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More detail when expecting expression but encountering bad macro argument

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Partially address #71039.
This commit is contained in:
Esteban Küber 2023-07-31 14:55:47 +00:00
parent 1be1e84872
commit 4e418805da
27 changed files with 200 additions and 67 deletions
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58
compiler/rustc_parse/src/parser/diagnostics.rs
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@ -24,11 +24,12 @@ use crate::parser;
use rustc_ast as ast;
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter, Lit, LitKind, TokenKind};
use rustc_ast::tokenstream::AttrTokenTree;
use rustc_ast::util::parser::AssocOp;
use rustc_ast::{
AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec, BinOpKind, BindingAnnotation, Block,
BlockCheckMode, Expr, ExprKind, GenericArg, Generics, Item, ItemKind, Param, Pat, PatKind,
Path, PathSegment, QSelf, Ty, TyKind,
BlockCheckMode, Expr, ExprKind, GenericArg, Generics, HasTokens, Item, ItemKind, Param, Pat,
PatKind, Path, PathSegment, QSelf, Ty, TyKind,
};
use rustc_ast_pretty::pprust;
use rustc_data_structures::fx::FxHashSet;
@ -2252,6 +2253,59 @@ impl<'a> Parser<'a> {
err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
}
err.span_label(span, "expected expression");
// Walk the chain of macro expansions for the current token to point at how the original
// code was interpreted. This helps the user realize when a macro argument of one type is
// later reinterpreted as a different type, like `$x:expr` being reinterpreted as `$x:pat`
// in a subsequent macro invocation (#71039).
let mut tok = self.token.clone();
let mut labels = vec![];
while let TokenKind::Interpolated(node) = &tok.kind {
let tokens = node.0.tokens();
labels.push(node.clone());
if let Some(tokens) = tokens
&& let tokens = tokens.to_attr_token_stream()
&& let tokens = tokens.0.deref()
&& let [AttrTokenTree::Token(token, _)] = &tokens[..]
{
tok = token.clone();
} else {
break;
}
}
let mut iter = labels.into_iter().peekable();
let mut show_link = false;
while let Some(node) = iter.next() {
let descr = node.0.descr();
if let Some(next) = iter.peek() {
let next_descr = next.0.descr();
if next_descr != descr {
err.span_label(next.1, format!("this macro fragment matcher is {next_descr}"));
err.span_label(node.1, format!("this macro fragment matcher is {descr}"));
err.span_label(
next.0.use_span(),
format!("this is expected to be {next_descr}"),
);
err.span_label(
node.0.use_span(),
format!(
"this is interpreted as {}, but it is expected to be {}",
next_descr, descr,
),
);
show_link = true;
} else {
err.span_label(node.1, "");
}
}
}
if show_link {
err.note(
"when forwarding a matched fragment to another macro-by-example, matchers in the \
second macro will see an opaque AST of the fragment type, not the underlying \
tokens",
);
}
err
}