Disallow newline between contextual keyword pairs in parentheses (#386)

Ensure that we never treat things like `"mutable\nstruct"` as a mutable
struct definition, even within parentheses where newline whitespace is
insignificant.

src/parser.jl

@@ -253,7 +253,7 @@ function peek_initial_reserved_words(ps::ParseState)
     if is_initial_reserved_word(ps, k)
         return true
     elseif is_contextual_keyword(k)
-        k2 = peek(ps,2)
+        k2 = peek(ps, 2, skip_newlines=false)
         return (k == K"mutable"   && k2 == K"struct") ||
                (k == K"primitive" && k2 == K"type")   ||
                (k == K"abstract"  && k2 == K"type")

test/parser.jl

@@ -986,6 +986,9 @@ end
 parsestmt_test_specs = [
     # whitespace before keywords in space-insensitive mode
     "(y::\nif x z end)" => "(parens (::-i y (if x (block z))))"
+    # Contextual keyword pairs inside parentheses
+    "(abstract type X end)" => "(parens (abstract X))"
+    "(mutable struct X end)" => "(parens (struct-mut X (block)))"
     # parsing of tricky primes
     "x in'c'"   => "(call-i x in (char 'c'))"
     "1where'c'" => "(where 1 (char 'c'))"
@@ -1001,6 +1004,9 @@ parsestmt_test_specs = [
     "|(&\nfunction" => "(call | (& (function (error (error)) (block (error)) (error-t))) (error-t))"
     "@(" => "(macrocall (parens (error-t)))"
     "x = @(" => "(= x (macrocall (parens (error-t))))"
+    # Contextual keyword pairs must not be separated by newlines even within parens
+    "(abstract\ntype X end)" => "(wrapper (parens abstract (error-t type X)) (error-t end ✘))"
+    "(mutable\nstruct X end)" => "(wrapper (parens mutable (error-t struct X)) (error-t end ✘))"
 
     # The following is currently broken but at least the parser shouldn't
     # crash.