7 @@ keychain
 LASTEXITCODE
 ldflags
 lechnerc77
+libc
 mgmt
 mgutz
 microsoftonline

cli/azd/pkg/tools/bicep/bicep.go

@@ -165,11 +165,11 @@ func downloadBicep(ctx context.Context, transporter policy.Transporter, bicepVer
 	case "darwin":
 		releaseName = fmt.Sprintf("bicep-osx-%s", arch)
 	case "linux":
-		if _, err := os.Stat("/lib/ld-musl-x86_64.so.1"); err == nil {
-			// As of 0.14.46, there is no version of for AM64 on musl based systems.
-			if arch == "arm64" {
+		if preferMuslBicep(os.Stat) {
+			if runtime.GOARCH != "arm64" {
 				return fmt.Errorf("unsupported architecture: %s", runtime.GOARCH)
 			}
+
 			releaseName = "bicep-linux-musl-x64"
 		} else {
 			releaseName = fmt.Sprintf("bicep-linux-%s", arch)
@@ -228,6 +228,23 @@ func downloadBicep(ctx context.Context, transporter policy.Transporter, bicepVer
 	return nil
 }
 
+type stater func(name string) (os.FileInfo, error)
+
+// preferMuslBicep determines if we should install the version of bicep that used musl instead of glibc. We prefer
+// musl bicep on linux systems that have musl installed and do not have glibc installed. If both musl and glibc are
+// installed, we prefer the glibc based version.  This behavior matches the `az` CLI (see: Azure/azure-cli#23040)
+func preferMuslBicep(stat stater) bool {
+	if _, err := stat("/lib/ld-musl-x86_64.so.1"); err == nil {
+		if _, err := stat("/lib/x86_64-linux-gnu/libc.so.6"); err == nil {
+			return false
+		}
+
+		return true
+	}
+
+	return false
+}
+
 func (cli *bicepCli) version(ctx context.Context) (semver.Version, error) {
 	bicepRes, err := cli.runCommand(ctx, nil, "--version")
 	if err != nil {

cli/azd/pkg/tools/bicep/bicep_test.go

@@ -10,12 +10,14 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/azure/azure-dev/cli/azd/pkg/exec"
 	"github.com/azure/azure-dev/cli/azd/pkg/input"
 	"github.com/azure/azure-dev/cli/azd/pkg/osutil"
 	"github.com/azure/azure-dev/cli/azd/test/mocks"
 	"github.com/azure/azure-dev/cli/azd/test/mocks/mockinput"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -137,3 +139,75 @@ func TestNewBicepCliWillUpgrade(t *testing.T) {
 
 	require.Equal(t, []byte(NEW_FILE_CONTENTS), contents)
 }
+
+func Test_preferMuslBicep(t *testing.T) {
+	tests := []struct {
+		name     string
+		hasMusl  bool
+		hasGlibc bool
+		want     bool
+	}{
+		{
+			name:     "musl preferred",
+			hasMusl:  true,
+			hasGlibc: false,
+			want:     true,
+		},
+		{
+			name:     "glibc preferred",
+			hasMusl:  false,
+			hasGlibc: true,
+			want:     false,
+		},
+		{
+			name:     "both available",
+			hasMusl:  true,
+			hasGlibc: true,
+			want:     false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockStat := func(name string) (os.FileInfo, error) {
+				if tt.hasMusl && name == "/lib/ld-musl-x86_64.so.1" {
+					return &fakeFileInfo{}, nil
+				}
+				if tt.hasGlibc && name == "/lib/x86_64-linux-gnu/libc.so.6" {
+					return &fakeFileInfo{}, nil
+				}
+
+				return nil, os.ErrNotExist
+			}
+			got := preferMuslBicep(mockStat)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+type fakeFileInfo struct {
+}
+
+func (f *fakeFileInfo) Name() string {
+	return ""
+}
+
+func (f *fakeFileInfo) Size() int64 {
+	return 0
+}
+
+func (f *fakeFileInfo) Mode() os.FileMode {
+	return 0
+}
+
+func (f *fakeFileInfo) ModTime() time.Time {
+	return time.Time{}
+}
+
+func (f *fakeFileInfo) IsDir() bool {
+	return false
+}
+
+func (f *fakeFileInfo) Sys() interface{} {
+	return nil
+}