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https://github.com/rust-lang/rust-clippy
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Adding try_err lint
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commit
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7 changed files with 231 additions and 2 deletions
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@ -1134,6 +1134,7 @@ Released 2018-09-13
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[`transmuting_null`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmuting_null
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[`trivial_regex`]: https://rust-lang.github.io/rust-clippy/master/index.html#trivial_regex
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[`trivially_copy_pass_by_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#trivially_copy_pass_by_ref
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[`try_err`]: https://rust-lang.github.io/rust-clippy/master/index.html#try_err
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[`type_complexity`]: https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity
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[`unicode_not_nfc`]: https://rust-lang.github.io/rust-clippy/master/index.html#unicode_not_nfc
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[`unimplemented`]: https://rust-lang.github.io/rust-clippy/master/index.html#unimplemented
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@ -6,7 +6,7 @@
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A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
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[There are 305 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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[There are 306 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
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We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
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@ -263,6 +263,7 @@ pub mod temporary_assignment;
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pub mod transmute;
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pub mod transmuting_null;
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pub mod trivially_copy_pass_by_ref;
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pub mod try_err;
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pub mod types;
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pub mod unicode;
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pub mod unsafe_removed_from_name;
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@ -546,6 +547,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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reg.register_early_lint_pass(box literal_representation::DecimalLiteralRepresentation::new(
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conf.literal_representation_threshold
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));
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reg.register_late_lint_pass(box try_err::TryErr);
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reg.register_late_lint_pass(box use_self::UseSelf);
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reg.register_late_lint_pass(box bytecount::ByteCount);
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reg.register_late_lint_pass(box infinite_iter::InfiniteIter);
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@ -861,6 +863,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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transmute::WRONG_TRANSMUTE,
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transmuting_null::TRANSMUTING_NULL,
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trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF,
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try_err::TRY_ERR,
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types::ABSURD_EXTREME_COMPARISONS,
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types::BORROWED_BOX,
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types::BOX_VEC,
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@ -963,6 +966,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
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returns::NEEDLESS_RETURN,
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returns::UNUSED_UNIT,
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strings::STRING_LIT_AS_BYTES,
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try_err::TRY_ERR,
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types::FN_TO_NUMERIC_CAST,
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types::FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
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types::IMPLICIT_HASHER,
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120
clippy_lints/src/try_err.rs
Normal file
120
clippy_lints/src/try_err.rs
Normal file
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@ -0,0 +1,120 @@
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use crate::utils::{match_qpath, paths, snippet, span_lint_and_then};
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use if_chain::if_chain;
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use rustc::hir::*;
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use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::ty::Ty;
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use rustc::{declare_lint_pass, declare_tool_lint};
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use rustc_errors::Applicability;
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declare_clippy_lint! {
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/// **What it does:** Checks for usages of `Err(x)?`.
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///
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/// **Why is this bad?** The `?` operator is designed to allow calls that
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/// can fail to be easily chained. For example, `foo()?.bar()` or
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/// `foo(bar()?)`. Because `Err(x)?` can't be used that way (it will
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/// always return), it is more clear to write `return Err(x)`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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///
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/// ```rust,ignore
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/// // Bad
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/// fn foo(fail: bool) -> Result<i32, String> {
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/// if fail {
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/// Err("failed")?;
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/// }
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/// Ok(0)
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/// }
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///
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/// // Good
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/// fn foo(fail: bool) -> Result<i32, String> {
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/// if fail {
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/// return Err("failed".into());
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/// }
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/// Ok(0)
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/// }
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/// ```
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pub TRY_ERR,
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style,
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"return errors explicitly rather than hiding them behind a `?`"
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}
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declare_lint_pass!(TryErr => [TRY_ERR]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TryErr {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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// Looks for a structure like this:
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// match ::std::ops::Try::into_result(Err(5)) {
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// ::std::result::Result::Err(err) =>
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// #[allow(unreachable_code)]
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// return ::std::ops::Try::from_error(::std::convert::From::from(err)),
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// ::std::result::Result::Ok(val) =>
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// #[allow(unreachable_code)]
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// val,
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// };
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if_chain! {
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if let ExprKind::Match(ref match_arg, _, MatchSource::TryDesugar) = expr.node;
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if let ExprKind::Call(ref match_fun, ref try_args) = match_arg.node;
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if let ExprKind::Path(ref match_fun_path) = match_fun.node;
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if match_qpath(match_fun_path, &["std", "ops", "Try", "into_result"]);
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if let Some(ref try_arg) = try_args.get(0);
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if let ExprKind::Call(ref err_fun, ref err_args) = try_arg.node;
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if let Some(ref err_arg) = err_args.get(0);
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if let ExprKind::Path(ref err_fun_path) = err_fun.node;
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if match_qpath(err_fun_path, &paths::RESULT_ERR);
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if let Some(return_type) = find_err_return_type(cx, &expr.node);
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then {
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let err_type = cx.tables.expr_ty(err_arg);
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let suggestion = if err_type == return_type {
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format!("return Err({})", snippet(cx, err_arg.span, "_"))
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} else {
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format!("return Err({}.into())", snippet(cx, err_arg.span, "_"))
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};
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span_lint_and_then(
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cx,
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TRY_ERR,
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expr.span,
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&format!("confusing error return, consider using `{}`", suggestion),
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|db| {
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db.span_suggestion(
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expr.span,
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"try this",
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suggestion,
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Applicability::MaybeIncorrect
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);
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},
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);
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}
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}
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}
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}
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// In order to determine whether to suggest `.into()` or not, we need to find the error type the
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// function returns. To do that, we look for the From::from call (see tree above), and capture
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// its output type.
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fn find_err_return_type<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx ExprKind) -> Option<Ty<'tcx>> {
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if let ExprKind::Match(_, ref arms, MatchSource::TryDesugar) = expr {
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arms.iter().filter_map(|ty| find_err_return_type_arm(cx, ty)).nth(0)
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} else {
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None
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}
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}
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// Check for From::from in one of the match arms.
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fn find_err_return_type_arm<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arm: &'tcx Arm) -> Option<Ty<'tcx>> {
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if_chain! {
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if let ExprKind::Ret(Some(ref err_ret)) = arm.body.node;
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if let ExprKind::Call(ref from_error_path, ref from_error_args) = err_ret.node;
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if let ExprKind::Path(ref from_error_fn) = from_error_path.node;
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if match_qpath(from_error_fn, &["std", "ops", "Try", "from_error"]);
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if let Some(from_error_arg) = from_error_args.get(0);
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then {
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Some(cx.tables.expr_ty(from_error_arg))
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} else {
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None
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}
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}
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}
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@ -6,7 +6,7 @@ pub use lint::Lint;
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pub use lint::LINT_LEVELS;
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// begin lint list, do not remove this comment, it’s used in `update_lints`
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pub const ALL_LINTS: [Lint; 305] = [
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pub const ALL_LINTS: [Lint; 306] = [
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Lint {
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name: "absurd_extreme_comparisons",
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group: "correctness",
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@ -1820,6 +1820,13 @@ pub const ALL_LINTS: [Lint; 305] = [
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deprecation: None,
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module: "trivially_copy_pass_by_ref",
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},
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Lint {
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name: "try_err",
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group: "style",
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desc: "TODO",
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deprecation: None,
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module: "try_err",
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},
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Lint {
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name: "type_complexity",
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group: "complexity",
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65
tests/ui/try_err.rs
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65
tests/ui/try_err.rs
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@ -0,0 +1,65 @@
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#![deny(clippy::try_err)]
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// Tests that a simple case works
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// Should flag `Err(err)?`
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pub fn basic_test() -> Result<i32, i32> {
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let err: i32 = 1;
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Err(err)?;
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Ok(0)
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}
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// Tests that `.into()` is added when appropriate
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pub fn into_test() -> Result<i32, i32> {
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let err: u8 = 1;
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Err(err)?;
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Ok(0)
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}
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// Tests that tries in general don't trigger the error
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pub fn negative_test() -> Result<i32, i32> {
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Ok(nested_error()? + 1)
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}
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// Tests that `.into()` isn't added when the error type
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// matches the surrounding closure's return type, even
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// when it doesn't match the surrounding function's.
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pub fn closure_matches_test() -> Result<i32, i32> {
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let res: Result<i32, i8> = Some(1).into_iter()
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.map(|i| {
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let err: i8 = 1;
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Err(err)?;
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Ok(i)
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})
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.next()
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.unwrap();
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Ok(res?)
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}
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// Tests that `.into()` isn't added when the error type
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// doesn't match the surrounding closure's return type.
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pub fn closure_into_test() -> Result<i32, i32> {
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let res: Result<i32, i16> = Some(1).into_iter()
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.map(|i| {
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let err: i8 = 1;
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Err(err)?;
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Ok(i)
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})
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.next()
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.unwrap();
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Ok(res?)
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}
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fn nested_error() -> Result<i32, i32> {
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Ok(1)
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}
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fn main() {
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basic_test().unwrap();
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into_test().unwrap();
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negative_test().unwrap();
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closure_matches_test().unwrap();
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closure_into_test().unwrap();
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}
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32
tests/ui/try_err.stderr
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32
tests/ui/try_err.stderr
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error: confusing error return, consider using `return Err(err)`
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--> $DIR/try_err.rs:7:5
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LL | Err(err)?;
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| ^^^^^^^^^ help: try this: `return Err(err)`
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note: lint level defined here
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--> $DIR/try_err.rs:1:9
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LL | #![deny(clippy::try_err)]
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| ^^^^^^^^^^^^^^^
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error: confusing error return, consider using `return Err(err.into())`
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--> $DIR/try_err.rs:14:5
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LL | Err(err)?;
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| ^^^^^^^^^ help: try this: `return Err(err.into())`
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error: confusing error return, consider using `return Err(err)`
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--> $DIR/try_err.rs:31:13
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LL | Err(err)?;
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| ^^^^^^^^^ help: try this: `return Err(err)`
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error: confusing error return, consider using `return Err(err.into())`
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--> $DIR/try_err.rs:46:13
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LL | Err(err)?;
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| ^^^^^^^^^ help: try this: `return Err(err.into())`
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error: aborting due to 4 previous errors
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