From ab73020d400d4eaba228cdc5ec2f16338e755360 Mon Sep 17 00:00:00 2001 From: Aaron Hill Date: Sun, 2 Aug 2020 19:52:16 -0400 Subject: [PATCH] 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`. --- clippy_lints/src/misc.rs | 2 +- clippy_lints/src/unit_types/unit_cmp.rs | 2 +- clippy_utils/src/lib.rs | 4 ++-- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/clippy_lints/src/misc.rs b/clippy_lints/src/misc.rs index 0b0cd9be46cf4..6966d798c537a 100644 --- a/clippy_lints/src/misc.rs +++ b/clippy_lints/src/misc.rs @@ -660,7 +660,7 @@ fn in_attributes_expansion(expr: &Expr<'_>) -> bool { use rustc_span::hygiene::MacroKind; if expr.span.from_expansion() { let data = expr.span.ctxt().outer_expn_data(); - matches!(data.kind, ExpnKind::Macro(MacroKind::Attr, _)) + matches!(data.kind, ExpnKind::Macro { kind: MacroKind::Attr, name: _, proc_macro: _ }) } else { false } diff --git a/clippy_lints/src/unit_types/unit_cmp.rs b/clippy_lints/src/unit_types/unit_cmp.rs index 85257f3113cb7..d22f7d9a96bf1 100644 --- a/clippy_lints/src/unit_types/unit_cmp.rs +++ b/clippy_lints/src/unit_types/unit_cmp.rs @@ -8,7 +8,7 @@ use super::UNIT_CMP; pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>) { if expr.span.from_expansion() { if let Some(callee) = expr.span.source_callee() { - if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind { + if let ExpnKind::Macro { kind: MacroKind::Bang, name: symbol, proc_macro: _ } = callee.kind { if let ExprKind::Binary(ref cmp, left, _) = expr.kind { let op = cmp.node; if op.is_comparison() && cx.typeck_results().expr_ty(left).is_unit() { diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs index f5ee49c7d5f99..9a0b72f06bbc9 100644 --- a/clippy_utils/src/lib.rs +++ b/clippy_utils/src/lib.rs @@ -947,7 +947,7 @@ pub fn is_expn_of(mut span: Span, name: &str) -> Option { let data = span.ctxt().outer_expn_data(); let new_span = data.call_site; - if let ExpnKind::Macro(MacroKind::Bang, mac_name) = data.kind { + if let ExpnKind::Macro { kind: MacroKind::Bang, name: mac_name, proc_macro: _ } = data.kind { if mac_name.as_str() == name { return Some(new_span); } @@ -975,7 +975,7 @@ pub fn is_direct_expn_of(span: Span, name: &str) -> Option { let data = span.ctxt().outer_expn_data(); let new_span = data.call_site; - if let ExpnKind::Macro(MacroKind::Bang, mac_name) = data.kind { + if let ExpnKind::Macro { kind: MacroKind::Bang, name: mac_name, proc_macro: _ } = data.kind { if mac_name.as_str() == name { return Some(new_span); }