From f916b0474a0443c8ce9915efb59b7465b42e03f8 Mon Sep 17 00:00:00 2001 From: Aaron Hill Date: Sun, 2 Aug 2020 19:52:16 -0400 Subject: Implement span quoting for proc-macros This PR implements span quoting, allowing proc-macros to produce spans pointing *into their own crate*. This is used by the unstable `proc_macro::quote!` macro, allowing us to get error messages like this: ``` error[E0412]: cannot find type `MissingType` in this scope --> $DIR/auxiliary/span-from-proc-macro.rs:37:20 | LL | pub fn error_from_attribute(_args: TokenStream, _input: TokenStream) -> TokenStream { | ----------------------------------------------------------------------------------- in this expansion of procedural macro `#[error_from_attribute]` ... LL | field: MissingType | ^^^^^^^^^^^ not found in this scope | ::: $DIR/span-from-proc-macro.rs:8:1 | LL | #[error_from_attribute] | ----------------------- in this macro invocation ``` Here, `MissingType` occurs inside the implementation of the proc-macro `#[error_from_attribute]`. Previosuly, this would always result in a span pointing at `#[error_from_attribute]` This will make many proc-macro-related error message much more useful - when a proc-macro generates code containing an error, users will get an error message pointing directly at that code (within the macro definition), instead of always getting a span pointing at the macro invocation site. This is implemented as follows: * When a proc-macro crate is being *compiled*, it causes the `quote!` macro to get run. This saves all of the sapns in the input to `quote!` into the metadata of *the proc-macro-crate* (which we are currently compiling). The `quote!` macro then expands to a call to `proc_macro::Span::recover_proc_macro_span(id)`, where `id` is an opaque identifier for the span in the crate metadata. * When the same proc-macro crate is *run* (e.g. it is loaded from disk and invoked by some consumer crate), the call to `proc_macro::Span::recover_proc_macro_span` causes us to load the span from the proc-macro crate's metadata. The proc-macro then produces a `TokenStream` containing a `Span` pointing into the proc-macro crate itself. The recursive nature of 'quote!' can be difficult to understand at first. The file `src/test/ui/proc-macro/quote-debug.stdout` shows the output of the `quote!` macro, which should make this eaier to understand. This PR also supports custom quoting spans in custom quote macros (e.g. the `quote` crate). All span quoting goes through the `proc_macro::quote_span` method, which can be called by a custom quote macro to perform span quoting. An example of this usage is provided in `src/test/ui/proc-macro/auxiliary/custom-quote.rs` Custom quoting currently has a few limitations: In order to quote a span, we need to generate a call to `proc_macro::Span::recover_proc_macro_span`. However, proc-macros support renaming the `proc_macro` crate, so we can't simply hardcode this path. Previously, the `quote_span` method used the path `crate::Span` - however, this only works when it is called by the builtin `quote!` macro in the same crate. To support being called from arbitrary crates, we need access to the name of the `proc_macro` crate to generate a path. This PR adds an additional argument to `quote_span` to specify the name of the `proc_macro` crate. Howver, this feels kind of hacky, and we may want to change this before stabilizing anything quote-related. Additionally, using `quote_span` currently requires enabling the `proc_macro_internals` feature. The builtin `quote!` macro has an `#[allow_internal_unstable]` attribute, but this won't work for custom quote implementations. This will likely require some additional tricks to apply `allow_internal_unstable` to the span of `proc_macro::Span::recover_proc_macro_span`. --- compiler/rustc_span/src/hygiene.rs | 15 ++++++++++++--- compiler/rustc_span/src/lib.rs | 5 ++++- 2 files changed, 16 insertions(+), 4 deletions(-) (limited to 'compiler/rustc_span/src') diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs index 8b611626fca..8f3b8cc2d0e 100644 --- a/compiler/rustc_span/src/hygiene.rs +++ b/compiler/rustc_span/src/hygiene.rs @@ -144,7 +144,10 @@ impl ExpnId { let expn_data = self.expn_data(); // Stop going up the backtrace once include! is encountered if expn_data.is_root() - || expn_data.kind == ExpnKind::Macro(MacroKind::Bang, sym::include) + || matches!( + expn_data.kind, + ExpnKind::Macro { kind: MacroKind::Bang, name: sym::include, proc_macro: _ } + ) { break; } @@ -839,7 +842,13 @@ pub enum ExpnKind { /// No expansion, aka root expansion. Only `ExpnId::root()` has this kind. Root, /// Expansion produced by a macro. - Macro(MacroKind, Symbol), + Macro { + kind: MacroKind, + name: Symbol, + /// If `true`, this macro is a procedural macro. This + /// flag is only used for diagnostic purposes + proc_macro: bool, + }, /// Transform done by the compiler on the AST. AstPass(AstPass), /// Desugaring done by the compiler during HIR lowering. @@ -852,7 +861,7 @@ impl ExpnKind { pub fn descr(&self) -> String { match *self { ExpnKind::Root => kw::PathRoot.to_string(), - ExpnKind::Macro(macro_kind, name) => match macro_kind { + ExpnKind::Macro { kind, name, proc_macro: _ } => match kind { MacroKind::Bang => format!("{}!", name), MacroKind::Attr => format!("#[{}]", name), MacroKind::Derive => format!("#[derive({})]", name), diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs index e0bc7544246..d56b434ca85 100644 --- a/compiler/rustc_span/src/lib.rs +++ b/compiler/rustc_span/src/lib.rs @@ -394,7 +394,10 @@ impl Span { /// Returns `true` if `span` originates in a derive-macro's expansion. pub fn in_derive_expansion(self) -> bool { - matches!(self.ctxt().outer_expn_data().kind, ExpnKind::Macro(MacroKind::Derive, _)) + matches!( + self.ctxt().outer_expn_data().kind, + ExpnKind::Macro { kind: MacroKind::Derive, name: _, proc_macro: _ } + ) } #[inline] -- cgit 1.4.1-3-g733a5