//! Machinery for hygienic macros, inspired by the `MTWT[1]` paper. //! //! `[1]` Matthew Flatt, Ryan Culpepper, David Darais, and Robert Bruce Findler. 2012. //! *Macros that work together: Compile-time bindings, partial expansion, //! and definition contexts*. J. Funct. Program. 22, 2 (March 2012), 181-216. //! DOI=10.1017/S0956796812000093 use crate::GLOBALS; use crate::Span; use crate::edition::Edition; use crate::symbol::{kw, Symbol}; use serialize::{Encodable, Decodable, Encoder, Decoder}; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_data_structures::sync::Lrc; use std::{fmt, mem}; /// A SyntaxContext represents a chain of macro expansions (represented by marks). #[derive(Clone, Copy, PartialEq, Eq, Default, PartialOrd, Ord, Hash)] pub struct SyntaxContext(u32); #[derive(Copy, Clone, Debug)] struct SyntaxContextData { outer_mark: Mark, transparency: Transparency, prev_ctxt: SyntaxContext, /// This context, but with all transparent and semi-transparent marks filtered away. opaque: SyntaxContext, /// This context, but with all transparent marks filtered away. opaque_and_semitransparent: SyntaxContext, /// Name of the crate to which `$crate` with this context would resolve. dollar_crate_name: Symbol, } /// A mark is a unique ID associated with a macro expansion. #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)] pub struct Mark(u32); #[derive(Clone, Debug)] struct MarkData { parent: Mark, default_transparency: Transparency, expn_info: Option, } /// A property of a macro expansion that determines how identifiers /// produced by that expansion are resolved. #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug)] pub enum Transparency { /// Identifier produced by a transparent expansion is always resolved at call-site. /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this. Transparent, /// Identifier produced by a semi-transparent expansion may be resolved /// either at call-site or at definition-site. /// If it's a local variable, label or `$crate` then it's resolved at def-site. /// Otherwise it's resolved at call-site. /// `macro_rules` macros behave like this, built-in macros currently behave like this too, /// but that's an implementation detail. SemiTransparent, /// Identifier produced by an opaque expansion is always resolved at definition-site. /// Def-site spans in procedural macros, identifiers from `macro` by default use this. Opaque, } impl Mark { pub fn fresh(parent: Mark) -> Self { HygieneData::with(|data| { data.marks.push(MarkData { parent, // By default expansions behave like `macro_rules`. default_transparency: Transparency::SemiTransparent, expn_info: None, }); Mark(data.marks.len() as u32 - 1) }) } /// The mark of the theoretical expansion that generates freshly parsed, unexpanded AST. #[inline] pub fn root() -> Self { Mark(0) } #[inline] pub fn as_u32(self) -> u32 { self.0 } #[inline] pub fn from_u32(raw: u32) -> Mark { Mark(raw) } #[inline] pub fn parent(self) -> Mark { HygieneData::with(|data| data.marks[self.0 as usize].parent) } #[inline] pub fn expn_info(self) -> Option { HygieneData::with(|data| data.marks[self.0 as usize].expn_info.clone()) } #[inline] pub fn set_expn_info(self, info: ExpnInfo) { HygieneData::with(|data| data.marks[self.0 as usize].expn_info = Some(info)) } #[inline] pub fn set_default_transparency(self, transparency: Transparency) { assert_ne!(self, Mark::root()); HygieneData::with(|data| data.marks[self.0 as usize].default_transparency = transparency) } pub fn is_descendant_of(mut self, ancestor: Mark) -> bool { HygieneData::with(|data| { while self != ancestor { if self == Mark::root() { return false; } self = data.marks[self.0 as usize].parent; } true }) } /// Computes a mark such that both input marks are descendants of (or equal to) the returned /// mark. That is, the following holds: /// /// ```rust /// let la = least_ancestor(a, b); /// assert!(a.is_descendant_of(la)) /// assert!(b.is_descendant_of(la)) /// ``` pub fn least_ancestor(mut a: Mark, mut b: Mark) -> Mark { HygieneData::with(|data| { // Compute the path from a to the root let mut a_path = FxHashSet::::default(); while a != Mark::root() { a_path.insert(a); a = data.marks[a.0 as usize].parent; } // While the path from b to the root hasn't intersected, move up the tree while !a_path.contains(&b) { b = data.marks[b.0 as usize].parent; } b }) } // Used for enabling some compatibility fallback in resolve. #[inline] pub fn looks_like_proc_macro_derive(self) -> bool { HygieneData::with(|data| { let mark_data = &data.marks[self.0 as usize]; if mark_data.default_transparency == Transparency::Opaque { if let Some(expn_info) = &mark_data.expn_info { if let ExpnFormat::MacroAttribute(name) = expn_info.format { if name.as_str().starts_with("derive(") { return true; } } } } false }) } } #[derive(Debug)] crate struct HygieneData { marks: Vec, syntax_contexts: Vec, markings: FxHashMap<(SyntaxContext, Mark, Transparency), SyntaxContext>, } impl HygieneData { crate fn new() -> Self { HygieneData { marks: vec![MarkData { parent: Mark::root(), // If the root is opaque, then loops searching for an opaque mark // will automatically stop after reaching it. default_transparency: Transparency::Opaque, expn_info: None, }], syntax_contexts: vec![SyntaxContextData { outer_mark: Mark::root(), transparency: Transparency::Opaque, prev_ctxt: SyntaxContext(0), opaque: SyntaxContext(0), opaque_and_semitransparent: SyntaxContext(0), dollar_crate_name: kw::DollarCrate, }], markings: FxHashMap::default(), } } fn with T>(f: F) -> T { GLOBALS.with(|globals| f(&mut *globals.hygiene_data.borrow_mut())) } } pub fn clear_markings() { HygieneData::with(|data| data.markings = FxHashMap::default()); } impl SyntaxContext { #[inline] pub const fn empty() -> Self { SyntaxContext(0) } #[inline] crate fn as_u32(self) -> u32 { self.0 } #[inline] crate fn from_u32(raw: u32) -> SyntaxContext { SyntaxContext(raw) } // Allocate a new SyntaxContext with the given ExpnInfo. This is used when // deserializing Spans from the incr. comp. cache. // FIXME(mw): This method does not restore MarkData::parent or // SyntaxContextData::prev_ctxt or SyntaxContextData::opaque. These things // don't seem to be used after HIR lowering, so everything should be fine // as long as incremental compilation does not kick in before that. pub fn allocate_directly(expansion_info: ExpnInfo) -> Self { HygieneData::with(|data| { data.marks.push(MarkData { parent: Mark::root(), default_transparency: Transparency::SemiTransparent, expn_info: Some(expansion_info), }); let mark = Mark(data.marks.len() as u32 - 1); data.syntax_contexts.push(SyntaxContextData { outer_mark: mark, transparency: Transparency::SemiTransparent, prev_ctxt: SyntaxContext::empty(), opaque: SyntaxContext::empty(), opaque_and_semitransparent: SyntaxContext::empty(), dollar_crate_name: kw::DollarCrate, }); SyntaxContext(data.syntax_contexts.len() as u32 - 1) }) } /// Extend a syntax context with a given mark and default transparency for that mark. pub fn apply_mark(self, mark: Mark) -> SyntaxContext { assert_ne!(mark, Mark::root()); self.apply_mark_with_transparency( mark, HygieneData::with(|data| data.marks[mark.0 as usize].default_transparency) ) } /// Extend a syntax context with a given mark and transparency pub fn apply_mark_with_transparency(self, mark: Mark, transparency: Transparency) -> SyntaxContext { assert_ne!(mark, Mark::root()); if transparency == Transparency::Opaque { return self.apply_mark_internal(mark, transparency); } let call_site_ctxt = mark.expn_info().map_or(SyntaxContext::empty(), |info| info.call_site.ctxt()); let call_site_ctxt = if transparency == Transparency::SemiTransparent { call_site_ctxt.modern() } else { call_site_ctxt.modern_and_legacy() }; if call_site_ctxt == SyntaxContext::empty() { return self.apply_mark_internal(mark, transparency); } // Otherwise, `mark` is a macros 1.0 definition and the call site is in a // macros 2.0 expansion, i.e., a macros 1.0 invocation is in a macros 2.0 definition. // // In this case, the tokens from the macros 1.0 definition inherit the hygiene // at their invocation. That is, we pretend that the macros 1.0 definition // was defined at its invocation (i.e., inside the macros 2.0 definition) // so that the macros 2.0 definition remains hygienic. // // See the example at `test/run-pass/hygiene/legacy_interaction.rs`. let mut ctxt = call_site_ctxt; for (mark, transparency) in self.marks() { ctxt = ctxt.apply_mark_internal(mark, transparency); } ctxt.apply_mark_internal(mark, transparency) } fn apply_mark_internal(self, mark: Mark, transparency: Transparency) -> SyntaxContext { HygieneData::with(|data| { let syntax_contexts = &mut data.syntax_contexts; let mut opaque = syntax_contexts[self.0 as usize].opaque; let mut opaque_and_semitransparent = syntax_contexts[self.0 as usize].opaque_and_semitransparent; if transparency >= Transparency::Opaque { let prev_ctxt = opaque; opaque = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| { let new_opaque = SyntaxContext(syntax_contexts.len() as u32); syntax_contexts.push(SyntaxContextData { outer_mark: mark, transparency, prev_ctxt, opaque: new_opaque, opaque_and_semitransparent: new_opaque, dollar_crate_name: kw::DollarCrate, }); new_opaque }); } if transparency >= Transparency::SemiTransparent { let prev_ctxt = opaque_and_semitransparent; opaque_and_semitransparent = *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| { let new_opaque_and_semitransparent = SyntaxContext(syntax_contexts.len() as u32); syntax_contexts.push(SyntaxContextData { outer_mark: mark, transparency, prev_ctxt, opaque, opaque_and_semitransparent: new_opaque_and_semitransparent, dollar_crate_name: kw::DollarCrate, }); new_opaque_and_semitransparent }); } let prev_ctxt = self; *data.markings.entry((prev_ctxt, mark, transparency)).or_insert_with(|| { let new_opaque_and_semitransparent_and_transparent = SyntaxContext(syntax_contexts.len() as u32); syntax_contexts.push(SyntaxContextData { outer_mark: mark, transparency, prev_ctxt, opaque, opaque_and_semitransparent, dollar_crate_name: kw::DollarCrate, }); new_opaque_and_semitransparent_and_transparent }) }) } /// Pulls a single mark off of the syntax context. This effectively moves the /// context up one macro definition level. That is, if we have a nested macro /// definition as follows: /// /// ```rust /// macro_rules! f { /// macro_rules! g { /// ... /// } /// } /// ``` /// /// and we have a SyntaxContext that is referring to something declared by an invocation /// of g (call it g1), calling remove_mark will result in the SyntaxContext for the /// invocation of f that created g1. /// Returns the mark that was removed. pub fn remove_mark(&mut self) -> Mark { HygieneData::with(|data| { let outer_mark = data.syntax_contexts[self.0 as usize].outer_mark; *self = data.syntax_contexts[self.0 as usize].prev_ctxt; outer_mark }) } pub fn marks(mut self) -> Vec<(Mark, Transparency)> { HygieneData::with(|data| { let mut marks = Vec::new(); while self != SyntaxContext::empty() { let ctxt_data = &data.syntax_contexts[self.0 as usize]; marks.push((ctxt_data.outer_mark, ctxt_data.transparency)); self = ctxt_data.prev_ctxt; } marks.reverse(); marks }) } /// Adjust this context for resolution in a scope created by the given expansion. /// For example, consider the following three resolutions of `f`: /// /// ```rust /// mod foo { pub fn f() {} } // `f`'s `SyntaxContext` is empty. /// m!(f); /// macro m($f:ident) { /// mod bar { /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`. /// pub fn $f() {} // `$f`'s `SyntaxContext` is empty. /// } /// foo::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m` /// //^ Since `mod foo` is outside this expansion, `adjust` removes the mark from `f`, /// //| and it resolves to `::foo::f`. /// bar::f(); // `f`'s `SyntaxContext` has a single `Mark` from `m` /// //^ Since `mod bar` not outside this expansion, `adjust` does not change `f`, /// //| and it resolves to `::bar::f`. /// bar::$f(); // `f`'s `SyntaxContext` is empty. /// //^ Since `mod bar` is not outside this expansion, `adjust` does not change `$f`, /// //| and it resolves to `::bar::$f`. /// } /// ``` /// This returns the expansion whose definition scope we use to privacy check the resolution, /// or `None` if we privacy check as usual (i.e., not w.r.t. a macro definition scope). pub fn adjust(&mut self, expansion: Mark) -> Option { let mut scope = None; while !expansion.is_descendant_of(self.outer()) { scope = Some(self.remove_mark()); } scope } /// Adjust this context for resolution in a scope created by the given expansion /// via a glob import with the given `SyntaxContext`. /// For example: /// /// ```rust /// m!(f); /// macro m($i:ident) { /// mod foo { /// pub fn f() {} // `f`'s `SyntaxContext` has a single `Mark` from `m`. /// pub fn $i() {} // `$i`'s `SyntaxContext` is empty. /// } /// n(f); /// macro n($j:ident) { /// use foo::*; /// f(); // `f`'s `SyntaxContext` has a mark from `m` and a mark from `n` /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::f`. /// $i(); // `$i`'s `SyntaxContext` has a mark from `n` /// //^ `glob_adjust` removes the mark from `n`, so this resolves to `foo::$i`. /// $j(); // `$j`'s `SyntaxContext` has a mark from `m` /// //^ This cannot be glob-adjusted, so this is a resolution error. /// } /// } /// ``` /// This returns `None` if the context cannot be glob-adjusted. /// Otherwise, it returns the scope to use when privacy checking (see `adjust` for details). pub fn glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext) -> Option> { let mut scope = None; while !expansion.is_descendant_of(glob_ctxt.outer()) { scope = Some(glob_ctxt.remove_mark()); if self.remove_mark() != scope.unwrap() { return None; } } if self.adjust(expansion).is_some() { return None; } Some(scope) } /// Undo `glob_adjust` if possible: /// /// ```rust /// if let Some(privacy_checking_scope) = self.reverse_glob_adjust(expansion, glob_ctxt) { /// assert!(self.glob_adjust(expansion, glob_ctxt) == Some(privacy_checking_scope)); /// } /// ``` pub fn reverse_glob_adjust(&mut self, expansion: Mark, mut glob_ctxt: SyntaxContext) -> Option> { if self.adjust(expansion).is_some() { return None; } let mut marks = Vec::new(); while !expansion.is_descendant_of(glob_ctxt.outer()) { marks.push(glob_ctxt.remove_mark()); } let scope = marks.last().cloned(); while let Some(mark) = marks.pop() { *self = self.apply_mark(mark); } Some(scope) } #[inline] pub fn modern(self) -> SyntaxContext { HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque) } #[inline] pub fn modern_and_legacy(self) -> SyntaxContext { HygieneData::with(|data| data.syntax_contexts[self.0 as usize].opaque_and_semitransparent) } #[inline] pub fn outer(self) -> Mark { HygieneData::with(|data| data.syntax_contexts[self.0 as usize].outer_mark) } pub fn dollar_crate_name(self) -> Symbol { HygieneData::with(|data| data.syntax_contexts[self.0 as usize].dollar_crate_name) } pub fn set_dollar_crate_name(self, dollar_crate_name: Symbol) { HygieneData::with(|data| { let prev_dollar_crate_name = mem::replace( &mut data.syntax_contexts[self.0 as usize].dollar_crate_name, dollar_crate_name ); assert!(dollar_crate_name == prev_dollar_crate_name || prev_dollar_crate_name == kw::DollarCrate, "$crate name is reset for a syntax context"); }) } } impl fmt::Debug for SyntaxContext { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { write!(f, "#{}", self.0) } } /// Extra information for tracking spans of macro and syntax sugar expansion #[derive(Clone, Hash, Debug, RustcEncodable, RustcDecodable)] pub struct ExpnInfo { /// The location of the actual macro invocation or syntax sugar , e.g. /// `let x = foo!();` or `if let Some(y) = x {}` /// /// This may recursively refer to other macro invocations, e.g., if /// `foo!()` invoked `bar!()` internally, and there was an /// expression inside `bar!`; the call_site of the expression in /// the expansion would point to the `bar!` invocation; that /// call_site span would have its own ExpnInfo, with the call_site /// pointing to the `foo!` invocation. pub call_site: Span, /// The span of the macro definition itself. The macro may not /// have a sensible definition span (e.g., something defined /// completely inside libsyntax) in which case this is None. /// This span serves only informational purpose and is not used for resolution. pub def_site: Option, /// The format with which the macro was invoked. pub format: ExpnFormat, /// List of #[unstable]/feature-gated features that the macro is allowed to use /// internally without forcing the whole crate to opt-in /// to them. pub allow_internal_unstable: Option>, /// Whether the macro is allowed to use `unsafe` internally /// even if the user crate has `#![forbid(unsafe_code)]`. pub allow_internal_unsafe: bool, /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`) /// for a given macro. pub local_inner_macros: bool, /// Edition of the crate in which the macro is defined. pub edition: Edition, } /// The source of expansion. #[derive(Clone, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)] pub enum ExpnFormat { /// e.g., #[derive(...)] MacroAttribute(Symbol), /// e.g., `format!()` MacroBang(Symbol), /// Desugaring done by the compiler during HIR lowering. CompilerDesugaring(CompilerDesugaringKind) } impl ExpnFormat { pub fn name(&self) -> Symbol { match *self { ExpnFormat::MacroBang(name) | ExpnFormat::MacroAttribute(name) => name, ExpnFormat::CompilerDesugaring(kind) => kind.name(), } } } /// The kind of compiler desugaring. #[derive(Clone, Copy, Hash, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable)] pub enum CompilerDesugaringKind { /// We desugar `if c { i } else { e }` to `match $ExprKind::Use(c) { true => i, _ => e }`. /// However, we do not want to blame `c` for unreachability but rather say that `i` /// is unreachable. This desugaring kind allows us to avoid blaming `c`. IfTemporary, QuestionMark, TryBlock, /// Desugaring of an `impl Trait` in return type position /// to an `existential type Foo: Trait;` and replacing the /// `impl Trait` with `Foo`. ExistentialReturnType, Async, Await, ForLoop, } impl CompilerDesugaringKind { pub fn name(self) -> Symbol { Symbol::intern(match self { CompilerDesugaringKind::IfTemporary => "if", CompilerDesugaringKind::Async => "async", CompilerDesugaringKind::Await => "await", CompilerDesugaringKind::QuestionMark => "?", CompilerDesugaringKind::TryBlock => "try block", CompilerDesugaringKind::ExistentialReturnType => "existential type", CompilerDesugaringKind::ForLoop => "for loop", }) } } impl Encodable for SyntaxContext { fn encode(&self, _: &mut E) -> Result<(), E::Error> { Ok(()) // FIXME(jseyfried) intercrate hygiene } } impl Decodable for SyntaxContext { fn decode(_: &mut D) -> Result { Ok(SyntaxContext::empty()) // FIXME(jseyfried) intercrate hygiene } }