The build session state is managed by the `BuildSessionState` class.
An instance is created at the start of a Gradle invocation and discarded at the end of that invocation.

The build session state also includes "cross session" state that is shared with any "nested" sessions that need to be created.

/**
 * An implementation of {@code Iterable} which throws an exception on all invocations of the {@link
 * #iterator()} method after the first, and whose iterator is always unmodifiable.
 *
 * <p>The {@code Iterable} specification does not make it absolutely clear what should happen on a
 * second invocation, so implementors have made various choices, including:
 *
 * <ul>
 *   <li>returning the same iterator again

/**
 * An implementation of {@code Iterable} which throws an exception on all invocations of the {@link
 * #iterator()} method after the first, and whose iterator is always unmodifiable.
 *
 * <p>The {@code Iterable} specification does not make it absolutely clear what should happen on a
 * second invocation, so implementors have made various choices, including:
 *
 * <ul>
 *   <li>returning the same iterator again

// for any Go type, but represents the same type for any given function
// invocation.
type Type int

// Type1 is here for the purposes of documentation only. It is a stand-in
// for any Go type, but represents the same type for any given function
// invocation.
type Type1 int

// IntegerType is here for the purposes of documentation only. It is a stand-in

            return ref.get() == null;
          }
        });
  }

  /**
   * Tries to perform a "full" garbage collection cycle (including processing of weak references and
   * invocation of finalize methods) and waits for it to complete. Ensures that at least one weak
   * reference has been cleared and one {@code finalize} method has been run before this method

            // Check if the project is part of the session (not filtered by -pl, -rf, etc). If so, we check
            // if a possible earlier Maven invocation produced some output for that project which we can use.
            boolean projectHasOutputFromPreviousSession =
                    !session.getProjects().contains(project) && outputDirectory.exists();

   * {@code setCount()} to throw an exception, as checking the return value could produce an
   * incorrect error message like "setCount() should return the original count" instead of the
   * message passed to a later invocation of {@code fail()}, like "setCount should throw
   * UnsupportedOperationException."
   */
  abstract void setCountNoCheckReturnValue(E element, int count);

   * {@code setCount()} to throw an exception, as checking the return value could produce an
   * incorrect error message like "setCount() should return the original count" instead of the
   * message passed to a later invocation of {@code fail()}, like "setCount should throw
   * UnsupportedOperationException."
   */
  abstract void setCountNoCheckReturnValue(E element, int count);

            return ref.get() == null;
          }
        });
  }

  /**
   * Tries to perform a "full" garbage collection cycle (including processing of weak references and
   * invocation of finalize methods) and waits for it to complete. Ensures that at least one weak
   * reference has been cleared and one {@code finalize} method has been run before this method

          <version>1.0.0+</version>
          <type>String</type>
          <description>Reference the invocation phase of the Mojo.</description>
        </field>
        <field>
          <name>executeGoal</name>
          <version>1.0.0+</version>
          <type>String</type>
          <description>Reference the invocation goal of the Mojo.</description>
        </field>
        <field>
          <name>executeLifecycle</name>