Filter: Implement soft scopes

Soft scopes are anonymous scopes that most likely do not contain any
symbol, so allocating regular scope is postponed when it is really
needed.

conf/cf-lex.l

@@ -574,6 +574,8 @@ check_eof(void)
   return 0;
 }
 
+static inline void cf_swap_soft_scope(void);
+
 static struct symbol *
 cf_new_symbol(const byte *c)
 {
@@ -583,6 +585,8 @@ cf_new_symbol(const byte *c)
   if (l > SYM_MAX_LEN)
     cf_error("Symbol too long");
 
+  cf_swap_soft_scope();
+
   s = cfg_allocz(sizeof(struct symbol) + l + 1);
   *s = (struct symbol) { .scope = conf_this_scope, .class = SYM_VOID, };
   strcpy(s->name, c);
@@ -656,8 +660,8 @@ cf_localize_symbol(struct symbol *sym)
     return sym;
 
   /* If the scope is the current, it is already defined in this scope. */
-  if (sym->scope == conf_this_scope)
-    cf_error("Symbol already defined");
+  if (cf_symbol_is_local(sym))
+    cf_error("Symbol '%s' already defined", sym->name);
 
   /* Not allocated here yet, doing it now. */
   return cf_new_symbol(sym->name);
@@ -787,12 +791,60 @@ cf_push_scope(struct symbol *sym)
 void
 cf_pop_scope(void)
 {
+  ASSERT(!conf_this_scope->soft_scopes);
+
   conf_this_scope->active = 0;
   conf_this_scope = conf_this_scope->next;
 
   ASSERT(conf_this_scope);
 }
 
+/**
+ * cf_push_soft_scope - enter new soft scope
+ *
+ * If we want to enter a new anonymous scope that most likely will not contain
+ * any symbols, we can use cf_push_soft_scope() insteas of cf_push_scope().
+ * Such scope will be converted to a regular scope on first use.
+ */
+void
+cf_push_soft_scope(void)
+{
+  if (conf_this_scope->soft_scopes < 0xfe)
+    conf_this_scope->soft_scopes++;
+  else
+    cf_push_scope(NULL);
+}
+
+/**
+ * cf_pop_soft_scope - leave a soft scope
+ *
+ * Leave a soft scope entered by cf_push_soft_scope().
+ */
+void
+cf_pop_soft_scope(void)
+{
+  if (conf_this_scope->soft_scopes)
+    conf_this_scope->soft_scopes--;
+  else
+    cf_pop_scope();
+}
+
+/**
+ * cf_swap_soft_scope - convert soft scope to regular scope
+ *
+ * Soft scopes cannot hold symbols, so they must be converted to regular scopes
+ * on first use. It is done automatically by cf_new_symbol().
+ */
+static inline void
+cf_swap_soft_scope(void)
+{
+  if (conf_this_scope->soft_scopes)
+  {
+    conf_this_scope->soft_scopes--;
+    cf_push_scope(NULL);
+  }
+}
+
 /**
  * cf_symbol_class_name - get name of a symbol class
  * @sym: symbol

conf/conf.h

@@ -133,7 +133,8 @@ struct sym_scope {
   struct sym_scope *next;		/* Next on scope stack */
   struct symbol *name;			/* Name of this scope */
   uint slots;				/* Variable slots */
-  int active;				/* Currently entered */
+  byte active;				/* Currently entered */
+  byte soft_scopes;			/* Number of soft scopes above */
 };
 
 struct bytestring {
@@ -190,6 +191,9 @@ struct symbol *cf_get_symbol(const byte *c);
 struct symbol *cf_default_name(char *template, int *counter);
 struct symbol *cf_localize_symbol(struct symbol *sym);
 
+static inline int cf_symbol_is_local(struct symbol *sym)
+{ return (sym->scope == conf_this_scope) && !conf_this_scope->soft_scopes; }
+
 /**
  * cf_define_symbol - define meaning of a symbol
  * @sym: symbol to be defined
@@ -213,6 +217,9 @@ struct symbol *cf_localize_symbol(struct symbol *sym);
 
 void cf_push_scope(struct symbol *);
 void cf_pop_scope(void);
+void cf_push_soft_scope(void);
+void cf_pop_soft_scope(void);
+
 char *cf_symbol_class_name(struct symbol *sym);
 
 /* Parser */

sysdep/unix/main.c

@@ -116,7 +116,7 @@ add_num_const(char *name, int val, const char *file, const uint line)
   struct f_val *v = cfg_alloc(sizeof(struct f_val));
   *v = (struct f_val) { .type = T_INT, .val.i = val };
   struct symbol *sym = cf_get_symbol(name);
-  if (sym->class && (sym->scope == conf_this_scope))
+  if (sym->class && cf_symbol_is_local(sym))
     cf_error("Error reading value for %s from %s:%d: already defined", name, file, line);
 
   cf_define_symbol(sym, SYM_CONSTANT | T_INT, val, v);