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Better errors when rustc cannot derive lifetimes #30102

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Merged
merged 3 commits into from
Dec 5, 2015
Merged

Better errors when rustc cannot derive lifetimes #30102

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a1a48c4
Better errors when rustc cannot derive lifetimes
Nov 29, 2015
9569c63
Avoid showing no-derivable-lifetime error message when there are no a…
Nov 29, 2015
829e8bf
Update lifetime compile tests
Dec 1, 2015
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25 changes: 19 additions & 6 deletions src/librustc_typeck/astconv.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -203,11 +203,15 @@ fn report_elision_failure(
{
let mut m = String::new();
let len = params.len();
let mut any_lifetimes = false;

for (i, info) in params.into_iter().enumerate() {
let ElisionFailureInfo {
name, lifetime_count: n, have_bound_regions
} = info;

any_lifetimes = any_lifetimes || (n > 0);

let help_name = if name.is_empty() {
format!("argument {}", i + 1)
} else {
Expand All @@ -229,17 +233,26 @@ fn report_elision_failure(
m.push_str(", ");
}
}
if len == 1 {
fileline_help!(tcx.sess, default_span,
"this function's return type contains a borrowed value, but \
the signature does not say which {} it is borrowed from",
m);
} else if len == 0 {

if len == 0 {
fileline_help!(tcx.sess, default_span,
"this function's return type contains a borrowed value, but \
there is no value for it to be borrowed from");
fileline_help!(tcx.sess, default_span,
"consider giving it a 'static lifetime");
} else if !any_lifetimes {
fileline_help!(tcx.sess, default_span,
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Why is the error message different between this case and the previous one?

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I was thinking the previous message implied that there were no arguments to draw from, and I was hoping to make the message as explicit as possible; I think if they were made the same they would be slightly more confusing. I don't feel strongly on this or anything, I'd be happy to change it so they have the same message if that's the consensus.

Also yeah, I'll do the tests.

"this function's return type contains a borrowed value with \
an elided lifetime, but the lifetime cannot be derived from \
the arguments");
fileline_help!(tcx.sess, default_span,
"consider giving it an explicit bounded or 'static \
lifetime");
} else if len == 1 {
fileline_help!(tcx.sess, default_span,
"this function's return type contains a borrowed value, but \
the signature does not say which {} it is borrowed from",
m);
} else {
fileline_help!(tcx.sess, default_span,
"this function's return type contains a borrowed value, but \
Expand Down
6 changes: 5 additions & 1 deletion src/test/compile-fail/issue-26638.rs
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Expand Up @@ -14,6 +14,10 @@ fn parse_type(iter: Box<Iterator<Item=&str>+'static>) -> &str { iter.next() }

fn parse_type_2(iter: fn(&u8)->&u8) -> &str { iter() }
//~^ ERROR missing lifetime specifier [E0106]
//~^^ HELP 0 elided free lifetimes
//~^^ HELP lifetime cannot be derived

fn parse_type_3() -> &str { unimplemented!() }
//~^ ERROR missing lifetime specifier [E0106]
//~^^ HELP no value for it to be borrowed from

fn main() {}