[gdb/cli] Don't let python colorize strip leading newlines

Consider the test-case gdb.base/async.exp.  Using the executable, I run to
main, and land on a line advertised as line 26:
...
$ gdb outputs/gdb.base/async/async -ex start
Reading symbols from outputs/gdb.base/async/async...
Temporary breakpoint 1 at 0x4004e4: file gdb.base/async.c, line 26.
Starting program: outputs/gdb.base/async/async

Temporary breakpoint 1, main () at gdb.base/async.c:26
26       y = foo ();
...

But actually, the line turns out to be line 28:
...
$ cat -n gdb.base/async.c
    ...
    26   y = 2;
    27   z = 9;
    28   y = foo ();
...

This is caused by the following: the python colorizer initializes the lexer
with default options (no second argument to get_lexer_for_filename):
...
    def colorize(filename, contents):
        # Don't want any errors.
        try:
            lexer = lexers.get_lexer_for_filename(filename)
            formatter = formatters.TerminalFormatter()
            return highlight(contents, lexer, formatter)
...
which include option stripnl=True, which strips leading and trailing newlines.

This causes the python colorizer to strip the two leading newlines of async.c.

Fix this by initializing the lexer with stripnl=False.

Build and reg-tested on x86_64-linux.

gdb/ChangeLog:

2020-04-10  Tom de Vries  <tdevries@suse.de>

	PR cli/25808
	* python/lib/gdb/__init__.py: Initialize lexer with stripnl=False.

gdb/testsuite/ChangeLog:

2020-04-10  Tom de Vries  <tdevries@suse.de>

	PR cli/25808
	* gdb.base/style.c: Add leading newlines.
	* gdb.base/style.exp: Use gdb_get_line_number to get specific lines.
	Check listing of main's one-line body.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2020-04-10  Tom de Vries  <tdevries@suse.de>
+
+	PR cli/25808
+	* python/lib/gdb/__init__.py: Initialize lexer with stripnl=False.
+
 2020-04-09  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* MAINTAINERS (Global Maintainers): Add Tom de Vries.

gdb/python/lib/gdb/__init__.py

@@ -216,7 +216,7 @@ try:
     def colorize(filename, contents):
         # Don't want any errors.
         try:
-            lexer = lexers.get_lexer_for_filename(filename)
+            lexer = lexers.get_lexer_for_filename(filename, stripnl=False)
             formatter = formatters.TerminalFormatter()
             return highlight(contents, lexer, formatter)
         except:

gdb/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2020-04-10  Tom de Vries  <tdevries@suse.de>
+
+	PR cli/25808
+	* gdb.base/style.c: Add leading newlines.
+	* gdb.base/style.exp: Use gdb_get_line_number to get specific lines.
+	Check listing of main's one-line body.
+
 2020-04-08  Tom de Vries  <tdevries@suse.de>
 
 	* lib/gdb.exp (psymtabs_p): New proc.

gdb/testsuite/gdb.base/style.c

@@ -1,3 +1,7 @@
+
+
+/* The leading newlines here are intentional, do not remove.  They are used to
+   test that the source highlighter doesn't strip them.  */
 /* Copyright 2018-2020 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify

gdb/testsuite/gdb.base/style.exp

@@ -39,6 +39,11 @@ save_vars { env(TERM) } {
 	return
     }
 
+    # Check that the source highlighter has not stripped away the leading
+    # newlines.
+    set main_line [gdb_get_line_number "break here"]
+    gdb_test "list $main_line,$main_line" "return.*some_called_function.*"
+
     gdb_test_no_output "set style enabled on"
 
     set main_expr [style main function]
@@ -79,8 +84,9 @@ save_vars { env(TERM) } {
     }
 
     if {$test_macros} {
+	set macro_line [gdb_get_line_number "\#define SOME_MACRO"]
 	gdb_test "info macro SOME_MACRO" \
-	    "Defined at $base_file_expr:16\r\n#define SOME_MACRO 23"
+	    "Defined at $base_file_expr:$macro_line\r\n#define SOME_MACRO 23"
     }
 
     set func [style some_called_function function]