Add operation-related methods to parser_state

This adds several operation-related methods to parser_state.  These
methods make it more convenient to change the parsers to be
operation-based.

Because byacc has poor support for C++, a stack of operations is added
to parser_state.  A parser can push operations, then later pop them
for combination into new operations.  This approach avoids the memory
leaks that would result if raw pointers were used in the parsers, at
the cost of parser productions not being type-safe (they can't
indicate that they return an operation).

This also introduces analogs of some write_exp functions, like
write_exp_string_vector, write_dollar_variable, and
write_exp_symbol_reference.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* parser-defs.h (struct parser_state) <push, push_new,
	push_c_string, push_symbol, push_dollar, pop, pop_vector, wrap,
	wrap2>: New methods.
	<m_operations>: New member.
	* parse.c (parser_state::push_c_string)
	(parser_state::push_symbol, parser_state::push_dollar): New
	methods.

gdb/parse.c

@@ -545,6 +545,133 @@ parser_state::mark_completion_tag (enum type_code tag, const char *ptr,
   m_completion_state.expout_completion_name.reset (xstrndup (ptr, length));
 }
 
+/* See parser-defs.h.  */
+
+void
+parser_state::push_c_string (int kind, struct stoken_vector *vec)
+{
+  std::vector<std::string> data (vec->len);
+  for (int i = 0; i < vec->len; ++i)
+    data[i] = std::string (vec->tokens[i].ptr, vec->tokens[i].length);
+
+  push_new<expr::c_string_operation> ((enum c_string_type_values) kind,
+				      std::move (data));
+}
+
+/* See parser-defs.h.  */
+
+void
+parser_state::push_symbol (const char *name, block_symbol sym)
+{
+  if (sym.symbol != nullptr)
+    {
+      if (symbol_read_needs_frame (sym.symbol))
+	block_tracker->update (sym);
+      push_new<expr::var_value_operation> (sym.symbol, sym.block);
+    }
+  else
+    {
+      struct bound_minimal_symbol msymbol = lookup_bound_minimal_symbol (name);
+      if (msymbol.minsym != NULL)
+	push_new<expr::var_msym_value_operation> (msymbol.minsym,
+						  msymbol.objfile);
+      else if (!have_full_symbols () && !have_partial_symbols ())
+	error (_("No symbol table is loaded.  Use the \"file\" command."));
+      else
+	error (_("No symbol \"%s\" in current context."), name);
+    }
+}
+
+/* See parser-defs.h.  */
+
+void
+parser_state::push_dollar (struct stoken str)
+{
+  struct block_symbol sym;
+  struct bound_minimal_symbol msym;
+  struct internalvar *isym = NULL;
+  std::string copy;
+
+  /* Handle the tokens $digits; also $ (short for $0) and $$ (short for $$1)
+     and $$digits (equivalent to $<-digits> if you could type that).  */
+
+  int negate = 0;
+  int i = 1;
+  /* Double dollar means negate the number and add -1 as well.
+     Thus $$ alone means -1.  */
+  if (str.length >= 2 && str.ptr[1] == '$')
+    {
+      negate = 1;
+      i = 2;
+    }
+  if (i == str.length)
+    {
+      /* Just dollars (one or two).  */
+      i = -negate;
+      goto handle_last;
+    }
+  /* Is the rest of the token digits?  */
+  for (; i < str.length; i++)
+    if (!(str.ptr[i] >= '0' && str.ptr[i] <= '9'))
+      break;
+  if (i == str.length)
+    {
+      i = atoi (str.ptr + 1 + negate);
+      if (negate)
+	i = -i;
+      goto handle_last;
+    }
+
+  /* Handle tokens that refer to machine registers:
+     $ followed by a register name.  */
+  i = user_reg_map_name_to_regnum (gdbarch (),
+				   str.ptr + 1, str.length - 1);
+  if (i >= 0)
+    goto handle_register;
+
+  /* Any names starting with $ are probably debugger internal variables.  */
+
+  copy = copy_name (str);
+  isym = lookup_only_internalvar (copy.c_str () + 1);
+  if (isym)
+    {
+      push_new<expr::internalvar_operation> (isym);
+      return;
+    }
+
+  /* On some systems, such as HP-UX and hppa-linux, certain system routines
+     have names beginning with $ or $$.  Check for those, first.  */
+
+  sym = lookup_symbol (copy.c_str (), NULL, VAR_DOMAIN, NULL);
+  if (sym.symbol)
+    {
+      push_new<expr::var_value_operation> (sym.symbol, sym.block);
+      return;
+    }
+  msym = lookup_bound_minimal_symbol (copy.c_str ());
+  if (msym.minsym)
+    {
+      push_new<expr::var_msym_value_operation> (msym.minsym, msym.objfile);
+      return;
+    }
+
+  /* Any other names are assumed to be debugger internal variables.  */
+
+  push_new<expr::internalvar_operation>
+    (create_internalvar (copy.c_str () + 1));
+  return;
+handle_last:
+  push_new<expr::last_operation> (i);
+  return;
+handle_register:
+  str.length--;
+  str.ptr++;
+  push_new<expr::register_operation> (copy_name (str));
+  block_tracker->update (expression_context_block,
+			 INNERMOST_BLOCK_FOR_REGISTERS);
+  return;
+}
+
 
 /* Recognize tokens that start with '$'.  These include: