Add ".plt" to Prolog extensions

[GeoffChurch]

.plt files are used by Gnuplot for saved plots, and by SWI-Prolog (and probably SICSTUS Prolog) for PlUnit tests. Most seem to be misclassified as Gnuplot.

We can try a simple ":-\s?begin_tests" heuristic, but hopefully the classifier will pick up on the vastly different syntax.

I wrote a Prolog .plt sample, and copied an existing Gnuplot sample to have the .plt extension.

Fixes #5074

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3Aplt+begin_tests+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s): I wrote the sample Prolog .plt for this PR, so it can fall under linguist's license.
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • samples/Gnuplot/defense_plotter.p
    • Sample license(s): MIT
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

Please update the OP to link to the source of the GNUplot sample and state the license.

[GeoffChurch]

Done

[Alhadis]

We can try a simple ":-\s?begin_tests" heuristic, but hopefully the classifier will pick up on the vastly different syntax.

Why not both? The heuristic will catch the most obvious Prolog cases, and any file not containing a :- token will fall through to the classifier strategy. This works because a line beginning with :- isn't valid Gnuplot syntax:

gnuplot> :- set key off
         ^
         invalid command

diff --git a/lib/linguist/heuristics.yml b/lib/linguist/heuristics.yml
index d948886c..449de061 100644
--- a/lib/linguist/heuristics.yml
+++ b/lib/linguist/heuristics.yml
@@ -485,6 +485,10 @@ disambiguations:
     named_pattern: perl5
   - language: Raku
     named_pattern: perl6
+- extensions: ['.plt']
+  rules:
+  - language: Prolog
+    pattern: '^\s*:-'
 - extensions: ['.plist']
   rules:
   - language: XML Property List

[GeoffChurch]

Is there anything remaining to be done before this can be merged?

[lildude]

Is there anything remaining to be done before this can be merged?

Yup. You need to fix the failing test 😉

[GeoffChurch]

@lildude okay hopefully that does it!

[GeoffChurch]

Hi, can this get merged now? I think it's good-to-go

[Alhadis]

@lildude, this LGTM. 👍

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.