Add prolog swipl linter (#1979)

* add prolog/swipl linter

* use load_files/2 instead of read_term/2

Because it also checks some semantic warnings / errors
not only syntactic warnings / errors.

e.g.:
* singleton warning
* discontiguous warning
* ...

cf. http://www.swi-prolog.org/pldoc/doc_for?object=style_check/1

* support error messages with no line number

    :- module(module_name, [pred/0]).

causes

    ERROR: Exported procedure module_name:pred/0 is not defined

* add test for prolog/swipl handler

* cosmetic fixes

* detect timeout using SIGALRM

* rename g:prolog_swipl_goals to g:prolog_swipl_load

* write doc for prolog/swipl linter

* update toc and README

* fix ignore patterns

2 files changed, 59 insertions, 0 deletions

diff --git a/doc/ale-prolog.txt b/doc/ale-prolog.txt
new file mode 100644
index 00000000..14062a5a
--- /dev/null
+++ b/doc/ale-prolog.txt
@@ -0,0 +1,56 @@
+===============================================================================
+ALE Prolog Integration                                     *ale-prolog-options*
+
+
+===============================================================================
+swipl                                                        *ale-prolog-swipl*
+
+g:ale_prolog_swipl_executable                   *g:ale_prolog_swipl_executable*
+                                                *b:ale_prolog_swipl_executable*
+  Type: |String|
+  Default: `'swipl'`
+
+  The executable that will be run for the `swipl` linter.
+
+g:ale_prolog_swipl_load                               *g:ale_prolog_swipl_load*
+                                                      *b:ale_prolog_swipl_load*
+  Type: |String|
+  Default: `'current_prolog_flag(argv, [File]), load_files(File, [sandboxed(true)]), halt.'`
+
+  The prolog goals that will be passed to |g:ale_prolog_swipl_executable| with `-g` option.
+
+  It does:
+  1. Takes the first command argument (current file path)
+  2. Checks (syntactic / semantic) problems and output to stderr
+
+  NOTE: `sandboxed(true)` prohibits executing some directives such as 'initialization main'.
+
+g:ale_prolog_swipl_timeout                         *g:ale_prolog_swipl_timeout*
+                                                   *b:ale_prolog_swipl_timeout*
+  Type: |Number|
+  Default: `3`
+
+  Timeout seconds to detect long-running linter.
+  It is done by setting SIGALRM.
+  See |g:ale_prolog_swipl_alarm| and |g:ale_prolog_swipl_alarm_handler|.
+
+g:ale_prolog_swipl_alarm                             *g:ale_prolog_swipl_alarm*
+                                                     *b:ale_prolog_swipl_alarm*
+  Type: |String|
+  Default: `'alarm(%t, (%h), _, [])'`
+
+  The prolog goals to be expected to set SIGALRM.
+  `%t` is replaced by |g:ale_prolog_swipl_timeout|.
+  `%h` is replaced by |g:ale_prolog_swipl_alarm_handler|.
+
+g:ale_prolog_swipl_alarm_handler             *g:ale_prolog_swipl_alarm_handler*
+                                             *b:ale_prolog_swipl_alarm_handler*
+  Type: |String|
+  Default: `'writeln(user_error, "ERROR: Exceeded %t seconds, Please change g:prolog_swipl_timeout to modify the limit."), halt(1)'`
+
+  The prolog goals to be expected that will be run on SIGALRM.
+  `%t` is replaced by |g:ale_prolog_swipl_timeout|.
+
+
+===============================================================================
+  vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:
diff --git a/doc/ale.txt b/doc/ale.txt
index 66ce8ab1..95110431 100644
--- a/doc/ale.txt
+++ b/doc/ale.txt
@@ -226,6 +226,8 @@ CONTENTS                                                         *ale-contents*
       write-good..........................|ale-pod-write-good|
     pony..................................|ale-pony-options|
       ponyc...............................|ale-pony-ponyc|
+    prolog................................|ale-prolog-options|
+      swipl...............................|ale-prolog-swipl|
     proto.................................|ale-proto-options|
       protoc-gen-lint.....................|ale-proto-protoc-gen-lint|
     pug...................................|ale-pug-options|
@@ -453,6 +455,7 @@ Notes:
 * PO: `alex`!!, `msgfmt`, `proselint`, `write-good`
 * Pod: `alex`!!, `proselint`, `write-good`
 * Pony: `ponyc`
+* Prolog: `swipl`
 * proto: `protoc-gen-lint`
 * Pug: `pug-lint`
 * Puppet: `languageserver`, `puppet`, `puppet-lint`