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Improve string concatenation suggestion #92843

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Jan 22, 2022
Merged

Improve string concatenation suggestion #92843

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2835ace
Improve suggestions for type errors with string concatenation
camelid Jan 13, 2022
69db5e2
Split up very long message
camelid Jan 13, 2022
935a99a
Add line breaks to make message easier to read
camelid Jan 13, 2022
6e42bc3
Fix formatting
camelid Jan 13, 2022
7507fb6
Shorten and improve messages
camelid Jan 19, 2022
7c4eca0
Make suggestions verbose
camelid Jan 19, 2022
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95 changes: 38 additions & 57 deletions compiler/rustc_typeck/src/check/op.rs
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Expand Up @@ -549,16 +549,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
is_assign: IsAssign,
op: hir::BinOp,
) -> bool {
let source_map = self.tcx.sess.source_map();
let remove_borrow_msg = "String concatenation appends the string on the right to the \
string on the left and may require reallocation. This \
requires ownership of the string on the left";

let msg = "`to_owned()` can be used to create an owned `String` \
from a string reference. String concatenation \
appends the string on the right to the string \
on the left and may require reallocation. This \
requires ownership of the string on the left";
let str_concat_note = "String concatenation appends the string on the right to the
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string on the left and may require reallocation.
This requires ownership of the string on the left.";
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let rm_borrow_msg = "remove the borrow to obtain an owned `String`";
let to_owned_msg = "use `to_owned()` to create an owned `String` from a string reference";
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let string_type = self.tcx.get_diagnostic_item(sym::String);
let is_std_string = |ty: Ty<'tcx>| match ty.ty_adt_def() {
Expand All @@ -574,31 +569,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
) =>
{
if let IsAssign::No = is_assign { // Do not supply this message if `&str += &str`
err.span_label(
op.span,
"`+` cannot be used to concatenate two `&str` strings",
);
match source_map.span_to_snippet(lhs_expr.span) {
Ok(lstring) => {
err.span_suggestion(
lhs_expr.span,
if lstring.starts_with('&') {
remove_borrow_msg
} else {
msg
},
if let Some(stripped) = lstring.strip_prefix('&') {
// let a = String::new();
// let _ = &a + "bar";
stripped.to_string()
} else {
format!("{}.to_owned()", lstring)
},
Applicability::MachineApplicable,
)
}
_ => err.help(msg),
};
err.span_label(op.span, "`+` cannot be used to concatenate two `&str` strings");
err.note(str_concat_note);
if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
err.span_suggestion(
lhs_expr.span.until(lhs_inner_expr.span),
rm_borrow_msg,
"".to_owned(),
Applicability::MachineApplicable
);
} else {
err.span_suggestion(
lhs_expr.span.shrink_to_hi(),
to_owned_msg,
".to_owned()".to_owned(),
Applicability::MachineApplicable
);
}
}
true
}
Expand All @@ -609,32 +596,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
op.span,
"`+` cannot be used to concatenate a `&str` with a `String`",
);
match (
source_map.span_to_snippet(lhs_expr.span),
source_map.span_to_snippet(rhs_expr.span),
is_assign,
) {
(Ok(l), Ok(r), IsAssign::No) => {
let to_string = if let Some(stripped) = l.strip_prefix('&') {
// let a = String::new(); let b = String::new();
// let _ = &a + b;
stripped.to_string()
match is_assign {
IsAssign::No => {
let sugg_msg;
let lhs_sugg = if let hir::ExprKind::AddrOf(_, _, lhs_inner_expr) = lhs_expr.kind {
sugg_msg = "remove the borrow on the left and add one on the right";
(lhs_expr.span.until(lhs_inner_expr.span), "".to_owned())
} else {
format!("{}.to_owned()", l)
sugg_msg = "call `.to_owned()` on the left and add a borrow on the right";
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(lhs_expr.span.shrink_to_hi(), ".to_owned()".to_owned())
};
err.multipart_suggestion(
msg,
vec![
(lhs_expr.span, to_string),
(rhs_expr.span, format!("&{}", r)),
],
Applicability::MachineApplicable,
);
let suggestions = vec![
lhs_sugg,
(rhs_expr.span.shrink_to_lo(), "&".to_owned()),
];
err.multipart_suggestion(sugg_msg, suggestions, Applicability::MachineApplicable);
}
_ => {
err.help(msg);
IsAssign::Yes => {
err.note(str_concat_note);
}
};
}
true
}
_ => false,
Expand Down
7 changes: 5 additions & 2 deletions src/test/ui/issues/issue-47377.stderr
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Expand Up @@ -7,10 +7,13 @@ LL | let _a = b + ", World!";
| | `+` cannot be used to concatenate two `&str` strings
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _a = b.to_owned() + ", World!";
| ~~~~~~~~~~~~
| +++++++++++

error: aborting due to previous error

Expand Down
7 changes: 5 additions & 2 deletions src/test/ui/issues/issue-47380.stderr
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Expand Up @@ -7,10 +7,13 @@ LL | println!("🦀🦀🦀🦀🦀"); let _a = b + ", World!";
| | `+` cannot be used to concatenate two `&str` strings
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | println!("🦀🦀🦀🦀🦀"); let _a = b.to_owned() + ", World!";
| ~~~~~~~~~~~~
| +++++++++++

error: aborting due to previous error

Expand Down
65 changes: 42 additions & 23 deletions src/test/ui/span/issue-39018.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -7,10 +7,13 @@ LL | let x = "Hello " + "World!";
| | `+` cannot be used to concatenate two `&str` strings
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let x = "Hello ".to_owned() + "World!";
| ~~~~~~~~~~~~~~~~~~~
| +++++++++++

error[E0369]: cannot add `World` to `World`
--> $DIR/issue-39018.rs:8:26
Expand Down Expand Up @@ -46,10 +49,10 @@ LL | let x = "Hello " + "World!".to_owned();
| | `+` cannot be used to concatenate a `&str` with a `String`
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
help: call `.to_owned()` on the left and add a borrow on the right
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|
LL | let x = "Hello ".to_owned() + &"World!".to_owned();
| ~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~
| +++++++++++ +

error[E0369]: cannot add `&String` to `&String`
--> $DIR/issue-39018.rs:26:16
Expand All @@ -59,11 +62,11 @@ LL | let _ = &a + &b;
| | |
| | `+` cannot be used to concatenate two `&str` strings
| &String
| help: remove the borrow to obtain an owned `String`
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|
help: String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
|
LL | let _ = a + &b;
| ~
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.

error[E0369]: cannot add `String` to `&String`
--> $DIR/issue-39018.rs:27:16
Expand All @@ -74,10 +77,11 @@ LL | let _ = &a + b;
| | `+` cannot be used to concatenate a `&str` with a `String`
| &String
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
help: remove the borrow on the left and add one on the right
|
LL | let _ = a + &b;
| ~ ~~
LL - let _ = &a + b;
LL + let _ = a + &b;
|

error[E0308]: mismatched types
--> $DIR/issue-39018.rs:29:17
Expand All @@ -97,10 +101,10 @@ LL | let _ = e + b;
| | `+` cannot be used to concatenate a `&str` with a `String`
| &String
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
help: call `.to_owned()` on the left and add a borrow on the right
|
LL | let _ = e.to_owned() + &b;
| ~~~~~~~~~~~~ ~~
| +++++++++++ +

error[E0369]: cannot add `&String` to `&String`
--> $DIR/issue-39018.rs:31:15
Expand All @@ -111,10 +115,13 @@ LL | let _ = e + &b;
| | `+` cannot be used to concatenate two `&str` strings
| &String
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _ = e.to_owned() + &b;
| ~~~~~~~~~~~~
| +++++++++++

error[E0369]: cannot add `&str` to `&String`
--> $DIR/issue-39018.rs:32:15
Expand All @@ -125,10 +132,13 @@ LL | let _ = e + d;
| | `+` cannot be used to concatenate two `&str` strings
| &String
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _ = e.to_owned() + d;
| ~~~~~~~~~~~~
| +++++++++++

error[E0369]: cannot add `&&str` to `&String`
--> $DIR/issue-39018.rs:33:15
Expand All @@ -139,10 +149,13 @@ LL | let _ = e + &d;
| | `+` cannot be used to concatenate two `&str` strings
| &String
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _ = e.to_owned() + &d;
| ~~~~~~~~~~~~
| +++++++++++

error[E0369]: cannot add `&&str` to `&&str`
--> $DIR/issue-39018.rs:34:16
Expand All @@ -169,10 +182,13 @@ LL | let _ = c + &d;
| | `+` cannot be used to concatenate two `&str` strings
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _ = c.to_owned() + &d;
| ~~~~~~~~~~~~
| +++++++++++

error[E0369]: cannot add `&str` to `&str`
--> $DIR/issue-39018.rs:37:15
Expand All @@ -183,10 +199,13 @@ LL | let _ = c + d;
| | `+` cannot be used to concatenate two `&str` strings
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _ = c.to_owned() + d;
| ~~~~~~~~~~~~
| +++++++++++

error: aborting due to 14 previous errors

Expand Down
7 changes: 5 additions & 2 deletions src/test/ui/str/str-concat-on-double-ref.stderr
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Expand Up @@ -7,10 +7,13 @@ LL | let c = a + b;
| | `+` cannot be used to concatenate two `&str` strings
| &String
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let c = a.to_owned() + b;
| ~~~~~~~~~~~~
| +++++++++++

error: aborting due to previous error

Expand Down
7 changes: 5 additions & 2 deletions src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr
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Expand Up @@ -7,10 +7,13 @@ LL | ...ཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔ
| | `+` cannot be used to concatenate two `&str` strings
| &str
|
help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left
= note: String concatenation appends the string on the right to the
string on the left and may require reallocation.
This requires ownership of the string on the left.
help: use `to_owned()` to create an owned `String` from a string reference
|
LL | let _ = "ༀ༁༂༃༄༅༆༇༈༉༊་༌།༎༏༐༑༒༓༔༕༖༗༘༙༚༛༜༝༞༟༠༡༢༣༤༥༦༧༨༩༪༫༬༭༮༯༰༱༲༳༴༵༶༷༸༹༺༻༼༽༾༿ཀཁགགྷངཅཆཇ཈ཉཊཋཌཌྷཎཏཐདདྷནཔཕབབྷམཙཚཛཛྷཝཞཟའཡརལཤཥསཧཨཀྵཪཫཬ཭཮཯཰ཱཱཱིིུུྲྀཷླྀཹེཻོཽཾཿ྄ཱྀྀྂྃ྅྆྇ྈྉྊྋྌྍྎྏྐྑྒྒྷྔྕྖྗ྘ྙྚྛྜྜྷྞྟྠྡྡྷྣྤྥྦྦྷྨྩྪྫྫྷྭྮྯྰྱྲླྴྵྶྷྸྐྵྺྻྼ྽྾྿࿀࿁࿂࿃࿄࿅࿆࿇࿈࿉࿊࿋࿌࿍࿎࿏࿐࿑࿒࿓࿔࿕࿖࿗࿘࿙࿚"; let _a = unicode_is_fun.to_owned() + " really fun!";
| ~~~~~~~~~~~~~~~~~~~~~~~~~
| +++++++++++

error: aborting due to previous error

Expand Down