Added lint for TryFrom for checked integer conversion #3947.

Author: pJunger

CHANGELOG.md

@@ -846,6 +846,7 @@ All notable changes to this project will be documented in this file.
 [`char_lit_as_u8`]: https://rust-lang.github.io/rust-clippy/master/index.html#char_lit_as_u8
 [`chars_last_cmp`]: https://rust-lang.github.io/rust-clippy/master/index.html#chars_last_cmp
 [`chars_next_cmp`]: https://rust-lang.github.io/rust-clippy/master/index.html#chars_next_cmp
+[`checked_conversions`]: https://rust-lang.github.io/rust-clippy/master/index.html#checked_conversions
 [`clone_double_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#clone_double_ref
 [`clone_on_copy`]: https://rust-lang.github.io/rust-clippy/master/index.html#clone_on_copy
 [`clone_on_ref_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#clone_on_ref_ptr

clippy_lints/src/checked_conversions.rs

@@ -0,0 +1,332 @@
+//! lint on manually implemented checked conversions that could be transformed into try_from
+
+use if_chain::if_chain;
+use rustc::hir::*;
+use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
+use rustc::{declare_lint_pass, declare_tool_lint};
+use syntax::ast::LitKind;
+
+use crate::utils::{span_lint, SpanlessEq};
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for explicit bounds checking when casting.
+    ///
+    /// **Why is this bad?** Reduces the readability of statements & is error prone.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// # let foo: u32 = 5;
+    /// # let _ =
+    /// foo <= i32::max_value() as u32
+    /// # ;
+    /// ```
+    ///
+    /// Could be written:
+    ///
+    /// ```rust
+    /// # let _ =
+    /// i32::try_from(foo).is_ok()
+    /// # ;
+    /// ```
+    pub CHECKED_CONVERSIONS,
+    pedantic,
+    "`try_from` could replace manual bounds checking when casting"
+}
+
+declare_lint_pass!(CheckedConversions => [CHECKED_CONVERSIONS]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
+    fn check_expr(&mut self, cx: &LateContext<'_, '_>, item: &Expr) {
+        let result = if_chain! {
+            if !in_external_macro(cx.sess(), item.span);
+            if let ExprKind::Binary(op, ref left, ref right) = &item.node;
+
+            then {
+                match op.node {
+                    BinOpKind::Ge | BinOpKind::Le => single_check(item),
+                    BinOpKind::And => double_check(cx, left, right),
+                    _ => None,
+                }
+            } else {
+                None
+            }
+        };
+
+        if let Some(cv) = result {
+            span_lint(
+                cx,
+                CHECKED_CONVERSIONS,
+                item.span,
+                &format!(
+                    "Checked cast can be simplified: `{}::try_from`",
+                    cv.to_type.unwrap_or("IntegerType".to_string()),
+                ),
+            );
+        }
+    }
+}
+
+/// Searches for a single check from unsigned to _ is done
+/// todo: check for case signed -> larger unsigned == only x >= 0
+fn single_check(expr: &Expr) -> Option<Conversion<'_>> {
+    check_upper_bound(expr).filter(|cv| cv.cvt == ConversionType::FromUnsigned)
+}
+
+/// Searches for a combination of upper & lower bound checks
+fn double_check<'a>(cx: &LateContext<'_, '_>, left: &'a Expr, right: &'a Expr) -> Option<Conversion<'a>> {
+    let upper_lower = |l, r| {
+        let upper = check_upper_bound(l);
+        let lower = check_lower_bound(r);
+
+        transpose(upper, lower).and_then(|(l, r)| l.combine(r, cx))
+    };
+
+    upper_lower(left, right).or_else(|| upper_lower(right, left))
+}
+
+/// Contains the result of a tried conversion check
+#[derive(Clone, Debug)]
+struct Conversion<'a> {
+    cvt: ConversionType,
+    expr_to_cast: &'a Expr,
+    to_type: Option<String>,
+}
+
+/// The kind of conversion that is checked
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum ConversionType {
+    SignedToUnsigned,
+    SignedToSigned,
+    FromUnsigned,
+}
+
+impl<'a> Conversion<'a> {
+    /// Combine multiple conversions if the are compatible
+    pub fn combine(self, other: Self, cx: &LateContext<'_, '_>) -> Option<Conversion<'a>> {
+        if self.is_compatible(&other, cx) {
+            // Prefer a Conversion that contains a type-constraint
+            Some(if self.to_type.is_some() { self } else { other })
+        } else {
+            None
+        }
+    }
+
+    /// Checks if two conversions are compatible
+    /// same type of conversion, same 'castee' and same 'to type'
+    pub fn is_compatible(&self, other: &Self, cx: &LateContext<'_, '_>) -> bool {
+        (self.cvt == other.cvt)
+            && (SpanlessEq::new(cx).eq_expr(self.expr_to_cast, other.expr_to_cast))
+            && (self.has_compatible_to_type(other))
+    }
+
+    /// Checks if the to-type is the same (if there is a type constraint)
+    fn has_compatible_to_type(&self, other: &Self) -> bool {
+        transpose(self.to_type.as_ref(), other.to_type.as_ref())
+            .map(|(l, r)| l == r)
+            .unwrap_or(true)
+    }
+
+    /// Try to construct a new conversion if the conversion type is valid
+    fn try_new<'b>(expr_to_cast: &'a Expr, from_type: &'b str, to_type: String) -> Option<Conversion<'a>> {
+        ConversionType::try_new(from_type, &to_type).map(|cvt| Conversion {
+            cvt,
+            expr_to_cast,
+            to_type: Some(to_type),
+        })
+    }
+
+    /// Construct a new conversion without type constraint
+    fn new_any(expr_to_cast: &'a Expr) -> Conversion<'a> {
+        Conversion {
+            cvt: ConversionType::SignedToUnsigned,
+            expr_to_cast,
+            to_type: None,
+        }
+    }
+}
+
+impl ConversionType {
+    /// Creates a conversion type if the type is allowed & conversion is valid
+    fn try_new(from: &str, to: &str) -> Option<ConversionType> {
+        if UNSIGNED_TYPES.contains(&from) {
+            Some(ConversionType::FromUnsigned)
+        } else if SIGNED_TYPES.contains(&from) {
+            if UNSIGNED_TYPES.contains(&to) {
+                Some(ConversionType::SignedToUnsigned)
+            } else if SIGNED_TYPES.contains(&to) {
+                Some(ConversionType::SignedToSigned)
+            } else {
+                None
+            }
+        } else {
+            None
+        }
+    }
+}
+
+/// Check for `expr <= (to_type::max_value() as from_type)`
+fn check_upper_bound(expr: &Expr) -> Option<Conversion<'_>> {
+    if_chain! {
+         if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node;
+         if let Some((candidate, check)) = normalize_le_ge(op, left, right);
+         if let Some((from, to)) = get_types_from_cast(check, "max_value", INT_TYPES);
+
+         then {
+             Conversion::try_new(candidate, &from, to)
+         } else {
+            None
+        }
+    }
+}
+
+/// Check for `expr >= 0|(to_type::min_value() as from_type)`
+fn check_lower_bound(expr: &Expr) -> Option<Conversion<'_>> {
+    fn check_function<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
+        (check_lower_bound_zero(candidate, check)).or_else(|| (check_lower_bound_min(candidate, check)))
+    }
+
+    // First of we need a binary containing the expression & the cast
+    if let ExprKind::Binary(ref op, ref left, ref right) = &expr.node {
+        normalize_le_ge(op, right, left).and_then(|(l, r)| check_function(l, r))
+    } else {
+        None
+    }
+}
+
+/// Check for `expr >= 0`
+fn check_lower_bound_zero<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
+    if_chain! {
+        if let ExprKind::Lit(ref lit) = &check.node;
+        if let LitKind::Int(0, _) = &lit.node;
+
+        then {
+            Some(Conversion::new_any(candidate))
+        } else {
+            None
+        }
+    }
+}
+
+/// Check for `expr >= (to_type::min_value() as from_type)`
+fn check_lower_bound_min<'a>(candidate: &'a Expr, check: &'a Expr) -> Option<Conversion<'a>> {
+    if let Some((from, to)) = get_types_from_cast(check, "min_value", SIGNED_TYPES) {
+        Conversion::try_new(candidate, &from, to)
+    } else {
+        None
+    }
+}
+
+/// Tries to extract the from- and to-type from a cast expression
+fn get_types_from_cast(expr: &Expr, func: &str, types: &[&str]) -> Option<(String, String)> {
+    // `to_type::maxmin_value() as from_type`
+    let call_from_cast: Option<(&Expr, String)> = if_chain! {
+        // to_type::maxmin_value(), from_type
+        if let ExprKind::Cast(ref limit, ref from_type) = &expr.node;
+        if let TyKind::Path(ref from_type_path) = &from_type.node;
+        if let Some(from_type_str) = int_ty_to_str(from_type_path);
+
+        then {
+            Some((limit, from_type_str.to_string()))
+        } else {
+            None
+        }
+    };
+
+    // `from_type::from(to_type::maxmin_value())`
+    let limit_from: Option<(&Expr, String)> = call_from_cast.or_else(|| {
+        if_chain! {
+            // `from_type::from, to_type::maxmin_value()`
+            if let ExprKind::Call(ref from_func, ref args) = &expr.node;
+            // `to_type::maxmin_value()`
+            if args.len() == 1;
+            if let limit = &args[0];
+            // `from_type::from`
+            if let ExprKind::Path(ref path) = &from_func.node;
+            if let Some(from_type) = get_implementing_type(path, INT_TYPES, "from");
+
+            then {
+                Some((limit, from_type))
+            } else {
+                None
+            }
+        }
+    });
+
+    if let Some((limit, from_type)) = limit_from {
+        if_chain! {
+            if let ExprKind::Call(ref fun_name, _) = &limit.node;
+            // `to_type, maxmin_value`
+            if let ExprKind::Path(ref path) = &fun_name.node;
+            // `to_type`
+            if let Some(to_type) = get_implementing_type(path, types, func);
+
+            then {
+                Some((from_type, to_type))
+            } else {
+                None
+            }
+        }
+    } else {
+        None
+    }
+}
+
+/// Gets the type which implements the called function
+fn get_implementing_type(path: &QPath, candidates: &[&str], function: &str) -> Option<String> {
+    if_chain! {
+        if let QPath::TypeRelative(ref ty, ref path) = &path;
+        if path.ident.name == function;
+        if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.node;
+        if let [int] = &*tp.segments;
+        let name = int.ident.as_str().get();
+        if candidates.contains(&name);
+
+        then {
+            Some(name.to_string())
+        } else {
+            None
+        }
+    }
+}
+
+/// Gets the type as a string, if it is a supported integer
+fn int_ty_to_str(path: &QPath) -> Option<&str> {
+    if_chain! {
+        if let QPath::Resolved(_, ref path) = *path;
+        if let [ty] = &*path.segments;
+
+        then {
+            INT_TYPES
+                .into_iter()
+                .find(|c| (&ty.ident.name) == *c)
+                .cloned()
+        } else {
+            None
+        }
+    }
+}
+
+/// (Option<T>, Option<U>) -> Option<(T, U)>
+fn transpose<T, U>(lhs: Option<T>, rhs: Option<U>) -> Option<(T, U)> {
+    match (lhs, rhs) {
+        (Some(l), Some(r)) => Some((l, r)),
+        _ => None,
+    }
+}
+
+/// Will return the expressions as if they were expr1 <= expr2
+fn normalize_le_ge<'a>(op: &'a BinOp, left: &'a Expr, right: &'a Expr) -> Option<(&'a Expr, &'a Expr)> {
+    match op.node {
+        BinOpKind::Le => Some((left, right)),
+        BinOpKind::Ge => Some((right, left)),
+        _ => None,
+    }
+}
+
+const UNSIGNED_TYPES: &[&str] = &["u8", "u16", "u32", "u64", "u128", "usize"];
+const SIGNED_TYPES: &[&str] = &["i8", "i16", "i32", "i64", "i128", "isize"];
+const INT_TYPES: &[&str] = &[
+    "u8", "u16", "u32", "u64", "u128", "usize", "i8", "i16", "i32", "i64", "i128", "isize",
+];

clippy_lints/src/lib.rs

@@ -154,6 +154,7 @@ pub mod block_in_if_condition;
 pub mod booleans;
 pub mod bytecount;
 pub mod cargo_common_metadata;
+pub mod checked_conversions;
 pub mod cognitive_complexity;
 pub mod collapsible_if;
 pub mod const_static_lifetime;
@@ -605,6 +606,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
 
     reg.register_lint_group("clippy::pedantic", Some("clippy_pedantic"), vec![
         attrs::INLINE_ALWAYS,
+        checked_conversions::CHECKED_CONVERSIONS,
         copies::MATCH_SAME_ARMS,
         copy_iterator::COPY_ITERATOR,
         default_trait_access::DEFAULT_TRAIT_ACCESS,