Support shellcheck in compilation-mode

* lisp/progmodes/compile.el
(compilation-error-regexp-alist-alist): Add shellcheck regexp.
* test/lisp/progmodes/compile-tests.el
(compile-tests--test-regexps-data):
(compile-test-error-regexps): Add test for shellcheck.
* etc/compilation.txt: Add shellcheck example.
* etc/NEWS: Announce the change.

foo

etc/NEWS

@@ -689,6 +689,9 @@ case-insensitive matching of messages when the old behavior is
 required, but the recommended solution is to use a correctly matching
 regexp instead.
 
+---
+*** Messages from ShellCheck are now recognized.
+
 ---
 *** Messages from Visual Studio that mention column numbers are now recognized.
 

etc/compilation.txt

@@ -536,6 +536,14 @@ cc-1070 cc: WARNING File = linkl.c, Line = 38
 cf90-113 f90comp: ERROR NSE, File = Hoved.f90, Line = 16, Column = 3
 
 
+* ShellCheck
+
+In autogen.sh line 38:
+autoconf_min=`sed -n 's/^ *AC_PREREQ(\([0-9\.]*\)).*/\1/p' configure.ac`
+^----------^ SC2034: autoconf_min appears unused. Verify use (or export if used externally).
+             ^-- SC2006: Use $(...) notation instead of legacy backticked `...`.
+
+
 * Sun Ada (VADS, Solaris)
 
 symbol: sun-ada

lisp/progmodes/compile.el

@@ -449,6 +449,9 @@ during global destruction\\.$\\)" 1 2)
  \\([0-9]+\\) of file://\\(.+\\)"
      4 2 3 (1))
 
+    (shellcheck
+     "^In \\(.+\\) line \\([0-9]+\\):" 1 2)
+
     (sparc-pascal-file
      "^\\w\\w\\w \\w\\w\\w +[0-3]?[0-9] +[0-2][0-9]:[0-5][0-9]:[0-5][0-9]\
  [12][09][0-9][0-9] +\\(.*\\):$"

test/lisp/progmodes/compile-tests.el

@@ -324,6 +324,9 @@
      1 8 71 "/home/reto/test/group.xml")
     ("Warning: Start tag for undeclared element geroup\nin unnamed entity at line 4 char 8 of file:///home/reto/test/group.xml"
      1 8 4 "/home/reto/test/group.xml")
+    ;; shellcheck
+    ("In autogen.sh line 48:"
+     1 nil 48 "autogen.sh")
     ;; sparc-pascal-file sparc-pascal-line sparc-pascal-example
     ("Thu May 14 10:46:12 1992  mom3.p:"
      1 nil nil "mom3.p")
@@ -436,7 +439,7 @@ The test data is in `compile-tests--test-regexps-data'."
           (compilation-num-warnings-found 0)
           (compilation-num-infos-found 0))
       (mapc #'compile--test-error-line compile-tests--test-regexps-data)
-      (should (eq compilation-num-errors-found 95))
+      (should (eq compilation-num-errors-found 96))
       (should (eq compilation-num-warnings-found 35))
       (should (eq compilation-num-infos-found 28)))))