1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Calculation and management of a Strict Version Hash for crates
13 //! # Today's ABI problem
15 //! In today's implementation of rustc, it is incredibly difficult to achieve
16 //! forward binary compatibility without resorting to C-like interfaces. Within
17 //! rust code itself, abi details such as symbol names suffer from a variety of
18 //! unrelated factors to code changing such as the "def id drift" problem. This
19 //! ends up yielding confusing error messages about metadata mismatches and
22 //! The core of this problem is when an upstream dependency changes and
23 //! downstream dependents are not recompiled. This causes compile errors because
24 //! the upstream crate's metadata has changed but the downstream crates are
25 //! still referencing the older crate's metadata.
27 //! This problem exists for many reasons, the primary of which is that rust does
28 //! not currently support forwards ABI compatibility (in place upgrades of a
31 //! # SVH and how it alleviates the problem
33 //! With all of this knowledge on hand, this module contains the implementation
34 //! of a notion of a "Strict Version Hash" for a crate. This is essentially a
35 //! hash of all contents of a crate which can somehow be exposed to downstream
38 //! This hash is currently calculated by just hashing the AST, but this is
39 //! obviously wrong (doc changes should not result in an incompatible ABI).
40 //! Implementation-wise, this is required at this moment in time.
42 //! By encoding this strict version hash into all crate's metadata, stale crates
43 //! can be detected immediately and error'd about by rustc itself.
47 //! Original issue: https://github.com/rust-lang/rust/issues/10207
50 use std::hash::{Hash, SipHasher, Hasher};
51 use std::iter::range_step;
55 #[derive(Clone, PartialEq)]
61 pub fn new(hash: &str) -> Svh {
62 assert!(hash.len() == 16);
63 Svh { hash: hash.to_string() }
66 pub fn as_str<'a>(&'a self) -> &'a str {
70 pub fn calculate(metadata: &Vec<String>, krate: &ast::Crate) -> Svh {
71 // FIXME (#14132): This is better than it used to be, but it still not
72 // ideal. We now attempt to hash only the relevant portions of the
73 // Crate AST as well as the top-level crate attributes. (However,
74 // the hashing of the crate attributes should be double-checked
75 // to ensure it is not incorporating implementation artifacts into
76 // the hash that are not otherwise visible.)
78 // FIXME: this should use SHA1, not SipHash. SipHash is not built to
80 let mut state = SipHasher::new();
82 for data in metadata.iter() {
83 data.hash(&mut state);
87 let mut visit = svh_visitor::make(&mut state);
88 visit::walk_crate(&mut visit, krate);
91 // FIXME (#14132): This hash is still sensitive to e.g. the
92 // spans of the crate Attributes and their underlying
93 // MetaItems; we should make ContentHashable impl for those
94 // types and then use hash_content. But, since all crate
95 // attributes should appear near beginning of the file, it is
96 // not such a big deal to be sensitive to their spans for now.
98 // We hash only the MetaItems instead of the entire Attribute
99 // to avoid hashing the AttrId
100 for attr in krate.attrs.iter() {
101 attr.node.value.hash(&mut state);
104 let hash = state.finish();
106 hash: range_step(0u, 64u, 4u).map(|i| hex(hash >> i)).collect()
109 fn hex(b: u64) -> char {
110 let b = (b & 0xf) as u8;
112 0 ... 9 => '0' as u8 + b,
113 _ => 'a' as u8 + b - 10,
120 impl fmt::Show for Svh {
121 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
122 write!(f, "Svh {{ {} }}", self.as_str())
126 impl fmt::String for Svh {
127 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
132 // FIXME (#14132): Even this SVH computation still has implementation
133 // artifacts: namely, the order of item declaration will affect the
134 // hash computation, but for many kinds of items the order of
135 // declaration should be irrelevant to the ABI.
138 pub use self::SawExprComponent::*;
139 pub use self::SawStmtComponent::*;
140 use self::SawAbiComponent::*;
143 use syntax::codemap::Span;
144 use syntax::parse::token;
145 use syntax::print::pprust;
147 use syntax::visit::{Visitor, FnKind};
149 use std::hash::{Hash, SipHasher};
151 pub struct StrictVersionHashVisitor<'a> {
152 pub st: &'a mut SipHasher,
155 pub fn make<'a>(st: &'a mut SipHasher) -> StrictVersionHashVisitor<'a> {
156 StrictVersionHashVisitor { st: st }
159 // To off-load the bulk of the hash-computation on deriving(Hash),
160 // we define a set of enums corresponding to the content that our
161 // crate visitor will encounter as it traverses the ast.
163 // The important invariant is that all of the Saw*Component enums
164 // do not carry any Spans, Names, or Idents.
166 // Not carrying any Names/Idents is the important fix for problem
167 // noted on PR #13948: using the ident.name as the basis for a
168 // hash leads to unstable SVH, because ident.name is just an index
169 // into intern table (i.e. essentially a random address), not
170 // computed from the name content.
172 // With the below enums, the SVH computation is not sensitive to
173 // artifacts of how rustc was invoked nor of how the source code
174 // was laid out. (Or at least it is *less* sensitive.)
176 // This enum represents the different potential bits of code the
177 // visitor could encounter that could affect the ABI for the crate,
178 // and assigns each a distinct tag to feed into the hash computation.
180 enum SawAbiComponent<'a> {
182 // FIXME (#14132): should we include (some function of)
183 // ident.ctxt as well?
184 SawIdent(token::InternedString),
185 SawStructDef(token::InternedString),
187 SawLifetimeRef(token::InternedString),
188 SawLifetimeDef(token::InternedString),
209 SawExpr(SawExprComponent<'a>),
210 SawStmt(SawStmtComponent),
213 /// SawExprComponent carries all of the information that we want
214 /// to include in the hash that *won't* be covered by the
215 /// subsequent recursive traversal of the expression's
216 /// substructure by the visitor.
218 /// We know every Expr_ variant is covered by a variant because
219 /// `fn saw_expr` maps each to some case below. Ensuring that
220 /// each variant carries an appropriate payload has to be verified
223 /// (However, getting that *exactly* right is not so important
224 /// because the SVH is just a developer convenience; there is no
225 /// guarantee of collision-freedom, hash collisions are just
226 /// (hopefully) unlikely.)
228 pub enum SawExprComponent<'a> {
230 SawExprLoop(Option<token::InternedString>),
231 SawExprField(token::InternedString),
232 SawExprTupField(uint),
233 SawExprBreak(Option<token::InternedString>),
234 SawExprAgain(Option<token::InternedString>),
241 SawExprBinary(ast::BinOp),
242 SawExprUnary(ast::UnOp),
243 SawExprLit(ast::Lit_),
251 SawExprAssignOp(ast::BinOp),
255 SawExprAddrOf(ast::Mutability),
257 SawExprInlineAsm(&'a ast::InlineAsm),
264 fn saw_expr<'a>(node: &'a Expr_) -> SawExprComponent<'a> {
266 ExprBox(..) => SawExprBox,
267 ExprVec(..) => SawExprVec,
268 ExprCall(..) => SawExprCall,
269 ExprMethodCall(..) => SawExprMethodCall,
270 ExprTup(..) => SawExprTup,
271 ExprBinary(op, _, _) => SawExprBinary(op),
272 ExprUnary(op, _) => SawExprUnary(op),
273 ExprLit(ref lit) => SawExprLit(lit.node.clone()),
274 ExprCast(..) => SawExprCast,
275 ExprIf(..) => SawExprIf,
276 ExprWhile(..) => SawExprWhile,
277 ExprLoop(_, id) => SawExprLoop(id.map(content)),
278 ExprMatch(..) => SawExprMatch,
279 ExprClosure(..) => SawExprClosure,
280 ExprBlock(..) => SawExprBlock,
281 ExprAssign(..) => SawExprAssign,
282 ExprAssignOp(op, _, _) => SawExprAssignOp(op),
283 ExprField(_, id) => SawExprField(content(id.node)),
284 ExprTupField(_, id) => SawExprTupField(id.node),
285 ExprIndex(..) => SawExprIndex,
286 ExprRange(..) => SawExprRange,
287 ExprPath(..) => SawExprPath,
288 ExprAddrOf(m, _) => SawExprAddrOf(m),
289 ExprBreak(id) => SawExprBreak(id.map(content)),
290 ExprAgain(id) => SawExprAgain(id.map(content)),
291 ExprRet(..) => SawExprRet,
292 ExprInlineAsm(ref asm) => SawExprInlineAsm(asm),
293 ExprStruct(..) => SawExprStruct,
294 ExprRepeat(..) => SawExprRepeat,
295 ExprParen(..) => SawExprParen,
296 ExprForLoop(..) => SawExprForLoop,
298 // just syntactic artifacts, expanded away by time of SVH.
299 ExprIfLet(..) => unreachable!(),
300 ExprWhileLet(..) => unreachable!(),
301 ExprMac(..) => unreachable!(),
305 /// SawStmtComponent is analogous to SawExprComponent, but for statements.
307 pub enum SawStmtComponent {
313 fn saw_stmt(node: &Stmt_) -> SawStmtComponent {
315 StmtDecl(..) => SawStmtDecl,
316 StmtExpr(..) => SawStmtExpr,
317 StmtSemi(..) => SawStmtSemi,
318 StmtMac(..) => unreachable!(),
322 // Ad-hoc overloading between Ident and Name to their intern table lookups.
323 trait InternKey { fn get_content(self) -> token::InternedString; }
324 impl InternKey for Ident {
325 fn get_content(self) -> token::InternedString { token::get_ident(self) }
327 impl InternKey for Name {
328 fn get_content(self) -> token::InternedString { token::get_name(self) }
330 fn content<K:InternKey>(k: K) -> token::InternedString { k.get_content() }
332 impl<'a, 'v> Visitor<'v> for StrictVersionHashVisitor<'a> {
334 fn visit_mac(&mut self, mac: &Mac) {
335 // macro invocations, namely macro_rules definitions,
336 // *can* appear as items, even in the expanded crate AST.
338 if macro_name(mac).get() == "macro_rules" {
339 // Pretty-printing definition to a string strips out
340 // surface artifacts (currently), such as the span
341 // information, yielding a content-based hash.
343 // FIXME (#14132): building temporary string is
344 // expensive; a direct content-based hash on token
345 // trees might be faster. Implementing this is far
346 // easier in short term.
347 let macro_defn_as_string = pprust::to_string(|pp_state| {
348 pp_state.print_mac(mac, token::Paren)
350 macro_defn_as_string.hash(self.st);
352 // It is not possible to observe any kind of macro
353 // invocation at this stage except `macro_rules!`.
354 panic!("reached macro somehow: {}",
355 pprust::to_string(|pp_state| {
356 pp_state.print_mac(mac, token::Paren)
360 visit::walk_mac(self, mac);
362 fn macro_name(mac: &Mac) -> token::InternedString {
364 &MacInvocTT(ref path, ref _tts, ref _stx_ctxt) => {
365 let s = &path.segments[];
366 assert_eq!(s.len(), 1);
367 content(s[0].identifier)
373 fn visit_struct_def(&mut self, s: &StructDef, ident: Ident,
374 g: &Generics, _: NodeId) {
375 SawStructDef(content(ident)).hash(self.st);
376 visit::walk_generics(self, g);
377 visit::walk_struct_def(self, s)
380 fn visit_variant(&mut self, v: &Variant, g: &Generics) {
381 SawVariant.hash(self.st);
382 // walk_variant does not call walk_generics, so do it here.
383 visit::walk_generics(self, g);
384 visit::walk_variant(self, v, g)
387 fn visit_opt_lifetime_ref(&mut self, _: Span, l: &Option<Lifetime>) {
388 SawOptLifetimeRef.hash(self.st);
389 // (This is a strange method in the visitor trait, in that
390 // it does not expose a walk function to do the subroutine
393 Some(ref l) => self.visit_lifetime_ref(l),
398 // All of the remaining methods just record (in the hash
399 // SipHasher) that the visitor saw that particular variant
400 // (with its payload), and continue walking as the default
403 // Some of the implementations have some notes as to how one
404 // might try to make their SVH computation less discerning
405 // (e.g. by incorporating reachability analysis). But
406 // currently all of their implementations are uniform and
409 // (If you edit a method such that it deviates from the
410 // pattern, please move that method up above this comment.)
412 fn visit_ident(&mut self, _: Span, ident: Ident) {
413 SawIdent(content(ident)).hash(self.st);
416 fn visit_lifetime_ref(&mut self, l: &Lifetime) {
417 SawLifetimeRef(content(l.name)).hash(self.st);
420 fn visit_lifetime_def(&mut self, l: &LifetimeDef) {
421 SawLifetimeDef(content(l.lifetime.name)).hash(self.st);
424 // We do recursively walk the bodies of functions/methods
425 // (rather than omitting their bodies from the hash) since
426 // monomorphization and cross-crate inlining generally implies
427 // that a change to a crate body will require downstream
428 // crates to be recompiled.
429 fn visit_expr(&mut self, ex: &Expr) {
430 SawExpr(saw_expr(&ex.node)).hash(self.st); visit::walk_expr(self, ex)
433 fn visit_stmt(&mut self, s: &Stmt) {
434 SawStmt(saw_stmt(&s.node)).hash(self.st); visit::walk_stmt(self, s)
437 fn visit_view_item(&mut self, i: &ViewItem) {
438 // Two kinds of view items can affect the ABI for a crate:
439 // exported `pub use` view items (since that may expose
440 // items that downstream crates can call), and `use
441 // foo::Trait`, since changing that may affect method
444 // The simplest approach to handling both of the above is
445 // just to adopt the same simple-minded (fine-grained)
446 // hash that I am deploying elsewhere here.
447 SawViewItem.hash(self.st); visit::walk_view_item(self, i)
450 fn visit_foreign_item(&mut self, i: &ForeignItem) {
451 // FIXME (#14132) ideally we would incorporate privacy (or
452 // perhaps reachability) somewhere here, so foreign items
453 // that do not leak into downstream crates would not be
455 SawForeignItem.hash(self.st); visit::walk_foreign_item(self, i)
458 fn visit_item(&mut self, i: &Item) {
459 // FIXME (#14132) ideally would incorporate reachability
460 // analysis somewhere here, so items that never leak into
461 // downstream crates (e.g. via monomorphisation or
462 // inlining) would not be part of the ABI.
463 SawItem.hash(self.st); visit::walk_item(self, i)
466 fn visit_mod(&mut self, m: &Mod, _s: Span, _n: NodeId) {
467 SawMod.hash(self.st); visit::walk_mod(self, m)
470 fn visit_decl(&mut self, d: &Decl) {
471 SawDecl.hash(self.st); visit::walk_decl(self, d)
474 fn visit_ty(&mut self, t: &Ty) {
475 SawTy.hash(self.st); visit::walk_ty(self, t)
478 fn visit_generics(&mut self, g: &Generics) {
479 SawGenerics.hash(self.st); visit::walk_generics(self, g)
482 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v FnDecl,
483 b: &'v Block, s: Span, _: NodeId) {
484 SawFn.hash(self.st); visit::walk_fn(self, fk, fd, b, s)
487 fn visit_ty_method(&mut self, t: &TypeMethod) {
488 SawTyMethod.hash(self.st); visit::walk_ty_method(self, t)
491 fn visit_trait_item(&mut self, t: &TraitItem) {
492 SawTraitMethod.hash(self.st); visit::walk_trait_item(self, t)
495 fn visit_struct_field(&mut self, s: &StructField) {
496 SawStructField.hash(self.st); visit::walk_struct_field(self, s)
499 fn visit_explicit_self(&mut self, es: &ExplicitSelf) {
500 SawExplicitSelf.hash(self.st); visit::walk_explicit_self(self, es)
503 fn visit_path(&mut self, path: &Path, _: ast::NodeId) {
504 SawPath.hash(self.st); visit::walk_path(self, path)
507 fn visit_block(&mut self, b: &Block) {
508 SawBlock.hash(self.st); visit::walk_block(self, b)
511 fn visit_pat(&mut self, p: &Pat) {
512 SawPat.hash(self.st); visit::walk_pat(self, p)
515 fn visit_local(&mut self, l: &Local) {
516 SawLocal.hash(self.st); visit::walk_local(self, l)
519 fn visit_arm(&mut self, a: &Arm) {
520 SawArm.hash(self.st); visit::walk_arm(self, a)