From 17f30b40f8a2d2ba5a2bea4c7c0cec5af14c04e5 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Sun, 11 May 2014 16:58:40 +1000
Subject: [PATCH] pargergen: support $<N in code fragments

This removes the need to add "$N = NULL" to avoid the referenced structure
being removed.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 csrc/parsergen.mdc | 41 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/csrc/parsergen.mdc b/csrc/parsergen.mdc
index ef01bf3..b3d1cf6 100644
--- a/csrc/parsergen.mdc
+++ b/csrc/parsergen.mdc
@@ -397,12 +397,15 @@ collected and forms the code-fragment for the production.  It must all
 be in one `code_node` of the literate code.  The `}$` must be
 at the end of a line.
 
-Text in the code fragment will undergo substitutions where `$N` for
-some numeric `N` will be replaced with a variable holding the parse
-information for the particular symbol in the production.  `$0` is the
-head of the production, `$1` is the first symbol of the body, etc.
-The type of `$N` for a terminal symbol is `struct token`.  For
-a non-terminal, it is whatever has been declared for that symbol.
+Text in the code fragment will undergo substitutions where `$N` or
+`$<N`,for some numeric `N`, will be replaced with a variable holding
+the parse information for the particular symbol in the production.
+`$0` is the head of the production, `$1` is the first symbol of the
+body, etc.  The type of `$N` for a terminal symbol is `struct token`.
+For a non-terminal, it is whatever has been declared for that symbol.
+The `<` may be included for symbols declared as storing a reference
+(not a structure) and means that the reference is being moved out, so
+it will not automatically be freed.
 
 While building productions we will need to add to an array which needs to
 grow dynamically.
@@ -1965,15 +1968,23 @@ structure returned by a previous reduction.  These pointers need to be cast
 to the appropriate type for each access.  All this is handling in
 `gen_code`.
 
+`gen_code` also allows symbol references to contain a '`<`' as in '`$<2`'.
+This applied only to symbols with references (or pointers), not those with structures.
+The `<` implies that the reference it being moved out, so the object will not be
+automatically freed.  This is equivalent to assigning `NULL` to the pointer.
 
 ###### functions
 
 	static void gen_code(struct production *p, FILE *f, struct grammar *g)
 	{
 		char *c;
+		char *used = calloc(1, p->body_size);
+		int i;
+
 		fprintf(f, "\t\t\t");
 		for (c = p->code.txt; c < p->code.txt + p->code.len; c++) {
 			int n;
+			int use = 0;
 			if (*c != '$') {
 				fputc(*c, f);
 				if (*c == '\n')
@@ -1981,7 +1992,13 @@ to the appropriate type for each access.  All this is handling in
 				continue;
 			}
 			c++;
+			if (*c == '<') {
+				use = 1;
+				c++;
+			}
 			if (*c < '0' || *c > '9') {
+				if (use)
+					fputc('<', f);
 				fputc(*c, f);
 				continue;
 			}
@@ -2002,13 +2019,23 @@ to the appropriate type for each access.  All this is handling in
 					n-1);
 			else if (p->body[n-1]->struct_name.txt == NULL)
 				fprintf(f, "$%d", n);
-			else
+			else {
 				fprintf(f, "(*(struct %.*s*%s)body[%d])",
 					p->body[n-1]->struct_name.len,
 					p->body[n-1]->struct_name.txt,
 					p->body[n-1]->isref ? "*":"", n-1);
+				used[n-1] = use;
+			}
 		}
 		fputs("\n", f);
+		for (i = 0; i < p->body_size; i++) {
+			if (p->body[i]->struct_name.txt &&
+			    p->body[i]->isref &&
+			    used[i])
+				// assume this has been copied out
+				fprintf(f, "\t\t*(void**)body[%d] = NULL;\n", i);
+		}
+		free(used);
 	}
 
 ###### functions
-- 
2.43.0