gdb/testsuite: fix failure in gdb.base/info_sources.exp

I ran into an unexpected failure in gdb.base/info_sources.exp.  The
test in question runs this command:

  (gdb) info sources -d -- -d

That is, list all the source files whose directory name matches the
regexp '-d'.  The expectation is that no source files will be listed.

Unfortunately, when I ran the test some source files are listed; the
directory I am running in contains the pattern '-d', and so the test
fails.

As we cannot control where the developer is building and testing GDB,
I propose that instead of just testing with '-d' we should search
through all the letters a-z and find one that isn't present in the
source file directory name.  I'm still including the leading '-'
character in the regexp.

So now, unless GDB is being built in a directory that contains '-a',
'-b', '-c', .... '-z', the test will find one letter which isn't
present, and use that for the test.

To avoid test names changing between runs in different directories
I've had to tweak the test name to something more generic, but there
should be no change in which parts of GDB are actually being tested.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/testsuite/gdb.base/info_sources.exp

@@ -23,17 +23,29 @@ if {[prepare_for_testing $testfile.exp $testfile \
     return -1
 }
 
-# Executes "info sources " $args.
-# EXPECT_SEEN_INFO_SOURCES 1 indicates that the source file info_sources.c must be seen
-# in the output.  Similarly, EXPECT_SEEN_INFO_SOURCES_BASE indicates that the source file
-# info_sources_base.c must be seen in the output.
-proc test_info_sources {args expect_seen_info_sources expect_seen_info_sources_base} {
+# Executes "info sources ARGS".
+#
+# EXPECT_SEEN_INFO_SOURCES 1 indicates that the source file info_sources.c
+# must be seen in the output.  Similarly, EXPECT_SEEN_INFO_SOURCES_BASE
+# indicates that the source file info_sources_base.c must be seen in the
+# output.
+#
+# If TESTNAME is not the empty string then this is the test name, otherwise
+# uses "info sources ARGS" as the test name.
+proc test_info_sources {args expect_seen_info_sources \
+			    expect_seen_info_sources_base \
+			    {testname ""}} {
     global gdb_prompt srcfile srcfile2
 
     set seen_info_sources 0
     set seen_info_sources_base 0
     set cmd [concat "info sources " $args]
-    gdb_test_multiple $cmd $cmd {
+
+    if { $testname eq "" } {
+	set $testname $cmd
+    }
+
+    gdb_test_multiple $cmd $testname {
 	-re "^\[^,\]*${srcfile}(, |\[\r\n\]+)" {
 	    incr seen_info_sources
 	    exp_continue
@@ -48,9 +60,9 @@ proc test_info_sources {args expect_seen_info_sources expect_seen_info_sources_b
 	-re "$gdb_prompt $" {
 	    if {$seen_info_sources == $expect_seen_info_sources \
 		    && $seen_info_sources_base == $expect_seen_info_sources_base} {
-		pass $cmd
+		pass $gdb_test_name
 	    } else {
-		fail $cmd
+		fail $gdb_test_name
 	    }
 	}
     }
@@ -99,6 +111,34 @@ if { ! [is_remote host] } {
     test_info_sources "-dirname base" 1 1
 }
 
-# Test non matching regexp, with option terminator:
+# Test non matching regexp against the basename, with option
+# terminator:
 test_info_sources "-b -- -d" 0 0
-test_info_sources "-d -- -d" 0 0
+
+# The following tests relies on using a regexp which will not match
+# either the directory name of the source files.  Unlike the basename
+# test above we need to be more careful picking the regexp as the
+# source filename might contain any simple character patterns, and so
+# could unexpectedly match the regexp.
+#
+# Loop through all the characters a-z trying regexp '-C' (where 'C' is
+# each character), looking for a regexp which doesn't match the
+# directory name.
+set re ""
+for {set i [scan a %c]} {$i <= [scan z %c]} {incr i} {
+    set tmp_re -[format %c $i]
+
+    if {$re eq "" && ![regexp $tmp_re $srcdir/$subdir/]} {
+	set re $tmp_re
+    }
+}
+
+# If we found a suitable regexp then test non matching regexp against
+# the directory name, with option terminator:
+if { $re ne "" } {
+    test_info_sources "-d -- $re" 0 0 \
+	"info sources -d -- <non matching regexp>"
+} else {
+    unresolved \
+	"info sources -d -- <non matching regexp> (failed to find regexp)"
+}