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rust/src/test/ui/proc-macro/span-from-proc-macro.stderr

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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`.
2020-08-02 23:52:16 +00:00
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
error[E0412]: cannot find type `OtherMissingType` in this scope
--> $DIR/auxiliary/span-from-proc-macro.rs:46:21
|
LL | pub fn error_from_derive(_input: TokenStream) -> TokenStream {
| ------------------------------------------------------------ in this expansion of procedural macro `#[derive(ErrorFromDerive)]`
...
LL | Variant(OtherMissingType)
| ^^^^^^^^^^^^^^^^ not found in this scope
|
::: $DIR/span-from-proc-macro.rs:11:10
|
LL | #[derive(ErrorFromDerive)]
| --------------- in this macro invocation
error[E0425]: cannot find value `my_ident` in this scope
--> $DIR/auxiliary/span-from-proc-macro.rs:29:9
|
LL | pub fn other_error_from_bang(_input: TokenStream) -> TokenStream {
| ---------------------------------------------------------------- in this expansion of procedural macro `other_error_from_bang!`
LL | custom_quote::custom_quote! {
LL | my_ident
| ^^^^^^^^ not found in this scope
|
::: $DIR/span-from-proc-macro.rs:16:5
|
LL | other_error_from_bang!();
| ------------------------- in this macro invocation
error[E0308]: mismatched types
--> $DIR/auxiliary/span-from-proc-macro.rs:16:36
|
LL | let bang_error: bool = 25;
| ---- ^^ expected `bool`, found integer
| |
| expected due to this
...
LL | pub fn error_from_bang(_input: TokenStream) -> TokenStream {
| ---------------------------------------------------------- in this expansion of procedural macro `error_from_bang!`
|
::: $DIR/span-from-proc-macro.rs:15:5
|
LL | error_from_bang!();
| ------------------- in this macro invocation
error: aborting due to 4 previous errors
Some errors have detailed explanations: E0308, E0412, E0425.
For more information about an error, try `rustc --explain E0308`.
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