Fluent Syntax 1.0

Fluent Syntax 1.0 is out! 🎉 With this release, we commit to no braking changes to the syntax and to the AST during the 1.x lifetime. The formal definition of the grammar can be found in the spec/ directory, together
with documents outlining good practices, validation rules, and the compatibility strategy for future releases.

• There are no grammar changes compared to version 0.9 of the specification.

  Version 0.9 served as the release candidate for 1.0. The grammar and
  the AST of Syntax 1.0 are identical to Syntax 0.9.

• Added the compatibility strategy document. (#251)

  The goal of this document is to define the strategy for introducing
  and deprecating syntax features after 1.0.

Fluent Syntax 0.9

• Flatten complex reference expressions. (#221)

  Reference expressions which may take complex forms, such as a reference
  to a message's attribute, or a parameterized reference to an attribute of
  a term, are now stored in a simplified manner. Instead of nesting
  multiple expression nodes (e.g. CallExpression of an
  AttributeExpression of a TermReference), all information is available
  directly in the reference expression.

  This change affects the following AST nodes:

  • MessageReference now has an optional attribute field,
  • FunctionReference now has a required arguments field,
  • TermReference now has an optional attribute field and an optional
    arguments field.

• Remove VariantLists. (#204)

  The VariantLists and the VariantExpression syntax and AST nodes were
  deprecated in Syntax 0.9 and have now been removed.

• Rename StringLiteral.raw to value. (#243)

  StringLiteral.value contains the exact contents of the string literal,
  character-for-character. Escape sequences are stored verbatim without
  processing.

  Implementations may decide how to process the raw value. When they do,
  however, they must comply with the behavior specified in Literal.parse.

• Rename args to arguments.

  The args field of MessageReference, TermReference,
  FunctionReference, and Annotation has been renamed to arguments.

Fluent Syntax 0.8

• Preserve content-indent in multiline Patterns. (#162)

  Multiline Patterns require to be indented by at least one space. In
  Syntax 0.7 all leading ident of every line was stripped. In Syntax 0.8
  only the maximum indent common to all indented lines is removed. This
  behavior works for all Patterns: in Messages, Terms, Attributes
  and Variants.

  multiline1 =
      This message has two spaces of indent
        on the second line of its value.

  This behavior also works when the first line of a block Pattern is
  indented relative to the following lines:

  multiline2 =
        This message has two spaces of indent
      on the first line of its value.

  Note that only indented lines participate in this behavior. Specifically,
  if a Pattern starts on the same line as the message identifier, then
  it's not considered as indented, and is excluded from the indent
  stripping.

  multiline3 = This message has two spaces of indent
        on the second line of its value. The first
      line is not considered indented at all.

  If a Pattern starts on the same line as the identifier, its first line
  is subject to the leading-whitespace stripping which is applied to all
  Patterns.

  # Same value as multiline3 above.
  multiline4 =     This message has two spaces of indent
        on the second line of its value. The first
      line is not considered indented at all.

  Note that if a multiline Pattern starts on the same line as the
  identifier and it only consists of one more line of text below it, then
  the maximum indent common to all indented lines is equal to the indent
  of the second line, i.e. the only indented line. All indent will be
  removed in this case. {" "} can be used to preserve it explicitly.

  multiline5 = This message has no indent
          on the second line of its value.

• Deprecate VariantLists. (#204)

  VariantLists and VariantExpression have been deprecated. They will be
  removed before Fluent 1.0 is released. Please use parameterized Terms
  instead (see below). Furthermore, in Syntax 0.8 it's not possible to nest
  VariantLists anymore (#220).

• Introduce parameterized Terms. (#176, #212)

  References to Terms can now receive parameters which will be used by
  the runtime as values of variables referenced from within the Term.
  This allows Terms to use regular Patterns as values, rather than
  VariantLists:

  # A Term with a VariantList as a value.
  -thing = {
     *[definite] the thing
      [indefinite] a thing
  }
  
  this = This is { -term[indefinite] }.

  # A parametrized Term with a Pattern as a value.
  -thing = { $article ->
     *[definite] the thing
      [indefinite] a thing
  }
  
  this = This is { -thing(article: "indefinite") }.

  Since Patterns can be nested, this feature allows more complex
  hierarchies of term values:

  # A parametrized Term with nested Patterns.
  -thing = { $article ->
     *[definite] { $first-letter ->
         *[lower] the thing
          [upper] The thing
      }
      [indefinite] { $first-letter ->
         *[lower] a thing
          [upper] A thing
      }
  }
  
  this = This is { -term(first-letter: "lower", article: "indefinite") }.

  Parameters must be named; positional parameters are ignored. If a
  parameter is omitted then the regular default variant logic applies. The
  above example could thus be written as {-term(article: "indefinite")}
  and the lower variant would be used because it is marked as the default
  one. If no parameters are specified, the paranthesis can be omitted:
  {-term()} and {-term} are functionally the same.

  Term attributes can be parameterized as well. To access them, use the
  -term.attr(param: "value") syntax.

• Support all Unicode characters in values. 🎉 (#174, #207)

  All Unicode characters can now be used in values of TextElements and
  StringLiterals, except those recognized as special by the syntax. Refer
  to spec/recommendations.md for information about character ranges which
  translation authors are encouraged to avoid.

• Don't store the - sigil in Identifiers of Terms. (#142)

  The - sigil is no longer part of the term's Identifier. This is now
  consistent with how Identifiers of variables don't include the $
  sigil either.

• Treat backslash (\) as a regular character in TextElements. (#123)

  Backslash does no longer have special escaping powers when used in
  TextElements. It's still recognized as special in StringLiterals,
  however. StringLiterals can be used to insert all special-purpose
  characters in text. For instance, {"{"} will insert the literal opening
  curly brace ({), {"\u00A0"} will insert the non-breaking space, and
  {" "} can be used to make a translation start or end with whitespace,
  which would otherwise by trimmed by Pattern.

• Forbid closing brace in TextElements. (#186)

  Both the opening and the closing brace are now considered special when
  present in TextElements. {"}"} can be used to insert a literal
  closing brace.

• Store both the raw and the unescaped value in StringLiteral. (#203)

  StringLiteral.value has been change to store the unescaped ("cooked")
  value of the string literal: all known escape sequences are replaced with
  the characters they represent. StringLiteral.raw has been added and
  stores the raw value as it was typed by the author of the string literal:
  escapes sequences are not processed in any way.

• Add the \UHHHHHH escape sequence. (#201)

  In addition to the already-supported \uHHHH escape sequence, \UHHHHHH
  is now also recognized and can be used to encode Unicode codepoints in the
  U+010000 to U+10FFFF range. For example, {"\U01F602"} can be used to
  represent 😂.

• Don't normalize line endings in Junk. (#184)

  Junk represents a literal slice of unparsed content and shouldn't have
  its line endings normalized to LF.

• Add the FunctionReference production. (#210)

  Function references in CallExpressions are now stored as
  FunctionReference AST nodes, with an id field which is an
  Identifier.

  The Function production and its corresponding AST node have been
  removed. The logic validating that function names are all upper-case has
  been moved to abstract.mjs.

Fluent Syntax 0.7

• Relax the indentation requirement. (#87)

  Attributes, variant keys and placeables may now be written without
  indent, including the closing curly brace, }.

  emails = { $unreadEmails ->
      [one] You have one unread email.
     *[other] You have { $unreadEmails } unread emails.
  }
  

  Multiline TextElements still require indent to aid error recovery.

  multiline-text =
      Lorem ipsum dolor sit amet, consectetur adipiscing elit,
      sed do eiusmod tempor incididunt ut labore et dolore
      magna aliqua.
  

• Forbid tab as syntax whitespace. (#165)

  Tabs are now parsed as part of TextElement's value and are not allowed
  outside of them.

• Remove support for CR as a line ending. (#154)

  Valid line endings for Fluent files are: LF (U+0A) and CRLF (U+0D U+0A).

• Normalize all EOLs as LF. (#163)

  The AST now stores line endings using the line feed character (LF, U+0A),
  even if the input file used CRLF or a mix of CRLF and LF.

• Restrict VariantKey to NumberLiteral and Identifier. (#127)

  The VariantName AST node has been removed

Fluent Syntax Spec 0.6.0

• Created the reference parser for Fluent Syntax.

  This version is the first to ship with the official reference
  implementation of the parser. The parser focuses on strictness and
  correctness at a cost of reduced performance.

  The ASDL description of the AST has been removed in favor of
  syntax/ast.mjs which defines the actual AST nodes returned by the
  reference parser.

  The EBNF is now auto-generated from the reference parser's
  syntax/grammar.mjs file. It provides an easy to read overview of the
  grammar and will continue to be updated in the future.

  Going forward, all changes to the grammar will be implemented in the
  reference parser first, which also ships with an extensive test suite.

• Added junk entries.

  The grammar now explicitly defines the junk_line production which is
  converted into Junk during the AST construction.

• Comments may now be attached to Messages or Terms.

  The grammar now encodes the behavior for Comments preceding Messages and
  Terms. If there are no blank lines between the Comment and the Message or
  the Term, the Comment becomes part of the Message or the Term AST node.

• Fixed many issues with the white-space grammar.

  The EBNF for Syntax 0.5 had many issues with its use of inline-space and
  break-indent. It defined undesirable or impossible parsing behavior.
  These issues have been fixed and the new test suite will help ensure the
  correctness of the grammar in the future.

• Named arguments to CallExpressions must now follow all positional ones.

  The order of arguments to CallExpressions is now strictly defined as
  positional first, named second. The CallExpression's arguments field
  was replaced by two new fields: positional and named.

• Named arguments to CallExpressions must now be unique.

• Added the TermReference expression.

  References to terms used to be stored as MessageReferences in the AST.
  They now have their own expression type.

• Store the referent expression in attribute and variant expressions.

  MessageAttributeExpression, TermAttributeExpression and
  TermVariantExpression now store the entire referent expression in a new
  ref field, rather than just the Identifier.

• ExternalArgument is now called VariableReference.

• Add the VariantList value type.

  Selector-less SelectExpressions have been removed in favor of
  VariantLists which share the same syntax but have more restricted usage.
  Values of Messages and all Attributes may only be Patterns. Values
  of Terms may either be Patterns or VariantLists. Values of
  Variants may only be VariantLists if they're defined in another
  VariantList.

• SelectExpression's expression field is now called selector.

• StringExpression is now called StringLiteral.

• NumberExpression is now called NumberLiteral.

• TextElement and Placeable are now subclasses of an abstract
  PatternElement class.

Fluent Syntax Spec 0.5.0

• Added terms. (#62, #85)

  Terms are entries which can only be referenced by other messages. Terms cannot be retrieved by the MessageContext runtime.

  Terms start their identifiers with a single dash -. Tools may introduce different checks for messages and terms.

• Removed tags. (#67)

  The same functionality can be achieved by using term attributes.

  -brand-name = Firefox
      .gender = masculine
  
  has-updated =
      { -brand-name.gender ->
          [masculine] { -brand-name} został zaktualizowany.
          [feminine] { -brand-name } została zaktualizowana.
         *[other] Program { -brand-name } został zaktualizowany.
      }

• Changed the comment sigil to #. (#58)

• Removed sections and introduced group and resource comments. (#58)

  Comments starting with ## and ### define the outline of the file and replace sections. ## denotes group-level comments (GroupComment in ASDL) and ### denotes resource-level comments (ResourceComment). These are always standalone Comment entries.

  The comment field on the Resource node was removed.

• Require = after the identifier in message definitions. (#63)

• Renamed Symbol to VariantName in the ASDL.

Fluent Syntax Spec 0.4.0

• Added the Placeable production as a wrapper for expressions in patterns.

  This allows storing more precise information about the whitespace around the placeable's braces.

• Separated the expr type into inline_expr and block_expr.

  This mirrors the EBNF, where a select expression cannot by an argument to a call expression nor selector of another select expression without being wrapped in braces.

• The dash - is not allowed at the beginning of identifiers.

  There's an ongoing discussion in #62 about using the leading - for private messages in the future.

• The question mark ? is not allowed in identifiers.

  We want to start with a more strict syntax for identifiers. See the discussion in #65.

• Small EBNF fixes:

  • Allowed multiline comments.
  • Allowed inline space in blank lines between entries.

Fluent Syntax Spec 0.3.0

• Added tags for language-specific grammatical information.

  Tags are binary values attached to messages. They are language-specific and
  can be used to describe grammatical characteristics of the message.

  brand-name = Firefox
      #masculine
  
  brand-name = Aurora
      #feminine
      #vowel
  

  Tags can be used in select expressions by matching a hashtag name to the
  message:

  has-updated = { brand-name ->
          [masculine] …
          [feminine] …
         *[other] …
      }
  

  Tags can only be defined on messages which have a value and don't have any
  attributes.

• The message body must be indented now.

  Quoted strings are now only valid in placeables and cannot contain other
  placeables. Removed | for multiline blocks.

• Added TextElement production for text elements of the Pattern.

• Added annotations and span to all entry types.

  Spans are { start, end } productions. Annotations are { code, args, message, span } productions.

• Allowed more characters in keys.

  Variant keys are now trimmed from both sides.

  Introduced word which replaces keyword and changes its semantics:
  words cannot contain spaces. Space-separated sequences of words are
  called symbols.

  variant-key may now be a number or a symbol.

  Keyword is now called Symbol in ASDL.

• Defined the behavior of backslash escapes as follows:

  • Escape sequences are only allowed in text and quoted-text.

  • Newlines are preserved by the parser. This allows proper serialization.

  • Known escape sequences are: \\ for the literal backslash, \" for the
    literal double quote, \{ for the literal opening brace and \u
    followed by 4 hex digits for Unicode code points. Representing code
    points from outside of the Basic Multilingual Plane is made possible with
    surrogate pairs (two \uXXXX sequences). Using the actual character is
    encouraged, however.

  • Any other escaped characters result in a parsing error.

• Changed the sigil for comments to //.

• Renamed SelectExpression's expr field to expression.

• Renamed Junk's and Comments body fields to content.

• Renamed CallExpression's args field to arguments.

• Renamed NamedArgument's val field to value.

• Renamed keyword-argument to named-argument

• Removed the list data type

  Removed LIST, LEN, TAKE, DROP.

Fluent Syntax Spec 0.2.0

• (9453242, 1d55148) Simplify Expressions

  ASDL's elem and expr types were merged into a single expr type.
  Pattern is now now part of expr.

  KeyValueArgument is no longer an Expression and is now called
  NamedArgument.

  CallExpression's callee is now a new type: fun`.

  EBNF's variable is now called external.

• (fbcdc07) Fix #10. Remove Section's body

  The list of entries in Resource.body is now guaranteed to be flat.

• (7120a0d) Remove dot as a valid character in builtin names

• (78ceed8) Fix #6. New syntax for attributes

  Replace traits which used the [key] value syntax with attributes:

  foo
      .attr = An attribute
  

• (a183bef) Fix #5. Allow select-expression with an empty selector

• (26ec797) Fix #3. Use { and } for explicit grouping

• (402cc2b) Fix #8. Forbid patterns as values of name-arguments.

• (a5811e1) Fix #2. Disallow multiple expressions in a placeable.

• (35d6ebe) Fix #1. Require one variant to be default.

• (104e11b) Use : between the name and the value of a named-argument.

• (ab27e60) Use W3C's EBNF

Fluent Syntax Spec 0.1.0

This is the intial release corresponding to FTL as implemented in l20n.js as of January 2017 and in the JavaScript implementation of Project Fluent: fluent@0.1.0.

• (be77dbb) Add ASDL description of the Fluent syntax.