Update vendored ruamel.yaml to v0.17.21 (#37008)

* Vendor ruamel.yaml v0.17.21

* Add unit test for whitespace regression

* Add an abstraction layer in Spack to wrap ruamel.yaml

All YAML operations are routed through spack.util.spack_yaml

The custom classes have been adapted to the new ruamel.yaml
class hierarchy.

Fixed line annotation issue in "spack config blame"

lib/spack/external/_vendoring/ruamel/yaml/scalarstring.py

@@ -0,0 +1,152 @@
+# coding: utf-8
+
+from ruamel.yaml.anchor import Anchor
+
+if False:  # MYPY
+    from typing import Text, Any, Dict, List  # NOQA
+
+__all__ = [
+    'ScalarString',
+    'LiteralScalarString',
+    'FoldedScalarString',
+    'SingleQuotedScalarString',
+    'DoubleQuotedScalarString',
+    'PlainScalarString',
+    # PreservedScalarString is the old name, as it was the first to be preserved on rt,
+    # use LiteralScalarString instead
+    'PreservedScalarString',
+]
+
+
+class ScalarString(str):
+    __slots__ = Anchor.attrib
+
+    def __new__(cls, *args, **kw):
+        # type: (Any, Any) -> Any
+        anchor = kw.pop('anchor', None)
+        ret_val = str.__new__(cls, *args, **kw)
+        if anchor is not None:
+            ret_val.yaml_set_anchor(anchor, always_dump=True)
+        return ret_val
+
+    def replace(self, old, new, maxreplace=-1):
+        # type: (Any, Any, int) -> Any
+        return type(self)((str.replace(self, old, new, maxreplace)))
+
+    @property
+    def anchor(self):
+        # type: () -> Any
+        if not hasattr(self, Anchor.attrib):
+            setattr(self, Anchor.attrib, Anchor())
+        return getattr(self, Anchor.attrib)
+
+    def yaml_anchor(self, any=False):
+        # type: (bool) -> Any
+        if not hasattr(self, Anchor.attrib):
+            return None
+        if any or self.anchor.always_dump:
+            return self.anchor
+        return None
+
+    def yaml_set_anchor(self, value, always_dump=False):
+        # type: (Any, bool) -> None
+        self.anchor.value = value
+        self.anchor.always_dump = always_dump
+
+
+class LiteralScalarString(ScalarString):
+    __slots__ = 'comment'  # the comment after the | on the first line
+
+    style = '|'
+
+    def __new__(cls, value, anchor=None):
+        # type: (Text, Any) -> Any
+        return ScalarString.__new__(cls, value, anchor=anchor)
+
+
+PreservedScalarString = LiteralScalarString
+
+
+class FoldedScalarString(ScalarString):
+    __slots__ = ('fold_pos', 'comment')  # the comment after the > on the first line
+
+    style = '>'
+
+    def __new__(cls, value, anchor=None):
+        # type: (Text, Any) -> Any
+        return ScalarString.__new__(cls, value, anchor=anchor)
+
+
+class SingleQuotedScalarString(ScalarString):
+    __slots__ = ()
+
+    style = "'"
+
+    def __new__(cls, value, anchor=None):
+        # type: (Text, Any) -> Any
+        return ScalarString.__new__(cls, value, anchor=anchor)
+
+
+class DoubleQuotedScalarString(ScalarString):
+    __slots__ = ()
+
+    style = '"'
+
+    def __new__(cls, value, anchor=None):
+        # type: (Text, Any) -> Any
+        return ScalarString.__new__(cls, value, anchor=anchor)
+
+
+class PlainScalarString(ScalarString):
+    __slots__ = ()
+
+    style = ''
+
+    def __new__(cls, value, anchor=None):
+        # type: (Text, Any) -> Any
+        return ScalarString.__new__(cls, value, anchor=anchor)
+
+
+def preserve_literal(s):
+    # type: (Text) -> Text
+    return LiteralScalarString(s.replace('\r\n', '\n').replace('\r', '\n'))
+
+
+def walk_tree(base, map=None):
+    # type: (Any, Any) -> None
+    """
+    the routine here walks over a simple yaml tree (recursing in
+    dict values and list items) and converts strings that
+    have multiple lines to literal scalars
+
+    You can also provide an explicit (ordered) mapping for multiple transforms
+    (first of which is executed):
+        map = ruamel.yaml.compat.ordereddict
+        map['\n'] = preserve_literal
+        map[':'] = SingleQuotedScalarString
+        walk_tree(data, map=map)
+    """
+    from collections.abc import MutableMapping, MutableSequence
+
+    if map is None:
+        map = {'\n': preserve_literal}
+
+    if isinstance(base, MutableMapping):
+        for k in base:
+            v = base[k]  # type: Text
+            if isinstance(v, str):
+                for ch in map:
+                    if ch in v:
+                        base[k] = map[ch](v)
+                        break
+            else:
+                walk_tree(v, map=map)
+    elif isinstance(base, MutableSequence):
+        for idx, elem in enumerate(base):
+            if isinstance(elem, str):
+                for ch in map:
+                    if ch in elem:
+                        base[idx] = map[ch](elem)
+                        break
+            else:
+                walk_tree(elem, map=map)