From 6cc78bf8d76383395e307cef5e601cfe561337e6 Mon Sep 17 00:00:00 2001 From: "Zack M. Davis" Date: Fri, 29 Jun 2018 22:02:52 -0700 Subject: [PATCH] in which we plug the crack where `?`-desugaring leaked into errors Most of the time, it's not a problem that the types of the arm bodies in a desugared-from-`?` match are different (that is, specifically: in `x?` where x is a `Result`, the `Ok` arm body is an `A`, whereas the `Err` arm diverges to return a `Result`), because they're being assigned to different places. But in tail position, the types do need to match, and our error message was explicitly referring to "match arms", which is confusing when there's no `match` in the sweetly sugared source. It is not without some misgivings that we pollute the clarity-of-purpose of `note_error_origin` with the suggestion to wrap with `Ok` (the other branches are pointing out the odd-arm-out in the HIR that is the origin of the error; the new branch that issues the `Ok` suggestion is serving a different purpose), but it's the natural place to do it given that we're already matching on `ObligationCauseCode::MatchExpressionArm { arm_span, source }` there. Resolves #51632. --- src/librustc/infer/error_reporting/mod.rs | 19 ++++++++++++-- ...51632-try-desugar-incompatible-types.fixed | 25 +++++++++++++++++++ ...ue-51632-try-desugar-incompatible-types.rs | 25 +++++++++++++++++++ ...1632-try-desugar-incompatible-types.stderr | 15 +++++++++++ 4 files changed, 82 insertions(+), 2 deletions(-) create mode 100644 src/test/ui/issue-51632-try-desugar-incompatible-types.fixed create mode 100644 src/test/ui/issue-51632-try-desugar-incompatible-types.rs create mode 100644 src/test/ui/issue-51632-try-desugar-incompatible-types.stderr diff --git a/src/librustc/infer/error_reporting/mod.rs b/src/librustc/infer/error_reporting/mod.rs index 482af9c005f..8f428c3e505 100644 --- a/src/librustc/infer/error_reporting/mod.rs +++ b/src/librustc/infer/error_reporting/mod.rs @@ -500,7 +500,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { } else { err.span_label(arm_span, msg); } - } + }, + hir::MatchSource::TryDesugar => { // Issue #51632 + if let Ok(try_snippet) = self.tcx.sess.codemap().span_to_snippet(arm_span) { + err.span_suggestion_with_applicability( + arm_span, + "try wrapping with a success variant", + format!("Ok({})", try_snippet), + Applicability::MachineApplicable + ); + } + }, _ => { let msg = "match arm with an incompatible type"; if self.tcx.sess.codemap().is_multiline(arm_span) { @@ -1294,7 +1304,12 @@ impl<'tcx> ObligationCause<'tcx> { match self.code { CompareImplMethodObligation { .. } => Error0308("method not compatible with trait"), MatchExpressionArm { source, .. } => Error0308(match source { - hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have incompatible types", + hir::MatchSource::IfLetDesugar { .. } => { + "`if let` arms have incompatible types" + }, + hir::MatchSource::TryDesugar => { + "try expression alternatives have incompatible types" + }, _ => "match arms have incompatible types", }), IfExpression => Error0308("if and else have incompatible types"), diff --git a/src/test/ui/issue-51632-try-desugar-incompatible-types.fixed b/src/test/ui/issue-51632-try-desugar-incompatible-types.fixed new file mode 100644 index 00000000000..016cff914bd --- /dev/null +++ b/src/test/ui/issue-51632-try-desugar-incompatible-types.fixed @@ -0,0 +1,25 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// run-rustfix + +#![allow(dead_code)] + +fn missing_discourses() -> Result { + Ok(1) +} + +fn forbidden_narratives() -> Result { + Ok(missing_discourses()?) + //~^ ERROR try expression alternatives have incompatible types + //~| HELP try wrapping with a success variant +} + +fn main() {} diff --git a/src/test/ui/issue-51632-try-desugar-incompatible-types.rs b/src/test/ui/issue-51632-try-desugar-incompatible-types.rs new file mode 100644 index 00000000000..315773a85f0 --- /dev/null +++ b/src/test/ui/issue-51632-try-desugar-incompatible-types.rs @@ -0,0 +1,25 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// run-rustfix + +#![allow(dead_code)] + +fn missing_discourses() -> Result { + Ok(1) +} + +fn forbidden_narratives() -> Result { + missing_discourses()? + //~^ ERROR try expression alternatives have incompatible types + //~| HELP try wrapping with a success variant +} + +fn main() {} diff --git a/src/test/ui/issue-51632-try-desugar-incompatible-types.stderr b/src/test/ui/issue-51632-try-desugar-incompatible-types.stderr new file mode 100644 index 00000000000..a50af5624c0 --- /dev/null +++ b/src/test/ui/issue-51632-try-desugar-incompatible-types.stderr @@ -0,0 +1,15 @@ +error[E0308]: try expression alternatives have incompatible types + --> $DIR/issue-51632-try-desugar-incompatible-types.rs:20:5 + | +LL | missing_discourses()? + | ^^^^^^^^^^^^^^^^^^^^^ + | | + | expected enum `std::result::Result`, found isize + | help: try wrapping with a success variant: `Ok(missing_discourses()?)` + | + = note: expected type `std::result::Result` + found type `isize` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0308`.