[m-rev.] for review: Document that `:- module' for separate submodules must be fully qualified.

[Peter Wang]

doc/reference_manual.texi:
    Document the new requrement on `:- module' declarations for separate
    submodules. Note that the implementation allows partial
    qualification in the corresponding `:- end_module' declaration.

    Clarify that a sentence applies to declarations for *nested*
    submodules.

    Reword the second of two paragraphs beginning with "Note that".

NEWS:
    Announce the change.

diff --git a/NEWS b/NEWS
index 9a10ff60c..737dcdaab 100644
--- a/NEWS
+++ b/NEWS
@@ -98,6 +98,9 @@ Changes that may break compatibility
   standard library module `lexer`, or a submodule of a user-written
   parent module. [Mantis bug #489].
 
+* The `:- module` declaration in a separate sub-module now must contain the
+  fully qualified module name.
+
 * References to everything imported via `:- use_module` declarations
   must now be fully module qualified.
 
diff --git a/doc/reference_manual.texi b/doc/reference_manual.texi
index 54656e5d2..10cbc76bb 100644
--- a/doc/reference_manual.texi
+++ b/doc/reference_manual.texi
@@ -5288,8 +5288,8 @@ matching @samp{:- module} and @samp{:- end_module} declarations.
 (Note that @samp{:- end_module} for nested sub-modules
 are mandatory, not optional,
 even if the nested sub-module is the last thing in the source file.
-Also note that the module name in a @samp{:- module} or @samp{:- end_module}
-declaration need not be fully-qualified.)
+The module name in a @samp{:- module} or @samp{:- end_module}
+declaration for a nested sub-module need not be fully-qualified.)
 The sequence of items thus delimited is known as a sub-module item sequence.
 
 The interface and implementation parts of a nested sub-module
@@ -5358,16 +5358,9 @@ with a list of the file names of all the Mercury modules in the program.)
 The source file of a separate sub-module must contain
 the declaration (interface) and definition (implementation) of the sub-module.
 It must start with a @samp{:- module} declaration
-which matches that in the @samp{:- include_module} declaration in the parent,
+containing the fully qualified module name,
 followed by the interface and (if necessary) implementation sections,
 and it may optionally end with a @samp{:- end_module} declaration.
-(Note: the module names in the @samp{:- module}, @samp{:- end_module},
-and @w{@samp{:- include_module}} declarations need not be fully-qualified.
-However, if the file name used for a particular module
-does not include all the module qualifiers,
-then the Melbourne Mercury implementation
-requires the module name in the @samp{:- module} declaration
-for that module to be fully qualified.)
 
 The semantics of separate sub-modules
 are identical to those of nested sub-modules.
@@ -5437,7 +5430,7 @@ occurs only in the implementation section of the parent module
 may only be imported or used by its parent module
 or by sub-modules of its parent module.
 
-Note that as mentioned previously,
+As mentioned previously,
 all @samp{:- import_module} and @samp{:- use_module} declarations
 must use fully-qualified module names.
 
-- 
2.24.1