Expand keyword lexing intelligence in the linespec parser.

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 0c000f2..e35878b 100644
--- a/gdb/breakpoint.c
+++ b/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
-      || (startswith ((*address), "if") && isspace ((*address)[2])))
+  if ((*address) == NULL || linespec_lexer_lex_keyword (*address))
     {
       /* The last displayed codepoint, if it's valid, is our default breakpoint
          address.  */
diff --git a/gdb/linespec.c b/gdb/linespec.c
index 9ec4a5e..90c07a2 100644
--- a/gdb/linespec.c
+++ b/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;
@@ -433,11 +429,34 @@  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,
-	     we have found a keyword.  */
+	     character is whitespace, we may 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] == '_'))
-	    return linespec_keywords[i];
+	      && 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];
+	    }
 	}
     }
 
@@ -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));
+      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);
diff --git a/gdb/linespec.h b/gdb/linespec.h
index 5520afa..7e66024 100644
--- a/gdb/linespec.h
+++ b/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) */
diff --git a/gdb/testsuite/gdb.linespec/keywords.c b/gdb/testsuite/gdb.linespec/keywords.c
new file mode 100644
index 0000000..de2db63
--- /dev/null
+++ b/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;
+}
diff --git a/gdb/testsuite/gdb.linespec/keywords.exp b/gdb/testsuite/gdb.linespec/keywords.exp
new file mode 100644
index 0000000..312fc92
--- /dev/null
+++ b/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"