chore: make valid connection properties public

Make the list of valid connection properties public, so tools that
depend on the Connection API can use this to for example generate
documentation for valid properties.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionProperties.java

@@ -115,7 +115,6 @@
 import com.google.common.collect.ImmutableMap;
 import com.google.spanner.v1.DirectedReadOptions;
 import java.time.Duration;
-import java.util.Map;
 
 /**
  * Utility class that defines all known connection properties. This class will eventually replace
@@ -541,7 +540,7 @@ class ConnectionProperties {
           BooleanConverter.INSTANCE,
           Context.USER);
 
-  static final Map<String, ConnectionProperty<?>> CONNECTION_PROPERTIES =
+  static final ImmutableMap<String, ConnectionProperty<?>> CONNECTION_PROPERTIES =
       CONNECTION_PROPERTIES_BUILDER.build();
 
   /** Utility method for creating a new core {@link ConnectionProperty}. */

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionProperty.java

@@ -19,6 +19,7 @@
 import com.google.cloud.spanner.ErrorCode;
 import com.google.cloud.spanner.SpannerExceptionFactory;
 import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableList;
 import java.util.Locale;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -37,12 +38,16 @@
  * connection state is an opt-in.
  */
 public class ConnectionProperty<T> {
+  /** The list of all supported connection properties. */
+  public static ImmutableList<ConnectionProperty<?>> VALID_CONNECTION_PROPERTIES =
+      ImmutableList.copyOf(ConnectionProperties.CONNECTION_PROPERTIES.values());
+
   /**
    * Context indicates when a {@link ConnectionProperty} may be set. Each higher-ordinal value
    * includes the preceding values, meaning that a {@link ConnectionProperty} with {@link
    * Context#USER} can be set both at connection startup and during the connection's lifetime.
    */
-  enum Context {
+  public enum Context {
     /** The property can only be set at startup of the connection. */
     STARTUP,
     /**
@@ -163,35 +168,38 @@ ConnectionPropertyValue<T> convert(@Nullable String stringValue) {
     return new ConnectionPropertyValue<>(this, convertedValue, convertedValue);
   }
 
-  String getKey() {
+  @Nonnull
+  public String getKey() {
     return this.key;
   }
 
-  boolean hasExtension() {
+  public boolean hasExtension() {
     return this.extension != null;
   }
 
-  String getExtension() {
+  public String getExtension() {
     return this.extension;
   }
 
-  String getName() {
+  @Nonnull
+  public String getName() {
     return this.name;
   }
 
-  String getDescription() {
+  @Nonnull
+  public String getDescription() {
     return this.description;
   }
 
-  T getDefaultValue() {
+  public T getDefaultValue() {
     return this.defaultValue;
   }
 
-  T[] getValidValues() {
+  public T[] getValidValues() {
     return this.validValues;
   }
 
-  Context getContext() {
+  public Context getContext() {
     return this.context;
   }
 }