Auto merge of #10496 - J-ZhengLi:issue_10366, r=Alexendoo

fix [`cast_possible_truncation`] offering wrong suggestion for casting float to integer

fixes: #10366

---

changelog: [`cast_possible_truncation`] Fix incorrect suggestions when casting from float types or to `_`

clippy_lints/src/casts/cast_possible_truncation.rs

@@ -2,8 +2,9 @@ use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::{span_lint, span_lint_and_then};
 use clippy_utils::expr_or_init;
 use clippy_utils::source::snippet;
+use clippy_utils::sugg::Sugg;
 use clippy_utils::ty::{get_discriminant_value, is_isize_or_usize};
-use rustc_errors::{Applicability, SuggestionStyle};
+use rustc_errors::{Applicability, Diagnostic, SuggestionStyle};
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{BinOpKind, Expr, ExprKind};
 use rustc_lint::LateContext;
@@ -163,19 +164,34 @@ pub(super) fn check(
         _ => return,
     };
 
-    let name_of_cast_from = snippet(cx, cast_expr.span, "..");
-    let cast_to_snip = snippet(cx, cast_to_span, "..");
-    let suggestion = format!("{cast_to_snip}::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_possible_truncation)]` ...");
-        diag.span_suggestion_with_style(
+        if !cast_from.is_floating_point() {
-            expr.span,
+            offer_suggestion(cx, expr, cast_expr, cast_to_span, diag);
-            "... or use `try_from` and handle the error accordingly",
+        }
-            suggestion,
-            Applicability::Unspecified,
-            // always show the suggestion in a separate line
-            SuggestionStyle::ShowAlways,
-        );
     });
 }
+
+fn offer_suggestion(
+    cx: &LateContext<'_>,
+    expr: &Expr<'_>,
+    cast_expr: &Expr<'_>,
+    cast_to_span: Span,
+    diag: &mut Diagnostic,
+) {
+    let cast_to_snip = snippet(cx, cast_to_span, "..");
+    let suggestion = if cast_to_snip == "_" {
+        format!("{}.try_into()", Sugg::hir(cx, cast_expr, "..").maybe_par())
+    } else {
+        format!("{cast_to_snip}::try_from({})", Sugg::hir(cx, cast_expr, ".."))
+    };
+
+    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,
+    );
+}

tests/ui/cast.rs

@@ -29,6 +29,12 @@ fn main() {
     1f64 as isize;
     1f64 as usize;
     1f32 as u32 as u16;
+    {
+        let _x: i8 = 1i32 as _;
+        1f32 as i32;
+        1f64 as i32;
+        1f32 as u8;
+    }
     // Test clippy::cast_possible_wrap
     1u8 as i8;
     1u16 as i16;

tests/ui/cast.stderr

@@ -44,10 +44,6 @@ LL |     1f32 as i32;
    |
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
    = 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
@@ -56,10 +52,6 @@ LL |     1f32 as u32;
    |     ^^^^^^^^^^^
    |
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
-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
@@ -76,10 +68,6 @@ LL |     1f64 as f32;
    |     ^^^^^^^^^^^
    |
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
-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
@@ -112,10 +100,6 @@ LL |     1f64 as isize;
    |     ^^^^^^^^^^^^^
    |
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
-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
@@ -124,10 +108,6 @@ LL |     1f64 as usize;
    |     ^^^^^^^^^^^^^
    |
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
-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
@@ -154,10 +134,6 @@ LL |     1f32 as u32 as u16;
    |     ^^^^^^^^^^^
    |
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
-help: ... or use `try_from` and handle the error accordingly
-   |
-LL |     u32::try_from(1f32) as u16;
-   |     ~~~~~~~~~~~~~~~~~~~
 
 error: casting `f32` to `u32` may lose the sign of the value
   --> $DIR/cast.rs:31:5
@@ -165,8 +141,50 @@ error: casting `f32` to `u32` may lose the sign of the value
 LL |     1f32 as u32 as u16;
    |     ^^^^^^^^^^^
 
+error: casting `i32` to `i8` may truncate the value
+  --> $DIR/cast.rs:33:22
+   |
+LL |         let _x: i8 = 1i32 as _;
+   |                      ^^^^^^^^^
+   |
+   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
+help: ... or use `try_from` and handle the error accordingly
+   |
+LL |         let _x: i8 = 1i32.try_into();
+   |                      ~~~~~~~~~~~~~~~
+
+error: casting `f32` to `i32` may truncate the value
+  --> $DIR/cast.rs:34:9
+   |
+LL |         1f32 as i32;
+   |         ^^^^^^^^^^^
+   |
+   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
+
+error: casting `f64` to `i32` may truncate the value
+  --> $DIR/cast.rs:35:9
+   |
+LL |         1f64 as i32;
+   |         ^^^^^^^^^^^
+   |
+   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
+
+error: casting `f32` to `u8` may truncate the value
+  --> $DIR/cast.rs:36:9
+   |
+LL |         1f32 as u8;
+   |         ^^^^^^^^^^
+   |
+   = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
+
+error: casting `f32` to `u8` may lose the sign of the value
+  --> $DIR/cast.rs:36:9
+   |
+LL |         1f32 as u8;
+   |         ^^^^^^^^^^
+
 error: casting `u8` to `i8` may wrap around the value
-  --> $DIR/cast.rs:33:5
+  --> $DIR/cast.rs:39:5
    |
 LL |     1u8 as i8;
    |     ^^^^^^^^^
@@ -174,43 +192,43 @@ LL |     1u8 as i8;
    = note: `-D clippy::cast-possible-wrap` implied by `-D warnings`
 
 error: casting `u16` to `i16` may wrap around the value
-  --> $DIR/cast.rs:34:5
+  --> $DIR/cast.rs:40:5
    |
 LL |     1u16 as i16;
    |     ^^^^^^^^^^^
 
 error: casting `u32` to `i32` may wrap around the value
-  --> $DIR/cast.rs:35:5
+  --> $DIR/cast.rs:41:5
    |
 LL |     1u32 as i32;
    |     ^^^^^^^^^^^
 
 error: casting `u64` to `i64` may wrap around the value
-  --> $DIR/cast.rs:36:5
+  --> $DIR/cast.rs:42:5
    |
 LL |     1u64 as i64;
    |     ^^^^^^^^^^^
 
 error: casting `usize` to `isize` may wrap around the value
-  --> $DIR/cast.rs:37:5
+  --> $DIR/cast.rs:43:5
    |
 LL |     1usize as isize;
    |     ^^^^^^^^^^^^^^^
 
 error: casting `i32` to `u32` may lose the sign of the value
-  --> $DIR/cast.rs:40:5
+  --> $DIR/cast.rs:46:5
    |
 LL |     -1i32 as u32;
    |     ^^^^^^^^^^^^
 
 error: casting `isize` to `usize` may lose the sign of the value
-  --> $DIR/cast.rs:42:5
+  --> $DIR/cast.rs:48:5
    |
 LL |     -1isize as usize;
    |     ^^^^^^^^^^^^^^^^
 
 error: casting `i64` to `i8` may truncate the value
-  --> $DIR/cast.rs:109:5
+  --> $DIR/cast.rs:115:5
    |
 LL |     (-99999999999i64).min(1) as i8; // should be linted because signed
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -222,7 +240,7 @@ LL |     i8::try_from((-99999999999i64).min(1)); // should be linted because sig
    |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error: casting `u64` to `u8` may truncate the value
-  --> $DIR/cast.rs:121:5
+  --> $DIR/cast.rs:127:5
    |
 LL |     999999u64.clamp(0, 256) as u8; // should still be linted
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -234,7 +252,7 @@ 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:142:21
+  --> $DIR/cast.rs:148:21
    |
 LL |             let _ = self as u8;
    |                     ^^^^^^^^^^
@@ -246,7 +264,7 @@ LL |             let _ = u8::try_from(self);
    |                     ~~~~~~~~~~~~~~~~~~
 
 error: casting `main::E2::B` to `u8` will truncate the value
-  --> $DIR/cast.rs:143:21
+  --> $DIR/cast.rs:149:21
    |
 LL |             let _ = Self::B as u8;
    |                     ^^^^^^^^^^^^^
@@ -254,7 +272,7 @@ LL |             let _ = Self::B as u8;
    = note: `-D clippy::cast-enum-truncation` implied by `-D warnings`
 
 error: casting `main::E5` to `i8` may truncate the value
-  --> $DIR/cast.rs:179:21
+  --> $DIR/cast.rs:185:21
    |
 LL |             let _ = self as i8;
    |                     ^^^^^^^^^^
@@ -266,13 +284,13 @@ LL |             let _ = i8::try_from(self);
    |                     ~~~~~~~~~~~~~~~~~~
 
 error: casting `main::E5::A` to `i8` will truncate the value
-  --> $DIR/cast.rs:180:21
+  --> $DIR/cast.rs:186:21
    |
 LL |             let _ = Self::A as i8;
    |                     ^^^^^^^^^^^^^
 
 error: casting `main::E6` to `i16` may truncate the value
-  --> $DIR/cast.rs:194:21
+  --> $DIR/cast.rs:200:21
    |
 LL |             let _ = self as i16;
    |                     ^^^^^^^^^^^
@@ -284,7 +302,7 @@ 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:209:21
+  --> $DIR/cast.rs:215:21
    |
 LL |             let _ = self as usize;
    |                     ^^^^^^^^^^^^^
@@ -296,7 +314,7 @@ LL |             let _ = usize::try_from(self);
    |                     ~~~~~~~~~~~~~~~~~~~~~
 
 error: casting `main::E10` to `u16` may truncate the value
-  --> $DIR/cast.rs:250:21
+  --> $DIR/cast.rs:256:21
    |
 LL |             let _ = self as u16;
    |                     ^^^^^^^^^^^
@@ -308,7 +326,7 @@ LL |             let _ = u16::try_from(self);
    |                     ~~~~~~~~~~~~~~~~~~~
 
 error: casting `u32` to `u8` may truncate the value
-  --> $DIR/cast.rs:258:13
+  --> $DIR/cast.rs:264:13
    |
 LL |     let c = (q >> 16) as u8;
    |             ^^^^^^^^^^^^^^^
@@ -316,11 +334,11 @@ LL |     let c = (q >> 16) as u8;
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
 help: ... or use `try_from` and handle the error accordingly
    |
-LL |     let c = u8::try_from((q >> 16));
+LL |     let c = u8::try_from(q >> 16);
-   |             ~~~~~~~~~~~~~~~~~~~~~~~
+   |             ~~~~~~~~~~~~~~~~~~~~~
 
 error: casting `u32` to `u8` may truncate the value
-  --> $DIR/cast.rs:261:13
+  --> $DIR/cast.rs:267:13
    |
 LL |     let c = (q / 1000) as u8;
    |             ^^^^^^^^^^^^^^^^
@@ -328,8 +346,8 @@ LL |     let c = (q / 1000) as u8;
    = help: if this is intentional allow the lint with `#[allow(clippy::cast_possible_truncation)]` ...
 help: ... or use `try_from` and handle the error accordingly
    |
-LL |     let c = u8::try_from((q / 1000));
+LL |     let c = u8::try_from(q / 1000);
-   |             ~~~~~~~~~~~~~~~~~~~~~~~~
+   |             ~~~~~~~~~~~~~~~~~~~~~~
 
-error: aborting due to 36 previous errors
+error: aborting due to 41 previous errors