revise commentary

gcc/cobol/Make-lang.in

@@ -150,16 +150,6 @@ gcobol$(exeext): \
 
 # First, files needed for parsing:
 
-# To establish prerequisites for parse.o, cdf.o, and scan.o,
-#   1. capture the "make -n" output 
-#   2. eliminate compiler options, leaving only preprocessor options (-D and -I)
-#   3. add -E -MM
-#
-# The below lists of include files for the the generated files is
-# postprocessed: the files are one per line, used "realpath
-# --relative-to=$PWD" to rationalize them, and sorted.  We include
-# parse.c in the list for scan.o because that's the one make(1) knows about.
-#
 cobol/parse.c: cobol/parse.y
 	$(BISON) -o $@ $(YFLAGS)				\
 		--defines=cobol/parse.h			\
@@ -169,6 +159,20 @@ cobol/cdf.c: cobol/cdf.y
 	$(BISON) -o $@ $(YFLAGS)						\
 		--defines=cobol/cdf.h --report-file=cobol/cdf.out $<
 
+
+# The src<foo> targets are executed if
+# ‘--enable-generated-files-in-srcdir’ was specified as a configure
+# option.
+#
+# srcextra copies generated dependencies into the source
+# directory. This is used for files such as Flex/Bison output: files
+# that are not version-controlled but should be included in any
+# release tarballs.
+#
+# Although versioned snapshots require Flex to be installed, they do
+# not require Bison.  Release tarballs always include Flex/Bison
+# output, and do not require those tools to be installed.
+
 cobol.srcextra: cobol/parse.c cobol/cdf.c
 	ln -f $^ cobol/parse.h cobol/cdf.h $(srcdir)/cobol/
 
@@ -183,6 +187,17 @@ cobol/scan.c: cobol/scan.l
 		  exit nerr}' $@~
 	@rm $@~
 
+
+# To establish prerequisites for parse.o, cdf.o, and scan.o,
+#   1. capture the "make -n" output 
+#   2. eliminate compiler options, leaving only preprocessor options (-D and -I)
+#   3. add -E -MM
+#
+# The below lists of include files for the the generated files is
+# postprocessed: the files are one per line, used "realpath
+# --relative-to=$PWD" to rationalize them, and sorted.  We include
+# parse.c in the list for scan.o because that's the one make(1) knows about.
+
 cobol/cdf.o: cobol/cdf.c			\
 	$(srcdir)/cobol/cbldiag.h		\
 	$(srcdir)/cobol/cdfval.h		\