PRE-PROPOSAL: Source and Encoding keyword

[Roel Spilker]

Good one :-) Javac won't even create a class file if the @Override
annotation is present but shouldn't be there.


On Sat, Mar 7, 2009 at 7:22 PM, Igor Karp <igor.v.karp at gmail.com> wrote:

> Roel,
>
> well, these were not my ideas anyway ;-). I would be equally unhappy
> using javadoc appoach.
> And as a side note: @Override does influence the result of the compiler
> already.
>
> Igor
>
> On Sat, Mar 7, 2009 at 9:55 AM, Roel Spilker <r.spilker at gmail.com> wrote:
> > I'd say javadoc, as well as annotation, should never influence the result
> of
> > the compiler. That's just not the right vehicle.
> >
> > Roel
> >
> > On Sat, Mar 7, 2009 at 6:27 PM, Igor Karp <igor.v.karp at gmail.com> wrote:
> >>
> >> Reiner,
> >>
> >> please see the comments inline.
> >>
> >> On Fri, Mar 6, 2009 at 11:39 PM, Reinier Zwitserloot
> >> <reinier at zwitserloot.com> wrote:
> >> > Igor,
> >> >
> >> > how could the command line options be expanded? Allow -encoding to
> >> > specify a
> >> > separate encoding for each file? I don't see how that can work.
> >> For example: allow multiple -encoding options and add optional path to
> >> encoding -encoding <encoding>[,<path>]
> >> Where path can be either a package (settings applied to the package
> >> and every package under it) or a single file for maximum precision.
> >> So one can have:
> >> -encoding X - encoding Y,a.b -encoding Z,a.b.c -encoding
> >> X,a.b.c.d.IAmSpecial
> >> IAMSpecial.java will get encoding X,
> >> everything else under a.b.c will get encoding Z,
> >> everything else under a.b will get encoding Y
> >> and the rest will get encoding X.
> >> Same approach can be applied to -source.
> >>
> >> > There's no
> >> > way I or anyone else is going to edit a build script (be it just
> javac,
> >> > a
> >> > home-rolled thing, ant, rake, make, maven, ivy, etcetera) to carefully
> >> > enumerate every file's source compatibility level.
> >> Sure, thats what argfiles are for: store the settings in a file and
> >> use javac @argfile.
> >>
> >> And doing it as proposed above on a package level would make it more
> >> manageable.
> >> Remember in your proposal the only option is to specify it on a file
> >> level (this is fixable i guess).
> >>
> >> > Changing the command line
> >> > options also incurs the neccessary wrath of all those build tool
> >> > developers
> >> > as they'd have to update their software to handle the new option
> (adding
> >> > an
> >> > option is a change too!)
> >> Not more than changing the language itself.
> >>
> >> >
> >> > Could you also elaborate on why you don't like it? For example, how
> can
> >> > the
> >> > benefits of having (more) portable source files, easier migration, and
> a
> >> > much cleaner solution to e.g. the assert-in-javac1.4 be achieved with
> >> > e.g.
> >> > command line options, or do you not consider any of those worthwhile?
> >> I fully support the goal. I even see it as is a bit too narrow (see
> >> below). But I do not see a need to change the language to achieve that
> >> goal.
> >>
> >> On a conceptual level I see these options as a metadata of the source
> >> files and I don't like the idea of coupling it with the file.
> >> One can avoid all this complexity of extra parsing by specifying the
> >> encoding in an external file. This external file does not have
> >> itself to be in that encoding. In fact it can be restricted to be
> >> always in ASCII.
> >>
> >> I think the addition of an optional path and allowing multiple use of
> >> the same option approach is much more scalable: it could be extended
> >> to the other existing options (like -deprecation, -Xlint, etc.) and to
> >> the options that might appear in the future.
> >>
> >> I wish I could concentrate on deprecations in a certain package and
> >> ignore them everywhere else for now:
> >> javac -deprecation,really.rusty.one ...
> >> Finished with (or gave up on ;) that one and want to switch to the next
> >> one:
> >> javac -deprecation,another.old.one
> >>
> >> Igor Karp
> >>
> >> >
> >> > As an aside, how do people approach project coin submissions? I tend
> to
> >> > look
> >> > at a proposal's value, which is its benefit divided by the
> disadvantages
> >> > (end-programmer complexity to learn, amount of changes needed to javac
> >> > and/or JVM, and restrictions on potential future expansions). One of
> the
> >> > reasons I'm writing this up with Roel is because the disadvantages
> >> > seemed to
> >> > be almost nonexistent on the outset (the encoding stuff made it more
> >> > complicated, but at least the complication is entirely hidden from
> java
> >> > developer's eyes, so it value proposal is still aces in my book). If
> >> > there's
> >> > a goal to keep the total language changes, no matter how simple they
> >> > are,
> >> > down to a small set, then benefit regardless of disadvantages is the
> >> > better
> >> > yardstick.
> >> >
> >> >  --Reinier Zwitserloot
> >> >
> >> >
> >> >
> >> > On Mar 7, 2009, at 08:15, Igor Karp wrote:
> >> >
> >> >> On Fri, Mar 6, 2009 at 10:03 PM, Reinier Zwitserloot
> >> >> <reinier at zwitserloot.com> wrote:
> >> >>>
> >> >>> We have written up a proposal for adding a 'source' and 'encoding'
> >> >>> keyword (alternatives to the -source and -encoding keywords on the
> >> >>> command line; they work pretty much just as you expect). The
> keywords
> >> >>> are context sensitive and must both appear before anything else
> other
> >> >>> than comments to be parsed. In case the benefit isn't obvious: It is
> a
> >> >>> great help when you are trying to port a big project to a new source
> >> >>> language compatibility. Leaving half your sourcebase in v1.6 and the
> >> >>> other half in v1.7 is pretty much impossible today, it's all-or-
> >> >>> nothing. It should also be a much nicer solution to the 'assert in
> >> >>> v1.4' dilemma, which I guess is going to happen to v1.7 as well,
> given
> >> >>> that 'module' is most likely going to become a keyword. Finally, it
> >> >>> makes java files a lot more portable; you no longer run into your
> >> >>> strings looking weird when you move your Windows-1252 codefile java
> >> >>> source to a mac, for example.
> >> >>>
> >> >>> Before we finish it though, some open questions we'd like some
> >> >>> feedback on:
> >> >>>
> >> >>> A) Technically, starting a file with "source 1.4" is obviously
> silly;
> >> >>> javac v1.4 doesn't know about the source keyword and would thus fail
> >> >>> immediately. However, practically, its still useful. Example: if
> >> >>> you've mostly converted a GWT project to GWT 1.5 (which uses java
> 1.5
> >> >>> syntax), but have a few files remaining on GWT v1.4 (which uses java
> >> >>> 1.4 syntax), then tossing a "source 1.4;" in those older files
> >> >>> eliminates all the generics warnings and serves as a reminder that
> you
> >> >>> should still convert those at some point. However, it isn't
> -actually-
> >> >>> compatible with a real javac 1.4. We're leaning to making "source
> >> >>> 1.6;"  (and below) legal even when using a javac v1.7 or above, but
> >> >>> perhaps that's a bridge too far? We could go with magic comments but
> >> >>> that seems like a very bad solution.
> >> >>>
> >> >>> also:
> >> >>>
> >> >>> Encoding is rather a hairy issue; javac will need to read the file
> to
> >> >>> find the encoding, but to read a file, it needs to know about
> >> >>> encoding! Fortunately, *every single* popular encoding on
> wikipedia's
> >> >>> popular encoding list at:
> >> >>>
> >> >>>
> >> >>>
> >> >>>
> http://en.wikipedia.org/wiki/Character_encoding#Popular_character_encodings
> >> >>>
> >> >>> will encode "encoding own-name-in-that-encoding;" the same as ASCII
> >> >>> would, except for KOI-7 and UTF-7, (both 7 bit encodings that I
> doubt
> >> >>> anyone ever uses to program java).
> >> >>>
> >> >>> Therefore, the proposal includes the following strategy to find the
> >> >>> encoding statement in a java source file without knowing the
> encoding
> >> >>> beforehand:
> >> >>>
> >> >>> An entirely separate parser (the encoding parser) is run repeatedly
> >> >>> until the right encoding is found. First it'll decode the input with
> >> >>> ISO-8859-1. If that doesn't work, UTF-16 (assume BE if no BOM, as
> per
> >> >>> the java standard), then as UTF-32 (BE if no BOM), then the current
> >> >>> behaviour (-encoding parameter's value if any, otherwise platform
> >> >>> default encoding). This separate parser works as follows:
> >> >>>
> >> >>> 1. Ignore any comments and whitespace.
> >> >>> 3. Ignore the pattern (regexp-like-syntax, ): source\s+[^\s]+\s*; -
> if
> >> >>> that pattern matches partially but is not correctly completed, that
> >> >>> parser run exits without finding an encoding, immediately.
> >> >>> 4. Find the pattern: encoding\s+([^\s]+)\s*; - if that pattern
> matches
> >> >>> partially but is not correctly completed, that parser run exists
> >> >>> without finding an encoding, immediately. If it does complete, the
> >> >>> parser also exists immediately and returns the captured value.
> >> >>> 5. If it finds anything else, stop immediately, returning no
> encoding
> >> >>> found.
> >> >>>
> >> >>> Once it's found something, the 'real' java parser will run using the
> >> >>> found encoding (this overrides any -encoding on the command line).
> >> >>> Note that the encoding parser stops quickly; For example, if it
> finds
> >> >>> a stray \0 or e.g. the letter 'i' (perhaps the first letter of an
> >> >>> import statement), it'll stop immediately.
> >> >>>
> >> >>> If an encoding is encountered that was not found during the standard
> >> >>> decoding strategy (ISO-8859-1, UTF-16, UTF-32), but worked only due
> to
> >> >>> a platform default/command line encoding param, (e.g. a platform
> that
> >> >>> defaults to UTF-16LE without a byte order mark) a warning explaining
> >> >>> that the encoding statement isn't doing anything is generated. Of
> >> >>> course, if the encoding doesn't match itself, you get an error
> >> >>> (putting "encoding UTF-16;" into a UTF-8 encoded file for example).
> If
> >> >>> there is no encoding statement, the 'real' java parser does what it
> >> >>> does now: Use the -encoding parameter of javac, and if that wasn't
> >> >>> present, the platform default.
> >> >>>
> >> >>> However, there is 1 major and 1 minor problem with this approach:
> >> >>>
> >> >>> B) This means javac will need to read every source file many times
> to
> >> >>> compile it.
> >> >>>
> >> >>> Worst case (no encoding keyword): 5 times.
> >> >>> Standard case if an encoding keyword: 2 times (3 times if UTF-16).
> >> >>>
> >> >>> Fortunately all runs should stop quickly, due to the encoding
> parser's
> >> >>> penchant to quit very early. Javacs out there will either stuff the
> >> >>> entire source file into memory, or if not, disk cache should take
> care
> >> >>> of it, but we can't prove beyond a doubt that this repeated parsing
> >> >>> will have no significant impact on compile time. Is this a
> >> >>> showstopper? Is the need to include a new (but small) parser into
> >> >>> javac a showstopper?
> >> >>>
> >> >>> C) Certain character sets, such as ISO-2022, can make the encoding
> >> >>> statement unreadable with the standard strategy if a comment
> including
> >> >>> non-ASCII characters precedes the encoding statement. These
> situations
> >> >>> are very rare (in fact, I haven't managed to find an example), so is
> >> >>> it okay to just ignore this issue? If you add the encoding statement
> >> >>> after a bunch of comments that make it invisible, and then compile
> it
> >> >>> with the right -encoding parameter, you WILL get a warning that the
> >> >>> encoding statement isn't going to help a javac on another platform /
> >> >>> without that encoding parameter to figure it out, so you just get
> the
> >> >>> current status quo: your source file won't compile without an
> explicit
> >> >>> -encoding parameter (or if that happens to be the platform default).
> >> >>> Should this be mentioned in the proposal? Should the compiler (and
> the
> >> >>> proposal) put effort into generating a useful warning message, such
> as
> >> >>> figuring out if it WOULD parse correctly if the encoding statement
> is
> >> >>> at the very top of the source file, vs. suggesting to recode in
> UTF-8?
> >> >>>
> >> >>> and a final dilemma:
> >> >>>
> >> >>> D) Should we separate the proposals for source and encoding
> keywords?
> >> >>> The source keyword is more useful and a lot simpler overall than the
> >> >>> encoding keyword, but they do sort of go together.
> >> >>
> >> >> Separate. Another reason is: the argument of applying different
> >> >> settings
> >> >> to
> >> >> different parts of the project is much less valid with encoding than
> >> >> with source.
> >> >>
> >> >>>
> >> >>> --Reinier Zwitserloot and Roel Spilker
> >> >>>
> >> >>>
> >> >> Overall: I would prefer command line options enhanced to handle the
> >> >> situation
> >> >> rather than language change.
> >> >>
> >> >> Igor Karp
> >> >
> >> >
> >>
> >
> >
>