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`.
This commit is contained in:
parent
ea3068efe4
commit
f916b0474a
34 changed files with 494 additions and 69 deletions
|
@ -309,7 +309,9 @@ pub trait Emitter {
|
|||
// are some which do actually involve macros.
|
||||
ExpnKind::Inlined | ExpnKind::Desugaring(..) | ExpnKind::AstPass(..) => None,
|
||||
|
||||
ExpnKind::Macro(macro_kind, _) => Some(macro_kind),
|
||||
ExpnKind::Macro { kind: macro_kind, name: _, proc_macro: _ } => {
|
||||
Some(macro_kind)
|
||||
}
|
||||
}
|
||||
});
|
||||
|
||||
|
@ -371,10 +373,19 @@ pub trait Emitter {
|
|||
new_labels
|
||||
.push((trace.call_site, "in the inlined copy of this code".to_string()));
|
||||
} else if always_backtrace {
|
||||
let proc_macro = if let ExpnKind::Macro { kind: _, name: _, proc_macro: true } =
|
||||
trace.kind
|
||||
{
|
||||
"procedural macro "
|
||||
} else {
|
||||
""
|
||||
};
|
||||
|
||||
new_labels.push((
|
||||
trace.def_site,
|
||||
format!(
|
||||
"in this expansion of `{}`{}",
|
||||
"in this expansion of {}`{}`{}",
|
||||
proc_macro,
|
||||
trace.kind.descr(),
|
||||
if macro_backtrace.len() > 1 {
|
||||
// if macro_backtrace.len() == 1 it'll be
|
||||
|
@ -400,7 +411,11 @@ pub trait Emitter {
|
|||
// and it needs an "in this macro invocation" label to match that.
|
||||
let redundant_span = trace.call_site.contains(sp);
|
||||
|
||||
if !redundant_span && matches!(trace.kind, ExpnKind::Macro(MacroKind::Bang, _))
|
||||
if !redundant_span
|
||||
&& matches!(
|
||||
trace.kind,
|
||||
ExpnKind::Macro { kind: MacroKind::Bang, name: _, proc_macro: _ }
|
||||
)
|
||||
|| always_backtrace
|
||||
{
|
||||
new_labels.push((
|
||||
|
|
Loading…
Add table
Add a link
Reference in a new issue