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Refactor while let loop to its own module
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,87 @@ | ||
| use super::WHILE_LET_LOOP; | ||
| use crate::utils::{snippet_with_applicability, span_lint_and_sugg}; | ||
| use rustc_errors::Applicability; | ||
| use rustc_hir::{Block, Expr, ExprKind, MatchSource, StmtKind}; | ||
| use rustc_lint::{LateContext, LintContext}; | ||
| use rustc_middle::lint::in_external_macro; | ||
|
|
||
| pub(super) fn check_while_let_loop(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) { | ||
| // extract the expression from the first statement (if any) in a block | ||
| let inner_stmt_expr = extract_expr_from_first_stmt(loop_block); | ||
| // or extract the first expression (if any) from the block | ||
| if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(loop_block)) { | ||
| if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind { | ||
| // ensure "if let" compatible match structure | ||
| match *source { | ||
| MatchSource::Normal | MatchSource::IfLetDesugar { .. } => { | ||
| if arms.len() == 2 | ||
| && arms[0].guard.is_none() | ||
| && arms[1].guard.is_none() | ||
| && is_simple_break_expr(&arms[1].body) | ||
| { | ||
| if in_external_macro(cx.sess(), expr.span) { | ||
| return; | ||
| } | ||
|
|
||
| // NOTE: we used to build a body here instead of using | ||
| // ellipsis, this was removed because: | ||
| // 1) it was ugly with big bodies; | ||
| // 2) it was not indented properly; | ||
| // 3) it wasn’t very smart (see #675). | ||
| let mut applicability = Applicability::HasPlaceholders; | ||
| span_lint_and_sugg( | ||
| cx, | ||
| WHILE_LET_LOOP, | ||
| expr.span, | ||
| "this loop could be written as a `while let` loop", | ||
| "try", | ||
| format!( | ||
| "while let {} = {} {{ .. }}", | ||
| snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability), | ||
| snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability), | ||
| ), | ||
| applicability, | ||
| ); | ||
| } | ||
| }, | ||
| _ => (), | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// If a block begins with a statement (possibly a `let` binding) and has an | ||
| /// expression, return it. | ||
| fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> { | ||
| if block.stmts.is_empty() { | ||
| return None; | ||
| } | ||
| if let StmtKind::Local(ref local) = block.stmts[0].kind { | ||
| local.init //.map(|expr| expr) | ||
| } else { | ||
| None | ||
| } | ||
| } | ||
|
|
||
| /// If a block begins with an expression (with or without semicolon), return it. | ||
| fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> { | ||
| match block.expr { | ||
| Some(ref expr) if block.stmts.is_empty() => Some(expr), | ||
| None if !block.stmts.is_empty() => match block.stmts[0].kind { | ||
| StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr), | ||
| StmtKind::Local(..) | StmtKind::Item(..) => None, | ||
| }, | ||
| _ => None, | ||
| } | ||
| } | ||
|
|
||
| /// Returns `true` if expr contains a single break expr without destination label | ||
| /// and | ||
| /// passed expression. The expression may be within a block. | ||
| fn is_simple_break_expr(expr: &Expr<'_>) -> bool { | ||
| match expr.kind { | ||
| ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true, | ||
| ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)), | ||
| _ => false, | ||
| } | ||
| } |