Properly detect underscore and apostrophe in declarations

haskell-font-lock.el

@@ -335,16 +335,16 @@ like ::, class, instance, data, newtype, type."
          ;; "^>", otherwise a line of code starts with "^".
          (line-prefix "^\\(?:> ?\\)?")
 
-         (varid "\\b[[:lower:]_][[:alnum:]'_]*\\b")
+         (varid "[[:lower:]_][[:alnum:]'_]*")
          ;; We allow ' preceding conids because of DataKinds/PolyKinds
-         (conid "\\b'?[[:upper:]][[:alnum:]'_]*\\b")
+         (conid "'?[[:upper:]][[:alnum:]'_]*")
          (sym "\\s.+")
 
          ;; Top-level declarations
          (topdecl-var
-          (concat line-prefix "\\(" varid "\\(?:\\s-*,\\s-*" varid "\\)*" "\\)\\s-*"
+          (concat line-prefix "\\(" varid "\\(?:\\s-*,\\s-*" varid "\\)*" "\\)"
                   ;; optionally allow for a single newline after identifier
-                  "\\([\n]\\s-+\\)?"
+                  "\\(\\s-+\\|\\s-*[\n]\\s-+\\)"
                   ;; A toplevel declaration can be followed by a definition
                   ;; (=), a type (::) or (∷), a guard, or a pattern which can
                   ;; either be a variable, a constructor, a parenthesized

tests/haskell-font-lock-tests.el

@@ -443,6 +443,17 @@
    '("Q +++ 12.12")
    '(("+++" t haskell-definition-face))))
 
+(ert-deftest haskell-syntactic-definition-face-4 ()
+  (check-properties
+   '("_test'")
+   '(("_test'" t nil))))
+
+(ert-deftest haskell-syntactic-definition-face-5 ()
+  (check-properties
+   '("_test' _")
+   '(("_test'" t haskell-definition-face))))
+
+
 (ert-deftest haskell-literate-bird-1 ()
   (check-properties
    '("Comment1"