chore: add warning for registry login with namespace

Signed-off-by: Terry Howe <terrylhowe@gmail.com>

pkg/registry/client.go

@@ -24,6 +24,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"net/http"
 	"net/url"
 	"os"
@@ -224,12 +225,25 @@ type (
 	}
 )
 
+// warnIfHostHasPath checks if the host contains a repository path and logs a warning if it does.
+// Returns true if the host contains a path component (i.e., contains a '/').
+func warnIfHostHasPath(host string) bool {
+	if strings.Contains(host, "/") {
+		registryHost := strings.Split(host, "/")[0]
+		slog.Warn("registry login currently only supports registry hostname, not a repository path", "host", host, "suggested", registryHost)
+		return true
+	}
+	return false
+}
+
 // Login logs into a registry
 func (c *Client) Login(host string, options ...LoginOption) error {
 	for _, option := range options {
 		option(&loginOperation{host, c})
 	}
 
+	warnIfHostHasPath(host)
+
 	reg, err := remote.NewRegistry(host)
 	if err != nil {
 		return err

pkg/registry/client_test.go

@@ -120,3 +120,49 @@ func TestLogin_ResetsForceAttemptOAuth2_OnFailure(t *testing.T) {
 		t.Errorf("ForceAttemptOAuth2 should be false after failed Login")
 	}
 }
+
+// TestWarnIfHostHasPath verifies that warnIfHostHasPath correctly detects path components.
+func TestWarnIfHostHasPath(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		host     string
+		wantWarn bool
+	}{
+		{
+			name:     "domain only",
+			host:     "ghcr.io",
+			wantWarn: false,
+		},
+		{
+			name:     "domain with port",
+			host:     "localhost:8000",
+			wantWarn: false,
+		},
+		{
+			name:     "domain with repository path",
+			host:     "ghcr.io/terryhowe",
+			wantWarn: true,
+		},
+		{
+			name:     "domain with nested path",
+			host:     "ghcr.io/terryhowe/myrepo",
+			wantWarn: true,
+		},
+		{
+			name:     "localhost with port and path",
+			host:     "localhost:8000/myrepo",
+			wantWarn: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := warnIfHostHasPath(tt.host)
+			if got != tt.wantWarn {
+				t.Errorf("warnIfHostHasPath(%q) = %v, want %v", tt.host, got, tt.wantWarn)
+			}
+		})
+	}
+}