Unrolled build for rust-lang#126187

Rollup merge of rust-lang#126187 - surechen:fix_125997, r=oli-obk

For E0277 suggest adding `Result` return type for function when using QuestionMark `?` in the body.

Adding suggestions for following function in E0277.

```rust
fn main() {
    let mut _file = File::create("foo.txt")?;
}
```

to

```rust
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut _file = File::create("foo.txt")?;

    return Ok(());
}
```

According to the issue rust-lang#125997, only the code examples in the issue are targeted, but the issue covers a wider range of situations.

<!--
If this PR is related to an unstable feature or an otherwise tracked effort,
please link to the relevant tracking issue here. If you don't know of a related
tracking issue or there are none, feel free to ignore this.

This PR will get automatically assigned to a reviewer. In case you would like
a specific user to review your work, you can assign it to them by using

    r​? <reviewer name>
-->

compiler/rustc_hir/src/hir.rs

@@ -1038,6 +1038,7 @@ pub struct Block<'hir> {
  pub hir_id: HirId,
  /// Distinguishes between `unsafe { ... }` and `{ ... }`.
  pub rules: BlockCheckMode,
+ /// The span includes the curly braces `{` and `}` around the block.
  pub span: Span,
  /// If true, then there may exist `break 'a` values that aim to
  /// break out of this block early.

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -4587,6 +4587,47 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
  _ => "/* value */".to_string(),
  })
  }
+
+ fn suggest_add_result_as_return_type(
+ &self,
+ obligation: &PredicateObligation<'tcx>,
+ err: &mut Diag<'_>,
+ trait_ref: ty::PolyTraitRef<'tcx>,
+ ) {
+ if ObligationCauseCode::QuestionMark != *obligation.cause.code().peel_derives() {
+ return;
+ }
+
+ let node = self.tcx.hir_node_by_def_id(obligation.cause.body_id);
+ if let hir::Node::Item(item) = node
+ && let hir::ItemKind::Fn(sig, _, body_id) = item.kind
+ && let hir::FnRetTy::DefaultReturn(ret_span) = sig.decl.output
+ && self.tcx.is_diagnostic_item(sym::FromResidual, trait_ref.def_id())
+ && let ty::Tuple(l) = trait_ref.skip_binder().args.type_at(0).kind()
+ && l.len() == 0
+ && let ty::Adt(def, _) = trait_ref.skip_binder().args.type_at(1).kind()
+ && self.tcx.is_diagnostic_item(sym::Result, def.did())
+ {
+ let body = self.tcx.hir().body(body_id);
+ let mut sugg_spans =
+ vec![(ret_span, " -> Result<(), Box<dyn std::error::Error>>".to_string())];
+
+ if let hir::ExprKind::Block(b, _) = body.value.kind
+ && b.expr.is_none()
+ {
+ sugg_spans.push((
+ // The span will point to the closing curly brace `}` of the block.
+ b.span.shrink_to_hi().with_lo(b.span.hi() - BytePos(1)),
+ "\n Ok(())\n}".to_string(),
+ ));
+ }
+ err.multipart_suggestion_verbose(
+ format!("consider adding return type"),
+ sugg_spans,
+ Applicability::MaybeIncorrect,
+ );
+ }
+ }
 }
 
 /// Add a hint to add a missing borrow or remove an unnecessary one.

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -611,6 +611,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
  &mut err,
  trait_predicate,
  );
+ self.suggest_add_result_as_return_type(&obligation,
+ &mut err,
+ trait_ref);
+
  if self.suggest_add_reference_to_arg(
  &obligation,
  &mut err,

tests/ui/return/return-from-residual-sugg-issue-125997.fixed

@@ -0,0 +1,42 @@
+//@ run-rustfix
+
+#![allow(unused_imports)]
+#![allow(dead_code)]
+
+use std::fs::File;
+use std::io::prelude::*;
+
+fn test1() -> Result<(), Box<dyn std::error::Error>> {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+
+ Ok(())
+}
+
+fn test2() -> Result<(), Box<dyn std::error::Error>> {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+ println!();
+
+ Ok(())
+}
+
+macro_rules! mac {
+ () => {
+ fn test3() -> Result<(), Box<dyn std::error::Error>> {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+ println!();
+
+ Ok(())
+}
+ };
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+ mac!();
+
+ Ok(())
+}

tests/ui/return/return-from-residual-sugg-issue-125997.rs

@@ -0,0 +1,34 @@
+//@ run-rustfix
+
+#![allow(unused_imports)]
+#![allow(dead_code)]
+
+use std::fs::File;
+use std::io::prelude::*;
+
+fn test1() {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+}
+
+fn test2() {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+ println!();
+}
+
+macro_rules! mac {
+ () => {
+ fn test3() {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+ println!();
+ }
+ };
+}
+
+fn main() {
+ let mut _file = File::create("foo.txt")?;
+ //~^ ERROR the `?` operator can only be used in a function
+ mac!();
+}

tests/ui/return/return-from-residual-sugg-issue-125997.stderr

@@ -0,0 +1,86 @@
+error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
+ --> $DIR/return-from-residual-sugg-issue-125997.rs:10:44
+ |
+LL | fn test1() {
+ | ---------- this function should return `Result` or `Option` to accept `?`
+LL | let mut _file = File::create("foo.txt")?;
+ | ^ cannot use the `?` operator in a function that returns `()`
+ |
+ = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
+help: consider adding return type
+ |
+LL ~ fn test1() -> Result<(), Box<dyn std::error::Error>> {
+LL | let mut _file = File::create("foo.txt")?;
+LL |
+LL + 
+LL + Ok(())
+LL + }
+ |
+
+error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
+ --> $DIR/return-from-residual-sugg-issue-125997.rs:15:44
+ |
+LL | fn test2() {
+ | ---------- this function should return `Result` or `Option` to accept `?`
+LL | let mut _file = File::create("foo.txt")?;
+ | ^ cannot use the `?` operator in a function that returns `()`
+ |
+ = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
+help: consider adding return type
+ |
+LL ~ fn test2() -> Result<(), Box<dyn std::error::Error>> {
+LL | let mut _file = File::create("foo.txt")?;
+LL |
+LL | println!();
+LL + 
+LL + Ok(())
+LL + }
+ |
+
+error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
+ --> $DIR/return-from-residual-sugg-issue-125997.rs:31:44
+ |
+LL | fn main() {
+ | --------- this function should return `Result` or `Option` to accept `?`
+LL | let mut _file = File::create("foo.txt")?;
+ | ^ cannot use the `?` operator in a function that returns `()`
+ |
+ = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
+help: consider adding return type
+ |
+LL ~ fn main() -> Result<(), Box<dyn std::error::Error>> {
+LL | let mut _file = File::create("foo.txt")?;
+LL |
+LL | mac!();
+LL + 
+LL + Ok(())
+LL + }
+ |
+
+error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
+ --> $DIR/return-from-residual-sugg-issue-125997.rs:23:52
+ |
+LL | fn test3() {
+ | ---------- this function should return `Result` or `Option` to accept `?`
+LL | let mut _file = File::create("foo.txt")?;
+ | ^ cannot use the `?` operator in a function that returns `()`
+...
+LL | mac!();
+ | ------ in this macro invocation
+ |
+ = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
+ = note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider adding return type
+ |
+LL ~ fn test3() -> Result<(), Box<dyn std::error::Error>> {
+LL | let mut _file = File::create("foo.txt")?;
+LL |
+LL | println!();
+LL ~ 
+LL + Ok(())
+LL + }
+ |
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/try-trait/try-operator-on-main.stderr

@@ -8,6 +8,16 @@ LL | std::fs::File::open("foo")?;
  | ^ cannot use the `?` operator in a function that returns `()`
  |
  = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
+help: consider adding return type
+ |
+LL ~ fn main() -> Result<(), Box<dyn std::error::Error>> {
+LL | // error for a `Try` type on a non-`Try` fn
+ ...
+LL | try_trait_generic::<()>();
+LL + 
+LL + Ok(())
+LL + }
+ |
 
 error[E0277]: the `?` operator can only be applied to values that implement `Try`
  --> $DIR/try-operator-on-main.rs:10:5