[ruby/csv] Add handling for ambiguous parsing options (https://github.com/ruby/csv/pull/226)

GitHub: fix GH-225

With Ruby 3.0.2 and csv 3.2.1, the file

```ruby
require "csv"
File.open("example.tsv", "w") { |f| f.puts("foo\t\tbar") }
CSV.read("example.tsv", col_sep: "\t", strip: true)
```

produces the error

```
lib/csv/parser.rb:935:in `parse_quotable_robust': TODO: Meaningful
message in line 1. (CSV::MalformedCSVError)
```

However, the CSV in this example is not malformed; instead, ambiguous
options were provided to the parser. It is not obvious (to me) whether
the string should be parsed as

- `["foo\t\tbar"]`,
- `["foo", "bar"]`,
- `["foo", "", "bar"]`, or
- `["foo", nil, "bar"]`.

This commit adds code that raises an exception when this situation is
encountered. Specifically, it checks if the column separator either ends
with or starts with the characters that would be stripped away.

This commit also adds unit tests and updates the documentation.

https://github.com/ruby/csv/commit/cc317dd42d

1 files changed, 29 insertions, 0 deletions

diff --git a/test/csv/parse/test_strip.rb b/test/csv/parse/test_strip.rb
index 3564fcb3ba..c5e35209cc 100644
--- a/test/csv/parse/test_strip.rb
+++ b/test/csv/parse/test_strip.rb
@@ -80,4 +80,33 @@ class TestCSVParseStrip < Test::Unit::TestCase
                            %Q{"a" ,"b " \r\n},
                            strip: true))
   end
+
+  def test_col_sep_incompatible_true
+    message = "The provided strip (true) and " \
+              "col_sep (\\t) options are incompatible."
+    assert_raise_with_message(ArgumentError, message) do
+      CSV.parse_line(%Q{"a"\t"b"\n},
+                     col_sep: "\t",
+                     strip: true)
+    end
+  end
+
+  def test_col_sep_incompatible_string
+    message = "The provided strip (\\t) and " \
+              "col_sep (\\t) options are incompatible."
+    assert_raise_with_message(ArgumentError, message) do
+      CSV.parse_line(%Q{"a"\t"b"\n},
+                     col_sep: "\t",
+                     strip: "\t")
+    end
+  end
+
+  def test_col_sep_compatible_string
+    assert_equal(
+      ["a", "b"],
+      CSV.parse_line(%Q{\va\tb\v\n},
+                     col_sep: "\t",
+                     strip: "\v")
+    )
+  end
 end