From 5d2a2a1caa1a12a5c445fcc99e2dee42e5a5f3d7 Mon Sep 17 00:00:00 2001 From: Camelid Date: Sat, 5 Dec 2020 13:12:39 -0800 Subject: Add explanations and suggestions to `irrefutable_let_patterns` lint --- .../src/thir/pattern/check_match.rs | 35 ++++++++++++++++------ 1 file changed, 26 insertions(+), 9 deletions(-) (limited to 'compiler/rustc_mir_build') diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs index e928f3c5d4d..fdecbb94788 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs @@ -366,14 +366,31 @@ fn unreachable_pattern(tcx: TyCtxt<'_>, span: Span, id: HirId, catchall: Option< } fn irrefutable_let_pattern(tcx: TyCtxt<'_>, span: Span, id: HirId, source: hir::MatchSource) { - tcx.struct_span_lint_hir(IRREFUTABLE_LET_PATTERNS, id, span, |lint| { - let msg = match source { - hir::MatchSource::IfLetDesugar { .. } => "irrefutable `if let` pattern", - hir::MatchSource::WhileLetDesugar => "irrefutable `while let` pattern", - hir::MatchSource::IfLetGuardDesugar => "irrefutable `if let` guard", - _ => bug!(), - }; - lint.build(msg).emit() + tcx.struct_span_lint_hir(IRREFUTABLE_LET_PATTERNS, id, span, |lint| match source { + hir::MatchSource::IfLetDesugar { .. } => { + let mut diag = lint.build("irrefutable `if let` pattern"); + diag.note("this pattern will always match, so the `if let` is useless"); + diag.help("consider replacing the `if let` with a `let`"); + diag.emit() + } + hir::MatchSource::WhileLetDesugar => { + let mut diag = lint.build("irrefutable `while let` pattern"); + diag.note("this pattern will always match, so the loop will never exit"); + diag.help("consider instead using a `loop { ... }` with a `let` inside it"); + diag.emit() + } + hir::MatchSource::IfLetGuardDesugar => { + let mut diag = lint.build("irrefutable `if let` guard pattern"); + diag.note("this pattern will always match, so the guard is useless"); + diag.help("consider removing the guard and adding a `let` inside the match arm"); + diag.emit() + } + _ => { + bug!( + "expected `if let`, `while let`, or `if let` guard HIR match source, found {:?}", + source, + ) + } }); } @@ -387,7 +404,7 @@ fn check_if_let_guard<'p, 'tcx>( report_arm_reachability(&cx, &report, hir::MatchSource::IfLetGuardDesugar); if report.non_exhaustiveness_witnesses.is_empty() { - // The match is exhaustive, i.e. the if let pattern is irrefutable. + // The match is exhaustive, i.e. the `if let` pattern is irrefutable. irrefutable_let_pattern(cx.tcx, pat.span, pat_id, hir::MatchSource::IfLetGuardDesugar) } } -- cgit 1.4.1-3-g733a5