1 files changed, 150 insertions, 0 deletions
diff --git a/third_party/python/fluent.migrate/fluent/migrate/helpers.py b/third_party/python/fluent.migrate/fluent/migrate/helpers.py
new file mode 100644
index 0000000000..6a8133661a
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+++ b/third_party/python/fluent.migrate/fluent/migrate/helpers.py
@@ -0,0 +1,150 @@
+# coding=utf8
+"""Fluent AST helpers.
+
+The functions defined in this module offer a shorthand for defining common AST
+nodes.
+
+They take a string argument and immediately return a corresponding AST node.
+(As opposed to Transforms which are AST nodes on their own and only return the
+migrated AST nodes when they are evaluated by a MigrationContext.) """
+
+from __future__ import unicode_literals
+from __future__ import absolute_import
+
+from fluent.syntax import FluentParser, ast as FTL
+from fluent.syntax.visitor import Transformer
+from .transforms import Transform, CONCAT, COPY, COPY_PATTERN
+from .errors import NotSupportedError, InvalidTransformError
+
+
+def VARIABLE_REFERENCE(name):
+    """Create an ExternalArgument expression."""
+
+    return FTL.VariableReference(
+        id=FTL.Identifier(name)
+    )
+
+
+def MESSAGE_REFERENCE(name):
+    """Create a MessageReference expression.
+
+    If the passed name contains a `.`, we're generating
+    a message reference with an attribute.
+    """
+    if '.' in name:
+        name, attribute = name.split('.')
+        attribute = FTL.Identifier(attribute)
+    else:
+        attribute = None
+
+    return FTL.MessageReference(
+        id=FTL.Identifier(name),
+        attribute=attribute,
+    )
+
+
+def TERM_REFERENCE(name):
+    """Create a TermReference expression."""
+
+    return FTL.TermReference(
+        id=FTL.Identifier(name)
+    )
+
+
+class IntoTranforms(Transformer):
+    IMPLICIT_TRANSFORMS = ("CONCAT",)
+    FORBIDDEN_TRANSFORMS = ("PLURALS", "REPLACE", "REPLACE_IN_TEXT")
+
+    def __init__(self, substitutions):
+        self.substitutions = substitutions
+
+    def visit_Junk(self, node):
+        anno = node.annotations[0]
+        raise InvalidTransformError(
+            "Transform contains parse error: {}, at {}".format(
+                anno.message, anno.span.start))
+
+    def visit_FunctionReference(self, node):
+        name = node.id.name
+        if name in self.IMPLICIT_TRANSFORMS:
+            raise NotSupportedError(
+                "{} may not be used with transforms_from(). It runs "
+                "implicitly on all Patterns anyways.".format(name))
+        if name in self.FORBIDDEN_TRANSFORMS:
+            raise NotSupportedError(
+                "{} may not be used with transforms_from(). It requires "
+                "additional logic in Python code.".format(name))
+        if name in ('COPY', 'COPY_PATTERN'):
+            args = (
+                self.into_argument(arg) for arg in node.arguments.positional
+            )
+            kwargs = {
+                arg.name.name: self.into_argument(arg.value)
+                for arg in node.arguments.named}
+            if name == 'COPY':
+                return COPY(*args, **kwargs)
+            return COPY_PATTERN(*args, **kwargs)
+        return self.generic_visit(node)
+
+    def visit_Placeable(self, node):
+        """If the expression is a Transform, replace this Placeable
+        with the Transform it's holding.
+        Transforms evaluate to Patterns, which are flattened as
+        elements of Patterns in Transform.pattern_of, but only
+        one level deep.
+        """
+        node = self.generic_visit(node)
+        if isinstance(node.expression, Transform):
+            return node.expression
+        return node
+
+    def visit_Pattern(self, node):
+        """Replace the Pattern with CONCAT which is more accepting of its
+        elements. CONCAT takes PatternElements, Expressions and other
+        Patterns (e.g. returned from evaluating transforms).
+        """
+        node = self.generic_visit(node)
+        return CONCAT(*node.elements)
+
+    def into_argument(self, node):
+        """Convert AST node into an argument to migration transforms."""
+        if isinstance(node, FTL.StringLiteral):
+            # Special cases for booleans which don't exist in Fluent.
+            if node.value == "True":
+                return True
+            if node.value == "False":
+                return False
+            return node.value
+        if isinstance(node, FTL.MessageReference):
+            try:
+                return self.substitutions[node.id.name]
+            except KeyError:
+                raise InvalidTransformError(
+                    "Unknown substitution in COPY: {}".format(
+                        node.id.name))
+        else:
+            raise InvalidTransformError(
+                "Invalid argument passed to COPY: {}".format(
+                    type(node).__name__))
+
+
+def transforms_from(ftl, **substitutions):
+    """Parse FTL code into a list of Message nodes with Transforms.
+
+    The FTL may use a fabricated COPY function inside of placeables which
+    will be converted into actual COPY migration transform.
+
+        new-key = Hardcoded text { COPY("filepath.dtd", "string.key") }
+
+    For convenience, COPY may also refer to transforms_from's keyword
+    arguments via the MessageReference syntax:
+
+        transforms_from(\"""
+        new-key = Hardcoded text { COPY(file_dtd, "string.key") }
+        \""", file_dtd="very/long/path/to/a/file.dtd")
+
+    """
+
+    parser = FluentParser(with_spans=False)
+    resource = parser.parse(ftl)
+    return IntoTranforms(substitutions).visit(resource).body