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Overhaul MacArgs::Eq.

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The value in `MacArgs::Eq` is currently represented as a `Token`.
Because of `TokenKind::Interpolated`, `Token` can be either a token or
an arbitrary AST fragment. In practice, a `MacArgs::Eq` starts out as a
literal or macro call AST fragment, and then is later lowered to a
literal token. But this is very non-obvious. `Token` is a much more
general type than what is needed.

This commit restricts things, by introducing a new type `MacArgsEqKind`
that is either an AST expression (pre-lowering) or an AST literal
(post-lowering). The downside is that the code is a bit more verbose in
a few places. The benefit is that makes it much clearer what the
possibilities are (though also shorter in some other places). Also, it
removes one use of `TokenKind::Interpolated`, taking us a step closer to
removing that variant, which will let us make `Token` impl `Copy` and
remove many "handle Interpolated" code paths in the parser.

Things to note:
- Error messages have improved. Messages like this:
  ```
  unexpected token: `"bug" + "found"`
  ```
  now say "unexpected expression", which makes more sense. Although
  arbitrary expressions can exist within tokens thanks to
  `TokenKind::Interpolated`, that's not obvious to anyone who doesn't
  know compiler internals.
- In `parse_mac_args_common`, we no longer need to collect tokens for
  the value expression.
This commit is contained in:
Nicholas Nethercote 2022-04-29 06:52:01 +10:00
parent ae5f67f9e8
commit 99f5945f85
21 changed files with 174 additions and 88 deletions
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39
compiler/rustc_parse/src/validate_attr.rs
View file

@ -2,8 +2,9 @@
use crate::parse_in;
use rustc_ast::tokenstream::{DelimSpan, TokenTree};
use rustc_ast::{self as ast, Attribute, MacArgs, MacDelimiter, MetaItem, MetaItemKind};
use rustc_ast::tokenstream::DelimSpan;
use rustc_ast::{self as ast, Attribute, MacArgs, MacArgsEq, MacDelimiter, MetaItem, MetaItemKind};
use rustc_ast_pretty::pprust;
use rustc_errors::{Applicability, FatalError, PResult};
use rustc_feature::{AttributeTemplate, BuiltinAttribute, BUILTIN_ATTRIBUTE_MAP};
use rustc_session::lint::builtin::ILL_FORMED_ATTRIBUTE_INPUT;
@ -42,16 +43,40 @@ pub fn parse_meta<'a>(sess: &'a ParseSess, attr: &Attribute) -> PResult<'a, Meta
path: item.path.clone(),
kind: match &item.args {
MacArgs::Empty => MetaItemKind::Word,
MacArgs::Eq(_, t) => {
let t = TokenTree::Token(t.clone()).into();
let v = parse_in(sess, t, "name value", |p| p.parse_unsuffixed_lit())?;
MetaItemKind::NameValue(v)
}
MacArgs::Delimited(dspan, delim, t) => {
check_meta_bad_delim(sess, *dspan, *delim, "wrong meta list delimiters");
let nmis = parse_in(sess, t.clone(), "meta list", |p| p.parse_meta_seq_top())?;
MetaItemKind::List(nmis)
}
MacArgs::Eq(_, MacArgsEq::Ast(expr)) => {
if let ast::ExprKind::Lit(lit) = &expr.kind {
if !lit.kind.is_unsuffixed() {
let mut err = sess.span_diagnostic.struct_span_err(
lit.span,
"suffixed literals are not allowed in attributes",
);
err.help(
"instead of using a suffixed literal (`1u8`, `1.0f32`, etc.), \
use an unsuffixed version (`1`, `1.0`, etc.)",
);
return Err(err);
} else {
MetaItemKind::NameValue(lit.clone())
}
} else {
// The non-error case can happen with e.g. `#[foo = 1+1]`. The error case can
// happen with e.g. `#[foo = include_str!("non-existent-file.rs")]`; in that
// case we delay the error because an earlier error will have already been
// reported.
let msg = format!("unexpected expression: `{}`", pprust::expr_to_string(expr));
let mut err = sess.span_diagnostic.struct_span_err(expr.span, msg);
if let ast::ExprKind::Err = expr.kind {
err.downgrade_to_delayed_bug();
}
return Err(err);
}
}
MacArgs::Eq(_, MacArgsEq::Hir(lit)) => MetaItemKind::NameValue(lit.clone()),
},
})
}