add test cases for #6139 and #6128

Author: stevengj

doc/stdlib/punctuation.rst

@@ -11,7 +11,7 @@ Extended documentation for mathematical symbols & functions is :ref:`here <mathe
    ``!``       prefix "not" operator
    ``a!( )``   at the end of a function name, `!` indicates that a function modifies its argument(s)
    ``#``       begin single line comment
-   ``#=``      begin multi-line comment
+   ``#=``      begin multi-line comment (these are nestable)
    ``=#``      end multi-line comment
    ``$``       xor operator, string and expression interpolation
    ``%``       remainder operator

test/core.jl

@@ -1454,3 +1454,8 @@ x6074 = 6074
 test5536(a::Union(Real, AbstractArray)...) = "Splatting"
 test5536(a::Union(Real, AbstractArray)) = "Non-splatting"
 @test test5536(5) == "Non-splatting"
+
+# multiline comments (#6139 and others raised in #6128)
+@test 3 == include_string("1 + #=# 2") == include_string("1 + #==# 2") == include_string("1 + #===# 2") == include_string("1 + #= #= blah =# =# 2") == include_string("1 + #= #= #= nested =# =# =# 2")
+@test_throws include_string("#=")
+@test_throws include_string("#= #= #= =# =# =")