[RFA] Remove a cleanup from parse_expression_for_completion

[RFA] Remove a cleanup from parse_expression_for_completion

[Tom Tromey]

This removes a cleanup from parse_expression_for_completion, by
changing various expression-completion functions to use std::string
rather than explicit malloc+free.

Regression tested by the buildbot.

gdb/ChangeLog
2018-02-16  Tom Tromey  <tom@tromey.com>

	* value.h: (extract_field_op): Update.
	* eval.c (extract_field_op): Return a const char *.
	* expression.h (parse_expression_for_completion): Update.
	* completer.c (complete_expression): Update.
	(add_struct_fields): Make fieldname const.
	* parse.c (expout_completion_name): Now a std::string.
	(mark_completion_tag, parse_exp_in_context_1): Update.
	(parse_expression_for_completion): Change "name" to std::string*.
---
 gdb/ChangeLog    | 11 +++++++++++
 gdb/completer.c  | 22 ++++++++--------------
 gdb/eval.c       |  2 +-
 gdb/expression.h |  3 ++-
 gdb/parse.c      | 20 +++++++-------------
 gdb/value.h      |  2 +-
 6 files changed, 30 insertions(+), 30 deletions(-)

diff --git a/gdb/completer.c b/gdb/completer.c
index a71bd368ff..c0d5778867 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -962,7 +962,7 @@ location_completer_handle_brkchars (struct cmd_list_element *ignore,
 
 static void
 add_struct_fields (struct type *type, completion_list &output,
-		   char *fieldname, int namelen)
+		   const char *fieldname, int namelen)
 {
   int i;
   int computed_type_name = 0;
@@ -1016,12 +1016,11 @@ complete_expression (completion_tracker &tracker,
 		     const char *text, const char *word)
 {
   struct type *type = NULL;
-  char *fieldname;
+  std::string fieldname;
   enum type_code code = TYPE_CODE_UNDEF;
 
   /* Perform a tentative parse of the expression, to see whether a
      field completion is required.  */
-  fieldname = NULL;
   TRY
     {
       type = parse_expression_for_completion (text, &fieldname, &code);
@@ -1032,7 +1031,7 @@ complete_expression (completion_tracker &tracker,
     }
   END_CATCH
 
-  if (fieldname && type)
+  if (!fieldname.empty () && type)
     {
       for (;;)
 	{
@@ -1045,25 +1044,20 @@ complete_expression (completion_tracker &tracker,
       if (TYPE_CODE (type) == TYPE_CODE_UNION
 	  || TYPE_CODE (type) == TYPE_CODE_STRUCT)
 	{
-	  int flen = strlen (fieldname);
 	  completion_list result;
 
-	  add_struct_fields (type, result, fieldname, flen);
-	  xfree (fieldname);
+	  add_struct_fields (type, result, fieldname.c_str (),
+			     fieldname.size ());
 	  tracker.add_completions (std::move (result));
 	  return;
 	}
     }
-  else if (fieldname && code != TYPE_CODE_UNDEF)
+  else if (!fieldname.empty () && code != TYPE_CODE_UNDEF)
     {
-      struct cleanup *cleanup = make_cleanup (xfree, fieldname);
-
-      collect_symbol_completion_matches_type (tracker, fieldname, fieldname,
-					      code);
-      do_cleanups (cleanup);
+      collect_symbol_completion_matches_type (tracker, fieldname.c_str (),
+					      fieldname.c_str (), code);
       return;
     }
-  xfree (fieldname);
 
   complete_files_symbols (tracker, text, word);
 }
diff --git a/gdb/eval.c b/gdb/eval.c
index 6f74c41b9f..4899011a58 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -272,7 +272,7 @@ fetch_subexp_value (struct expression *exp, int *pc, struct value **valp,
    subexpression of the left-hand-side of the dereference.  This is
    used when completing field names.  */
 
-char *
+const char *
 extract_field_op (struct expression *exp, int *subexp)
 {
   int tem;
diff --git a/gdb/expression.h b/gdb/expression.h
index 030f2f08e7..f9b5b1e820 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -101,7 +101,8 @@ extern expression_up parse_expression (const char *);
 extern expression_up parse_expression_with_language (const char *string,
 						     enum language lang);
 
-extern struct type *parse_expression_for_completion (const char *, char **,
+extern struct type *parse_expression_for_completion (const char *,
+						     std::string *,
 						     enum type_code *);
 
 extern expression_up parse_exp_1 (const char **, CORE_ADDR pc,
diff --git a/gdb/parse.c b/gdb/parse.c
index e3f1306a17..1d1ede4f56 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -88,7 +88,7 @@ static int expout_last_struct = -1;
 static enum type_code expout_tag_completion_type = TYPE_CODE_UNDEF;
 
 /* The token for tagged type name completion.  */
-static char *expout_completion_name;
+static std::string expout_completion_name;
 
 \f
 static unsigned int expressiondebug = 0;
@@ -569,15 +569,13 @@ mark_completion_tag (enum type_code tag, const char *ptr, int length)
 {
   gdb_assert (parse_completion
 	      && expout_tag_completion_type == TYPE_CODE_UNDEF
-	      && expout_completion_name == NULL
+	      && expout_completion_name.empty ()
 	      && expout_last_struct == -1);
   gdb_assert (tag == TYPE_CODE_UNION
 	      || tag == TYPE_CODE_STRUCT
 	      || tag == TYPE_CODE_ENUM);
   expout_tag_completion_type = tag;
-  expout_completion_name = (char *) xmalloc (length + 1);
-  memcpy (expout_completion_name, ptr, length);
-  expout_completion_name[length] = '\0';
+  expout_completion_name = std::string (ptr, length);
 }
 
 \f
@@ -1137,8 +1135,7 @@ parse_exp_in_context_1 (const char **stringptr, CORE_ADDR pc,
   type_stack.depth = 0;
   expout_last_struct = -1;
   expout_tag_completion_type = TYPE_CODE_UNDEF;
-  xfree (expout_completion_name);
-  expout_completion_name = NULL;
+  expout_completion_name = "";
 
   comma_terminates = comma;
 
@@ -1281,7 +1278,7 @@ parse_expression_with_language (const char *string, enum language lang)
    *NAME must be freed by the caller.  */
 
 struct type *
-parse_expression_for_completion (const char *string, char **name,
+parse_expression_for_completion (const char *string, std::string *name,
 				 enum type_code *code)
 {
   expression_up exp;
@@ -1306,8 +1303,7 @@ parse_expression_for_completion (const char *string, char **name,
   if (expout_tag_completion_type != TYPE_CODE_UNDEF)
     {
       *code = expout_tag_completion_type;
-      *name = expout_completion_name;
-      expout_completion_name = NULL;
+      *name = std::move (expout_completion_name);
       return NULL;
     }
 
@@ -1315,14 +1311,12 @@ parse_expression_for_completion (const char *string, char **name,
     return NULL;
 
   *name = extract_field_op (exp.get (), &subexp);
-  if (!*name)
+  if (name->empty ())
     return NULL;
 
   /* This might throw an exception.  If so, we want to let it
      propagate.  */
   val = evaluate_subexpression_type (exp.get (), subexp);
-  /* (*NAME) is a part of the EXP memory block freed below.  */
-  *name = xstrdup (*name);
 
   return value_type (val);
 }
diff --git a/gdb/value.h b/gdb/value.h
index e0ea22d4e5..5676d245b9 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -889,7 +889,7 @@ extern void fetch_subexp_value (struct expression *exp, int *pc,
 				struct value **val_chain,
 				int preserve_errors);
 
-extern char *extract_field_op (struct expression *exp, int *subexp);
+extern const char *extract_field_op (struct expression *exp, int *subexp);
 
 extern struct value *evaluate_subexp_with_coercion (struct expression *,
 						    int *, enum noside);
-- 
2.13.6

Re: [RFA] Remove a cleanup from parse_expression_for_completion

[Simon Marchi]

On 2018-02-16 18:02, Tom Tromey wrote:
> This removes a cleanup from parse_expression_for_completion, by
> changing various expression-completion functions to use std::string
> rather than explicit malloc+free.

That looks good to me.  You can go a bit further if you want and make 
add_struct_fields take a const std::string reference as well.

Simon

Re: [RFA] Remove a cleanup from parse_expression_for_completion

[Tom Tromey]

>>>>> "Simon" == Simon Marchi <simon.marchi@polymtl.ca> writes:

Simon> On 2018-02-16 18:02, Tom Tromey wrote:
>> This removes a cleanup from parse_expression_for_completion, by
>> changing various expression-completion functions to use std::string
>> rather than explicit malloc+free.

Simon> That looks good to me.  You can go a bit further if you want and make
Simon> add_struct_fields take a const std::string reference as well.

Here's an updated patch.  Let me know what you think.

Tom

commit a922232c1fc11a5f932140d8dfa8fcea963cecad
Author: Tom Tromey <tom@tromey.com>
Date:   Thu Feb 15 22:41:03 2018 -0700

    Remove a cleanup from parse_expression_for_completion
    
    This removes a cleanup from parse_expression_for_completion, by
    changing various expression-completion functions to use std::string
    rather than explicit malloc+free.
    
    Regression tested by the buildbot.
    
    gdb/ChangeLog
    2018-02-19  Tom Tromey  <tom@tromey.com>
    
            * value.h: (extract_field_op): Update.
            * eval.c (extract_field_op): Return a const char *.
            * expression.h (parse_expression_for_completion): Update.
            * completer.c (complete_expression): Update.
            (add_struct_fields): Make fieldname std::string.  Remove namelen.
            * parse.c (expout_completion_name): Now a std::string.
            (mark_completion_tag, parse_exp_in_context_1): Update.
            (parse_expression_for_completion): Change "name" to std::string*.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cd8ef6653d..ac2840d0cb 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+2018-02-19  Tom Tromey  <tom@tromey.com>
+
+	* value.h: (extract_field_op): Update.
+	* eval.c (extract_field_op): Return a const char *.
+	* expression.h (parse_expression_for_completion): Update.
+	* completer.c (complete_expression): Update.
+	(add_struct_fields): Make fieldname std::string.  Remove namelen.
+	* parse.c (expout_completion_name): Now a std::string.
+	(mark_completion_tag, parse_exp_in_context_1): Update.
+	(parse_expression_for_completion): Change "name" to std::string*.
+
 2018-02-19  Alan Hayward  <alan.hayward@arm.com>
 
 	* Makefile.in: (COMMON_SFILES): Add common/*.c files.
diff --git a/gdb/completer.c b/gdb/completer.c
index a71bd368ff..6d6d52a109 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -962,7 +962,7 @@ location_completer_handle_brkchars (struct cmd_list_element *ignore,
 
 static void
 add_struct_fields (struct type *type, completion_list &output,
-		   char *fieldname, int namelen)
+		   const std::string &fieldname)
 {
   int i;
   int computed_type_name = 0;
@@ -973,20 +973,20 @@ add_struct_fields (struct type *type, completion_list &output,
     {
       if (i < TYPE_N_BASECLASSES (type))
 	add_struct_fields (TYPE_BASECLASS (type, i),
-			   output, fieldname, namelen);
+			   output, fieldname);
       else if (TYPE_FIELD_NAME (type, i))
 	{
 	  if (TYPE_FIELD_NAME (type, i)[0] != '\0')
 	    {
 	      if (! strncmp (TYPE_FIELD_NAME (type, i), 
-			     fieldname, namelen))
+			     fieldname.c_str (), fieldname.size ()))
 		output.emplace_back (xstrdup (TYPE_FIELD_NAME (type, i)));
 	    }
 	  else if (TYPE_CODE (TYPE_FIELD_TYPE (type, i)) == TYPE_CODE_UNION)
 	    {
 	      /* Recurse into anonymous unions.  */
 	      add_struct_fields (TYPE_FIELD_TYPE (type, i),
-				 output, fieldname, namelen);
+				 output, fieldname);
 	    }
 	}
     }
@@ -995,7 +995,7 @@ add_struct_fields (struct type *type, completion_list &output,
     {
       const char *name = TYPE_FN_FIELDLIST_NAME (type, i);
 
-      if (name && ! strncmp (name, fieldname, namelen))
+      if (name && ! strncmp (name, fieldname.c_str (), fieldname.size ()))
 	{
 	  if (!computed_type_name)
 	    {
@@ -1016,12 +1016,11 @@ complete_expression (completion_tracker &tracker,
 		     const char *text, const char *word)
 {
   struct type *type = NULL;
-  char *fieldname;
+  std::string fieldname;
   enum type_code code = TYPE_CODE_UNDEF;
 
   /* Perform a tentative parse of the expression, to see whether a
      field completion is required.  */
-  fieldname = NULL;
   TRY
     {
       type = parse_expression_for_completion (text, &fieldname, &code);
@@ -1032,7 +1031,7 @@ complete_expression (completion_tracker &tracker,
     }
   END_CATCH
 
-  if (fieldname && type)
+  if (!fieldname.empty () && type)
     {
       for (;;)
 	{
@@ -1045,25 +1044,19 @@ complete_expression (completion_tracker &tracker,
       if (TYPE_CODE (type) == TYPE_CODE_UNION
 	  || TYPE_CODE (type) == TYPE_CODE_STRUCT)
 	{
-	  int flen = strlen (fieldname);
 	  completion_list result;
 
-	  add_struct_fields (type, result, fieldname, flen);
-	  xfree (fieldname);
+	  add_struct_fields (type, result, fieldname);
 	  tracker.add_completions (std::move (result));
 	  return;
 	}
     }
-  else if (fieldname && code != TYPE_CODE_UNDEF)
+  else if (!fieldname.empty () && code != TYPE_CODE_UNDEF)
     {
-      struct cleanup *cleanup = make_cleanup (xfree, fieldname);
-
-      collect_symbol_completion_matches_type (tracker, fieldname, fieldname,
-					      code);
-      do_cleanups (cleanup);
+      collect_symbol_completion_matches_type (tracker, fieldname.c_str (),
+					      fieldname.c_str (), code);
       return;
     }
-  xfree (fieldname);
 
   complete_files_symbols (tracker, text, word);
 }
diff --git a/gdb/eval.c b/gdb/eval.c
index 6f74c41b9f..4899011a58 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -272,7 +272,7 @@ fetch_subexp_value (struct expression *exp, int *pc, struct value **valp,
    subexpression of the left-hand-side of the dereference.  This is
    used when completing field names.  */
 
-char *
+const char *
 extract_field_op (struct expression *exp, int *subexp)
 {
   int tem;
diff --git a/gdb/expression.h b/gdb/expression.h
index 030f2f08e7..f9b5b1e820 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -101,7 +101,8 @@ extern expression_up parse_expression (const char *);
 extern expression_up parse_expression_with_language (const char *string,
 						     enum language lang);
 
-extern struct type *parse_expression_for_completion (const char *, char **,
+extern struct type *parse_expression_for_completion (const char *,
+						     std::string *,
 						     enum type_code *);
 
 extern expression_up parse_exp_1 (const char **, CORE_ADDR pc,
diff --git a/gdb/parse.c b/gdb/parse.c
index e3f1306a17..4c09ebec7d 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -88,7 +88,7 @@ static int expout_last_struct = -1;
 static enum type_code expout_tag_completion_type = TYPE_CODE_UNDEF;
 
 /* The token for tagged type name completion.  */
-static char *expout_completion_name;
+static std::string expout_completion_name;
 
 \f
 static unsigned int expressiondebug = 0;
@@ -569,15 +569,13 @@ mark_completion_tag (enum type_code tag, const char *ptr, int length)
 {
   gdb_assert (parse_completion
 	      && expout_tag_completion_type == TYPE_CODE_UNDEF
-	      && expout_completion_name == NULL
+	      && expout_completion_name.empty ()
 	      && expout_last_struct == -1);
   gdb_assert (tag == TYPE_CODE_UNION
 	      || tag == TYPE_CODE_STRUCT
 	      || tag == TYPE_CODE_ENUM);
   expout_tag_completion_type = tag;
-  expout_completion_name = (char *) xmalloc (length + 1);
-  memcpy (expout_completion_name, ptr, length);
-  expout_completion_name[length] = '\0';
+  expout_completion_name = std::string (ptr, length);
 }
 
 \f
@@ -1137,8 +1135,7 @@ parse_exp_in_context_1 (const char **stringptr, CORE_ADDR pc,
   type_stack.depth = 0;
   expout_last_struct = -1;
   expout_tag_completion_type = TYPE_CODE_UNDEF;
-  xfree (expout_completion_name);
-  expout_completion_name = NULL;
+  expout_completion_name.clear ();
 
   comma_terminates = comma;
 
@@ -1277,11 +1274,10 @@ parse_expression_with_language (const char *string, enum language lang)
    reference; furthermore, if the parsing ends in the field name,
    return the field name in *NAME.  If the parsing ends in the middle
    of a field reference, but the reference is somehow invalid, throw
-   an exception.  In all other cases, return NULL.  Returned non-NULL
-   *NAME must be freed by the caller.  */
+   an exception.  In all other cases, return NULL.  */
 
 struct type *
-parse_expression_for_completion (const char *string, char **name,
+parse_expression_for_completion (const char *string, std::string *name,
 				 enum type_code *code)
 {
   expression_up exp;
@@ -1306,23 +1302,21 @@ parse_expression_for_completion (const char *string, char **name,
   if (expout_tag_completion_type != TYPE_CODE_UNDEF)
     {
       *code = expout_tag_completion_type;
-      *name = expout_completion_name;
-      expout_completion_name = NULL;
+      *name = std::move (expout_completion_name);
       return NULL;
     }
 
   if (expout_last_struct == -1)
     return NULL;
 
-  *name = extract_field_op (exp.get (), &subexp);
-  if (!*name)
+  const char *fieldname = extract_field_op (exp.get (), &subexp);
+  if (fieldname == NULL)
     return NULL;
 
+  *name = fieldname;
   /* This might throw an exception.  If so, we want to let it
      propagate.  */
   val = evaluate_subexpression_type (exp.get (), subexp);
-  /* (*NAME) is a part of the EXP memory block freed below.  */
-  *name = xstrdup (*name);
 
   return value_type (val);
 }
diff --git a/gdb/value.h b/gdb/value.h
index e0ea22d4e5..5676d245b9 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -889,7 +889,7 @@ extern void fetch_subexp_value (struct expression *exp, int *pc,
 				struct value **val_chain,
 				int preserve_errors);
 
-extern char *extract_field_op (struct expression *exp, int *subexp);
+extern const char *extract_field_op (struct expression *exp, int *subexp);
 
 extern struct value *evaluate_subexp_with_coercion (struct expression *,
 						    int *, enum noside);

Re: [RFA] Remove a cleanup from parse_expression_for_completion

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:

Tom> Here's an updated patch.  Let me know what you think.

Actually, this patch is wrong, and I didn't realize it until this
revision.  There was a failure in the buildbot report that I didn't
notice in the noise :(

There is a case in here where the NULL/empty string distinction matters.
So I think we can't use std::string but must instead use
unique_xmalloc_ptr.  I'll update the patch.

Tom

Re: [RFA] Remove a cleanup from parse_expression_for_completion

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:

Tom> There is a case in here where the NULL/empty string distinction matters.
Tom> So I think we can't use std::string but must instead use
Tom> unique_xmalloc_ptr.  I'll update the patch.

Here's the new version.  Re-tested on the buildbot & I looked more
carefully at the results this time; also I tried all the
completion-related tests locally as well.

Tom

commit 3de98da217150149d26dadee2c0ca9825463adda
Author: Tom Tromey <tom@tromey.com>
Date:   Thu Feb 15 22:41:03 2018 -0700

    Remove a cleanup from parse_expression_for_completion
    
    This removes a cleanup from parse_expression_for_completion, by
    changing various expression-completion functions to use
    gdb::unique_xmalloc_ptry rather than explicit malloc+free.
    
    Regression tested by the buildbot.
    
    gdb/ChangeLog
    2018-02-19  Tom Tromey  <tom@tromey.com>
    
            * value.h: (extract_field_op): Update.
            * eval.c (extract_field_op): Return a const char *.
            * expression.h (parse_expression_for_completion): Update.
            * completer.c (complete_expression): Update.
            (add_struct_fields): Make fieldname const.
            * parse.c (expout_completion_name): Now a unique_xmalloc_ptr.
            (mark_completion_tag, parse_exp_in_context_1): Update.
            (parse_expression_for_completion): Change "name" to
            unique_xmalloc_ptr*.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cd8ef6653d..ca660163fa 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,15 @@
+2018-02-19  Tom Tromey  <tom@tromey.com>
+
+	* value.h: (extract_field_op): Update.
+	* eval.c (extract_field_op): Return a const char *.
+	* expression.h (parse_expression_for_completion): Update.
+	* completer.c (complete_expression): Update.
+	(add_struct_fields): Make fieldname const.
+	* parse.c (expout_completion_name): Now a unique_xmalloc_ptr.
+	(mark_completion_tag, parse_exp_in_context_1): Update.
+	(parse_expression_for_completion): Change "name" to
+	unique_xmalloc_ptr*.
+
 2018-02-19  Alan Hayward  <alan.hayward@arm.com>
 
 	* Makefile.in: (COMMON_SFILES): Add common/*.c files.
diff --git a/gdb/completer.c b/gdb/completer.c
index a71bd368ff..4de1bcff32 100644
--- a/gdb/completer.c
+++ b/gdb/completer.c
@@ -962,7 +962,7 @@ location_completer_handle_brkchars (struct cmd_list_element *ignore,
 
 static void
 add_struct_fields (struct type *type, completion_list &output,
-		   char *fieldname, int namelen)
+		   const char *fieldname, int namelen)
 {
   int i;
   int computed_type_name = 0;
@@ -1016,12 +1016,11 @@ complete_expression (completion_tracker &tracker,
 		     const char *text, const char *word)
 {
   struct type *type = NULL;
-  char *fieldname;
+  gdb::unique_xmalloc_ptr<char> fieldname;
   enum type_code code = TYPE_CODE_UNDEF;
 
   /* Perform a tentative parse of the expression, to see whether a
      field completion is required.  */
-  fieldname = NULL;
   TRY
     {
       type = parse_expression_for_completion (text, &fieldname, &code);
@@ -1032,7 +1031,7 @@ complete_expression (completion_tracker &tracker,
     }
   END_CATCH
 
-  if (fieldname && type)
+  if (fieldname != nullptr && type)
     {
       for (;;)
 	{
@@ -1045,25 +1044,20 @@ complete_expression (completion_tracker &tracker,
       if (TYPE_CODE (type) == TYPE_CODE_UNION
 	  || TYPE_CODE (type) == TYPE_CODE_STRUCT)
 	{
-	  int flen = strlen (fieldname);
 	  completion_list result;
 
-	  add_struct_fields (type, result, fieldname, flen);
-	  xfree (fieldname);
+	  add_struct_fields (type, result, fieldname.get (),
+			     strlen (fieldname.get ()));
 	  tracker.add_completions (std::move (result));
 	  return;
 	}
     }
-  else if (fieldname && code != TYPE_CODE_UNDEF)
+  else if (fieldname != nullptr && code != TYPE_CODE_UNDEF)
     {
-      struct cleanup *cleanup = make_cleanup (xfree, fieldname);
-
-      collect_symbol_completion_matches_type (tracker, fieldname, fieldname,
-					      code);
-      do_cleanups (cleanup);
+      collect_symbol_completion_matches_type (tracker, fieldname.get (),
+					      fieldname.get (), code);
       return;
     }
-  xfree (fieldname);
 
   complete_files_symbols (tracker, text, word);
 }
diff --git a/gdb/eval.c b/gdb/eval.c
index 6f74c41b9f..4899011a58 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -272,7 +272,7 @@ fetch_subexp_value (struct expression *exp, int *pc, struct value **valp,
    subexpression of the left-hand-side of the dereference.  This is
    used when completing field names.  */
 
-char *
+const char *
 extract_field_op (struct expression *exp, int *subexp)
 {
   int tem;
diff --git a/gdb/expression.h b/gdb/expression.h
index 030f2f08e7..59a0898805 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -101,7 +101,8 @@ extern expression_up parse_expression (const char *);
 extern expression_up parse_expression_with_language (const char *string,
 						     enum language lang);
 
-extern struct type *parse_expression_for_completion (const char *, char **,
+extern struct type *parse_expression_for_completion (const char *,
+						     gdb::unique_xmalloc_ptr<char> *,
 						     enum type_code *);
 
 extern expression_up parse_exp_1 (const char **, CORE_ADDR pc,
diff --git a/gdb/parse.c b/gdb/parse.c
index e3f1306a17..3abb9d4219 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -88,7 +88,7 @@ static int expout_last_struct = -1;
 static enum type_code expout_tag_completion_type = TYPE_CODE_UNDEF;
 
 /* The token for tagged type name completion.  */
-static char *expout_completion_name;
+static gdb::unique_xmalloc_ptr<char> expout_completion_name;
 
 \f
 static unsigned int expressiondebug = 0;
@@ -575,9 +575,7 @@ mark_completion_tag (enum type_code tag, const char *ptr, int length)
 	      || tag == TYPE_CODE_STRUCT
 	      || tag == TYPE_CODE_ENUM);
   expout_tag_completion_type = tag;
-  expout_completion_name = (char *) xmalloc (length + 1);
-  memcpy (expout_completion_name, ptr, length);
-  expout_completion_name[length] = '\0';
+  expout_completion_name.reset (xstrndup (ptr, length));
 }
 
 \f
@@ -1137,8 +1135,7 @@ parse_exp_in_context_1 (const char **stringptr, CORE_ADDR pc,
   type_stack.depth = 0;
   expout_last_struct = -1;
   expout_tag_completion_type = TYPE_CODE_UNDEF;
-  xfree (expout_completion_name);
-  expout_completion_name = NULL;
+  expout_completion_name.reset ();
 
   comma_terminates = comma;
 
@@ -1277,11 +1274,11 @@ parse_expression_with_language (const char *string, enum language lang)
    reference; furthermore, if the parsing ends in the field name,
    return the field name in *NAME.  If the parsing ends in the middle
    of a field reference, but the reference is somehow invalid, throw
-   an exception.  In all other cases, return NULL.  Returned non-NULL
-   *NAME must be freed by the caller.  */
+   an exception.  In all other cases, return NULL.  */
 
 struct type *
-parse_expression_for_completion (const char *string, char **name,
+parse_expression_for_completion (const char *string,
+				 gdb::unique_xmalloc_ptr<char> *name,
 				 enum type_code *code)
 {
   expression_up exp;
@@ -1306,23 +1303,24 @@ parse_expression_for_completion (const char *string, char **name,
   if (expout_tag_completion_type != TYPE_CODE_UNDEF)
     {
       *code = expout_tag_completion_type;
-      *name = expout_completion_name;
-      expout_completion_name = NULL;
+      *name = std::move (expout_completion_name);
       return NULL;
     }
 
   if (expout_last_struct == -1)
     return NULL;
 
-  *name = extract_field_op (exp.get (), &subexp);
-  if (!*name)
-    return NULL;
+  const char *fieldname = extract_field_op (exp.get (), &subexp);
+  if (fieldname == NULL)
+    {
+      name->reset ();
+      return NULL;
+    }
 
+  name->reset (xstrdup (fieldname));
   /* This might throw an exception.  If so, we want to let it
      propagate.  */
   val = evaluate_subexpression_type (exp.get (), subexp);
-  /* (*NAME) is a part of the EXP memory block freed below.  */
-  *name = xstrdup (*name);
 
   return value_type (val);
 }
diff --git a/gdb/value.h b/gdb/value.h
index e0ea22d4e5..5676d245b9 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -889,7 +889,7 @@ extern void fetch_subexp_value (struct expression *exp, int *pc,
 				struct value **val_chain,
 				int preserve_errors);
 
-extern char *extract_field_op (struct expression *exp, int *subexp);
+extern const char *extract_field_op (struct expression *exp, int *subexp);
 
 extern struct value *evaluate_subexp_with_coercion (struct expression *,
 						    int *, enum noside);

Re: [RFA] Remove a cleanup from parse_expression_for_completion

[Simon Marchi]

On 2018-02-20 03:23 PM, Tom Tromey wrote:
>>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:
> 
> Tom> There is a case in here where the NULL/empty string distinction matters.
> Tom> So I think we can't use std::string but must instead use
> Tom> unique_xmalloc_ptr.  I'll update the patch.

Woops!

> diff --git a/gdb/expression.h b/gdb/expression.h
> index 030f2f08e7..59a0898805 100644
> --- a/gdb/expression.h
> +++ b/gdb/expression.h
> @@ -101,7 +101,8 @@ extern expression_up parse_expression (const char *);
>  extern expression_up parse_expression_with_language (const char *string,
>  						     enum language lang);
>  
> -extern struct type *parse_expression_for_completion (const char *, char **,
> +extern struct type *parse_expression_for_completion (const char *,
> +						     gdb::unique_xmalloc_ptr<char> *,

This line is now too long.

Otherwise it looks good to me.

Simon