Fix detection of feature gate use inside of println! #20661
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nominating for 1.0, this allows one to subvert feature gates |
brson
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Jan 7, 2015
This partially implements the feature staging described in the [release channel RFC][rc]. It does not yet fully conform to the RFC as written, but does accomplish its goals sufficiently for the 1.0 alpha release. It has three primary user-visible effects: * On the nightly channel, use of unstable APIs generates a warning. * On the beta channel, use of unstable APIs generates a warning. * On the beta channel, use of feature gates generates a warning. Code that does not trigger these warnings is considered 'stable', modulo pre-1.0 bugs. Disabling the warnings for unstable APIs continues to be done in the existing (i.e. old) style, via `#[allow(...)]`, not that specified in the RFC. I deem this marginally acceptable since any code that must do this is not using the stable dialect of Rust. Use of feature gates is itself gated with the new 'unstable_features' lint, on nightly set to 'allow', and on beta 'warn'. The attribute scheme used here corresponds to an older version of the RFC, with the `#[staged_api]` crate attribute toggling the staging behavior of the stability attributes, but the user impact is only in-tree so I'm not concerned about having to make design changes later (and I may ultimately prefer the scheme here after all, with the `#[staged_api]` crate attribute). Since the Rust codebase itself makes use of unstable features the compiler and build system to a midly elaborate dance to allow it to bootstrap while disobeying these lints (which would otherwise be errors because Rust builds with `-D warnings`). This patch includes one significant hack that causes a regression. Because the `format_args!` macro emits calls to unstable APIs it would trigger the lint. I added a hack to the lint to make it not trigger, but this in turn causes arguments to `println!` not to be checked for feature gates. I don't presently understand macro expansion well enough to fix. This is bug rust-lang#20661. Closes rust-lang#16678 [rc]: https://github.com/rust-lang/rfcs/blob/master/text/0507-release-channels.md
alexcrichton
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Jan 8, 2015
This partially implements the feature staging described in the [release channel RFC][rc]. It does not yet fully conform to the RFC as written, but does accomplish its goals sufficiently for the 1.0 alpha release. It has three primary user-visible effects: * On the nightly channel, use of unstable APIs generates a warning. * On the beta channel, use of unstable APIs generates a warning. * On the beta channel, use of feature gates generates a warning. Code that does not trigger these warnings is considered 'stable', modulo pre-1.0 bugs. Disabling the warnings for unstable APIs continues to be done in the existing (i.e. old) style, via `#[allow(...)]`, not that specified in the RFC. I deem this marginally acceptable since any code that must do this is not using the stable dialect of Rust. Use of feature gates is itself gated with the new 'unstable_features' lint, on nightly set to 'allow', and on beta 'warn'. The attribute scheme used here corresponds to an older version of the RFC, with the `#[staged_api]` crate attribute toggling the staging behavior of the stability attributes, but the user impact is only in-tree so I'm not concerned about having to make design changes later (and I may ultimately prefer the scheme here after all, with the `#[staged_api]` crate attribute). Since the Rust codebase itself makes use of unstable features the compiler and build system do a midly elaborate dance to allow it to bootstrap while disobeying these lints (which would otherwise be errors because Rust builds with `-D warnings`). This patch includes one significant hack that causes a regression. Because the `format_args!` macro emits calls to unstable APIs it would trigger the lint. I added a hack to the lint to make it not trigger, but this in turn causes arguments to `println!` not to be checked for feature gates. I don't presently understand macro expansion well enough to fix. This is bug rust-lang#20661. Closes rust-lang#16678 [rc]: https://github.com/rust-lang/rfcs/blob/master/text/0507-release-channels.md Next steps are to disable the existing out-of-tree behavior for stability attributes, and convert the remaining system to be feature-based per the RFC. During the first beta cycle we will set these lints to 'forbid'.
alexcrichton
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Jan 14, 2015
This commit performs a final stabilization pass over the std::fmt module, marking all necessary APIs as stable. One of the more interesting aspects of this module is that it exposes a good deal of its runtime representation to the outside world in order for `format_args!` to be able to construct the format strings. Instead of hacking the compiler to assume that these items are stable, this commit instead lays out a story for the stabilization and evolution of these APIs. There are three primary details used by the `format_args!` macro: 1. `Arguments` - an opaque package of a "compiled format string". This structure is passed around and the `write` function is the source of truth for transforming a compiled format string into a string at runtime. This must be able to be constructed in stable code. 2. `Argument` - an opaque structure representing an argument to a format string. This is *almost* a trait object as it's just a pointer/function pair, but due to the function originating from one of many traits, it's not actually a trait object. Like `Arguments`, this must be constructed from stable code. 3. `fmt::rt` - this module contains the runtime type definitions primarily for the `rt::Argument` structure. Whenever an argument is formatted with nonstandard flags, a corresponding `rt::Argument` is generated describing how the argument is being formatted. This can be used to construct an `Arguments`. The primary interface to `std::fmt` is the `Arguments` structure, and as such this type name is stabilize as-is today. It is expected for libraries to pass around an `Arguments` structure to represent a pending formatted computation. The remaining portions are largely "cruft" which would rather not be stabilized, but due to the stability checks they must be. As a result, almost all pieces have been renamed to represent that they are "version 1" of the formatting representation. The theory is that at a later date if we change the representation of these types we can add new definitions called "version 2" and corresponding constructors for `Arguments`. One of the other remaining large questions about the fmt module were how the pending I/O reform would affect the signatures of methods in the module. Due to [RFC 526][rfc], however, the writers of fmt are now incompatible with the writers of io, so this question has largely been solved. As a result the interfaces are largely stabilized as-is today. [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0526-fmt-text-writer.md Specifically, the following changes were made: * The contents of `fmt::rt` were all moved under `fmt::rt::v1` * `fmt::rt` is stable * `fmt::rt::v1` is stable * `Error` is stable * `Writer` is stable * `Writer::write_str` is stable * `Writer::write_fmt` is stable * `Formatter` is stable * `Argument` has been renamed to `ArgumentV1` and is stable * `ArgumentV1::new` is stable * `ArgumentV1::from_uint` is stable * `Arguments::new_v1` is stable (renamed from `new`) * `Arguments::new_v1_formatted` is stable (renamed from `with_placeholders`) * All formatting traits are now stable, as well as the `fmt` method. * `fmt::write` is stable * `fmt::format` is stable * `Formatter::pad_integral` is stable * `Formatter::pad` is stable * `Formatter::write_str` is stable * `Formatter::write_fmt` is stable * Some assorted top level items which were only used by `format_args!` were removed in favor of static functions on `ArgumentV1` as well. * The formatting-flag-accessing methods remain unstable Within the contents of the `fmt::rt::v1` module, the following actions were taken: * Reexports of all enum variants were removed * All prefixes on enum variants were removed * A few miscellaneous enum variants were renamed * Otherwise all structs, fields, and variants were marked stable. In addition to these actions in the `std::fmt` module, many implementations of `Show` and `String` were stabilized as well. In some other modules: * `ToString` is now stable * `ToString::to_string` is now stable * `Vec` no longer implements `fmt::Writer` (this has moved to `String`) While stabilize the formatting traits, the following change was also made to the `result` module: * `Result::unwrap` now requires `String` instead of `Show` * `Result::unwrap_err` now requires `String` instead of `Show` This is a breaking change due to all of the changes to the `fmt::rt` module, but this likely will not have much impact on existing programs. It is also a breaking change due to the usage of `String` for `unwrap()` on `Result` instead of `Show`. Error types should implement `String` for human readable errors and `Show` for inspecting their representation. Closes rust-lang#20661 [breaking-change]
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I've fixed this in #21125 |
alexcrichton
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Jan 30, 2015
This commit performs a final stabilization pass over the std::fmt module, marking all necessary APIs as stable. One of the more interesting aspects of this module is that it exposes a good deal of its runtime representation to the outside world in order for `format_args!` to be able to construct the format strings. Instead of hacking the compiler to assume that these items are stable, this commit instead lays out a story for the stabilization and evolution of these APIs. There are three primary details used by the `format_args!` macro: 1. `Arguments` - an opaque package of a "compiled format string". This structure is passed around and the `write` function is the source of truth for transforming a compiled format string into a string at runtime. This must be able to be constructed in stable code. 2. `Argument` - an opaque structure representing an argument to a format string. This is *almost* a trait object as it's just a pointer/function pair, but due to the function originating from one of many traits, it's not actually a trait object. Like `Arguments`, this must be constructed from stable code. 3. `fmt::rt` - this module contains the runtime type definitions primarily for the `rt::Argument` structure. Whenever an argument is formatted with nonstandard flags, a corresponding `rt::Argument` is generated describing how the argument is being formatted. This can be used to construct an `Arguments`. The primary interface to `std::fmt` is the `Arguments` structure, and as such this type name is stabilize as-is today. It is expected for libraries to pass around an `Arguments` structure to represent a pending formatted computation. The remaining portions are largely "cruft" which would rather not be stabilized, but due to the stability checks they must be. As a result, almost all pieces have been renamed to represent that they are "version 1" of the formatting representation. The theory is that at a later date if we change the representation of these types we can add new definitions called "version 2" and corresponding constructors for `Arguments`. One of the other remaining large questions about the fmt module were how the pending I/O reform would affect the signatures of methods in the module. Due to [RFC 526][rfc], however, the writers of fmt are now incompatible with the writers of io, so this question has largely been solved. As a result the interfaces are largely stabilized as-is today. [rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0526-fmt-text-writer.md Specifically, the following changes were made: * The contents of `fmt::rt` were all moved under `fmt::rt::v1` * `fmt::rt` is stable * `fmt::rt::v1` is stable * `Error` is stable * `Writer` is stable * `Writer::write_str` is stable * `Writer::write_fmt` is stable * `Formatter` is stable * `Argument` has been renamed to `ArgumentV1` and is stable * `ArgumentV1::new` is stable * `ArgumentV1::from_uint` is stable * `Arguments::new_v1` is stable (renamed from `new`) * `Arguments::new_v1_formatted` is stable (renamed from `with_placeholders`) * All formatting traits are now stable, as well as the `fmt` method. * `fmt::write` is stable * `fmt::format` is stable * `Formatter::pad_integral` is stable * `Formatter::pad` is stable * `Formatter::write_str` is stable * `Formatter::write_fmt` is stable * Some assorted top level items which were only used by `format_args!` were removed in favor of static functions on `ArgumentV1` as well. * The formatting-flag-accessing methods remain unstable Within the contents of the `fmt::rt::v1` module, the following actions were taken: * Reexports of all enum variants were removed * All prefixes on enum variants were removed * A few miscellaneous enum variants were renamed * Otherwise all structs, fields, and variants were marked stable. In addition to these actions in the `std::fmt` module, many implementations of `Show` and `String` were stabilized as well. In some other modules: * `ToString` is now stable * `ToString::to_string` is now stable * `Vec` no longer implements `fmt::Writer` (this has moved to `String`) This is a breaking change due to all of the changes to the `fmt::rt` module, but this likely will not have much impact on existing programs. Closes rust-lang#20661 [breaking-change]
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I'm going to submit a patch that breaks feature gate detection inside of the arguments to println! in order to get feature staging turned on.
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