rust/src/librustc_back/svh.rs

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// 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 an upstream dependency changes and
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//! downstream dependents 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
//!
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//! Original issue: https://github.com/rust-lang/rust/issues/10207
use std::fmt;
use std::hash::Hash;
use std::hash::sip::SipState;
use std::iter::range_step;
use syntax::ast;
use syntax::visit;
#[derive(Clone, PartialEq)]
pub struct Svh {
hash: String,
}
impl Svh {
pub fn new(hash: &str) -> Svh {
assert!(hash.len() == 16);
Svh { hash: hash.to_string() }
}
pub fn as_str<'a>(&'a self) -> &'a str {
self.hash.index(&FullRange)
}
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pub fn calculate(metadata: &Vec<String>, krate: &ast::Crate) -> Svh {
// FIXME (#14132): This is better than it used to be, but it still not
// ideal. We now attempt to hash only the relevant portions of the
// Crate AST as well as the top-level crate attributes. (However,
// the hashing of the crate attributes should be double-checked
// to ensure it is not incorporating implementation artifacts into
// the hash that are not otherwise visible.)
// FIXME: this should use SHA1, not SipHash. SipHash is not built to
// avoid collisions.
let mut state = SipState::new();
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for data in metadata.iter() {
data.hash(&mut state);
}
{
let mut visit = svh_visitor::make(&mut state);
visit::walk_crate(&mut visit, krate);
}
// FIXME (#14132): This hash is still sensitive to e.g. the
// spans of the crate Attributes and their underlying
// MetaItems; we should make ContentHashable impl for those
// types and then use hash_content. But, since all crate
// attributes should appear near beginning of the file, it is
// not such a big deal to be sensitive to their spans for now.
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//
// We hash only the MetaItems instead of the entire Attribute
// to avoid hashing the AttrId
for attr in krate.attrs.iter() {
attr.node.value.hash(&mut state);
}
let hash = state.result();
return Svh {
hash: range_step(0u, 64u, 4u).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 {
//NOTE(stage0): uncomment after snapshot
//write!(f, "Svh {{ {} }}", self.as_str())
fmt::String::fmt(self, f)
}
}
impl fmt::String for Svh {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.pad(self.as_str())
}
}
// FIXME (#14132): Even this SVH computation still has implementation
// artifacts: namely, the order of item declaration will affect the
// hash computation, but for many kinds of items the order of
// declaration should be irrelevant to the ABI.
mod svh_visitor {
pub use self::SawExprComponent::*;
pub use self::SawStmtComponent::*;
use self::SawAbiComponent::*;
use syntax::ast;
use syntax::ast::*;
use syntax::codemap::Span;
use syntax::parse::token;
use syntax::print::pprust;
use syntax::visit;
use syntax::visit::{Visitor, FnKind};
use std::hash::Hash;
use std::hash::sip::SipState;
pub struct StrictVersionHashVisitor<'a> {
pub st: &'a mut SipState,
}
pub fn make<'a>(st: &'a mut SipState) -> StrictVersionHashVisitor<'a> {
StrictVersionHashVisitor { st: st }
}
// To off-load the bulk of the hash-computation on deriving(Hash),
// we define a set of enums corresponding to the content that our
// crate visitor will encounter as it traverses the ast.
//
// The important invariant is that all of the Saw*Component enums
// do not carry any Spans, Names, or Idents.
//
// Not carrying any Names/Idents is the important fix for problem
// noted on PR #13948: using the ident.name as the basis for a
// hash leads to unstable SVH, because ident.name is just an index
// into intern table (i.e. essentially a random address), not
// computed from the name content.
//
// With the below enums, the SVH computation is not sensitive to
// artifacts of how rustc was invoked nor of how the source code
// was laid out. (Or at least it is *less* sensitive.)
// This enum represents the different potential bits of code the
// visitor could encounter that could affect the ABI for the crate,
// and assigns each a distinct tag to feed into the hash computation.
#[derive(Hash)]
enum SawAbiComponent<'a> {
// FIXME (#14132): should we include (some function of)
// ident.ctxt as well?
SawIdent(token::InternedString),
SawStructDef(token::InternedString),
SawLifetimeRef(token::InternedString),
SawLifetimeDef(token::InternedString),
SawMod,
SawViewItem,
SawForeignItem,
SawItem,
SawDecl,
SawTy,
SawGenerics,
SawFn,
SawTyMethod,
SawTraitMethod,
SawStructField,
SawVariant,
SawExplicitSelf,
SawPath,
SawOptLifetimeRef,
SawBlock,
SawPat,
SawLocal,
SawArm,
SawExpr(SawExprComponent<'a>),
SawStmt(SawStmtComponent),
}
/// SawExprComponent carries all of the information that we want
/// to include in the hash that *won't* be covered by the
/// subsequent recursive traversal of the expression's
/// substructure by the visitor.
///
/// We know every Expr_ variant is covered by a variant because
/// `fn saw_expr` maps each to some case below. Ensuring that
/// each variant carries an appropriate payload has to be verified
/// by hand.
///
/// (However, getting that *exactly* right is not so important
/// because the SVH is just a developer convenience; there is no
/// guarantee of collision-freedom, hash collisions are just
/// (hopefully) unlikely.)
#[derive(Hash)]
pub enum SawExprComponent<'a> {
SawExprLoop(Option<token::InternedString>),
SawExprField(token::InternedString),
SawExprTupField(uint),
SawExprBreak(Option<token::InternedString>),
SawExprAgain(Option<token::InternedString>),
SawExprBox,
SawExprVec,
SawExprCall,
SawExprMethodCall,
SawExprTup,
SawExprBinary(ast::BinOp),
SawExprUnary(ast::UnOp),
SawExprLit(ast::Lit_),
SawExprCast,
SawExprIf,
SawExprWhile,
SawExprMatch,
SawExprClosure,
SawExprBlock,
SawExprAssign,
SawExprAssignOp(ast::BinOp),
SawExprIndex,
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SawExprRange,
SawExprPath,
SawExprAddrOf(ast::Mutability),
SawExprRet,
SawExprInlineAsm(&'a ast::InlineAsm),
SawExprStruct,
SawExprRepeat,
SawExprParen,
SawExprForLoop,
}
fn saw_expr<'a>(node: &'a Expr_) -> SawExprComponent<'a> {
match *node {
ExprBox(..) => SawExprBox,
ExprVec(..) => SawExprVec,
ExprCall(..) => SawExprCall,
ExprMethodCall(..) => SawExprMethodCall,
ExprTup(..) => SawExprTup,
ExprBinary(op, _, _) => SawExprBinary(op),
ExprUnary(op, _) => SawExprUnary(op),
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ExprLit(ref lit) => SawExprLit(lit.node.clone()),
ExprCast(..) => SawExprCast,
ExprIf(..) => SawExprIf,
ExprWhile(..) => SawExprWhile,
ExprLoop(_, id) => SawExprLoop(id.map(content)),
ExprMatch(..) => SawExprMatch,
ExprClosure(..) => SawExprClosure,
ExprBlock(..) => SawExprBlock,
ExprAssign(..) => SawExprAssign,
ExprAssignOp(op, _, _) => SawExprAssignOp(op),
ExprField(_, id) => SawExprField(content(id.node)),
ExprTupField(_, id) => SawExprTupField(id.node),
ExprIndex(..) => SawExprIndex,
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ExprRange(..) => SawExprRange,
ExprPath(..) => SawExprPath,
ExprAddrOf(m, _) => SawExprAddrOf(m),
ExprBreak(id) => SawExprBreak(id.map(content)),
ExprAgain(id) => SawExprAgain(id.map(content)),
ExprRet(..) => SawExprRet,
ExprInlineAsm(ref asm) => SawExprInlineAsm(asm),
ExprStruct(..) => SawExprStruct,
ExprRepeat(..) => SawExprRepeat,
ExprParen(..) => SawExprParen,
ExprForLoop(..) => SawExprForLoop,
// just syntactic artifacts, expanded away by time of SVH.
ExprIfLet(..) => unreachable!(),
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ExprWhileLet(..) => unreachable!(),
ExprMac(..) => unreachable!(),
}
}
/// SawStmtComponent is analogous to SawExprComponent, but for statements.
#[derive(Hash)]
pub enum SawStmtComponent {
SawStmtDecl,
SawStmtExpr,
SawStmtSemi,
}
fn saw_stmt(node: &Stmt_) -> SawStmtComponent {
match *node {
StmtDecl(..) => SawStmtDecl,
StmtExpr(..) => SawStmtExpr,
StmtSemi(..) => SawStmtSemi,
StmtMac(..) => unreachable!(),
}
}
// Ad-hoc overloading between Ident and Name to their intern table lookups.
trait InternKey { fn get_content(self) -> token::InternedString; }
impl InternKey for Ident {
fn get_content(self) -> token::InternedString { token::get_ident(self) }
}
impl InternKey for Name {
fn get_content(self) -> token::InternedString { token::get_name(self) }
}
fn content<K:InternKey>(k: K) -> token::InternedString { k.get_content() }
impl<'a, 'v> Visitor<'v> for StrictVersionHashVisitor<'a> {
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fn visit_mac(&mut self, mac: &Mac) {
// macro invocations, namely macro_rules definitions,
// *can* appear as items, even in the expanded crate AST.
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if macro_name(mac).get() == "macro_rules" {
// Pretty-printing definition to a string strips out
// surface artifacts (currently), such as the span
// information, yielding a content-based hash.
// FIXME (#14132): building temporary string is
// expensive; a direct content-based hash on token
// trees might be faster. Implementing this is far
// easier in short term.
let macro_defn_as_string = pprust::to_string(|pp_state| {
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pp_state.print_mac(mac, token::Paren)
});
macro_defn_as_string.hash(self.st);
} else {
// It is not possible to observe any kind of macro
// invocation at this stage except `macro_rules!`.
panic!("reached macro somehow: {}",
pprust::to_string(|pp_state| {
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pp_state.print_mac(mac, token::Paren)
}));
}
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visit::walk_mac(self, mac);
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fn macro_name(mac: &Mac) -> token::InternedString {
match &mac.node {
&MacInvocTT(ref path, ref _tts, ref _stx_ctxt) => {
let s = path.segments.index(&FullRange);
assert_eq!(s.len(), 1);
content(s[0].identifier)
}
}
}
}
fn visit_struct_def(&mut self, s: &StructDef, ident: Ident,
g: &Generics, _: NodeId) {
SawStructDef(content(ident)).hash(self.st);
visit::walk_generics(self, g);
visit::walk_struct_def(self, s)
}
fn visit_variant(&mut self, v: &Variant, g: &Generics) {
SawVariant.hash(self.st);
// walk_variant does not call walk_generics, so do it here.
visit::walk_generics(self, g);
visit::walk_variant(self, v, g)
}
fn visit_opt_lifetime_ref(&mut self, _: Span, l: &Option<Lifetime>) {
SawOptLifetimeRef.hash(self.st);
// (This is a strange method in the visitor trait, in that
// it does not expose a walk function to do the subroutine
// calls.)
match *l {
Some(ref l) => self.visit_lifetime_ref(l),
None => ()
}
}
// All of the remaining methods just record (in the hash
// SipState) that the visitor saw that particular variant
// (with its payload), and continue walking as the default
// visitor would.
//
// Some of the implementations have some notes as to how one
// might try to make their SVH computation less discerning
// (e.g. by incorporating reachability analysis). But
// currently all of their implementations are uniform and
// uninteresting.
//
// (If you edit a method such that it deviates from the
// pattern, please move that method up above this comment.)
fn visit_ident(&mut self, _: Span, ident: Ident) {
SawIdent(content(ident)).hash(self.st);
}
fn visit_lifetime_ref(&mut self, l: &Lifetime) {
SawLifetimeRef(content(l.name)).hash(self.st);
}
fn visit_lifetime_def(&mut self, l: &LifetimeDef) {
SawLifetimeDef(content(l.lifetime.name)).hash(self.st);
}
// We do recursively walk the bodies of functions/methods
// (rather than omitting their bodies from the hash) since
// monomorphization and cross-crate inlining generally implies
// that a change to a crate body will require downstream
// crates to be recompiled.
fn visit_expr(&mut self, ex: &Expr) {
SawExpr(saw_expr(&ex.node)).hash(self.st); visit::walk_expr(self, ex)
}
fn visit_stmt(&mut self, s: &Stmt) {
SawStmt(saw_stmt(&s.node)).hash(self.st); visit::walk_stmt(self, s)
}
fn visit_view_item(&mut self, i: &ViewItem) {
// Two kinds of view items can affect the ABI for a crate:
// exported `pub use` view items (since that may expose
// items that downstream crates can call), and `use
// foo::Trait`, since changing that may affect method
// resolution.
//
// The simplest approach to handling both of the above is
// just to adopt the same simple-minded (fine-grained)
// hash that I am deploying elsewhere here.
SawViewItem.hash(self.st); visit::walk_view_item(self, i)
}
fn visit_foreign_item(&mut self, i: &ForeignItem) {
// FIXME (#14132) ideally we would incorporate privacy (or
// perhaps reachability) somewhere here, so foreign items
// that do not leak into downstream crates would not be
// part of the ABI.
SawForeignItem.hash(self.st); visit::walk_foreign_item(self, i)
}
fn visit_item(&mut self, i: &Item) {
// FIXME (#14132) ideally would incorporate reachability
// analysis somewhere here, so items that never leak into
// downstream crates (e.g. via monomorphisation or
// inlining) would not be part of the ABI.
SawItem.hash(self.st); visit::walk_item(self, i)
}
fn visit_mod(&mut self, m: &Mod, _s: Span, _n: NodeId) {
SawMod.hash(self.st); visit::walk_mod(self, m)
}
fn visit_decl(&mut self, d: &Decl) {
SawDecl.hash(self.st); visit::walk_decl(self, d)
}
fn visit_ty(&mut self, t: &Ty) {
SawTy.hash(self.st); visit::walk_ty(self, t)
}
fn visit_generics(&mut self, g: &Generics) {
SawGenerics.hash(self.st); visit::walk_generics(self, g)
}
fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v FnDecl,
b: &'v Block, s: Span, _: NodeId) {
SawFn.hash(self.st); visit::walk_fn(self, fk, fd, b, s)
}
fn visit_ty_method(&mut self, t: &TypeMethod) {
SawTyMethod.hash(self.st); visit::walk_ty_method(self, t)
}
fn visit_trait_item(&mut self, t: &TraitItem) {
SawTraitMethod.hash(self.st); visit::walk_trait_item(self, t)
}
fn visit_struct_field(&mut self, s: &StructField) {
SawStructField.hash(self.st); visit::walk_struct_field(self, s)
}
fn visit_explicit_self(&mut self, es: &ExplicitSelf) {
SawExplicitSelf.hash(self.st); visit::walk_explicit_self(self, es)
}
fn visit_path(&mut self, path: &Path, _: ast::NodeId) {
SawPath.hash(self.st); visit::walk_path(self, path)
}
fn visit_block(&mut self, b: &Block) {
SawBlock.hash(self.st); visit::walk_block(self, b)
}
fn visit_pat(&mut self, p: &Pat) {
SawPat.hash(self.st); visit::walk_pat(self, p)
}
fn visit_local(&mut self, l: &Local) {
SawLocal.hash(self.st); visit::walk_local(self, l)
}
fn visit_arm(&mut self, a: &Arm) {
SawArm.hash(self.st); visit::walk_arm(self, a)
}
}
}