Repository: sdispater/tomlkit (python)

Issue:
Multiline dump?
If a string contains `\n`, is it possible to dump as multiline? e.g
```
foo = """
my 
string
"""
```


Pull request description:
Allow string type to be controlled from the public API
Hello, it would be interesting to expose a way of controlling the string style (e.g. allowing multi line strings).

This PR is an attempt to provide such API.

I ended up going for a very verbose API (with explicit keywords) because I believe that it is easier to use, but please let me know if you prefer exposing `StringType` as part of the public API.

I think this closes #44.

Patch:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 949185a..eb91c6c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@
 - Fix the only child detection when creating tables. ([#175](https://github.com/sdispater/tomlkit/issues/175))
 - Include the `docs/` directory and `CHANGELOG.md` in sdist tarball. ([#176](https://github.com/sdispater/tomlkit/issues/176))
 
+### Added
+
+- Add keyword arguments to `string` API to allow selecting the representation type. ([#177](https://github.com/sdispater/tomlkit/pull/177))
+
 ## [0.9.2] - 2022-02-08
 
 ### Changed
diff --git a/tomlkit/_utils.py b/tomlkit/_utils.py
index f3fa49f..5c8113f 100644
--- a/tomlkit/_utils.py
+++ b/tomlkit/_utils.py
@@ -6,6 +6,7 @@ from datetime import datetime
 from datetime import time
 from datetime import timedelta
 from datetime import timezone
+from typing import Collection
 from typing import Union
 
 from ._compat import decode
@@ -97,31 +98,49 @@ def parse_rfc3339(string: str) -> Union[datetime, date, time]:
     raise ValueError("Invalid RFC 339 string")
 
 
-_escaped = {"b": "\b", "t": "\t", "n": "\n", "f": "\f", "r": "\r", '"': '"', "\\": "\\"}
-_escapes = {v: k for k, v in _escaped.items()}
+# https://toml.io/en/v1.0.0#string
+CONTROL_CHARS = frozenset(chr(c) for c in range(0x20)) | {chr(0x7F)}
+_escaped = {
+    "b": "\b",
+    "t": "\t",
+    "n": "\n",
+    "f": "\f",
+    "r": "\r",
+    '"': '"',
+    "\\": "\\",
+}
+_compact_escapes = {
+    **{v: f"\\{k}" for k, v in _escaped.items()},
+    '"""': '""\\"',
+}
+_basic_escapes = CONTROL_CHARS | {'"'}
 
 
-def escape_string(s: str) -> str:
+def _unicode_escape(seq: str) -> str:
+    return "".join(f"\\u{ord(c):04x}" for c in seq)
+
+
+def escape_string(s: str, escape_sequences: Collection[str] = _basic_escapes) -> str:
     s = decode(s)
 
     res = []
     start = 0
+    l = len(s)
 
-    def flush():
+    def flush(inc=1):
         if start != i:
             res.append(s[start:i])
 
-        return i + 1
+        return i + inc
 
     i = 0
-    while i < len(s):
-        c = s[i]
-        if c in '"\\\n\r\t\b\f':
-            start = flush()
-            res.append("\\" + _escapes[c])
-        elif ord(c) < 0x20:
-            start = flush()
-            res.append("\\u%04x" % ord(c))
+    while i < l:
+        for seq in escape_sequences:
+            seq_len = len(seq)
+            if s[i:].startswith(seq):
+                start = flush(seq_len)
+                res.append(_compact_escapes.get(seq) or _unicode_escape(seq))
+                i += seq_len - 1  # fast-forward escape sequence
         i += 1
 
     flush()
diff --git a/tomlkit/api.py b/tomlkit/api.py
index c4cc07f..273efc5 100644
--- a/tomlkit/api.py
+++ b/tomlkit/api.py
@@ -23,6 +23,7 @@ from .items import Item as _Item
 from .items import Key
 from .items import SingleKey
 from .items import String
+from .items import StringType as _StringType
 from .items import Table
 from .items import Time
 from .items import Trivia
@@ -104,9 +105,28 @@ def boolean(raw: str) -> Bool:
     return item(raw == "true")
 
 
-def string(raw: str) -> String:
-    """Create a string item."""
-    return item(raw)
+def string(
+    raw: str,
+    *,
+    literal: bool = False,
+    multiline: bool = False,
+    escape: bool = True,
+) -> String:
+    """Create a string item.
+
+    By default, this function will create *single line basic* strings, but
+    boolean flags (e.g. ``literal=True`` and/or ``multiline=True``)
+    can be used for personalization.
+
+    For more information, please check the spec: `https://toml.io/en/v1.0.0#string`_.
+
+    Common escaping rules will be applied for basic strings.
+    This can be controlled by explicitly setting ``escape=False``.
+    Please note that, if you disable escaping, you will have to make sure that
+    the given strings don't contain any forbidden character or sequence.
+    """
+    type_ = _StringType.select(literal, multiline)
+    return String.from_raw(raw, type_, escape)
 
 
 def date(raw: str) -> Date:
diff --git a/tomlkit/exceptions.py b/tomlkit/exceptions.py
index 66370db..6c2c7a1 100644
--- a/tomlkit/exceptions.py
+++ b/tomlkit/exceptions.py
@@ -1,3 +1,4 @@
+from typing import Collection
 from typing import Optional
 
 
@@ -213,3 +214,12 @@ class InvalidControlChar(ParseError):
         )
 
         super().__init__(line, col, message=message)
+
+
+class InvalidStringError(ValueError, TOMLKitError):
+    def __init__(self, value: str, invalid_sequences: Collection[str], delimiter: str):
+        repr_ = repr(value)[1:-1]
+        super().__init__(
+            f"Invalid string: {delimiter}{repr_}{delimiter}. "
+            f"The character sequences {invalid_sequences} are invalid."
+        )
diff --git a/tomlkit/items.py b/tomlkit/items.py
index c1eac02..ba7f848 100644
--- a/tomlkit/items.py
+++ b/tomlkit/items.py
@@ -11,6 +11,7 @@ from enum import Enum
 from functools import lru_cache
 from typing import TYPE_CHECKING
 from typing import Any
+from typing import Collection
 from typing import Dict
 from typing import Iterable
 from typing import Iterator
@@ -23,7 +24,9 @@ from typing import overload
 
 from ._compat import PY38
 from ._compat import decode
+from ._utils import CONTROL_CHARS
 from ._utils import escape_string
+from .exceptions import InvalidStringError
 from .toml_char import TOMLChar
 
 
@@ -124,9 +127,7 @@ def item(
 
         return a
     elif isinstance(value, str):
-        escaped = escape_string(value)
-
-        return String(StringType.SLB, decode(value), escaped, Trivia())
+        return String.from_raw(value)
     elif isinstance(value, datetime):
         return DateTime(
             value.year,
@@ -166,6 +167,39 @@ class StringType(Enum):
     # Multi Line Literal
     MLL = "'''"
 
+    @classmethod
+    def select(cls, literal=False, multiline=False) -> "StringType":
+        return {
+            (False, False): cls.SLB,
+            (False, True): cls.MLB,
+            (True, False): cls.SLL,
+            (True, True): cls.MLL,
+        }[(literal, multiline)]
+
+    @property
+    def escaped_sequences(self) -> Collection[str]:
+        # https://toml.io/en/v1.0.0#string
+        escaped_in_basic = CONTROL_CHARS | {"\\"}
+        allowed_in_multiline = {"\n", "\r"}
+        return {
+            StringType.SLB: escaped_in_basic | {'"'},
+            StringType.MLB: (escaped_in_basic | {'"""'}) - allowed_in_multiline,
+            StringType.SLL: (),
+            StringType.MLL: (),
+        }[self]
+
+    @property
+    def invalid_sequences(self) -> Collection[str]:
+        # https://toml.io/en/v1.0.0#string
+        forbidden_in_literal = CONTROL_CHARS - {"\t"}
+        allowed_in_multiline = {"\n", "\r"}
+        return {
+            StringType.SLB: (),
+            StringType.MLB: (),
+            StringType.SLL: forbidden_in_literal | {"'"},
+            StringType.MLL: (forbidden_in_literal | {"'''"}) - allowed_in_multiline,
+        }[self]
+
     @property
     @lru_cache(maxsize=None)
     def unit(self) -> str:
@@ -1512,6 +1546,19 @@ class String(str, Item):
     def _getstate(self, protocol=3):
         return self._t, str(self), self._original, self._trivia
 
+    @classmethod
+    def from_raw(cls, value: str, type_=StringType.SLB, escape=True) -> "String":
+        value = decode(value)
+
+        invalid = type_.invalid_sequences
+        if any(c in value for c in invalid):
+            raise InvalidStringError(value, invalid, type_.value)
+
+        escaped = type_.escaped_sequences
+        string_value = escape_string(value, escaped) if escape and escaped else value
+
+        return cls(type_, decode(value), string_value, Trivia())
+
 
 class AoT(Item, _CustomList):
     """


Test patch:
diff --git a/tests/test_api.py b/tests/test_api.py
index 88b9772..3a27db4 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -21,6 +21,7 @@ from tomlkit.exceptions import InvalidControlChar
 from tomlkit.exceptions import InvalidDateError
 from tomlkit.exceptions import InvalidDateTimeError
 from tomlkit.exceptions import InvalidNumberError
+from tomlkit.exceptions import InvalidStringError
 from tomlkit.exceptions import InvalidTimeError
 from tomlkit.exceptions import UnexpectedCharError
 from tomlkit.items import AoT
@@ -392,3 +393,68 @@ def test_create_super_table_with_table():
 def test_create_super_table_with_aot():
     data = {"foo": {"bar": [{"a": 1}]}}
     assert dumps(data) == "[[foo.bar]]\na = 1\n"
+
+
+@pytest.mark.parametrize(
+    "kwargs, example, expected",
+    [
+        ({}, "My\nString", '"My\\nString"'),
+        ({"escape": False}, "My String\t", '"My String\t"'),
+        ({"literal": True}, "My String\t", "'My String\t'"),
+        ({"escape": True, "literal": True}, "My String\t", "'My String\t'"),
+        ({}, "My String\u0001", '"My String\\u0001"'),
+        ({}, "My String\u000b", '"My String\\u000b"'),
+        ({}, "My String\x08", '"My String\\b"'),
+        ({}, "My String\x0c", '"My String\\f"'),
+        ({}, "My String\x01", '"My String\\u0001"'),
+        ({}, "My String\x06", '"My String\\u0006"'),
+        ({}, "My String\x12", '"My String\\u0012"'),
+        ({}, "My String\x7f", '"My String\\u007f"'),
+        ({"escape": False}, "My String\u0001", '"My String\u0001"'),
+        ({"multiline": True}, "\nMy\nString\n", '"""\nMy\nString\n"""'),
+        ({"multiline": True}, 'My"String', '"""My"String"""'),
+        ({"multiline": True}, 'My""String', '"""My""String"""'),
+        ({"multiline": True}, 'My"""String', '"""My""\\"String"""'),
+        ({"multiline": True}, 'My""""String', '"""My""\\""String"""'),
+        (
+            {"multiline": True},
+            '"""My"""Str"""ing"""',
+            '"""""\\"My""\\"Str""\\"ing""\\""""',
+        ),
+        ({"multiline": True, "literal": True}, "My\nString", "'''My\nString'''"),
+        ({"multiline": True, "literal": True}, "My'String", "'''My'String'''"),
+        ({"multiline": True, "literal": True}, "My\r\nString", "'''My\r\nString'''"),
+        (
+            {"literal": True},
+            r"C:\Users\nodejs\templates",
+            r"'C:\Users\nodejs\templates'",
+        ),
+        ({"literal": True}, r"<\i\c*\s*>", r"'<\i\c*\s*>'"),
+        (
+            {"multiline": True, "literal": True},
+            r"I [dw]on't need \d{2} apples",
+            r"'''I [dw]on't need \d{2} apples'''",
+        ),
+    ],
+)
+def test_create_string(kwargs, example, expected):
+    value = tomlkit.string(example, **kwargs)
+    assert value.as_string() == expected
+
+
+@pytest.mark.parametrize(
+    "kwargs, example",
+    [
+        ({"literal": True}, "My'String"),
+        ({"literal": True}, "My\nString"),
+        ({"literal": True}, "My\r\nString"),
+        ({"literal": True}, "My\bString"),
+        ({"literal": True}, "My\x08String"),
+        ({"literal": True}, "My\x0cString"),
+        ({"literal": True}, "My\x7fString"),
+        ({"multiline": True, "literal": True}, "My'''String"),
+    ],
+)
+def test_create_string_with_invalid_characters(kwargs, example):
+    with pytest.raises(InvalidStringError):
+        tomlkit.string(example, **kwargs)