Expand keyword lexing intelligence in the linespec parser.

This patch changes the heuristic the linespec lexer uses to
    detect a keyword in the input stream.

    Currently, the heuristic is: a word is a keyword if it
    1) points to a string that is a keyword
    2) is followed by a non-identifier character

    This is strictly more correct than using whitespace. For example,
    it allows constructs such as "break foo if(i == 1)". However,
    find_condition_and_thread in breakpoint.c does not support this expanded
    usage. It requires whitespace to follow the keyword.

    The proposed new heuristic is: a word is a keyword if it
    1) points to a string that is a keyword
    2) is followed by whitespace
    3) is not followed by another keyword string followed by whitespace

    This additional complexity allows constructs such as
    "break thread thread 3" and "break thread 3".  In the former case,
    the actual location is a symbol named "thread" to be set on thread #3.
    In the later case, the location is NULL, i.e., the default location,
    to be set on thread #3.

    In order to pass all the new tests added here, I've also had to add a
    new feature to parse_breakpoint_sals, which expands recognition of the
    default location to keywords other than "if", which is the only keyword
    currently permitted with the default (NULL) location, but there is no
    reason to exclude other keywords.

    Consequently, it will be possible to use "break thread 1" or
    "break task 1".

    In addition to all of this, it is now possible to remove the keyword_ok
    state from the linespec parser.

    gdb/ChangeLog

    	* breakpoint.c (parse_breakpoint_sals): Use
    	linespec_lexer_lex_keyword to ascertain if the user specified
    	a NULL location.
    	* linespec.c [IF_KEYWORD_INDEX]: Define.
    	(linespec_lexer_lex_keyword): Export.
    	(struct ls_parser) <keyword_ok>: Remove.
    	A keyword is only a keyword if not followed by another keyword.
    	(linespec_lexer_lex_one): Remove keyword_ok handling.
    	Add comment explaining why the parsing stream is not advanced
    	when a keyword is seen.
    	(parse_linespec): Remove parser->keyword_ok.
    	* linespec.h (linespec_lexer_lex_keyword): Add declaration.

    gdb/testsuite/ChangeLog

    	* gdb.linespec/keywords.c: New file.
    	* gdb.linespec/keywords.exp: New file.

gdb/breakpoint.c

@@ -9335,8 +9335,7 @@ parse_breakpoint_sals (char **address,
 {
   /* If no arg given, or if first arg is 'if ', use the default
      breakpoint.  */
-  if ((*address) == NULL
+  if ((*address) == NULL || linespec_lexer_lex_keyword (*address))
-      || (startswith ((*address), "if") && isspace ((*address)[2])))
     {
       /* The last displayed codepoint, if it's valid, is our default breakpoint
          address.  */

gdb/linespec.c

@@ -246,6 +246,7 @@ typedef enum ls_token_type linespec_token_type;
 /* List of keywords  */
 
 static const char * const linespec_keywords[] = { "if", "thread", "task" };
+#define IF_KEYWORD_INDEX 0
 
 /* A token of the linespec lexer  */
 
@@ -290,11 +291,6 @@ struct ls_parser
   /* Is the entire linespec quote-enclosed?  */
   int is_quote_enclosed;
 
-  /* Is a keyword syntactically valid at this point?
-     In, e.g., "break thread thread 1", the leading "keyword" must not
-     be interpreted as such.  */
-  int keyword_ok;
-
   /* The state of the parse.  */
   struct linespec_state state;
 #define PARSER_STATE(PPTR) (&(PPTR)->state)
@@ -421,7 +417,7 @@ linespec_lexer_lex_number (linespec_parser *parser, linespec_token *tokenp)
 /* Does P represent one of the keywords?  If so, return
    the keyword.  If not, return NULL.  */
 
-static const char *
+const char *
 linespec_lexer_lex_keyword (const char *p)
 {
   int i;
@@ -433,13 +429,36 @@ linespec_lexer_lex_keyword (const char *p)
 	  int len = strlen (linespec_keywords[i]);
 
 	  /* If P begins with one of the keywords and the next
-	     character is not a valid identifier character,
+	     character is whitespace, we may have found a keyword.
-	     we have found a keyword.  */
+	     It is only a keyword if it is not followed by another
+	     keyword.  */
 	  if (strncmp (p, linespec_keywords[i], len) == 0
-	      && !(isalnum (p[len]) || p[len] == '_'))
+	      && isspace (p[len]))
+	    {
+	      int j;
+
+	      /* Special case: "if" ALWAYS stops the lexer, since it
+		 is not possible to predict what is going to appear in
+		 the condition, which can only be parsed after SaLs have
+		 been found.  */
+	      if (i != IF_KEYWORD_INDEX)
+		{
+		  p += len;
+		  p = skip_spaces_const (p);
+		  for (j = 0; j < ARRAY_SIZE (linespec_keywords); ++j)
+		    {
+		      int nextlen = strlen (linespec_keywords[j]);
+
+		      if (strncmp (p, linespec_keywords[j], nextlen) == 0
+			  && isspace (p[nextlen]))
+			return NULL;
+		    }
+		}
+
 	      return linespec_keywords[i];
 	    }
 	}
+    }
 
   return NULL;
 }
@@ -734,13 +753,16 @@ linespec_lexer_lex_one (linespec_parser *parser)
       PARSER_STREAM (parser) = skip_spaces_const (PARSER_STREAM (parser));
 
       /* Check for a keyword, they end the linespec.  */
-      keyword = NULL;
-      if (parser->keyword_ok)
       keyword = linespec_lexer_lex_keyword (PARSER_STREAM (parser));
       if (keyword != NULL)
 	{
 	  parser->lexer.current.type = LSTOKEN_KEYWORD;
 	  LS_TOKEN_KEYWORD (parser->lexer.current) = keyword;
+	  /* We do not advance the stream here intentionally:
+	     we would like lexing to stop when a keyword is seen.
+
+	     PARSER_STREAM (parser) +=  strlen (keyword);  */
+
 	  return parser->lexer.current;
 	}
 
@@ -2175,10 +2197,6 @@ parse_linespec (linespec_parser *parser, const char **argptr)
 	}
     }
 
-  /* A keyword at the start cannot be interpreted as such.
-     Consider "b thread thread 42".  */
-  parser->keyword_ok = 0;
-
   parser->lexer.saved_arg = *argptr;
   parser->lexer.stream = argptr;
 
@@ -2250,9 +2268,6 @@ parse_linespec (linespec_parser *parser, const char **argptr)
   else if (token.type != LSTOKEN_STRING && token.type != LSTOKEN_NUMBER)
     unexpected_linespec_error (parser);
 
-  /* Now we can recognize keywords.  */
-  parser->keyword_ok = 1;
-
   /* Shortcut: If the next token is not LSTOKEN_COLON, we know that
      this token cannot represent a filename.  */
   token = linespec_lexer_peek_token (parser);

gdb/linespec.h

@@ -152,4 +152,8 @@ extern struct symtabs_and_lines decode_line_with_current_source (char *, int);
 
 extern struct symtabs_and_lines decode_line_with_last_displayed (char *, int);
 
+/* Does P represent one of the keywords?  If so, return
+   the keyword.  If not, return NULL.  */
+
+extern const char *linespec_lexer_lex_keyword (const char *p);
 #endif /* defined (LINESPEC_H) */

gdb/testsuite/gdb.linespec/keywords.c

@@ -0,0 +1,36 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2015 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+static int
+task (int task)
+{
+  return task - 1;
+}
+
+static int
+thread (int thread)
+{
+  return task (thread) + 1;
+}
+
+int
+main (void)
+{
+  int x = 0;
+  x += thread (0);
+  return x;
+}

gdb/testsuite/gdb.linespec/keywords.exp

@@ -0,0 +1,77 @@
+# Copyright 2015 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test keyword parsing in the linespec parser.
+
+standard_testfile
+set exefile $testfile
+
+if {[prepare_for_testing $testfile $exefile $srcfile {debug}]} {
+    return -1
+}
+
+if ![runto_main] {
+    fail "Can't run to main"
+    return 0
+}
+
+# Turn off pending breakpoints to facilitate testing errors.
+gdb_test_no_output "set breakpoint pending off"
+
+# The linespec lexer ignores the language setting when lexing
+# keywords.
+gdb_test "break if" "Function \"if\" not defined."
+gdb_breakpoint "thread" "message"
+gdb_breakpoint "task" "message"
+
+# The lexer should prune any trailing whitesapce, so the expected
+# outcome of the following tests should be the same as the previous
+# tests.
+with_test_prefix "trailing whitespace" {
+    gdb_test "break if " "Function \"if\" not defined."
+    gdb_breakpoint "thread " "message"
+    gdb_breakpoint "task " "message"
+}
+
+# With a single keyword specified first in the location,
+# we assume we have a NULL location, i.e., the actual location
+# of the event is the current default location.
+#
+# break if XX --> okay if XX is a valid expression
+# (the lexer cannot know whether the expression is valid or not)
+# break {thread,task} NUMBER --> invalid thread/task
+# break {thread,task} STUFF --> "junk" after keyword (STUFF is not numeric)
+gdb_test "break thread 123" "Unknown thread 123\\."
+gdb_test "break thread foo" "Junk after thread keyword\\."
+gdb_test "break task 123" "Unknown task 123\\."
+gdb_test "break task foo" "Junk after task keyword\\."
+gdb_breakpoint "thread if 0" "message"
+
+# These are also NULL locations, but using a subsequent keyword
+# as the "junk".
+gdb_test "break thread thread" "Junk after thread keyword\\."
+gdb_test "break thread task" "Junk after thread keyword\\."
+gdb_test "break thread if" "Junk after thread keyword\\."
+gdb_test "break task task" "Junk after task keyword\\."
+gdb_test "break task thread" "Junk after task keyword\\."
+gdb_test "break task if" "Junk after task keyword\\."
+
+# Test locations containing keyword followed by keyword.
+gdb_test "break thread thread 123" "Unknown thread 123\\."
+gdb_test "break task task 123" "Unknown task 123\\."
+
+# Test NULL location with valid conditional containing a keyword.
+gdb_breakpoint "thread if thread == 0"
+gdb_breakpoint "task if task == 0"