demand.rs

use crate::check::FnCtxt;
use rustc_infer::infer::InferOk;
use rustc_trait_selection::infer::InferCtxtExt as _;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_trait_selection::traits::{self, ObligationCause};

use rustc_ast::util::parser::PREC_POSTFIX;
use rustc_errors::{Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_hir::{is_range_literal, Node};
use rustc_middle::ty::adjustment::AllowTwoPhase;
use rustc_middle::ty::{self, AssocItem, Ty};
use rustc_span::symbol::sym;
use rustc_span::Span;

use super::method::probe;

impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
    pub fn emit_coerce_suggestions(
        &self,
        err: &mut DiagnosticBuilder<'_>,
        expr: &hir::Expr<'_>,
        expr_ty: Ty<'tcx>,
        expected: Ty<'tcx>,
    ) {
        self.annotate_expected_due_to_let_ty(err, expr);
        self.suggest_compatible_variants(err, expr, expected, expr_ty);
        self.suggest_ref_or_into(err, expr, expected, expr_ty);
        if self.suggest_calling_boxed_future_when_appropriate(err, expr, expected, expr_ty) {
            return;
        }
        self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
        self.suggest_missing_await(err, expr, expected, expr_ty);
    }

    // Requires that the two types unify, and prints an error message if
    // they don't.
    pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
        self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
    }

    pub fn demand_suptype_diag(
        &self,
        sp: Span,
        expected: Ty<'tcx>,
        actual: Ty<'tcx>,
    ) -> Option<DiagnosticBuilder<'tcx>> {
        self.demand_suptype_with_origin(&self.misc(sp), expected, actual)
    }

    pub fn demand_suptype_with_origin(
        &self,
        cause: &ObligationCause<'tcx>,
        expected: Ty<'tcx>,
        actual: Ty<'tcx>,
    ) -> Option<DiagnosticBuilder<'tcx>> {
        match self.at(cause, self.param_env).sup(expected, actual) {
            Ok(InferOk { obligations, value: () }) => {
                self.register_predicates(obligations);
                None
            }
            Err(e) => Some(self.report_mismatched_types(&cause, expected, actual, e)),
        }
    }

    pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
        if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
            err.emit();
        }
    }

    pub fn demand_eqtype_diag(
        &self,
        sp: Span,
        expected: Ty<'tcx>,
        actual: Ty<'tcx>,
    ) -> Option<DiagnosticBuilder<'tcx>> {
        self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
    }

    pub fn demand_eqtype_with_origin(
        &self,
        cause: &ObligationCause<'tcx>,
        expected: Ty<'tcx>,
        actual: Ty<'tcx>,
    ) -> Option<DiagnosticBuilder<'tcx>> {
        match self.at(cause, self.param_env).eq(expected, actual) {
            Ok(InferOk { obligations, value: () }) => {
                self.register_predicates(obligations);
                None
            }
            Err(e) => Some(self.report_mismatched_types(cause, expected, actual, e)),
        }
    }

    pub fn demand_coerce(
        &self,
        expr: &hir::Expr<'_>,
        checked_ty: Ty<'tcx>,
        expected: Ty<'tcx>,
        allow_two_phase: AllowTwoPhase,
    ) -> Ty<'tcx> {
        let (ty, err) = self.demand_coerce_diag(expr, checked_ty, expected, allow_two_phase);
        if let Some(mut err) = err {
            err.emit();
        }
        ty
    }

    // Checks that the type of `expr` can be coerced to `expected`.
    //
    // N.B., this code relies on `self.diverges` to be accurate. In
    // particular, assignments to `!` will be permitted if the
    // diverges flag is currently "always".
    pub fn demand_coerce_diag(
        &self,
        expr: &hir::Expr<'_>,
        checked_ty: Ty<'tcx>,
        expected: Ty<'tcx>,
        allow_two_phase: AllowTwoPhase,
    ) -> (Ty<'tcx>, Option<DiagnosticBuilder<'tcx>>) {
        let expected = self.resolve_vars_with_obligations(expected);

        let e = match self.try_coerce(expr, checked_ty, expected, allow_two_phase) {
            Ok(ty) => return (ty, None),
            Err(e) => e,
        };

        let expr = expr.peel_drop_temps();
        let cause = self.misc(expr.span);
        let expr_ty = self.resolve_vars_with_obligations(checked_ty);
        let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);

        if self.is_assign_to_bool(expr, expected) {
            // Error reported in `check_assign` so avoid emitting error again.
            err.delay_as_bug();
            return (expected, None);
        }

        self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected);

        (expected, Some(err))
    }

    fn annotate_expected_due_to_let_ty(
        &self,
        err: &mut DiagnosticBuilder<'_>,
        expr: &hir::Expr<'_>,
    ) {
        let parent = self.tcx.hir().get_parent_node(expr.hir_id);
        if let Some(hir::Node::Local(hir::Local { ty: Some(ty), init: Some(init), .. })) =
            self.tcx.hir().find(parent)
        {
            if init.hir_id == expr.hir_id {
                // Point at `let` assignment type.
                err.span_label(ty.span, "expected due to this");
            }
        }
    }

    /// Returns whether the expected type is `bool` and the expression is `x = y`.
    pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
        if let hir::ExprKind::Assign(..) = expr.kind {
            return expected == self.tcx.types.bool;
        }
        false
    }

    /// If the expected type is an enum (Issue #55250) with any variants whose
    /// sole field is of the found type, suggest such variants. (Issue #42764)
    fn suggest_compatible_variants(
        &self,
        err: &mut DiagnosticBuilder<'_>,
        expr: &hir::Expr<'_>,
        expected: Ty<'tcx>,
        expr_ty: Ty<'tcx>,
    ) {
        if let ty::Adt(expected_adt, substs) = expected.kind {
            if !expected_adt.is_enum() {
                return;
            }

            let mut compatible_variants = expected_adt
                .variants
                .iter()
                .filter(|variant| variant.fields.len() == 1)
                .filter_map(|variant| {
                    let sole_field = &variant.fields[0];
                    let sole_field_ty = sole_field.ty(self.tcx, substs);
                    if self.can_coerce(expr_ty, sole_field_ty) {
                        let variant_path = self.tcx.def_path_str(variant.def_id);
                        // FIXME #56861: DRYer prelude filtering
                        Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
                    } else {
                        None
                    }
                })
                .peekable();

            if compatible_variants.peek().is_some() {
                if let Ok(expr_text) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
                    let suggestions = compatible_variants.map(|v| format!("{}({})", v, expr_text));
                    let msg = "try using a variant of the expected enum";
                    err.span_suggestions(
                        expr.span,
                        msg,
                        suggestions,
                        Applicability::MaybeIncorrect,
                    );
                }
            }
        }
    }

    pub fn get_conversion_methods(
        &self,
        span: Span,
        expected: Ty<'tcx>,
        checked_ty: Ty<'tcx>,
        hir_id: hir::HirId,
    ) -> Vec<AssocItem> {
        let mut methods =
            self.probe_for_return_type(span, probe::Mode::MethodCall, expected, checked_ty, hir_id);
        methods.retain(|m| {
            self.has_no_input_arg(m)
                && self
                    .tcx
                    .get_attrs(m.def_id)
                    .iter()
                    // This special internal attribute is used to whitelist
                    // "identity-like" conversion methods to be suggested here.
                    //
                    // FIXME (#46459 and #46460): ideally
                    // `std::convert::Into::into` and `std::borrow:ToOwned` would
                    // also be `#[rustc_conversion_suggestion]`, if not for
                    // method-probing false-positives and -negatives (respectively).
                    //
                    // FIXME? Other potential candidate methods: `as_ref` and
                    // `as_mut`?
                    .any(|a| a.check_name(sym::rustc_conversion_suggestion))
        });

        methods
    }

    // This function checks if the method isn't static and takes other arguments than `self`.
    fn has_no_input_arg(&self, method: &AssocItem) -> bool {
        match method.kind {
            ty::AssocKind::Fn => self.tcx.fn_sig(method.def_id).inputs().skip_binder().len() == 1,
            _ => false,
        }
    }

    /// Identify some cases where `as_ref()` would be appropriate and suggest it.
    ///
    /// Given the following code:
    /// ```
    /// struct Foo;
    /// fn takes_ref(_: &Foo) {}
    /// let ref opt = Some(Foo);
    ///
    /// opt.map(|param| takes_ref(param));
    /// ```
    /// Suggest using `opt.as_ref().map(|param| takes_ref(param));` instead.
    ///
    /// It only checks for `Option` and `Result` and won't work with
    /// ```
    /// opt.map(|param| { takes_ref(param) });
    /// ```
    fn can_use_as_ref(&self, expr: &hir::Expr<'_>) -> Option<(Span, &'static str, String)> {
        let path = match expr.kind {
            hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => path,
            _ => return None,
        };

        let local_id = match path.res {
            hir::def::Res::Local(id) => id,
            _ => return None,
        };

        let local_parent = self.tcx.hir().get_parent_node(local_id);
        let param_hir_id = match self.tcx.hir().find(local_parent) {
            Some(Node::Param(hir::Param { hir_id, .. })) => hir_id,
            _ => return None,
        };

        let param_parent = self.tcx.hir().get_parent_node(*param_hir_id);
        let (expr_hir_id, closure_fn_decl) = match self.tcx.hir().find(param_parent) {
            Some(Node::Expr(hir::Expr {
                hir_id,
                kind: hir::ExprKind::Closure(_, decl, ..),
                ..
            })) => (hir_id, decl),
            _ => return None,
        };

        let expr_parent = self.tcx.hir().get_parent_node(*expr_hir_id);
        let hir = self.tcx.hir().find(expr_parent);
        let closure_params_len = closure_fn_decl.inputs.len();
        let (method_path, method_span, method_expr) = match (hir, closure_params_len) {
            (
                Some(Node::Expr(hir::Expr {
                    kind: hir::ExprKind::MethodCall(path, span, expr),
                    ..
                })),
                1,
            ) => (path, span, expr),
            _ => return None,
        };

        let self_ty = self.tables.borrow().node_type(method_expr[0].hir_id);
        let self_ty = format!("{:?}", self_ty);
        let name = method_path.ident.as_str();
        let is_as_ref_able = (self_ty.starts_with("&std::option::Option")
            || self_ty.starts_with("&std::result::Result")
            || self_ty.starts_with("std::option::Option")
            || self_ty.starts_with("std::result::Result"))
            && (name == "map" || name == "and_then");
        match (is_as_ref_able, self.sess().source_map().span_to_snippet(*method_span)) {
            (true, Ok(src)) => {
                let suggestion = format!("as_ref().{}", src);
                Some((*method_span, "consider using `as_ref` instead", suggestion))
            }
            _ => None,
        }
    }

    crate fn is_hir_id_from_struct_pattern_shorthand_field(
        &self,
        hir_id: hir::HirId,
        sp: Span,
    ) -> bool {
        let sm = self.sess().source_map();
        let parent_id = self.tcx.hir().get_parent_node(hir_id);
        if let Some(parent) = self.tcx.hir().find(parent_id) {
            // Account for fields
            if let Node::Expr(hir::Expr { kind: hir::ExprKind::Struct(_, fields, ..), .. }) = parent
            {
                if let Ok(src) = sm.span_to_snippet(sp) {
                    for field in *fields {
                        if field.ident.as_str() == src && field.is_shorthand {
                            return true;
                        }
                    }
                }
            }
        }
        false
    }

    /// This function is used to determine potential "simple" improvements or users' errors and
    /// provide them useful help. For example:
    ///
    /// ```
    /// fn some_fn(s: &str) {}
    ///
    /// let x = "hey!".to_owned();
    /// some_fn(x); // error
    /// ```
    ///
    /// No need to find every potential function which could make a coercion to transform a
    /// `String` into a `&str` since a `&` would do the trick!
    ///
    /// In addition of this check, it also checks between references mutability state. If the
    /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
    /// `&mut`!".
    pub fn check_ref(
        &self,
        expr: &hir::Expr<'_>,
        checked_ty: Ty<'tcx>,
        expected: Ty<'tcx>,
    ) -> Option<(Span, &'static str, String)> {
        let sm = self.sess().source_map();
        let sp = expr.span;
        if sm.is_imported(sp) {
            // Ignore if span is from within a macro #41858, #58298. We previously used the macro
            // call span, but that breaks down when the type error comes from multiple calls down.
            return None;
        }

        let is_struct_pat_shorthand_field =
            self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, sp);

        // If the span is from a macro, then it's hard to extract the text
        // and make a good suggestion, so don't bother.
        let is_macro = sp.from_expansion() && sp.desugaring_kind().is_none();

        // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
        let expr = expr.peel_drop_temps();

        match (&expr.kind, &expected.kind, &checked_ty.kind) {
            (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
                (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
                    if let hir::ExprKind::Lit(_) = expr.kind {
                        if let Ok(src) = sm.span_to_snippet(sp) {
                            if src.starts_with("b\"") {
                                return Some((
                                    sp,
                                    "consider removing the leading `b`",
                                    src[1..].to_string(),
                                ));
                            }
                        }
                    }
                }
                (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
                    if let hir::ExprKind::Lit(_) = expr.kind {
                        if let Ok(src) = sm.span_to_snippet(sp) {
                            if src.starts_with('"') {
                                return Some((
                                    sp,
                                    "consider adding a leading `b`",
                                    format!("b{}", src),
                                ));
                            }
                        }
                    }
                }
                _ => {}
            },
            (_, &ty::Ref(_, _, mutability), _) => {
                // Check if it can work when put into a ref. For example:
                //
                // ```
                // fn bar(x: &mut i32) {}
                //
                // let x = 0u32;
                // bar(&x); // error, expected &mut
                // ```
                let ref_ty = match mutability {
                    hir::Mutability::Mut => {
                        self.tcx.mk_mut_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
                    }
                    hir::Mutability::Not => {
                        self.tcx.mk_imm_ref(self.tcx.mk_region(ty::ReStatic), checked_ty)
                    }
                };
                if self.can_coerce(ref_ty, expected) {
                    let mut sugg_sp = sp;
                    if let hir::ExprKind::MethodCall(segment, _sp, args) = &expr.kind {
                        let clone_trait = self.tcx.lang_items().clone_trait().unwrap();
                        if let ([arg], Some(true), sym::clone) = (
                            &args[..],
                            self.tables.borrow().type_dependent_def_id(expr.hir_id).map(|did| {
                                let ai = self.tcx.associated_item(did);
                                ai.container == ty::TraitContainer(clone_trait)
                            }),
                            segment.ident.name,
                        ) {
                            // If this expression had a clone call when suggesting borrowing
                            // we want to suggest removing it because it'd now be unnecessary.
                            sugg_sp = arg.span;
                        }
                    }
                    if let Ok(src) = sm.span_to_snippet(sugg_sp) {
                        let needs_parens = match expr.kind {
                            // parenthesize if needed (Issue #46756)
                            hir::ExprKind::Cast(_, _) | hir::ExprKind::Binary(_, _, _) => true,
                            // parenthesize borrows of range literals (Issue #54505)
                            _ if is_range_literal(self.tcx.sess.source_map(), expr) => true,
                            _ => false,
                        };
                        let sugg_expr = if needs_parens { format!("({})", src) } else { src };

                        if let Some(sugg) = self.can_use_as_ref(expr) {
                            return Some(sugg);
                        }
                        let field_name = if is_struct_pat_shorthand_field {
                            format!("{}: ", sugg_expr)
                        } else {
                            String::new()
                        };
                        if let Some(hir::Node::Expr(hir::Expr {
                            kind: hir::ExprKind::Assign(left_expr, ..),
                            ..
                        })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
                        {
                            if mutability == hir::Mutability::Mut {
                                // Found the following case:
                                // fn foo(opt: &mut Option<String>){ opt = None }
                                //                                   ---   ^^^^
                                //                                   |     |
                                //    consider dereferencing here: `*opt`  |
                                // expected mutable reference, found enum `Option`
                                if let Ok(src) = sm.span_to_snippet(left_expr.span) {
                                    return Some((
                                        left_expr.span,
                                        "consider dereferencing here to assign to the mutable \
                                         borrowed piece of memory",
                                        format!("*{}", src),
                                    ));
                                }
                            }
                        }

                        return Some(match mutability {
                            hir::Mutability::Mut => (
                                sp,
                                "consider mutably borrowing here",
                                format!("{}&mut {}", field_name, sugg_expr),
                            ),
                            hir::Mutability::Not => (
                                sp,
                                "consider borrowing here",
                                format!("{}&{}", field_name, sugg_expr),
                            ),
                        });
                    }
                }
            }
            (
                hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref expr),
                _,
                &ty::Ref(_, checked, _),
            ) if {
                self.infcx.can_sub(self.param_env, checked, &expected).is_ok() && !is_macro
            } =>
            {
                // We have `&T`, check if what was expected was `T`. If so,
                // we may want to suggest removing a `&`.
                if sm.is_imported(expr.span) {
                    if let Ok(code) = sm.span_to_snippet(sp) {
                        if code.starts_with('&') {
                            return Some((
                                sp,
                                "consider removing the borrow",
                                code[1..].to_string(),
                            ));
                        }
                    }
                    return None;
                }
                if let Ok(code) = sm.span_to_snippet(expr.span) {
                    return Some((sp, "consider removing the borrow", code));
                }
            }
            _ if sp == expr.span && !is_macro => {
                // Check for `Deref` implementations by constructing a predicate to
                // prove: `<T as Deref>::Output == U`
                let deref_trait = self.tcx.lang_items().deref_trait().unwrap();
                let item_def_id = self
                    .tcx
                    .associated_items(deref_trait)
                    .in_definition_order()
                    .find(|item| item.kind == ty::AssocKind::Type)
                    .unwrap()
                    .def_id;
                let predicate =
                    ty::Predicate::Projection(ty::Binder::bind(ty::ProjectionPredicate {
                        // `<T as Deref>::Output`
                        projection_ty: ty::ProjectionTy {
                            // `T`
                            substs: self.tcx.intern_substs(&[checked_ty.into()]),
                            // `Deref::Output`
                            item_def_id,
                        },
                        // `U`
                        ty: expected,
                    }));
                let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
                let impls_deref = self.infcx.predicate_may_hold(&obligation);

                // For a suggestion to make sense, the type would need to be `Copy`.
                let is_copy = self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp);

                if is_copy && impls_deref {
                    if let Ok(code) = sm.span_to_snippet(sp) {
                        let message = if checked_ty.is_region_ptr() {
                            "consider dereferencing the borrow"
                        } else {
                            "consider dereferencing the type"
                        };
                        let suggestion = if is_struct_pat_shorthand_field {
                            format!("{}: *{}", code, code)
                        } else {
                            format!("*{}", code)
                        };
                        return Some((sp, message, suggestion));
                    }
                }
            }
            _ => {}
        }
        None
    }

    pub fn check_for_cast(
        &self,
        err: &mut DiagnosticBuilder<'_>,
        expr: &hir::Expr<'_>,
        checked_ty: Ty<'tcx>,
        expected_ty: Ty<'tcx>,
    ) -> bool {
        if self.tcx.hir().is_const_context(expr.hir_id) {
            // Shouldn't suggest `.into()` on `const`s.
            // FIXME(estebank): modify once we decide to suggest `as` casts
            return false;
        }
        if self.tcx.sess.source_map().is_imported(expr.span) {
            // Ignore if span is from within a macro.
            return false;
        }

        // If casting this expression to a given numeric type would be appropriate in case of a type
        // mismatch.
        //
        // We want to minimize the amount of casting operations that are suggested, as it can be a
        // lossy operation with potentially bad side effects, so we only suggest when encountering
        // an expression that indicates that the original type couldn't be directly changed.
        //
        // For now, don't suggest casting with `as`.
        let can_cast = false;

        let mut prefix = String::new();
        if let Some(hir::Node::Expr(hir::Expr {
            kind: hir::ExprKind::Struct(_, fields, _), ..
        })) = self.tcx.hir().find(self.tcx.hir().get_parent_node(expr.hir_id))
        {
            // `expr` is a literal field for a struct, only suggest if appropriate
            for field in *fields {
                if field.expr.hir_id == expr.hir_id && field.is_shorthand {
                    // This is a field literal
                    prefix = format!("{}: ", field.ident);
                    break;
                }
            }
            if &prefix == "" {
                // Likely a field was meant, but this field wasn't found. Do not suggest anything.
                return false;
            }
        }
        if let hir::ExprKind::Call(path, args) = &expr.kind {
            if let (hir::ExprKind::Path(hir::QPath::TypeRelative(base_ty, path_segment)), 1) =
                (&path.kind, args.len())
            {
                // `expr` is a conversion like `u32::from(val)`, do not suggest anything (#63697).
                if let (hir::TyKind::Path(hir::QPath::Resolved(None, base_ty_path)), sym::from) =
                    (&base_ty.kind, path_segment.ident.name)
                {
                    if let Some(ident) = &base_ty_path.segments.iter().map(|s| s.ident).next() {
                        match ident.name {
                            sym::i128
                            | sym::i64
                            | sym::i32
                            | sym::i16
                            | sym::i8
                            | sym::u128
                            | sym::u64
                            | sym::u32
                            | sym::u16
                            | sym::u8
                            | sym::isize
                            | sym::usize
                                if base_ty_path.segments.len() == 1 =>
                            {
                                return false;
                            }
                            _ => {}
                        }
                    }
                }
            }
        }

        let msg = format!("you can convert an `{}` to `{}`", checked_ty, expected_ty);
        let cast_msg = format!("you can cast an `{} to `{}`", checked_ty, expected_ty);
        let try_msg = format!("{} and panic if the converted value wouldn't fit", msg);
        let lit_msg = format!(
            "change the type of the numeric literal from `{}` to `{}`",
            checked_ty, expected_ty,
        );

        let needs_paren = expr.precedence().order() < (PREC_POSTFIX as i8);

        if let Ok(src) = self.tcx.sess.source_map().span_to_snippet(expr.span) {
            let cast_suggestion = format!(
                "{}{}{}{} as {}",
                prefix,
                if needs_paren { "(" } else { "" },
                src,
                if needs_paren { ")" } else { "" },
                expected_ty,
            );
            let try_into_suggestion = format!(
                "{}{}{}{}.try_into().unwrap()",
                prefix,
                if needs_paren { "(" } else { "" },
                src,
                if needs_paren { ")" } else { "" },
            );
            let into_suggestion = format!(
                "{}{}{}{}.into()",
                prefix,
                if needs_paren { "(" } else { "" },
                src,
                if needs_paren { ")" } else { "" },
            );
            let suffix_suggestion = format!(
                "{}{}{}{}",
                if needs_paren { "(" } else { "" },
                if let (ty::Int(_) | ty::Uint(_), ty::Float(_)) =
                    (&expected_ty.kind, &checked_ty.kind,)
                {
                    // Remove fractional part from literal, for example `42.0f32` into `42`
                    let src = src.trim_end_matches(&checked_ty.to_string());
                    src.split('.').next().unwrap()
                } else {
                    src.trim_end_matches(&checked_ty.to_string())
                },
                expected_ty,
                if needs_paren { ")" } else { "" },
            );
            let literal_is_ty_suffixed = |expr: &hir::Expr<'_>| {
                if let hir::ExprKind::Lit(lit) = &expr.kind {
                    lit.node.is_suffixed()
                } else {
                    false
                }
            };

            let suggest_to_change_suffix_or_into =
                |err: &mut DiagnosticBuilder<'_>, is_fallible: bool| {
                    let into_sugg = into_suggestion.clone();
                    err.span_suggestion(
                        expr.span,
                        if literal_is_ty_suffixed(expr) {
                            &lit_msg
                        } else if is_fallible {
                            &try_msg
                        } else {
                            &msg
                        },
                        if literal_is_ty_suffixed(expr) {
                            suffix_suggestion.clone()
                        } else if is_fallible {
                            try_into_suggestion
                        } else {
                            into_sugg
                        },
                        Applicability::MachineApplicable,
                    );
                };

            match (&expected_ty.kind, &checked_ty.kind) {
                (&ty::Int(ref exp), &ty::Int(ref found)) => {
                    let is_fallible = match (exp.bit_width(), found.bit_width()) {
                        (Some(exp), Some(found)) if exp < found => true,
                        (None, Some(8 | 16)) => false,
                        (None, _) | (_, None) => true,
                        _ => false,
                    };
                    suggest_to_change_suffix_or_into(err, is_fallible);
                    true
                }
                (&ty::Uint(ref exp), &ty::Uint(ref found)) => {
                    let is_fallible = match (exp.bit_width(), found.bit_width()) {
                        (Some(exp), Some(found)) if exp < found => true,
                        (None, Some(8 | 16)) => false,
                        (None, _) | (_, None) => true,
                        _ => false,
                    };
                    suggest_to_change_suffix_or_into(err, is_fallible);
                    true
                }
                (&ty::Int(_), &ty::Uint(_)) | (&ty::Uint(_), &ty::Int(_)) => {
                    suggest_to_change_suffix_or_into(err, true);
                    true
                }
                (&ty::Float(ref exp), &ty::Float(ref found)) => {
                    if found.bit_width() < exp.bit_width() {
                        suggest_to_change_suffix_or_into(err, false);
                    } else if literal_is_ty_suffixed(expr) {
                        err.span_suggestion(
                            expr.span,
                            &lit_msg,
                            suffix_suggestion,
                            Applicability::MachineApplicable,
                        );
                    } else if can_cast {
                        // Missing try_into implementation for `f64` to `f32`
                        err.span_suggestion(
                            expr.span,
                            &format!("{}, producing the closest possible value", cast_msg),
                            cast_suggestion,
                            Applicability::MaybeIncorrect, // lossy conversion
                        );
                    }
                    true
                }
                (&ty::Uint(_) | &ty::Int(_), &ty::Float(_)) => {
                    if literal_is_ty_suffixed(expr) {
                        err.span_suggestion(
                            expr.span,
                            &lit_msg,
                            suffix_suggestion,
                            Applicability::MachineApplicable,
                        );
                    } else if can_cast {
                        // Missing try_into implementation for `{float}` to `{integer}`
                        err.span_suggestion(
                            expr.span,
                            &format!("{}, rounding the float towards zero", msg),
                            cast_suggestion,
                            Applicability::MaybeIncorrect, // lossy conversion
                        );
                        err.warn(
                            "if the rounded value cannot be represented by the target \
                                integer type, including `Inf` and `NaN`, casting will cause \
                                undefined behavior \
                                (see issue #10184 <https://github.com/rust-lang/rust/issues/10184> \
                                for more information)",
                        );
                    }
                    true
                }
                (&ty::Float(ref exp), &ty::Uint(ref found)) => {
                    // if `found` is `None` (meaning found is `usize`), don't suggest `.into()`
                    if exp.bit_width() > found.bit_width().unwrap_or(256) {
                        err.span_suggestion(
                            expr.span,
                            &format!(
                                "{}, producing the floating point representation of the integer",
                                msg,
                            ),
                            into_suggestion,
                            Applicability::MachineApplicable,
                        );
                    } else if literal_is_ty_suffixed(expr) {
                        err.span_suggestion(
                            expr.span,
                            &lit_msg,
                            suffix_suggestion,
                            Applicability::MachineApplicable,
                        );
                    } else {
                        // Missing try_into implementation for `{integer}` to `{float}`
                        err.span_suggestion(
                            expr.span,
                            &format!(
                                "{}, producing the floating point representation of the integer,
                                 rounded if necessary",
                                cast_msg,
                            ),
                            cast_suggestion,
                            Applicability::MaybeIncorrect, // lossy conversion
                        );
                    }
                    true
                }
                (&ty::Float(ref exp), &ty::Int(ref found)) => {
                    // if `found` is `None` (meaning found is `isize`), don't suggest `.into()`
                    if exp.bit_width() > found.bit_width().unwrap_or(256) {
                        err.span_suggestion(
                            expr.span,
                            &format!(
                                "{}, producing the floating point representation of the integer",
                                &msg,
                            ),
                            into_suggestion,
                            Applicability::MachineApplicable,
                        );
                    } else if literal_is_ty_suffixed(expr) {
                        err.span_suggestion(
                            expr.span,
                            &lit_msg,
                            suffix_suggestion,
                            Applicability::MachineApplicable,
                        );
                    } else {
                        // Missing try_into implementation for `{integer}` to `{float}`
                        err.span_suggestion(
                            expr.span,
                            &format!(
                                "{}, producing the floating point representation of the integer, \
                                 rounded if necessary",
                                &msg,
                            ),
                            cast_suggestion,
                            Applicability::MaybeIncorrect, // lossy conversion
                        );
                    }
                    true
                }
                _ => false,
            }
        } else {
            false
        }
    }
}