Auto merge of #4088 - pJunger:check1, r=oli-obk

Added lint for TryFrom for checked integer conversion.

works towards #3947

Added lint for try_from for checked integer conversion.
Should recognize simple & straight-forward checked integer conversions.

CHANGELOG.md

@@ -872,6 +872,7 @@ 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

README.md

@@ -7,7 +7,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 302 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 303 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

clippy_lints/src/checked_conversions.rs

@@ -0,0 +1,341 @@
+//! 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 rustc_errors::Applicability;
+use syntax::ast::LitKind;
+
+use crate::utils::{snippet_with_applicability, span_lint_and_sugg, 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_chain! {
+            if let Some(cv) = result;
+            if let Some(to_type) = cv.to_type;
+
+            then {
+                let mut applicability = Applicability::MachineApplicable;
+                let snippet = snippet_with_applicability(cx, cv.expr_to_cast.span, "_", &mut
+                                applicability);
+                span_lint_and_sugg(
+                    cx,
+                    CHECKED_CONVERSIONS,
+                    item.span,
+                    "Checked cast can be simplified.",
+                    "try",
+                    format!("{}::try_from({}).is_ok()",
+                            to_type,
+                            snippet),
+                    applicability
+                );
+            }
+        }
+    }
+}
+
+/// 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<&'a str>,
+}
+
+/// 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_or(true, |(l, r)| l == r)
+    }
+
+    /// Try to construct a new conversion if the conversion type is valid
+    fn try_new(expr_to_cast: &'a Expr, from_type: &str, to_type: &'a str) -> 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<Self> {
+        if UINTS.contains(&from) {
+            Some(ConversionType::FromUnsigned)
+        } else if SINTS.contains(&from) {
+            if UINTS.contains(&to) {
+                Some(ConversionType::SignedToUnsigned)
+            } else if SINTS.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, INTS);
+
+         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, SINTS) {
+        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<'a>(expr: &'a Expr, func: &'a str, types: &'a [&str]) -> Option<(&'a str, &'a str)> {
+    // `to_type::maxmin_value() as from_type`
+    let call_from_cast: Option<(&Expr, &str)> = 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_sym) = int_ty_to_sym(from_type_path);
+
+        then {
+            Some((limit, from_sym))
+        } else {
+            None
+        }
+    };
+
+    // `from_type::from(to_type::maxmin_value())`
+    let limit_from: Option<(&Expr, &str)> = 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_sym) = get_implementing_type(path, INTS, FROM);
+
+            then {
+                Some((limit, from_sym))
+            } 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<'a>(path: &QPath, candidates: &'a [&str], function: &str) -> Option<&'a str> {
+    if_chain! {
+        if let QPath::TypeRelative(ref ty, ref path) = &path;
+        if path.ident.name.as_str() == function;
+        if let TyKind::Path(QPath::Resolved(None, ref tp)) = &ty.node;
+        if let [int] = &*tp.segments;
+        let name = &int.ident.name.as_str();
+
+        then {
+            candidates.iter().find(|c| name == *c).cloned()
+        } else {
+            None
+        }
+    }
+}
+
+/// Gets the type as a string, if it is a supported integer
+fn int_ty_to_sym(path: &QPath) -> Option<&str> {
+    if_chain! {
+        if let QPath::Resolved(_, ref path) = *path;
+        if let [ty] = &*path.segments;
+        let name = &ty.ident.name.as_str();
+
+        then {
+            INTS.iter().find(|c| 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: &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,
+    }
+}
+
+// Constants
+const FROM: &str = "from";
+const MAX_VALUE: &str = "max_value";
+const MIN_VALUE: &str = "min_value";
+
+const UINTS: &[&str] = &["u8", "u16", "u32", "u64", "usize"];
+const SINTS: &[&str] = &["i8", "i16", "i32", "i64", "isize"];
+const INTS: &[&str] = &["u8", "u16", "u32", "u64", "usize", "i8", "i16", "i32", "i64", "isize"];

clippy_lints/src/enum_clike.rs

@@ -10,6 +10,7 @@ use rustc::ty;
 use rustc::ty::subst::InternalSubsts;
 use rustc::ty::util::IntTypeExt;
 use rustc::{declare_lint_pass, declare_tool_lint};
+use std::convert::TryFrom;
 use syntax::ast::{IntTy, UintTy};
 
 declare_clippy_lint! {
@@ -65,7 +66,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnportableVariant {
                         match ty.sty {
                             ty::Int(IntTy::Isize) => {
                                 let val = ((val as i128) << 64) >> 64;
-                                if val <= i128::from(i32::max_value()) && val >= i128::from(i32::min_value()) {
+                                if i32::try_from(val).is_ok() {
                                     continue;
                                 }
                             },

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;
@@ -575,6 +576,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
     reg.register_late_lint_pass(box missing_const_for_fn::MissingConstForFn);
     reg.register_late_lint_pass(box transmuting_null::TransmutingNull);
     reg.register_late_lint_pass(box path_buf_push_overwrite::PathBufPushOverwrite);
+    reg.register_late_lint_pass(box checked_conversions::CheckedConversions);
 
     reg.register_lint_group("clippy::restriction", Some("clippy_restriction"), vec![
         arithmetic::FLOAT_ARITHMETIC,
@@ -605,6 +607,7 @@ 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,

tests/ui/checked_conversions.fixed

@@ -0,0 +1,106 @@
+// run-rustfix
+
+#![warn(clippy::checked_conversions)]
+#![allow(clippy::cast_lossless)]
+#![allow(dead_code)]
+use std::convert::TryFrom;
+
+// Positive tests
+
+// Signed to unsigned
+
+fn i64_to_u32(value: i64) -> Option<u32> {
+    if u32::try_from(value).is_ok() {
+        Some(value as u32)
+    } else {
+        None
+    }
+}
+
+fn i64_to_u16(value: i64) -> Option<u16> {
+    if u16::try_from(value).is_ok() {
+        Some(value as u16)
+    } else {
+        None
+    }
+}
+
+fn isize_to_u8(value: isize) -> Option<u8> {
+    if u8::try_from(value).is_ok() {
+        Some(value as u8)
+    } else {
+        None
+    }
+}
+
+// Signed to signed
+
+fn i64_to_i32(value: i64) -> Option<i32> {
+    if i32::try_from(value).is_ok() {
+        Some(value as i32)
+    } else {
+        None
+    }
+}
+
+fn i64_to_i16(value: i64) -> Option<i16> {
+    if i16::try_from(value).is_ok() {
+        Some(value as i16)
+    } else {
+        None
+    }
+}
+
+// Unsigned to X
+
+fn u32_to_i32(value: u32) -> Option<i32> {
+    if i32::try_from(value).is_ok() {
+        Some(value as i32)
+    } else {
+        None
+    }
+}
+
+fn usize_to_isize(value: usize) -> isize {
+    if isize::try_from(value).is_ok() && value as i32 == 5 {
+        5
+    } else {
+        1
+    }
+}
+
+fn u32_to_u16(value: u32) -> isize {
+    if u16::try_from(value).is_ok() && value as i32 == 5 {
+        5
+    } else {
+        1
+    }
+}
+
+// Negative tests
+
+fn no_i64_to_i32(value: i64) -> Option<i32> {
+    if value <= (i32::max_value() as i64) && value >= 0 {
+        Some(value as i32)
+    } else {
+        None
+    }
+}
+
+fn no_isize_to_u8(value: isize) -> Option<u8> {
+    if value <= (u8::max_value() as isize) && value >= (u8::min_value() as isize) {
+        Some(value as u8)
+    } else {
+        None
+    }
+}
+
+fn i8_to_u8(value: i8) -> Option<u8> {
+    if value >= 0 {
+        Some(value as u8)
+    } else {
+        None
+    }
+}
+
+fn main() {}

tests/ui/checked_conversions.rs

@@ -0,0 +1,106 @@
+// run-rustfix
+
+#![warn(clippy::checked_conversions)]
+#![allow(clippy::cast_lossless)]
+#![allow(dead_code)]
+use std::convert::TryFrom;
+
+// Positive tests
+
+// Signed to unsigned
+
+fn i64_to_u32(value: i64) -> Option<u32> {
+    if value <= (u32::max_value() as i64) && value >= 0 {
+        Some(value as u32)
+    } else {
+        None
+    }
+}
+
+fn i64_to_u16(value: i64) -> Option<u16> {
+    if value <= i64::from(u16::max_value()) && value >= 0 {
+        Some(value as u16)
+    } else {
+        None
+    }
+}
+
+fn isize_to_u8(value: isize) -> Option<u8> {
+    if value <= (u8::max_value() as isize) && value >= 0 {
+        Some(value as u8)
+    } else {
+        None
+    }
+}
+
+// Signed to signed
+
+fn i64_to_i32(value: i64) -> Option<i32> {
+    if value <= (i32::max_value() as i64) && value >= (i32::min_value() as i64) {
+        Some(value as i32)
+    } else {
+        None
+    }
+}
+
+fn i64_to_i16(value: i64) -> Option<i16> {
+    if value <= i64::from(i16::max_value()) && value >= i64::from(i16::min_value()) {
+        Some(value as i16)
+    } else {
+        None
+    }
+}
+
+// Unsigned to X
+
+fn u32_to_i32(value: u32) -> Option<i32> {
+    if value <= i32::max_value() as u32 {
+        Some(value as i32)
+    } else {
+        None
+    }
+}
+
+fn usize_to_isize(value: usize) -> isize {
+    if value <= isize::max_value() as usize && value as i32 == 5 {
+        5
+    } else {
+        1
+    }
+}
+
+fn u32_to_u16(value: u32) -> isize {
+    if value <= u16::max_value() as u32 && value as i32 == 5 {
+        5
+    } else {
+        1
+    }
+}
+
+// Negative tests
+
+fn no_i64_to_i32(value: i64) -> Option<i32> {
+    if value <= (i32::max_value() as i64) && value >= 0 {
+        Some(value as i32)
+    } else {
+        None
+    }
+}
+
+fn no_isize_to_u8(value: isize) -> Option<u8> {
+    if value <= (u8::max_value() as isize) && value >= (u8::min_value() as isize) {
+        Some(value as u8)
+    } else {
+        None
+    }
+}
+
+fn i8_to_u8(value: i8) -> Option<u8> {
+    if value >= 0 {
+        Some(value as u8)
+    } else {
+        None
+    }
+}
+
+fn main() {}

tests/ui/checked_conversions.stderr

@@ -0,0 +1,52 @@
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:13:8
+   |
+LL |     if value <= (u32::max_value() as i64) && value >= 0 {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `u32::try_from(value).is_ok()`
+   |
+   = note: `-D clippy::checked-conversions` implied by `-D warnings`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:21:8
+   |
+LL |     if value <= i64::from(u16::max_value()) && value >= 0 {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `u16::try_from(value).is_ok()`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:29:8
+   |
+LL |     if value <= (u8::max_value() as isize) && value >= 0 {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `u8::try_from(value).is_ok()`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:39:8
+   |
+LL |     if value <= (i32::max_value() as i64) && value >= (i32::min_value() as i64) {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `i32::try_from(value).is_ok()`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:47:8
+   |
+LL |     if value <= i64::from(i16::max_value()) && value >= i64::from(i16::min_value()) {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `i16::try_from(value).is_ok()`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:57:8
+   |
+LL |     if value <= i32::max_value() as u32 {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `i32::try_from(value).is_ok()`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:65:8
+   |
+LL |     if value <= isize::max_value() as usize && value as i32 == 5 {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `isize::try_from(value).is_ok()`
+
+error: Checked cast can be simplified.
+  --> $DIR/checked_conversions.rs:73:8
+   |
+LL |     if value <= u16::max_value() as u32 && value as i32 == 5 {
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `u16::try_from(value).is_ok()`
+
+error: aborting due to 8 previous errors
+