PRE-PROPOSAL: Source and Encoding keyword

[Igor Karp]

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
>> >
>> >
>>
>
>