[PATCH] Add a string_view version of startswith

["Christian Biesinger via gdb-patches" <gdb-patches@sourceware.org>]

[Thanks Pedro, both comments are fixed now. Note that this patch depends on
https://sourceware.org/ml/gdb-patches/2019-10/msg00032.html]

Makes sure that the string is longer than prefix, so that strncmp will
do the right thing even if the string is not null-terminated.

For use in my string_view conversion patch:
https://sourceware.org/ml/gdb-patches/2019-10/msg00030.html

gdb/ChangeLog:

2019-10-01  Christian Biesinger  <cbiesinger@google.com>

	* gdbsupport/common-utils.h (startswith): Add an overloaded version
	that takes gdb::string_view arguments.
---
 gdb/gdbsupport/common-utils.h | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/gdb/gdbsupport/common-utils.h b/gdb/gdbsupport/common-utils.h
index a5312cb0c4..4a20a665cc 100644
--- a/gdb/gdbsupport/common-utils.h
+++ b/gdb/gdbsupport/common-utils.h
@@ -23,6 +23,7 @@
 #include <string>
 #include <vector>
 
+#include "gdb_string_view.h"
 #include "poison.h"
 
 /* If possible, define FUNCTION_NAME, a macro containing the name of
@@ -110,15 +111,25 @@ std::string extract_string_maybe_quoted (const char **arg);
 
 extern char *safe_strerror (int);
 
-/* Return non-zero if the start of STRING matches PATTERN, zero
+/* Return true if the start of STRING matches PATTERN, false
    otherwise.  */
 
-static inline int
+static inline bool
 startswith (const char *string, const char *pattern)
 {
   return strncmp (string, pattern, strlen (pattern)) == 0;
 }
 
+/* Version of startswith that takes string_view arguments.  See comment
+   above.  */
+
+static inline bool
+startswith (gdb::string_view string, gdb::string_view pattern)
+{
+  return (string.length() >= pattern.length ()
+	  && strncmp (string.data (), pattern.data (), pattern.length ()) == 0);
+}
+
 ULONGEST strtoulst (const char *num, const char **trailer, int base);
 
 /* Skip leading whitespace characters in INP, returning an updated
-- 
2.23.0.444.g18eeb5a265-goog