From 51aaba6e8cf50289d55f53ac85aab4c95d601439 Mon Sep 17 00:00:00 2001 From: navh Date: Tue, 6 Dec 2022 19:05:22 +0100 Subject: [PATCH] `cast_possible_truncation` Suggest TryFrom when truncation possible --- .../src/casts/cast_possible_truncation.rs | 24 ++++- clippy_lints/src/casts/mod.rs | 2 +- tests/ui/cast.stderr | 95 +++++++++++++++++++ tests/ui/cast_size.stderr | 53 +++++++++++ 4 files changed, 170 insertions(+), 4 deletions(-) diff --git a/clippy_lints/src/casts/cast_possible_truncation.rs b/clippy_lints/src/casts/cast_possible_truncation.rs index a6376484914..d9898aeb92c 100644 --- a/clippy_lints/src/casts/cast_possible_truncation.rs +++ b/clippy_lints/src/casts/cast_possible_truncation.rs @@ -1,7 +1,11 @@ use clippy_utils::consts::{constant, Constant}; -use clippy_utils::diagnostics::span_lint; +use clippy_utils::diagnostics::{span_lint, span_lint_and_then}; use clippy_utils::expr_or_init; +use clippy_utils::source::snippet; use clippy_utils::ty::{get_discriminant_value, is_isize_or_usize}; +use rustc_ast::ast; +use rustc_attr::IntType; +use rustc_errors::{Applicability, SuggestionStyle}; use rustc_hir::def::{DefKind, Res}; use rustc_hir::{BinOpKind, Expr, ExprKind}; use rustc_lint::LateContext; @@ -139,7 +143,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, ); return; } - format!("casting `{cast_from}` to `{cast_to}` may truncate the value{suffix}",) + format!("casting `{cast_from}` to `{cast_to}` may truncate the value{suffix}") }, (ty::Float(_), true) => { @@ -153,5 +157,19 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, _ => return, }; - span_lint(cx, CAST_POSSIBLE_TRUNCATION, expr.span, &msg); + let snippet = snippet(cx, expr.span, "x"); + let name_of_cast_from = snippet.split(" as").next().unwrap_or("x"); + let suggestion = format!("{cast_to}::try_from({name_of_cast_from})"); + + span_lint_and_then(cx, CAST_POSSIBLE_TRUNCATION, expr.span, &msg, |diag| { + diag.help("if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ..."); + diag.span_suggestion_with_style( + expr.span, + "... or use `try_from` and handle the error accordingly", + suggestion, + Applicability::Unspecified, + // always show the suggestion in a separate line + SuggestionStyle::ShowAlways, + ); + }); } diff --git a/clippy_lints/src/casts/mod.rs b/clippy_lints/src/casts/mod.rs index 161e3a698e9..38b1c5c1c7e 100644 --- a/clippy_lints/src/casts/mod.rs +++ b/clippy_lints/src/casts/mod.rs @@ -85,7 +85,7 @@ declare_clippy_lint! { /// ### Why is this bad? /// In some problem domains, it is good practice to avoid /// truncation. This lint can be activated to help assess where additional - /// checks could be beneficial. + /// checks could be beneficial, and suggests implementing TryFrom trait. /// /// ### Example /// ```rust diff --git a/tests/ui/cast.stderr b/tests/ui/cast.stderr index 0c63b4af308..eceb135d62b 100644 --- a/tests/ui/cast.stderr +++ b/tests/ui/cast.stderr @@ -42,13 +42,24 @@ error: casting `f32` to `i32` may truncate the value LL | 1f32 as i32; | ^^^^^^^^^^^ | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... = note: `-D clippy::cast-possible-truncation` implied by `-D warnings` +help: ... or use `try_from` and handle the error accordingly + | +LL | i32::try_from(1f32); + | ~~~~~~~~~~~~~~~~~~~ error: casting `f32` to `u32` may truncate the value --> $DIR/cast.rs:25:5 | LL | 1f32 as u32; | ^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | u32::try_from(1f32); + | ~~~~~~~~~~~~~~~~~~~ error: casting `f32` to `u32` may lose the sign of the value --> $DIR/cast.rs:25:5 @@ -63,30 +74,60 @@ error: casting `f64` to `f32` may truncate the value | LL | 1f64 as f32; | ^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | f32::try_from(1f64); + | ~~~~~~~~~~~~~~~~~~~ error: casting `i32` to `i8` may truncate the value --> $DIR/cast.rs:27:5 | LL | 1i32 as i8; | ^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | i8::try_from(1i32); + | ~~~~~~~~~~~~~~~~~~ error: casting `i32` to `u8` may truncate the value --> $DIR/cast.rs:28:5 | LL | 1i32 as u8; | ^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | u8::try_from(1i32); + | ~~~~~~~~~~~~~~~~~~ error: casting `f64` to `isize` may truncate the value --> $DIR/cast.rs:29:5 | LL | 1f64 as isize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | isize::try_from(1f64); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `f64` to `usize` may truncate the value --> $DIR/cast.rs:30:5 | LL | 1f64 as usize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | usize::try_from(1f64); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `f64` to `usize` may lose the sign of the value --> $DIR/cast.rs:30:5 @@ -143,18 +184,36 @@ error: casting `i64` to `i8` may truncate the value | LL | (-99999999999i64).min(1) as i8; // should be linted because signed | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | i8::try_from((-99999999999i64).min(1)); // should be linted because signed + | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: casting `u64` to `u8` may truncate the value --> $DIR/cast.rs:120:5 | LL | 999999u64.clamp(0, 256) as u8; // should still be linted | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | u8::try_from(999999u64.clamp(0, 256)); // should still be linted + | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: casting `main::E2` to `u8` may truncate the value --> $DIR/cast.rs:141:21 | LL | let _ = self as u8; | ^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let _ = u8::try_from(self); + | ~~~~~~~~~~~~~~~~~~ error: casting `main::E2::B` to `u8` will truncate the value --> $DIR/cast.rs:142:21 @@ -169,6 +228,12 @@ error: casting `main::E5` to `i8` may truncate the value | LL | let _ = self as i8; | ^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let _ = i8::try_from(self); + | ~~~~~~~~~~~~~~~~~~ error: casting `main::E5::A` to `i8` will truncate the value --> $DIR/cast.rs:179:21 @@ -181,30 +246,60 @@ error: casting `main::E6` to `i16` may truncate the value | LL | let _ = self as i16; | ^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let _ = i16::try_from(self); + | ~~~~~~~~~~~~~~~~~~~ error: casting `main::E7` to `usize` may truncate the value on targets with 32-bit wide pointers --> $DIR/cast.rs:208:21 | LL | let _ = self as usize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let _ = usize::try_from(self); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `main::E10` to `u16` may truncate the value --> $DIR/cast.rs:249:21 | LL | let _ = self as u16; | ^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let _ = u16::try_from(self); + | ~~~~~~~~~~~~~~~~~~~ error: casting `u32` to `u8` may truncate the value --> $DIR/cast.rs:257:13 | LL | let c = (q >> 16) as u8; | ^^^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let c = u8::try_from((q >> 16)); + | ~~~~~~~~~~~~~~~~~~~~~~~ error: casting `u32` to `u8` may truncate the value --> $DIR/cast.rs:260:13 | LL | let c = (q / 1000) as u8; | ^^^^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | let c = u8::try_from((q / 1000)); + | ~~~~~~~~~~~~~~~~~~~~~~~~ error: aborting due to 33 previous errors diff --git a/tests/ui/cast_size.stderr b/tests/ui/cast_size.stderr index 95552f2e285..8acf26049f4 100644 --- a/tests/ui/cast_size.stderr +++ b/tests/ui/cast_size.stderr @@ -4,7 +4,12 @@ error: casting `isize` to `i8` may truncate the value LL | 1isize as i8; | ^^^^^^^^^^^^ | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... = note: `-D clippy::cast-possible-truncation` implied by `-D warnings` +help: ... or use `try_from` and handle the error accordingly + | +LL | i8::try_from(1isize); + | ~~~~~~~~~~~~~~~~~~~~ error: casting `isize` to `f64` causes a loss of precision on targets with 64-bit wide pointers (`isize` is 64 bits wide, but `f64`'s mantissa is only 52 bits wide) --> $DIR/cast_size.rs:15:5 @@ -37,24 +42,48 @@ error: casting `isize` to `i32` may truncate the value on targets with 64-bit wi | LL | 1isize as i32; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | i32::try_from(1isize); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `isize` to `u32` may truncate the value on targets with 64-bit wide pointers --> $DIR/cast_size.rs:20:5 | LL | 1isize as u32; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | u32::try_from(1isize); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `usize` to `u32` may truncate the value on targets with 64-bit wide pointers --> $DIR/cast_size.rs:21:5 | LL | 1usize as u32; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | u32::try_from(1usize); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `usize` to `i32` may truncate the value on targets with 64-bit wide pointers --> $DIR/cast_size.rs:22:5 | LL | 1usize as i32; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | i32::try_from(1usize); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `usize` to `i32` may wrap around the value on targets with 32-bit wide pointers --> $DIR/cast_size.rs:22:5 @@ -69,18 +98,36 @@ error: casting `i64` to `isize` may truncate the value on targets with 32-bit wi | LL | 1i64 as isize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | isize::try_from(1i64); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `i64` to `usize` may truncate the value on targets with 32-bit wide pointers --> $DIR/cast_size.rs:25:5 | LL | 1i64 as usize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | usize::try_from(1i64); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `u64` to `isize` may truncate the value on targets with 32-bit wide pointers --> $DIR/cast_size.rs:26:5 | LL | 1u64 as isize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | isize::try_from(1u64); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `u64` to `isize` may wrap around the value on targets with 64-bit wide pointers --> $DIR/cast_size.rs:26:5 @@ -93,6 +140,12 @@ error: casting `u64` to `usize` may truncate the value on targets with 32-bit wi | LL | 1u64 as usize; | ^^^^^^^^^^^^^ + | + = help: if this is intentional allow the lint with `#[allow(clippy::cast_precision_loss)]` ... +help: ... or use `try_from` and handle the error accordingly + | +LL | usize::try_from(1u64); + | ~~~~~~~~~~~~~~~~~~~~~ error: casting `u32` to `isize` may wrap around the value on targets with 32-bit wide pointers --> $DIR/cast_size.rs:28:5