blob: 827d25635c20cba80f7764c5a7d1c6dca2ed0883 [file] [log] [blame]
// Copyright (c) 2014, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
library pub.preprocess;
import 'package:string_scanner/string_scanner.dart';
import 'version.dart';
/// Runs a simple preprocessor over [input] to remove sections that are
/// incompatible with the available barback version.
///
/// [barbackVersion] is the version of barback that's available, and [sourceUrl]
/// is a [String] or [Uri] indicating where [input] came from. It's used for
/// error reporting.
///
/// For the most part, the preprocessor leaves text in the source document
/// alone. However, it handles two types of lines specially. Lines that begin
/// with `//>` are uncommented by the preprocessor, and lines that begin with
/// `//#` are operators.
///
/// The preprocessor currently supports one top-level operator, "if":
///
/// //# if barback >=0.14.1
/// ...
/// //# else
/// ...
/// //# end
///
/// If the current barback version matches the constraint, everything within the
/// first block is included in the output and everything within the second block
/// is removed; otherwise, the first block is removed and the second block is
/// included. The `else` block is optional.
///
/// It's important that the preprocessor syntax also be valid Dart code, because
/// pub loads the source files before preprocessing and runs them against the
/// version of barback that was compiled into pub. This is why the `//>` syntax
/// exists: so that code can be hidden from the running pub process but still be
/// visible to the barback isolate. For example:
///
/// //# if barback >= 0.14.1
/// ClassMirror get aggregateClass => reflectClass(AggregateTransformer);
/// //# else
/// //> ClassMirror get aggregateClass => null;
/// //# end
String preprocess(String input, Version barbackVersion, sourceUrl) {
// Short-circuit if there are no preprocessor directives in the file.
if (!input.contains(new RegExp(r"^//[>#]", multiLine: true))) return input;
return new _Preprocessor(input, barbackVersion, sourceUrl).run();
}
/// The preprocessor class.
class _Preprocessor {
/// The scanner over the input string.
final StringScanner _scanner;
/// The version of barback to match against.
final Version _barbackVersion;
/// The buffer to which the output is written.
final _buffer = new StringBuffer();
_Preprocessor(String input, this._barbackVersion, sourceUrl)
: _scanner = new StringScanner(input, sourceUrl: sourceUrl);
/// Run the preprocessor and return the processed output.
String run() {
while (!_scanner.isDone) {
if (_scanner.scan(new RegExp(r"//#\s*"))) {
_if();
} else {
_emitText();
}
}
_scanner.expectDone();
return _buffer.toString();
}
/// Emit lines of the input document directly until an operator is
/// encountered.
void _emitText() {
while (!_scanner.isDone && !_scanner.matches("//#")) {
if (_scanner.scan("//>")) {
if (!_scanner.matches("\n")) _scanner.expect(" ");
}
_scanner.scan(new RegExp(r"[^\n]*\n?"));
_buffer.write(_scanner.lastMatch[0]);
}
}
/// Move through lines of the input document without emitting them until an
/// operator is encountered.
void _ignoreText() {
while (!_scanner.isDone && !_scanner.matches("//#")) {
_scanner.scan(new RegExp(r"[^\n]*\n?"));
}
}
/// Handle an `if` operator.
void _if() {
_scanner.expect(new RegExp(r"if\s+"), name: "if statement");
_scanner.expect(new RegExp(r"[a-zA-Z0-9_]+"), name: "package name");
var package = _scanner.lastMatch[0];
if (package != 'barback') _scanner.error('Unknown package "$package".');
_scanner.scan(new RegExp(r"\s*"));
_scanner.expect(new RegExp(r"[^\n]+"), name: "version constraint");
var constraint;
try {
constraint = new VersionConstraint.parse(_scanner.lastMatch[0]);
} on FormatException catch (error) {
_scanner.error("Invalid version constraint: ${error.message}");
}
_scanner.expect("\n");
var allowed = constraint.allows(_barbackVersion);
if (allowed) {
_emitText();
} else {
_ignoreText();
}
_scanner.expect("//#");
_scanner.scan(new RegExp(r"\s*"));
if (_scanner.scan("else")) {
_scanner.expect("\n");
if (allowed) {
_ignoreText();
} else {
_emitText();
}
_scanner.expect("//#");
_scanner.scan(new RegExp(r"\s*"));
}
_scanner.expect("end");
if (!_scanner.isDone) _scanner.expect("\n");
}
}