Fix the second Value() example in the manpage

CHANGES.txt

@@ -44,6 +44,11 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
     - Remove the legacy job scheduler and the "legacy_sched_deprecated"
       experimental feature flag.
 
+  From Roshan Ramani:
+    - Fix the second Value() example in the manpage, which never ran its
+      builder: it wrapped the Value Nodes in another Value() and nothing
+      depended on the target. Fixes #4499.
+
   From Mats Wichmann:
     - Add more unit tests for UNC path handling. These tests expose some
       current issues so they are marked expectedFailure. The intent is to

RELEASE.txt

@@ -82,6 +82,8 @@ DOCUMENTATION
 - Removed the out-of-date table of option names for SetOption and
   GetOption and instead point to the maintained tables in Appendix D.
 
+- Fixed the second Value() example in the manpage, which did not work.
+
 * Added scons-ai.md, a condensed version of the manpage intended for
   consumption by AI tools, built into build/doc/MD. It keeps every documented
   option, tool, builder, function and construction variable together with its

SCons/Environment.xml

@@ -3625,7 +3625,6 @@ the <parameter>name</parameter> parameter was added.
 Examples:
 </para>
 
-<!-- TODO fix second example or replace - still doesn't work -->
 <example_commands>
 env = Environment()
 
@@ -3659,7 +3658,17 @@ input = env.Value('after')
 # Attach a builder named UpdateValue to the construction environment
 # using the 'build_value' action function above.
 env['BUILDERS']['UpdateValue'] = Builder(action=build_value)
-env.UpdateValue(target=Value(output), source=Value(input))
+env.UpdateValue(target=output, source=input)
+
+def write_value(target, source, env):
+    """Action function to write the built value of $SOURCE into $TARGET."""
+    with open(target[0], 'wb') as f:
+        f.write(source[0].read())
+
+# A Value Node is only built when a target being built depends on it,
+# so write the updated Value to a file. output.txt contains "after".
+env['BUILDERS']['WriteValue'] = Builder(action=write_value)
+env.WriteValue(target='output.txt', source=output)
 </example_commands>
 </summary>
 </scons_function>