[PATCH 2/2] gdb: add SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT

[Andrew Burgess <aburgess@redhat.com>]

After the previous commit converted symbol lookup debug to use the new
debug scheme, this commit adds SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT.

The previous commit updated 'set debug symbol-lookup' to use the new
debug scheme, however SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT still does
not exist.  The reason for this is that 'set debug symbol-lookup'
controls an integer variable, rather than a bool, and, depending on
the value of this variable, different amounts of debug will be
produced.

Currently the *_SCOPED_DEBUG_ENTER_EXIT mechanism will only work for
control variables of type bool, this is because the underlying
scoped_debug_start_end class can only handle variables of type bool.

This commit templates scoped_debug_start_end so that the class can
accept either a 'bool &' or an invokable object, e.g. a lambda
function, or a function pointer.

The existing scoped_debug_start_end and scoped_debug_enter_exit macros
in common-debug.h are updated to support scoped_debug_enter_exit being
templated, however, nothing outside of common-debug.h needs to change.

I've then added SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT in symtab.h, and
added a couple of token uses in symtab.c.  I didn't want to add too
much in this first commit, this is really about updating
common-debug.h to support this new ability.
---
 gdb/symtab.c              |  4 ++
 gdb/symtab.h              |  7 +++
 gdbsupport/common-debug.h | 92 +++++++++++++++++++++++++++++++--------
 3 files changed, 84 insertions(+), 19 deletions(-)

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 14d81f5468d..a7a54159b6d 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -1950,6 +1950,8 @@ lookup_symbol_in_language (const char *name, const struct block *block,
 			   const domain_enum domain, enum language lang,
 			   struct field_of_this_result *is_a_field_of_this)
 {
+  SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT;
+
   demangle_result_storage storage;
   const char *modified_name = demangle_for_lookup (name, lang, storage);
 
@@ -2072,6 +2074,8 @@ lookup_symbol_aux (const char *name, symbol_name_match_type match_type,
 		   const domain_enum domain, enum language language,
 		   struct field_of_this_result *is_a_field_of_this)
 {
+  SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT;
+
   struct block_symbol result;
   const struct language_defn *langdef;
 
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 6eca61a759a..2d1f0cec877 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -2637,6 +2637,13 @@ extern unsigned int symbol_lookup_debug;
   debug_prefixed_printf_cond (symbol_lookup_debug >= 2, "symbol-lookup", fmt, \
 			      ##__VA_ARGS__)
 
+/* Print "symbol-lookup" enter/exit debug statements.  */
+
+#define SYMBOL_LOOKUP_SCOPED_DEBUG_ENTER_EXIT \
+  scoped_debug_enter_exit ([&] () -> bool { \
+    return symbol_lookup_debug > 0; \
+  }, "symbol-lookup")
+
 extern bool basenames_may_differ;
 
 bool compare_filenames_for_search (const char *filename,
diff --git a/gdbsupport/common-debug.h b/gdbsupport/common-debug.h
index 00a1e1599bc..904c1a1ea24 100644
--- a/gdbsupport/common-debug.h
+++ b/gdbsupport/common-debug.h
@@ -88,6 +88,7 @@ extern int debug_print_depth;
    it on destruction, such that nested debug statements will be printed with
    an indent and appear "inside" this one.  */
 
+template<typename PT>
 struct scoped_debug_start_end
 {
   /* DEBUG_ENABLED is a reference to a variable that indicates whether debugging
@@ -95,35 +96,35 @@ struct scoped_debug_start_end
      separately at construction and destruction, such that the start statement
      could be printed but not the end statement, or vice-versa.
 
+     DEBUG_ENABLED should either be of type 'bool &' or should be a type
+     that can be invoked.
+
      MODULE and FUNC are forwarded to debug_prefixed_printf.
 
      START_PREFIX and END_PREFIX are the statements to print on construction and
      destruction, respectively.
 
      If the FMT format string is non-nullptr, then a `: ` is appended to the
-     messages, followed by the rendering of that format string.  The format
-     string is rendered during construction and is re-used as is for the
-     message on exit.  */
+     messages, followed by the rendering of that format string with ARGS.
+     The format string is rendered during construction and is re-used as is
+     for the message on exit.  */
 
-  scoped_debug_start_end (bool &debug_enabled, const char *module,
+  scoped_debug_start_end (PT &debug_enabled, const char *module,
 			  const char *func, const char *start_prefix,
-			  const char *end_prefix, const char *fmt, ...)
-    ATTRIBUTE_NULL_PRINTF (7, 8)
+			  const char *end_prefix, const char *fmt,
+			  va_list args)
+    ATTRIBUTE_NULL_PRINTF (7, 0)
     : m_debug_enabled (debug_enabled),
       m_module (module),
       m_func (func),
       m_end_prefix (end_prefix),
       m_with_format (fmt != nullptr)
   {
-    if (m_debug_enabled)
+    if (is_debug_enabled ())
       {
 	if (fmt != nullptr)
 	  {
-	    va_list args;
-	    va_start (args, fmt);
 	    m_msg = string_vprintf (fmt, args);
-	    va_end (args);
-
 	    debug_prefixed_printf (m_module, m_func, "%s: %s",
 				   start_prefix, m_msg->c_str ());
 	  }
@@ -137,6 +138,8 @@ struct scoped_debug_start_end
 
   DISABLE_COPY_AND_ASSIGN (scoped_debug_start_end);
 
+  scoped_debug_start_end (scoped_debug_start_end &&other) = default;
+
   ~scoped_debug_start_end ()
   {
     if (m_must_decrement_print_depth)
@@ -145,7 +148,7 @@ struct scoped_debug_start_end
 	--debug_print_depth;
       }
 
-    if (m_debug_enabled)
+    if (is_debug_enabled ())
       {
 	if (m_with_format)
 	  {
@@ -167,7 +170,16 @@ struct scoped_debug_start_end
   }
 
 private:
-  bool &m_debug_enabled;
+
+  /* This function is specialized based on the type PT.  Returns true if
+     M_DEBUG_ENABLED indicates this debug setting is enabled, otherwise,
+     return false.  */
+  bool is_debug_enabled () const;
+
+  /* Reference to the debug setting, or a callback that can read the debug
+     setting.  Access the value of this by calling IS_DEBUG_ENABLED.  */
+  PT &m_debug_enabled;
+
   const char *m_module;
   const char *m_func;
   const char *m_end_prefix;
@@ -184,18 +196,60 @@ struct scoped_debug_start_end
   bool m_must_decrement_print_depth = false;
 };
 
+/* Implementation of is_debug_enabled when PT is an invokable type.  */
+
+template<typename PT>
+inline bool
+scoped_debug_start_end<PT>::is_debug_enabled () const
+{
+  return m_debug_enabled ();
+}
+
+/* Implementation of is_debug_enabled when PT is 'bool &'.  */
+
+template<>
+inline bool
+scoped_debug_start_end<bool &>::is_debug_enabled () const
+{
+  return m_debug_enabled;
+}
+
+/* Wrapper around the scoped_debug_start_end constructor to allow the
+   caller to create an object using 'auto' type, the actual type will be
+   based on the type of the PRED argument.  All arguments are forwarded to
+   the scoped_debug_start_end constructor.  */
+
+template<typename PT>
+static inline scoped_debug_start_end<PT &> ATTRIBUTE_NULL_PRINTF (6, 7)
+make_scoped_debug_start_end (PT &&pred, const char *module, const char *func,
+			     const char *start_prefix,
+			     const char *end_prefix, const char *fmt, ...)
+{
+  va_list args;
+  va_start (args, fmt);
+  auto res = scoped_debug_start_end<PT &> (pred, module, func, start_prefix,
+					   end_prefix, fmt, args);
+  va_end (args);
+
+  return res;
+}
+
 /* Helper to define a module-specific start/end debug macro.  */
 
-#define scoped_debug_start_end(debug_enabled, module, fmt, ...) \
-  scoped_debug_start_end CONCAT(scoped_debug_start_end, __LINE__) \
-    (debug_enabled, module, __func__, "start", "end", fmt, ##__VA_ARGS__)
+#define scoped_debug_start_end(debug_enabled, module, fmt, ...)		\
+  auto CONCAT(scoped_debug_start_end, __LINE__)				\
+    = make_scoped_debug_start_end (debug_enabled, module, 	\
+				   __func__, "start", "end",	\
+				   fmt, ##__VA_ARGS__)
 
 /* Helper to define a module-specific enter/exit debug macro.  This is a special
    case of `scoped_debug_start_end` where the start and end messages are "enter"
    and "exit", to denote entry and exit of a function.  */
 
-#define scoped_debug_enter_exit(debug_enabled, module) \
-  scoped_debug_start_end CONCAT(scoped_debug_start_end, __LINE__) \
-    (debug_enabled, module, __func__, "enter", "exit", nullptr)
+#define scoped_debug_enter_exit(debug_enabled, module)	\
+  auto CONCAT(scoped_debug_start_end, __LINE__)				\
+    = make_scoped_debug_start_end (debug_enabled, module, 	\
+				   __func__, "enter", "exit",	\
+				   nullptr)
 
 #endif /* COMMON_COMMON_DEBUG_H */
-- 
2.25.4