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PEG.js v0.10.0 Release Notes

Release Date: 2016-08-19 // about 8 years ago

  • Major Changes

    📜 Parsers can be generated in multiple module formats. The available
    0️⃣ formats are: CommonJS (the default), AMD, UMD, globals, and bare (not
    available from the command-line).

    The format can be specified using the format option of the peg.generate
    function or the --format option on the command-line.

    📜 It is also possible to specify parser dependencies using the dependencies
    option of the peg.generate function or the --dependency/-d option on
    the command-line. This is mainly useful for the UMD format, where the
    dependencies are translated into both AMD dependencies and CommonJS
    require calls.

    💻 Browser version of PEG.js is now in the UMD format. This means it will try
    to detect AMD or Node.js/CommonJS module loader and define itself as a
    module. If no loader is found, it will export itself using a global
    variable.

    💅 API polishing. The peg.buildParser function was renamed to
    💻 peg.generate. The global variable the browser version of PEG.js is
    available in when no loader is detected was renamed from PEG to peg.

    CLI improvements. There is new --output/-o command-line option which
    👍 allows to specify the output file. The old way of specifying the output file
    🚚 using a second argument was removed. To make room for the new -o option
    ⚡️ the old one (a shortcut for --optimize) was renamed to -O. All these
    🔄 changes make PEG.js conform to traditional compiler command-line interface.

    It is now also possible to use - as a file name on the command-line (with
    the usual meaning of standard input/output).

    👌 Improved error messages. Both messages produced by PEG.js and generated
    📜 parsers were improved.

    Duplicate rule definitions are reported as errors.

    Duplicate labels are reported as errors.

    Minor Changes

    • 🔦 Exposed the AST node visitor builder as peg.compiler.visitor. This is
      🔌 useful mainly for plugins which manipulate the AST.
    • 🔦 Exposed the function which builds messages of exceptions produced by
      🏗 generated parsers as SyntaxError.buildMessage. This is useful mainly for
      customizing these error messages.
    • The error and expected functions now accept an optional location
      parameter. This allows to customize the location in which the resulting
      syntax error is reported.
    • 🔨 Refactored expectations reported in the expected property of exceptions
      📜 produced by generated parsers. They are no longer de-duplicated and sorted,
      their format changed to be more machine-readable, and they no longer contain
      human-readable descriptions.
    • The found property of exceptions produced by the error function is now
      set to null.
    • ✂ Removed access to the parser object in parser code via the parser
      variable.
    • Made handling of optional parameters consistent with ES 2015. Specifically,
      passing undefined as a parameter value is now equivalent to not passing
      the parameter at all.
    • 📇 Renamed several compiler passes.
    • 📜 Generated parsers no longer consider \r, \u2028, and \u2029 as
      🆕 newlines (only \n and \r\n).
    • Simplified the arithmetics example grammar.
    • Switched from first/rest to head/tail in PEG.js grammar and example
      grammars.
    • 👕 Started using ESLint instead of JSHint and fixed various problems it found.
    • ➕ Added contribution
      guidelines      .
    • ✂ Removed support for io.js.

    🐛 Bug Fixes

    • 🛠 Fixed bin/pegjs so that invoking it with one non-option argument which is
      an extension-less file doesn’t cause that file to be overwritten.
    • 🛠 Fixed label scoping so that labels in expressions like (a:"a") or (a:"a" b:"b" c:"c") aren’t visible from the outside.
    • 🛠 Fixed escaping of generated JavaScript strings & regexps to also escape DEL
      (U+007F).
    • 🛠 Fixed the JSON example grammar to correctly handle characters with code
      points above U+10FF in strings.
    • 🛠 Fixed multiple compatibility issues of tools/impact on OS X.
    • 🛠 Fixed slow deduplication of expectation descriptions.

    Complete set of changes


Previous changes from v0.9.0

  • Major Changes

    • 👍 Tracing support. Parsers can be compiled with support for tracing their
      progress, which can help debugging complex grammars. This feature is
      experimental and is expected to evolve over time as experience is gained.
      More details
    • Infinite loop detection. Grammar constructs that could cause infinite
      📜 loops in generated parsers are detected during compilation and cause errors.
    • 👌 Improved location information API. The line, column, and offset
      📜 functions available in parser code were replaced by a single location
      function which returns an object describing the current location. Similarly,
      the line, column, and offset properties of exceptions were replaced by
      a single location property. The location is no longer a single point but a
      character range, which is meaningful mainly in actions where the range
      covers action’s expression.
      More details
    • 👌 Improved error reporting. All exceptions thrown when generating a parser
      have associated location information. And all exceptions thrown by generated
      📜 parser and PEG.js itself have a stack trace (the stack property) in
      👍 environments that support Error.captureStackTrace.
    • Strict mode code. All PEG.js and generated parser code is written using
      🌐 JavaScript strict mode.

    Minor Changes

    • 👀 Labels behave like block-scoped variables. This means parser code can see
      labels defined outside expressions containing code.
    • Empty sequences are no longer allowed.
    • Label names can’t be JavaScript reserved words.
    • Rule and label names can contain Unicode characters like in JavaScript.
    • Rules have to be separated either by ; or a newline (until now, any
      whitespace was enough).
    • The PEG.js grammar and all the example grammars were completely rewritten.
      This rewrite included a number of cleanups, formatting changes, naming
      🔄 changes, and bug fixes.
    • 📜 The parser object can now be accessed as parser in parser code.
    • Location information computation is faster.
    • ➕ Added support for Node.js >= 0.10.x, io.js, and Edge. Removed support for
      Node.js < 0.10.x.

    🐛 Bug Fixes

    • 🛠 Fixed left recursion detector which missed many cases.
    • 🛠 Fixed escaping of U+0100—U+107F and U+1000—U+107F in generated code and
      error messages.
    • 📜 Renamed parse and SyntaxError to peg$parse and peg$SyntaxError to
      mark them as internal identifiers.

    Complete set of changes