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auto merge of #12533 : alexcrichton/rust/svh, r=brson
These hashes are used to detect changes to upstream crates and generate errors which mention that crates possibly need recompilation. More details can be found in the respective commit messages below. This change is also accompanied with a much needed refactoring of some of the crate loading code to focus more on crate ids instead of name/version pairs. Closes #12601
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,112 @@ | ||
| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
|
|
||
| //! Calculation and management of a Strict Version Hash for crates | ||
| //! | ||
| //! # Today's ABI problem | ||
| //! | ||
| //! In today's implementation of rustc, it is incredibly difficult to achieve | ||
| //! forward binary compatibility without resorting to C-like interfaces. Within | ||
| //! rust code itself, abi details such as symbol names suffer from a variety of | ||
| //! unrelated factors to code changing such as the "def id drift" problem. This | ||
| //! ends up yielding confusing error messages about metadata mismatches and | ||
| //! such. | ||
| //! | ||
| //! The core of this problem is when when an upstream dependency changes and | ||
| //! downstream dependants are not recompiled. This causes compile errors because | ||
| //! the upstream crate's metadata has changed but the downstream crates are | ||
| //! still referencing the older crate's metadata. | ||
| //! | ||
| //! This problem exists for many reasons, the primary of which is that rust does | ||
| //! not currently support forwards ABI compatibility (in place upgrades of a | ||
| //! crate). | ||
| //! | ||
| //! # SVH and how it alleviates the problem | ||
| //! | ||
| //! With all of this knowledge on hand, this module contains the implementation | ||
| //! of a notion of a "Strict Version Hash" for a crate. This is essentially a | ||
| //! hash of all contents of a crate which can somehow be exposed to downstream | ||
| //! crates. | ||
| //! | ||
| //! This hash is currently calculated by just hashing the AST, but this is | ||
| //! obviously wrong (doc changes should not result in an incompatible ABI). | ||
| //! Implementation-wise, this is required at this moment in time. | ||
| //! | ||
| //! By encoding this strict version hash into all crate's metadata, stale crates | ||
| //! can be detected immediately and error'd about by rustc itself. | ||
| //! | ||
| //! # Relevant links | ||
| //! | ||
| //! Original issue: https://github.com/mozilla/rust/issues/10207 | ||
| use std::fmt; | ||
| use std::hash::Hash; | ||
| use std::hash::sip::SipState; | ||
| use std::iter::range_step; | ||
| use syntax::ast; | ||
|
|
||
| #[deriving(Clone, Eq)] | ||
| pub struct Svh { | ||
| priv hash: ~str, | ||
| } | ||
|
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||
| impl Svh { | ||
| pub fn new(hash: &str) -> Svh { | ||
| assert!(hash.len() == 16); | ||
| Svh { hash: hash.to_owned() } | ||
| } | ||
|
|
||
| pub fn as_str<'a>(&'a self) -> &'a str { | ||
| self.hash.as_slice() | ||
| } | ||
|
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| pub fn calculate(krate: &ast::Crate) -> Svh { | ||
| // FIXME: see above for why this is wrong, it shouldn't just hash the | ||
| // crate. Fixing this would require more in-depth analysis in | ||
| // this function about what portions of the crate are reachable | ||
| // in tandem with bug fixes throughout the rest of the compiler. | ||
| // | ||
| // Note that for now we actually exclude some top-level things | ||
| // from the crate like the CrateConfig/span. The CrateConfig | ||
| // contains command-line `--cfg` flags, so this means that the | ||
| // stage1/stage2 AST for libstd and such is different hash-wise | ||
| // when it's actually the exact same representation-wise. | ||
| // | ||
| // As a first stab at only hashing the relevant parts of the | ||
| // AST, this only hashes the module/attrs, not the CrateConfig | ||
| // field. | ||
| // | ||
| // FIXME: this should use SHA1, not SipHash. SipHash is not built to | ||
| // avoid collisions. | ||
| let mut state = SipState::new(); | ||
| krate.module.hash(&mut state); | ||
| krate.attrs.hash(&mut state); | ||
|
|
||
| let hash = state.result(); | ||
| return Svh { | ||
| hash: range_step(0, 64, 4).map(|i| hex(hash >> i)).collect() | ||
| }; | ||
|
|
||
| fn hex(b: u64) -> char { | ||
| let b = (b & 0xf) as u8; | ||
| let b = match b { | ||
| 0 .. 9 => '0' as u8 + b, | ||
| _ => 'a' as u8 + b - 10, | ||
| }; | ||
| b as char | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl fmt::Show for Svh { | ||
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| f.pad(self.as_str()) | ||
| } | ||
| } |
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