Don't warn on final missing value when EOF has been reached

Fixes #948. As noted in the included code comment, if the last expected
value to be parsed is `missing`, the delimited file may not include a
final newline, so the EOF, while abrupt, can be treated as valid. In
this specific case, we can avoid emitting the warning and just ensure
that column is marked as having a `missing` value parsed.

Author: quinnj

src/file.jl

@@ -720,9 +720,17 @@ Base.@propagate_inbounds function parserow(startpos, row, numwarnings, ctx::Cont
         else
             if i < ncols
                 if Parsers.newline(code) || pos > len
-                    ctx.silencewarnings || numwarnings[] > ctx.maxwarnings || notenoughcolumns(i, ncols, rowoffset + row)
-                    !ctx.silencewarnings && numwarnings[] == ctx.maxwarnings && toomanywwarnings()
-                    numwarnings[] += 1
+                    # in https://github.com/JuliaData/CSV.jl/issues/948,
+                    # it was noticed that if we reached the EOF right before parsing
+                    # the last expected column, then the warning is a bit spurious.
+                    # The final value is `missing` and the csv writer chose to just
+                    # "close" the file w/o including a final newline
+                    # we can treat this special-case as "valid" and not emit a warning
+                    if !(pos > len && i == (ncols - 1))
+                        ctx.silencewarnings || numwarnings[] > ctx.maxwarnings || notenoughcolumns(i, ncols, rowoffset + row)
+                        !ctx.silencewarnings && numwarnings[] == ctx.maxwarnings && toomanywwarnings()
+                        numwarnings[] += 1
+                    end
                     for j = (i + 1):ncols
                         columns[j].anymissing = true
                     end

test/basics.jl

@@ -743,4 +743,9 @@ f = CSV.File(IOBuffer(data); header=false, types=Dict(1 => String), typemap=Dict
 f = CSV.File(IOBuffer(data); header=false, types=Dict(1 => String), downcast=true);
 @test f.types == [i == 1 ? String : Int8 for i = 1:60_000]
 
+# 948
+f = CSV.File(IOBuffer("a,b\n1,2\n3,"))
+@test f.a == [1, 3]
+@test isequal(f.b, [2, missing])
+
 end