[PATCHv2] gdb: Rewrite argument handling for user-defined commands

[Andrew Burgess <andrew dot burgess at embecosm dot com>]

Here's a new version of the quoting patch which now uses single and
double quotes for quoting arguments.

I look forward to any feedback.

Eli - I suspect that the documentation changes would need some work,
but you should probably wait to review, as I suspect this patch will
change again before it can be merged.

Thanks,
Andrew

---

This commit rewrites argument passing for user-defined commands.  The
rewrite was inspired after this mailing list thread:

    https://sourceware.org/ml/gdb-patches/2018-08/msg00391.html

The summary is that it was felt that in order to pass arguments that
include whitespace, then single or double quotes should be used for
quoting the argument.

The problem is that currently, the quotes are included in the argument
that is passed into the user-defined command, so passing the argument
"1 + 1" will currently litterally pass "1 + 1" (including the quotes)
to GDB, which is no good if what you want to do is to pass an
expression.

This commit changes how quoting works so that the quotes are NOT now
included in the argument passed.  If the user wants to include quotes,
they would now need to use nested quotes, so "\"abc\"" will pass the
argument "abc".

It is also possible to use single quotes, so '"abc"' will also pass
the argument "abc".

As currently there's no documentation for how quoting works in
user-defined commands this commit adds documentation for the new
behaviour.

The big risk with this commit is that this does change how arguments
are passed to user-defined commands, and this might causes issues for
existing users.

gdb/ChangeLog:

	* cli/cli-script.c (user_args::m_command_line): Remove.
	(user_args::m_args): Change type.
	(user_args::user_args): Rewrite to build arguments into
	std::string.
	(user_args::insert_args): Update to take account of m_args type
	change.

gdb/doc/ChangeLog:

	* gdb.texinfo (Define): Additional documentation about argument
	syntax.

gdb/testsuite/ChangeLog:

	* gdb.base/commands.exp (user_defined_command_arg_quoting): New
	proc, which is added to the list of procs to call.
	* gdb.base/run.c (global_var): Defined global.
---
 gdb/ChangeLog                       |  9 ++++
 gdb/cli/cli-script.c                | 88 ++++++++++++++++++-------------------
 gdb/doc/ChangeLog                   |  5 +++
 gdb/doc/gdb.texinfo                 | 66 +++++++++++++++++++++++++---
 gdb/testsuite/ChangeLog             |  6 +++
 gdb/testsuite/gdb.base/commands.exp | 45 +++++++++++++++++++
 gdb/testsuite/gdb.base/run.c        |  3 ++
 7 files changed, 172 insertions(+), 50 deletions(-)

diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index 8496fb85e6f..f2110331765 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -78,12 +78,8 @@ private:
   user_args (const user_args &) =delete;
   user_args &operator= (const user_args &) =delete;
 
-  /* It is necessary to store a copy of the command line to ensure
-     that the arguments are not overwritten before they are used.  */
-  std::string m_command_line;
-
-  /* The arguments.  Each element points inside M_COMMAND_LINE.  */
-  std::vector<gdb::string_view> m_args;
+  /* The arguments.  Parsed from the LINE passed into the constructor.  */
+  std::vector<std::string> m_args;
 };
 
 /* The stack of arguments passed to user defined functions.  We need a
@@ -749,56 +745,58 @@ user_args::user_args (const char *command_line)
   if (command_line == NULL)
     return;
 
-  m_command_line = command_line;
-  p = m_command_line.c_str ();
+  p = command_line;
 
   while (*p)
     {
-      const char *start_arg;
-      int squote = 0;
-      int dquote = 0;
-      int bsquote = 0;
+      std::string arg;
+
+      bool bquote = false;
+      bool squote = false;
+      bool dquote = false;
 
       /* Strip whitespace.  */
-      while (*p == ' ' || *p == '\t')
+      while (isspace (*p))
 	p++;
 
-      /* P now points to an argument.  */
-      start_arg = p;
-
       /* Get to the end of this argument.  */
       while (*p)
 	{
-	  if (((*p == ' ' || *p == '\t')) && !squote && !dquote && !bsquote)
-	    break;
-	  else
-	    {
-	      if (bsquote)
-		bsquote = 0;
-	      else if (*p == '\\')
-		bsquote = 1;
-	      else if (squote)
-		{
-		  if (*p == '\'')
-		    squote = 0;
-		}
-	      else if (dquote)
-		{
-		  if (*p == '"')
-		    dquote = 0;
-		}
-	      else
-		{
-		  if (*p == '\'')
-		    squote = 1;
-		  else if (*p == '"')
-		    dquote = 1;
-		}
-	      p++;
-	    }
+          /* If we find whitespace and we're not inside a single or double
+             quote then we have found the end of this argument.  */
+          if (isspace (*p) && !(squote || dquote))
+            break;
+          else if (bquote)
+            bquote = 0;
+          else
+            {
+              /* If we're inside a single quote and we find another single
+                 quote then this is the end of the argument.  */
+              if (*p == '\'' && !dquote)
+                {
+                  ++p;
+                  squote = !squote;
+                  continue;
+                }
+
+              /* If we're inside a double quote and we find another double
+                 quote then this is the end of the argument.  */
+              if (*p == '"' && !squote)
+                {
+                  ++p;
+                  dquote = !dquote;
+                  continue;
+                }
+
+              if (*p == '\\' && !squote)
+                bquote = true;
+            }
+
+          arg += *p;
+          ++p;
 	}
 
-      m_args.emplace_back (start_arg, p - start_arg);
+      m_args.emplace_back (arg);
     }
 }
 
@@ -863,7 +861,7 @@ user_args::insert_args (const char *line) const
 	    error (_("Missing argument %ld in user function."), i);
 	  else
 	    {
-	      new_line.append (m_args[i].data (), m_args[i].length ());
+	      new_line.append (m_args[i]);
 	      line = tmp;
 	    }
 	}
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index f2d1155b4db..b159df3b217 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -25245,14 +25245,70 @@
 
 @noindent
 This defines the command @code{adder}, which prints the sum of
-its three arguments.  Note the arguments are text substitutions, so they may
-reference variables, use complex expressions, or even perform inferior
-functions calls.
+its three arguments.
+
+The arguments to user-defined commands are text substitutions, so they
+may reference variables, use complex expressions, or even perform
+inferior functions calls.  Each argument is separated with whitespace,
+so in the previous example three arguments were passed.  The following
+example also passes three arguments, though the arguments are more
+complex:
+
+@smallexample
+adder 10+1 10+2 10+3
+@end smallexample
+
+@noindent
+However, if whitespace were added around the @code{+} characters, then
+9 arguments would be passed, @code{adder} only uses the first 3 of
+these arguments, and the others would be silently ignored, for example:
+
+@smallexample
+adder 10 + 1 10 + 2 10 + 3
+@end smallexample
+
+Causes @value{GDBN} to try and evaluate the following, which is likely
+invalid:
+
+@smallexample
+print 10 + + + 1
+@end smallexample
+
+@noindent
+Arguments can be quoted with double (@code{"}) or single (@code{'})
+quotes.  These quotes are not passed through as part of the argument,
+so the complex arguments from the previous example can be written as:
+
+@smallexample
+adder '10 + 1' '10 + 2' '10 + 3'
+@end smallexample
+
+@noindent
+As the quotes are not passed through, then the previous example causes
+@value{GDBN} to evaluate:
+
+@smallexample
+print 10 + 1 + 10 + 2 + 10 + 3
+@end smallexample
+
+@noindent
+Outside of quotes, a backslash can be used to pass a quote as part of
+an argument, for example, @code{\'} will pass a single quote as an
+argument, and @code{\"} passes a double quote as an argument.
+
+Within double quotes a backslash can be used to pass a literal double
+quote, so @code{"\"abc\""} will pass the argument @code{"abc"}.
+
+Within single quotes a backslash does not escape a single quote, the
+next single quote always ends a single quoted argument, and
+backslashes within a single quoted argument are passed straight
+through, so @code{'abc\'} will pass the argument @code{abc\}.
 
 @cindex argument count in user-defined commands
 @cindex how many arguments (user-defined commands)
-In addition, @code{$argc} may be used to find out how many arguments have
-been passed.
+@noindent
+Within a user-defined command @code{$argc} may be used to find out how
+many arguments have been passed.
 
 @smallexample
 define adder
diff --git a/gdb/testsuite/gdb.base/commands.exp b/gdb/testsuite/gdb.base/commands.exp
index 52a22bb5ddc..4e398b84a95 100644
--- a/gdb/testsuite/gdb.base/commands.exp
+++ b/gdb/testsuite/gdb.base/commands.exp
@@ -1167,6 +1167,50 @@ proc_with_prefix backslash_in_multi_line_command_test {} {
     gdb_test "print 1" "" "run command"
 }
 
+proc_with_prefix user_defined_command_arg_quoting {} {
+    gdb_test_multiple "define show_args" "define show_args" {
+	-re "End with"  {
+	    pass "define show_args"
+	}
+    }
+
+    # This test should alternate between 0xdeadbeef and 0xfeedface two times.
+    gdb_test \
+	[multi_line_input \
+	     {printf "nargs=%d:", $argc} \
+	     {set $i = 0} \
+	     {while $i < $argc} \
+	     {printf " "} \
+	     {eval "echo '$arg%d'", $i} \
+	     {set $i = $i + 1} \
+	     {end} \
+	     {printf "\n"} \
+	     {end}] \
+	"" \
+	"enter commands"
+
+    gdb_test "show_args 1 2 3" \
+	"nargs=3: '1' '2' '3'"
+
+    gdb_test "show_args 1 '1 + 1' '1 + (1 + 1)'" \
+	"nargs=3: '1' '1 \\+ 1' '1 \\+ \\(1 \\+ 1\\)'"
+
+    gdb_test "show_args '{unsigned long long} &global_var'" \
+	"nargs=1: '{unsigned long long} &global_var'"
+
+    gdb_test "show_args '*((unsigned long long *) &global_var)'" \
+	"nargs=1: '\\*\\(\\(unsigned long long \\*\\) &global_var\\)'"
+
+    gdb_test "show_args '\"' \"'\" \"''\"" \
+	"nargs=3: '\"' ''' ''''"
+
+    gdb_test "show_args \\n a\\'b" \
+	"nargs=2: '\r\n' 'a'b'"
+
+    gdb_test "show_args \"This\\nIs\\nA\\nMulti Line\\nMessage" \
+	"nargs=1: 'This\r\nIs\r\nA\r\nMulti Line\r\nMessage'"
+}
+
 gdbvar_simple_if_test
 gdbvar_simple_while_test
 gdbvar_complex_if_while_test
@@ -1182,6 +1226,7 @@ user_defined_command_case_sensitivity
 user_defined_command_args_eval
 user_defined_command_args_stack_test
 user_defined_command_manyargs_test
+user_defined_command_arg_quoting
 watchpoint_command_test
 test_command_prompt_position
 deprecated_command_test
diff --git a/gdb/testsuite/gdb.base/run.c b/gdb/testsuite/gdb.base/run.c
index 614b018260d..d89bad78bb4 100644
--- a/gdb/testsuite/gdb.base/run.c
+++ b/gdb/testsuite/gdb.base/run.c
@@ -8,6 +8,9 @@
 
 #include "../lib/unbuffer_output.c"
 
+/* Used by commands.exp test script.  */
+volatile unsigned long long global_var = 34;
+
 int factorial (int);
 
 int
-- 
2.14.4