ada: Improve documentation for -gnatw.h warnings

The -gnatw.h option enables warnings about "gaps" in record layout
specifications. In the case of a "partial" layout specification, where the
locations of some components are left unspecified, the resulting warnings
may be incomplete or incorrect. Document this implementation limitation.

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst: Improve
	the description of how the -gnatw.h switch interacts with
	"partial" record layout specifications (i.e., specifications where
	the locations of some components are left unspecified).
	* gnat_ugn.texi: Regenerate.

diff --git a/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst b/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
index 87fb108..fe0b567 100644 (file)
--- a/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
+++ b/gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst
@@ -3221,8 +3221,13 @@ of the pragma in the :title:`GNAT_Reference_manual`).
 
   This switch activates warnings on component clauses in record
   representation clauses that leave holes (gaps) in the record layout.
-  If this warning option is active, then record representation clauses
-  should specify a contiguous layout, adding unused fill fields if needed.
+  If a record representation clause does not specify a location for
+  every component of the record type, then the warnings generated (or not
+  generated) are unspecified. For example, there may be gaps for which
+  either no warning is generated or a warning is generated that
+  incorrectly describes the location of the gap. This undesirable situation
+  can sometimes be avoided by adding (and specifying the location for) unused
+  fill fields.
 
 
 .. index:: -gnatw.H  (gcc)

diff --git a/gcc/ada/gnat_ugn.texi b/gcc/ada/gnat_ugn.texi
index 2f43b4f..12eb494 100644 (file)
--- a/gcc/ada/gnat_ugn.texi
+++ b/gcc/ada/gnat_ugn.texi
@@ -19,7 +19,7 @@
 
 @copying
 @quotation
-GNAT User's Guide for Native Platforms , Nov 14, 2022
+GNAT User's Guide for Native Platforms , Nov 18, 2022
 
 AdaCore
 
@@ -11305,8 +11305,13 @@ This switch suppresses warnings on hiding declarations.
 
 This switch activates warnings on component clauses in record
 representation clauses that leave holes (gaps) in the record layout.
-If this warning option is active, then record representation clauses
-should specify a contiguous layout, adding unused fill fields if needed.
+If a record representation clause does not specify a location for
+every component of the record type, then the warnings generated (or not
+generated) are unspecified. For example, there may be gaps for which
+either no warning is generated or a warning is generated that
+incorrectly describes the location of the gap. This undesirable situation
+can sometimes be avoided by adding (and specifying the location for) unused
+fill fields.
 @end table
 
 @geindex -gnatw.H (gcc)