pytracediff: implement pager ('less') invocation internally

In order to get rid of the ntracediff.sh wrapper script, implement
invocation of 'less' internally, if the stdout is determined to
be a tty. Otherwise just print out normally.

Signed-off-by: Matti Hamalainen <ccr@tnsp.org>
Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17135>

src/gallium/tools/trace/pytracediff.py

@@ -26,12 +26,14 @@
 ##########################################################################
 
 from parse import *
+import os
 import sys
 import re
 import signal
 import functools
 import argparse
 import difflib
+import subprocess
 
 assert sys.version_info >= (3, 6), 'Python >= 3.6 required'
 
@@ -54,6 +56,8 @@ PKK_ANSI_ITALIC    = '3m'
 ###
 def pkk_fatal(msg):
     print(f"ERROR: {msg}", file=sys.stderr)
+    if outpipe is not None:
+        outpipe.terminate()
     sys.exit(1)
 
 
@@ -61,8 +65,17 @@ def pkk_info(msg):
     print(msg, file=sys.stderr)
 
 
+def pkk_output(outpipe, msg):
+    if outpipe is not None:
+        print(msg, file=outpipe.stdin)
+    else:
+        print(msg)
+
+
 def pkk_signal_handler(signal, frame):
     print("\nQuitting due to SIGINT / Ctrl+C!")
+    if outpipe is not None:
+        outpipe.terminate()
     sys.exit(1)
 
 
@@ -259,6 +272,16 @@ def pkk_format_line(line, indent, width):
 ### Main program starts
 ###
 if __name__ == "__main__":
+    ### Check if output is a terminal
+    outpipe = None
+    redirect = False
+
+    try:
+        defwidth = os.get_terminal_size().columns
+        redirect = True
+    except OSError:
+        defwidth = 80
+
     signal.signal(signal.SIGINT, pkk_signal_handler)
 
     ### Parse arguments
@@ -307,7 +330,7 @@ if __name__ == "__main__":
 
     optparser.add_argument("-w", "--width",
         dest="output_width",
-        type=functools.partial(pkk_arg_range, vmin=16, vmax=512), default=80,
+        type=functools.partial(pkk_arg_range, vmin=16, vmax=512), default=defwidth,
         metavar="N",
         help="output width (default: %(default)s)")
 
@@ -327,6 +350,11 @@ if __name__ == "__main__":
         print("The files are identical.")
         sys.exit(0)
 
+    ### Redirect output to 'less' if stdout is a tty
+    try:
+        if redirect:
+            outpipe = subprocess.Popen(["less", "-S", "-R"], stdin=subprocess.PIPE, encoding="utf8")
+
         ### Output results
         pkk_info("Outputting diff ...")
         colwidth = int((options.output_width - 3) / 2)
@@ -340,7 +368,7 @@ if __name__ == "__main__":
                 show_args = False
                 if options.suppress_common:
                     if tag != prevtag:
-                    print("[...]")
+                        pkk_output(outpipe, "[...]")
                     continue
 
                 sep = "|"
@@ -427,7 +455,7 @@ if __name__ == "__main__":
                             ansi1 = ansi2 = ansi1 + PKK_ANSI_ESC + PKK_ANSI_YELLOW
 
                     # Output line
-                print(colfmt.format(
+                    pkk_output(outpipe, colfmt.format(
                         ansi1, pkk_format_line(line1, indent, colwidth), ansiend,
                         ansisep, sep, ansiend,
                         ansi2, pkk_format_line(line2, indent, colwidth), ansiend).
@@ -436,6 +464,12 @@ if __name__ == "__main__":
                     nline += 1
 
             if tag == "equal" and options.suppress_common:
-            print("[...]")
+                pkk_output(outpipe, "[...]")
 
             prevtag = tag
+
+    except Exception as e:
+        pkk_fatal(str(e))
+
+    if outpipe is not None:
+        outpipe.communicate()