Add ".plt" to Prolog extensions (#6141)

* Create plunit_test_example.plt

* Add ".plt" to Prolog extensions in languages.yml

* Copy Gnuplot sample defense_plotter.p to defense_plotter.plt

* Add heuristic for Prolog .plt files

Per suggestion: https://github.com/github/linguist/pull/6141#issuecomment-1312517712

* Update test_heuristics.rb

* Fix test_heuristics.rb

---------

Co-authored-by: Colin Seymour <colin@github.com>

lib/linguist/heuristics.yml

@@ -506,6 +506,10 @@ disambiguations:
   - language: XML Property List
     pattern: '^\s*(?:<\?xml\s|<!DOCTYPE\s+plist|<plist(?:\s+version\s*=\s*(["''])\d+(?:\.\d+)?\1)?\s*>\s*$)'
   - language: OpenStep Property List
+- extensions: ['.plt']
+  rules:
+  - language: Prolog
+    pattern: '^\s*:-'
 - extensions: ['.pm']
   rules:
   - language: Perl

lib/linguist/languages.yml

@@ -5163,6 +5163,7 @@ Prolog:
   color: "#74283c"
   extensions:
   - ".pl"
+  - ".plt"
   - ".pro"
   - ".prolog"
   - ".yap"

samples/Gnuplot/defense_plotter.plt

@@ -0,0 +1,40 @@
+#
+# defense_plotter.plt
+#
+# This is a gnuplot script that creates the graphs for defense values.
+#
+# Defense values are from:
+#
+#   http://wiki.starsautohost.org/wiki/Guts_of_bombing
+#   Author:  Leonard Dickens
+#   Date:  1998/07/17
+#   Forums:  rec.games.computer.stars
+#
+# :author: Brandon Arrendondo
+# :license: MIT
+#
+set terminal pngcairo transparent truecolor font "Arial Bold,10" size 350, 250
+set output "out.png"
+
+set title "Shield Coverage vs. Defense Quantity"
+set grid
+set xrange [0:100]
+set xlabel "Number of Defenses"
+
+set format y '%2.0f%%'
+set yrange [0:100]
+
+set key right bottom
+
+sdi = 0.0099
+missile_battery = 0.0199
+laser_battery = 0.0239
+planetary_shield = 0.0299
+neutron_shield = 0.0379
+
+val = neutron_shield
+
+f(x) = (1.0 - ((1.0 - (val)) ** x)) * 100.0
+g(x) = (1.0 - ((1.0 - (val/2.0)) ** x)) * 100.0
+
+plot f(x) title "Standard" lt rgb "#000080", g(x) title "Smart" lt rgb "#000000"

samples/Prolog/plunit_test_example.plt

@@ -0,0 +1,11 @@
+:- use_module(library(plunit)).
+
+:- begin_tests(plunit_test_example).
+
+test(true_succeeds) :-
+  true.
+
+test(fail_fails, [fail]) :-
+  fail.  % Interchangeable with false/0.
+
+:- end_tests(plunit_test_example).

test/test_heuristics.rb

@@ -734,6 +734,14 @@ class TestHeuristics < Minitest::Test
     })
   end
 
+  def test_plt_by_heuristics
+    assert_heuristics({
+      "Prolog" => all_fixtures("Prolog", "*.plt"),
+      # Gnuplot lacks a heuristic
+      nil => all_fixtures("Gnuplot", "*.plt")
+    })
+  end
+
   def test_pm_by_heuristics
     assert_heuristics({
       "Perl" => all_fixtures("Perl", "*.pm"),