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Fix the span of generated #[derive_*] attributes #33926

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Merged
bors merged 4 commits into from
May 30, 2016
+38 −60
Merged

Fix the span of generated #[derive_*] attributes #33926

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074f4c2
Fix spans of generated `#[derive_*]` attributes
jseyfried May 23, 2016
6019816
Refactor away `set_expn_info`
jseyfried May 23, 2016
40f047d
Add test
jseyfried May 23, 2016
a0e606c
Use the span of `#[derive_Eq]` for `#[structural_match]`
jseyfried May 28, 2016
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56 changes: 14 additions & 42 deletions src/libsyntax_ext/deriving/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,7 @@ fn expand_derive(cx: &mut ExtCtxt,
}

let mut found_partial_eq = false;
let mut found_eq = false;
let mut eq_span = None;

for titem in traits.iter().rev() {
let tname = match titem.node {
Expand All @@ -114,12 +114,6 @@ fn expand_derive(cx: &mut ExtCtxt,
continue;
}

if &tname[..] == "Eq" {
found_eq = true;
} else if &tname[..] == "PartialEq" {
found_partial_eq = true;
}

let span = Span {
expn_id: cx.codemap().record_expansion(codemap::ExpnInfo {
call_site: titem.span,
Expand All @@ -131,48 +125,26 @@ fn expand_derive(cx: &mut ExtCtxt,
}), ..titem.span
};

if &tname[..] == "Eq" {
eq_span = Some(span);
} else if &tname[..] == "PartialEq" {
found_partial_eq = true;
}

// #[derive(Foo, Bar)] expands to #[derive_Foo] #[derive_Bar]
item.attrs.push(cx.attribute(span, cx.meta_word(titem.span,
intern_and_get_ident(&format!("derive_{}", tname)))));
}

// RFC #1445. `#[derive(PartialEq, Eq)]` adds a (trusted)
// `#[structural_match]` attribute.
if found_partial_eq && found_eq {
// This span is **very** sensitive and crucial to
// getting the stability behavior we want. What we are
// doing is marking `#[structural_match]` with the
// span of the `#[deriving(...)]` attribute (the
// entire attribute, not just the `PartialEq` or `Eq`
// part), but with the current backtrace. The current
// backtrace will contain a topmost entry that IS this
// `#[deriving(...)]` attribute and with the
// "allow-unstable" flag set to true.
//
// Note that we do NOT use the span of the `Eq`
// text itself. You might think this is
// equivalent, because the `Eq` appears within the
// `#[deriving(Eq)]` attribute, and hence we would
// inherit the "allows unstable" from the
// backtrace. But in fact this is not always the
// case. The actual source text that led to
// deriving can be `#[$attr]`, for example, where
// `$attr == deriving(Eq)`. In that case, the
// "#[structural_match]" would be considered to
// originate not from the deriving call but from
// text outside the deriving call, and hence would
// be forbidden from using unstable
// content.
//
// See tests src/run-pass/rfc1445 for
// examples. --nmatsakis
let span = Span { expn_id: cx.backtrace(), .. span };
assert!(cx.parse_sess.codemap().span_allows_unstable(span));
debug!("inserting structural_match with span {:?}", span);
let structural_match = intern_and_get_ident("structural_match");
item.attrs.push(cx.attribute(span,
cx.meta_word(span,
structural_match)));
if let Some(eq_span) = eq_span {
if found_partial_eq {
let structural_match = intern_and_get_ident("structural_match");
item.attrs.push(cx.attribute(eq_span,
cx.meta_word(eq_span,
structural_match)));
}
}

item
Expand Down