Auto merge of #12070 - roife:fix/issue-12034, r=Centri3

Fix issue #12034: add autofixes for unnecessary_fallible_conversions

fixes #12034

Currently, the `unnecessary_fallible_conversions` lint was capable of autofixing expressions like `0i32.try_into().unwrap()`. However, it couldn't autofix expressions in the form of `i64::try_from(0i32).unwrap()` or `<i64 as TryFrom<i32>>::try_from(0).unwrap()`.

This pull request extends the functionality to correctly autofix these latter forms as well.

changelog: [`unnecessary_fallible_conversions`]: Add autofixes for more forms

4 files changed, 293 insertions, 46 deletions

diff --git a/clippy_lints/src/methods/unnecessary_fallible_conversions.rs b/clippy_lints/src/methods/unnecessary_fallible_conversions.rs
index 89cf20c14fc..d46b584f8f4 100644
--- a/clippy_lints/src/methods/unnecessary_fallible_conversions.rs
+++ b/clippy_lints/src/methods/unnecessary_fallible_conversions.rs
@@ -2,7 +2,7 @@ use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::get_parent_expr;
 use clippy_utils::ty::implements_trait;
 use rustc_errors::Applicability;
-use rustc_hir::{Expr, ExprKind};
+use rustc_hir::{Expr, ExprKind, QPath};
 use rustc_lint::LateContext;
 use rustc_middle::ty;
 use rustc_middle::ty::print::with_forced_trimmed_paths;
@@ -10,17 +10,71 @@ use rustc_span::{sym, Span};
 
 use super::UNNECESSARY_FALLIBLE_CONVERSIONS;
 
+#[derive(Copy, Clone)]
+enum SpansKind {
+    TraitFn { trait_span: Span, fn_span: Span },
+    Fn { fn_span: Span },
+}
+
 /// What function is being called and whether that call is written as a method call or a function
 /// call
 #[derive(Copy, Clone)]
 #[expect(clippy::enum_variant_names)]
 enum FunctionKind {
     /// `T::try_from(U)`
-    TryFromFunction,
+    TryFromFunction(Option<SpansKind>),
     /// `t.try_into()`
     TryIntoMethod,
     /// `U::try_into(t)`
-    TryIntoFunction,
+    TryIntoFunction(Option<SpansKind>),
+}
+
+impl FunctionKind {
+    fn appl_sugg(&self, parent_unwrap_call: Option<Span>, primary_span: Span) -> (Applicability, Vec<(Span, String)>) {
+        let Some(unwrap_span) = parent_unwrap_call else {
+            return (Applicability::Unspecified, self.default_sugg(primary_span));
+        };
+
+        match &self {
+            FunctionKind::TryFromFunction(None) | FunctionKind::TryIntoFunction(None) => {
+                (Applicability::Unspecified, self.default_sugg(primary_span))
+            },
+            _ => (
+                Applicability::MachineApplicable,
+                self.machine_applicable_sugg(primary_span, unwrap_span),
+            ),
+        }
+    }
+
+    fn default_sugg(&self, primary_span: Span) -> Vec<(Span, String)> {
+        let replacement = match *self {
+            FunctionKind::TryFromFunction(_) => "From::from",
+            FunctionKind::TryIntoFunction(_) => "Into::into",
+            FunctionKind::TryIntoMethod => "into",
+        };
+
+        vec![(primary_span, String::from(replacement))]
+    }
+
+    fn machine_applicable_sugg(&self, primary_span: Span, unwrap_span: Span) -> Vec<(Span, String)> {
+        let (trait_name, fn_name) = match self {
+            FunctionKind::TryFromFunction(_) => ("From".to_owned(), "from".to_owned()),
+            FunctionKind::TryIntoFunction(_) | FunctionKind::TryIntoMethod => ("Into".to_owned(), "into".to_owned()),
+        };
+
+        let mut sugg = match *self {
+            FunctionKind::TryFromFunction(Some(spans)) | FunctionKind::TryIntoFunction(Some(spans)) => match spans {
+                SpansKind::TraitFn { trait_span, fn_span } => vec![(trait_span, trait_name), (fn_span, fn_name)],
+                SpansKind::Fn { fn_span } => vec![(fn_span, fn_name)],
+            },
+            FunctionKind::TryIntoMethod => vec![(primary_span, fn_name)],
+            // Or the suggestion is not machine-applicable
+            _ => unreachable!(),
+        };
+
+        sugg.push((unwrap_span, String::new()));
+        sugg
+    }
 }
 
 fn check<'tcx>(
@@ -35,8 +89,8 @@ fn check<'tcx>(
         && self_ty != other_ty
         && let Some(self_ty) = self_ty.as_type()
         && let Some(from_into_trait) = cx.tcx.get_diagnostic_item(match kind {
-            FunctionKind::TryFromFunction => sym::From,
-            FunctionKind::TryIntoMethod | FunctionKind::TryIntoFunction => sym::Into,
+            FunctionKind::TryFromFunction(_) => sym::From,
+            FunctionKind::TryIntoMethod | FunctionKind::TryIntoFunction(_) => sym::Into,
         })
         // If `T: TryFrom<U>` and `T: From<U>` both exist, then that means that the `TryFrom`
         // _must_ be from the blanket impl and cannot have been manually implemented
@@ -45,49 +99,37 @@ fn check<'tcx>(
         && implements_trait(cx, self_ty, from_into_trait, &[other_ty])
         && let Some(other_ty) = other_ty.as_type()
     {
+        // Extend the span to include the unwrap/expect call:
+        // `foo.try_into().expect("..")`
+        //      ^^^^^^^^^^^^^^^^^^^^^^^
+        //
+        // `try_into().unwrap()` specifically can be trivially replaced with just `into()`,
+        // so that can be machine-applicable
         let parent_unwrap_call = get_parent_expr(cx, expr).and_then(|parent| {
             if let ExprKind::MethodCall(path, .., span) = parent.kind
                 && let sym::unwrap | sym::expect = path.ident.name
             {
-                Some(span)
+                // include `.` before `unwrap`/`expect`
+                Some(span.with_lo(expr.span.hi()))
             } else {
                 None
             }
         });
-        let (source_ty, target_ty, sugg, span, applicability) = match kind {
-            FunctionKind::TryIntoMethod if let Some(unwrap_span) = parent_unwrap_call => {
-                // Extend the span to include the unwrap/expect call:
-                // `foo.try_into().expect("..")`
-                //      ^^^^^^^^^^^^^^^^^^^^^^^
-                //
-                // `try_into().unwrap()` specifically can be trivially replaced with just `into()`,
-                // so that can be machine-applicable
-
-                (
-                    self_ty,
-                    other_ty,
-                    "into()",
-                    primary_span.with_hi(unwrap_span.hi()),
-                    Applicability::MachineApplicable,
-                )
-            },
-            FunctionKind::TryFromFunction => (
-                other_ty,
-                self_ty,
-                "From::from",
-                primary_span,
-                Applicability::Unspecified,
-            ),
-            FunctionKind::TryIntoFunction => (
-                self_ty,
-                other_ty,
-                "Into::into",
-                primary_span,
-                Applicability::Unspecified,
-            ),
-            FunctionKind::TryIntoMethod => (self_ty, other_ty, "into", primary_span, Applicability::Unspecified),
+
+        // If there is an unwrap/expect call, extend the span to include the call
+        let span = if let Some(unwrap_call) = parent_unwrap_call {
+            primary_span.with_hi(unwrap_call.hi())
+        } else {
+            primary_span
+        };
+
+        let (source_ty, target_ty) = match kind {
+            FunctionKind::TryIntoMethod | FunctionKind::TryIntoFunction(_) => (self_ty, other_ty),
+            FunctionKind::TryFromFunction(_) => (other_ty, self_ty),
         };
 
+        let (applicability, sugg) = kind.appl_sugg(parent_unwrap_call, primary_span);
+
         span_lint_and_then(
             cx,
             UNNECESSARY_FALLIBLE_CONVERSIONS,
@@ -97,7 +139,7 @@ fn check<'tcx>(
                 with_forced_trimmed_paths!({
                     diag.note(format!("converting `{source_ty}` to `{target_ty}` cannot fail"));
                 });
-                diag.span_suggestion(span, "use", sugg, applicability);
+                diag.multipart_suggestion("use", sugg, applicability);
             },
         );
     }
@@ -125,13 +167,30 @@ pub(super) fn check_function(cx: &LateContext<'_>, expr: &Expr<'_>, callee: &Exp
         && let Some(item_def_id) = cx.qpath_res(qpath, callee.hir_id).opt_def_id()
         && let Some(trait_def_id) = cx.tcx.trait_of_item(item_def_id)
     {
+        let qpath_spans = match qpath {
+            QPath::Resolved(_, path) => {
+                if let [trait_seg, fn_seg] = path.segments {
+                    Some(SpansKind::TraitFn {
+                        trait_span: trait_seg.ident.span,
+                        fn_span: fn_seg.ident.span,
+                    })
+                } else {
+                    None
+                }
+            },
+            QPath::TypeRelative(_, seg) => Some(SpansKind::Fn {
+                fn_span: seg.ident.span,
+            }),
+            QPath::LangItem(_, _) => unreachable!("`TryFrom` and `TryInto` are not lang items"),
+        };
+
         check(
             cx,
             expr,
             cx.typeck_results().node_args(callee.hir_id),
             match cx.tcx.get_diagnostic_name(trait_def_id) {
-                Some(sym::TryFrom) => FunctionKind::TryFromFunction,
-                Some(sym::TryInto) => FunctionKind::TryIntoFunction,
+                Some(sym::TryFrom) => FunctionKind::TryFromFunction(qpath_spans),
+                Some(sym::TryInto) => FunctionKind::TryIntoFunction(qpath_spans),
                 _ => return,
             },
             callee.span,
diff --git a/tests/ui/unnecessary_fallible_conversions.fixed b/tests/ui/unnecessary_fallible_conversions.fixed
index 9668a6b99bf..b6dd1f26774 100644
--- a/tests/ui/unnecessary_fallible_conversions.fixed
+++ b/tests/ui/unnecessary_fallible_conversions.fixed
@@ -1,6 +1,43 @@
 #![warn(clippy::unnecessary_fallible_conversions)]
 
 fn main() {
+    // --- TryFromMethod `T::try_from(u)` ---
+
     let _: i64 = 0i32.into();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
     let _: i64 = 0i32.into();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryFromFunction `T::try_from(U)` ---
+
+    let _ = i64::from(0i32);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _ = i64::from(0i32);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryIntoFunction `U::try_into(t)` ---
+
+    let _: i64 = i32::into(0);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _: i64 = i32::into(0i32);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryFromFunction `<T as TryFrom<U>>::try_from(U)` ---
+
+    let _ = <i64 as From<i32>>::from(0);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _ = <i64 as From<i32>>::from(0);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryIntoFunction `<U as TryInto<_>>::try_into(U)` ---
+
+    let _: i64 = <i32 as Into<_>>::into(0);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _: i64 = <i32 as Into<_>>::into(0);
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
 }
diff --git a/tests/ui/unnecessary_fallible_conversions.rs b/tests/ui/unnecessary_fallible_conversions.rs
index 9fa6c08b1b0..6f8df7365e8 100644
--- a/tests/ui/unnecessary_fallible_conversions.rs
+++ b/tests/ui/unnecessary_fallible_conversions.rs
@@ -1,6 +1,43 @@
 #![warn(clippy::unnecessary_fallible_conversions)]
 
 fn main() {
+    // --- TryFromMethod `T::try_from(u)` ---
+
     let _: i64 = 0i32.try_into().unwrap();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
     let _: i64 = 0i32.try_into().expect("can't happen");
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryFromFunction `T::try_from(U)` ---
+
+    let _ = i64::try_from(0i32).unwrap();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _ = i64::try_from(0i32).expect("can't happen");
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryIntoFunction `U::try_into(t)` ---
+
+    let _: i64 = i32::try_into(0).unwrap();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _: i64 = i32::try_into(0i32).expect("can't happen");
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryFromFunction `<T as TryFrom<U>>::try_from(U)` ---
+
+    let _ = <i64 as TryFrom<i32>>::try_from(0).unwrap();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _ = <i64 as TryFrom<i32>>::try_from(0).expect("can't happen");
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    // --- TryIntoFunction `<U as TryInto<_>>::try_into(U)` ---
+
+    let _: i64 = <i32 as TryInto<_>>::try_into(0).unwrap();
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
+
+    let _: i64 = <i32 as TryInto<_>>::try_into(0).expect("can't happen");
+    //~^ ERROR: use of a fallible conversion when an infallible one could be used
 }
diff --git a/tests/ui/unnecessary_fallible_conversions.stderr b/tests/ui/unnecessary_fallible_conversions.stderr
index 26b152515ac..598f4ba91b3 100644
--- a/tests/ui/unnecessary_fallible_conversions.stderr
+++ b/tests/ui/unnecessary_fallible_conversions.stderr
@@ -1,20 +1,134 @@
 error: use of a fallible conversion when an infallible one could be used
-  --> $DIR/unnecessary_fallible_conversions.rs:4:23
+  --> $DIR/unnecessary_fallible_conversions.rs:6:23
    |
 LL |     let _: i64 = 0i32.try_into().unwrap();
-   |                       ^^^^^^^^^^^^^^^^^^^ help: use: `into()`
+   |                       ^^^^^^^^^^^^^^^^^^^
    |
    = note: converting `i32` to `i64` cannot fail
    = note: `-D clippy::unnecessary-fallible-conversions` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::unnecessary_fallible_conversions)]`
+help: use
+   |
+LL -     let _: i64 = 0i32.try_into().unwrap();
+LL +     let _: i64 = 0i32.into();
+   |
 
 error: use of a fallible conversion when an infallible one could be used
-  --> $DIR/unnecessary_fallible_conversions.rs:5:23
+  --> $DIR/unnecessary_fallible_conversions.rs:9:23
    |
 LL |     let _: i64 = 0i32.try_into().expect("can't happen");
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use: `into()`
+   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _: i64 = 0i32.try_into().expect("can't happen");
+LL +     let _: i64 = 0i32.into();
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:14:13
+   |
+LL |     let _ = i64::try_from(0i32).unwrap();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _ = i64::try_from(0i32).unwrap();
+LL +     let _ = i64::from(0i32);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:17:13
+   |
+LL |     let _ = i64::try_from(0i32).expect("can't happen");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _ = i64::try_from(0i32).expect("can't happen");
+LL +     let _ = i64::from(0i32);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:22:18
+   |
+LL |     let _: i64 = i32::try_into(0).unwrap();
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _: i64 = i32::try_into(0).unwrap();
+LL +     let _: i64 = i32::into(0);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:25:18
+   |
+LL |     let _: i64 = i32::try_into(0i32).expect("can't happen");
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _: i64 = i32::try_into(0i32).expect("can't happen");
+LL +     let _: i64 = i32::into(0i32);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:30:13
+   |
+LL |     let _ = <i64 as TryFrom<i32>>::try_from(0).unwrap();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _ = <i64 as TryFrom<i32>>::try_from(0).unwrap();
+LL +     let _ = <i64 as From<i32>>::from(0);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:33:13
+   |
+LL |     let _ = <i64 as TryFrom<i32>>::try_from(0).expect("can't happen");
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _ = <i64 as TryFrom<i32>>::try_from(0).expect("can't happen");
+LL +     let _ = <i64 as From<i32>>::from(0);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:38:18
+   |
+LL |     let _: i64 = <i32 as TryInto<_>>::try_into(0).unwrap();
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _: i64 = <i32 as TryInto<_>>::try_into(0).unwrap();
+LL +     let _: i64 = <i32 as Into<_>>::into(0);
+   |
+
+error: use of a fallible conversion when an infallible one could be used
+  --> $DIR/unnecessary_fallible_conversions.rs:41:18
+   |
+LL |     let _: i64 = <i32 as TryInto<_>>::try_into(0).expect("can't happen");
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: converting `i32` to `i64` cannot fail
+help: use
+   |
+LL -     let _: i64 = <i32 as TryInto<_>>::try_into(0).expect("can't happen");
+LL +     let _: i64 = <i32 as Into<_>>::into(0);
+   |
 
-error: aborting due to 2 previous errors
+error: aborting due to 10 previous errors