Added final lint and tests

clippy_lints/src/implicit_saturating_sub.rs

@@ -1,4 +1,4 @@
-use crate::utils::{higher, in_macro, span_lint_and_sugg};
+use crate::utils::{higher, in_macro, match_qpath, span_lint_and_sugg, SpanlessEq};
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
@@ -9,17 +9,17 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 declare_clippy_lint! {
     /// **What it does:** Checks for implicit saturating subtraction.
     ///
-    /// **Why is this bad?** Simplicity and readability. Instead we can easily use an inbuilt function.
+    /// **Why is this bad?** Simplicity and readability. Instead we can easily use an builtin function.
     ///
     /// **Known problems:** None.
     ///
     /// **Example:**
     ///
     /// ```rust
-    /// let end = 10;
-    /// let start = 5;
+    /// let end: u32 = 10;
+    /// let start: u32 = 5;
     ///
-    /// let mut i = end - start;
+    /// let mut i: u32 = end - start;
     ///
     /// // Bad
     /// if i != 0 {
@@ -28,13 +28,13 @@ declare_clippy_lint! {
     /// ```
     /// Use instead:
     /// ```rust
-    /// let end = 10;
-    /// let start = 5;
+    /// let end: u32 = 10;
+    /// let start: u32 = 5;
     ///
-    /// let mut i = end - start;
+    /// let mut i: u32 = end - start;
     ///
     /// // Good
-    /// i.saturating_sub(1);
+    /// i = i.saturating_sub(1);
     /// ```
     pub IMPLICIT_SATURATING_SUB,
     pedantic,
@@ -50,41 +50,124 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
         }
         if_chain! {
             if let Some((ref cond, ref then, None)) = higher::if_block(&expr);
+
             // Check if the conditional expression is a binary operation
-            if let ExprKind::Binary(ref op, ref left, ref right) = cond.kind;
-            // Ensure that the binary operator is > or !=
-            if BinOpKind::Ne == op.node || BinOpKind::Gt == op.node;
-            if let ExprKind::Path(ref cond_path) = left.kind;
-            // Get the literal on the right hand side
-            if let ExprKind::Lit(ref lit) = right.kind;
-            if let LitKind::Int(0, _) = lit.node;
+            if let ExprKind::Binary(ref cond_op, ref cond_left, ref cond_right) = cond.kind;
+
+            // Ensure that the binary operator is >, != and <
+            if BinOpKind::Ne == cond_op.node || BinOpKind::Gt == cond_op.node || BinOpKind::Lt == cond_op.node;
+
             // Check if the true condition block has only one statement
             if let ExprKind::Block(ref block, _) = then.kind;
-            if block.stmts.len() == 1;
+            if block.stmts.len() == 1 && block.expr.is_none();
+
             // Check if assign operation is done
             if let StmtKind::Semi(ref e) = block.stmts[0].kind;
-            if let ExprKind::AssignOp(ref op1, ref target, ref value) = e.kind;
-            if BinOpKind::Sub == op1.node;
+            if let Some(target) = subtracts_one(cx, e);
+
+            // Extracting out the variable name
             if let ExprKind::Path(ref assign_path) = target.kind;
-            // Check if the variable in the condition and assignment statement are the same
-            if let (QPath::Resolved(_, ref cres_path), QPath::Resolved(_, ref ares_path)) = (cond_path, assign_path);
-            if cres_path.res == ares_path.res;
-            if let ExprKind::Lit(ref lit1) = value.kind;
-            if let LitKind::Int(assign_lit, _) = lit1.node;
+            if let QPath::Resolved(_, ref ares_path) = assign_path;
+
             then {
+                // Handle symmetric conditions in the if statement
+                let (cond_var, cond_num_val) = if SpanlessEq::new(cx).eq_expr(cond_left, target) {
+                    if BinOpKind::Gt == cond_op.node || BinOpKind::Ne == cond_op.node {
+                        (cond_left, cond_right)
+                    } else {
+                        return;
+                    }
+                } else if SpanlessEq::new(cx).eq_expr(cond_right, target) {
+                    if BinOpKind::Lt == cond_op.node || BinOpKind::Ne == cond_op.node {
+                        (cond_right, cond_left)
+                    } else {
+                        return;
+                    }
+                } else {
+                    return;
+                };
+
+                // Check if the variable in the condition statement is an integer
+                if !cx.tables.expr_ty(cond_var).is_integral() {
+                    return;
+                }
+
                 // Get the variable name
                 let var_name = ares_path.segments[0].ident.name.as_str();
-                let applicability = Applicability::MaybeIncorrect;
-                span_lint_and_sugg(
-                    cx,
-                    IMPLICIT_SATURATING_SUB,
-                    expr.span,
-                    "Implicitly performing saturating subtraction",
-                    "try",
-                    format!("{}.saturating_sub({});", var_name, assign_lit.to_string()),
-                    applicability
-                );
+                const INT_TYPES: [&str; 5] = ["i8", "i16", "i32", "i64", "i128"];
+
+                match cond_num_val.kind {
+                    ExprKind::Lit(ref cond_lit) => {
+                        // Check if the constant is zero
+                        if let LitKind::Int(0, _) = cond_lit.node {
+                            if cx.tables.expr_ty(cond_left).is_signed() {
+                            } else {
+                                print_lint_and_sugg(cx, &var_name, expr);
+                            };
+                        }
+                    },
+                    ExprKind::Path(ref cond_num_path) => {
+                        if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "MIN"])) {
+                            print_lint_and_sugg(cx, &var_name, expr);
+                        };
+                    },
+                    ExprKind::Call(ref func, _) => {
+                        if let ExprKind::Path(ref cond_num_path) = func.kind {
+                            if INT_TYPES.iter().any(|int_type| match_qpath(cond_num_path, &[int_type, "min_value"])) {
+                                print_lint_and_sugg(cx, &var_name, expr);
+                            }
+                        };
+                    },
+                    _ => (),
+                }
             }
         }
     }
 }
+
+fn subtracts_one<'a>(cx: &LateContext<'_, '_>, expr: &Expr<'a>) -> Option<&'a Expr<'a>> {
+    match expr.kind {
+        ExprKind::AssignOp(ref op1, ref target, ref value) => {
+            if_chain! {
+                if BinOpKind::Sub == op1.node;
+                // Check if literal being subtracted is one
+                if let ExprKind::Lit(ref lit1) = value.kind;
+                if let LitKind::Int(1, _) = lit1.node;
+                then {
+                    Some(target)
+                } else {
+                    None
+                }
+            }
+        },
+        ExprKind::Assign(ref target, ref value, _) => {
+            if_chain! {
+                if let ExprKind::Binary(ref op1, ref left1, ref right1) = value.kind;
+                if BinOpKind::Sub == op1.node;
+
+                if SpanlessEq::new(cx).eq_expr(left1, target);
+
+                if let ExprKind::Lit(ref lit1) = right1.kind;
+                if let LitKind::Int(1, _) = lit1.node;
+                then {
+                    Some(target)
+                } else {
+                    None
+                }
+            }
+        },
+        _ => None,
+    }
+}
+
+fn print_lint_and_sugg(cx: &LateContext<'_, '_>, var_name: &str, expr: &Expr<'_>) {
+    span_lint_and_sugg(
+        cx,
+        IMPLICIT_SATURATING_SUB,
+        expr.span,
+        "Implicitly performing saturating subtraction",
+        "try",
+        format!("{} = {}.saturating_sub({});", var_name, var_name, 1.to_string()),
+        Applicability::MachineApplicable,
+    );
+}

tests/ui/implicit_saturating_sub.fixed

@@ -0,0 +1,160 @@
+// run-rustfix
+#![allow(unused_assignments, unused_mut)]
+#![warn(clippy::implicit_saturating_sub)]
+
+fn main() {
+    // Tests for unsigned integers
+
+    let end_8: u8 = 10;
+    let start_8: u8 = 5;
+    let mut u_8: u8 = end_8 - start_8;
+
+    // Lint
+    u_8 = u_8.saturating_sub(1);
+
+    match end_8 {
+        10 => {
+            // Lint
+            u_8 = u_8.saturating_sub(1);
+        },
+        11 => u_8 += 1,
+        _ => u_8 = 0,
+    }
+
+    let end_16: u16 = 35;
+    let start_16: u16 = 40;
+
+    let mut u_16: u16 = end_16 - start_16;
+
+    // Lint
+    u_16 = u_16.saturating_sub(1);
+
+    let mut end_32: u32 = 7000;
+    let mut start_32: u32 = 7010;
+
+    let mut u_32: u32 = end_32 - start_32;
+
+    // Lint
+    u_32 = u_32.saturating_sub(1);
+
+    // No Lint
+    if u_32 > 0 {
+        u_16 += 1;
+    }
+
+    // No Lint
+    if u_32 != 0 {
+        end_32 -= 1;
+        start_32 += 1;
+    }
+
+    let mut end_64: u64 = 75001;
+    let mut start_64: u64 = 75000;
+
+    let mut u_64: u64 = end_64 - start_64;
+
+    // Lint
+    u_64 = u_64.saturating_sub(1);
+
+    // Lint
+    u_64 = u_64.saturating_sub(1);
+
+    // Lint
+    u_64 = u_64.saturating_sub(1);
+
+    // No Lint
+    if u_64 >= 1 {
+        u_64 -= 1;
+    }
+
+    // No Lint
+    if u_64 > 0 {
+        end_64 -= 1;
+    }
+
+    // Tests for usize
+    let end_usize: usize = 8054;
+    let start_usize: usize = 8050;
+
+    let mut u_usize: usize = end_usize - start_usize;
+
+    // Lint
+    u_usize = u_usize.saturating_sub(1);
+
+    // Tests for signed integers
+
+    let endi_8: i8 = 10;
+    let starti_8: i8 = 50;
+
+    let mut i_8: i8 = endi_8 - starti_8;
+
+    // Lint
+    i_8 = i_8.saturating_sub(1);
+
+    // Lint
+    i_8 = i_8.saturating_sub(1);
+
+    // Lint
+    i_8 = i_8.saturating_sub(1);
+
+    // Lint
+    i_8 = i_8.saturating_sub(1);
+
+    let endi_16: i16 = 45;
+    let starti_16: i16 = 44;
+
+    let mut i_16: i16 = endi_16 - starti_16;
+
+    // Lint
+    i_16 = i_16.saturating_sub(1);
+
+    // Lint
+    i_16 = i_16.saturating_sub(1);
+
+    // Lint
+    i_16 = i_16.saturating_sub(1);
+
+    // Lint
+    i_16 = i_16.saturating_sub(1);
+
+    let endi_32: i32 = 45;
+    let starti_32: i32 = 44;
+
+    let mut i_32: i32 = endi_32 - starti_32;
+
+    // Lint
+    i_32 = i_32.saturating_sub(1);
+
+    // Lint
+    i_32 = i_32.saturating_sub(1);
+
+    // Lint
+    i_32 = i_32.saturating_sub(1);
+
+    // Lint
+    i_32 = i_32.saturating_sub(1);
+
+    let endi_64: i64 = 45;
+    let starti_64: i64 = 44;
+
+    let mut i_64: i64 = endi_64 - starti_64;
+
+    // Lint
+    i_64 = i_64.saturating_sub(1);
+
+    // Lint
+    i_64 = i_64.saturating_sub(1);
+
+    // Lint
+    i_64 = i_64.saturating_sub(1);
+
+    // No Lint
+    if i_64 > 0 {
+        i_64 -= 1;
+    }
+
+    // No Lint
+    if i_64 != 0 {
+        i_64 -= 1;
+    }
+}

tests/ui/implicit_saturating_sub.rs

@@ -1,21 +1,206 @@
+// run-rustfix
+#![allow(unused_assignments, unused_mut)]
 #![warn(clippy::implicit_saturating_sub)]
 
 fn main() {
-    let mut end = 10;
-    let mut start = 5;
-    let mut i: u32 = end - start;
+    // Tests for unsigned integers
 
-    if i > 0 {
-        i -= 1;
+    let end_8: u8 = 10;
+    let start_8: u8 = 5;
+    let mut u_8: u8 = end_8 - start_8;
+
+    // Lint
+    if u_8 > 0 {
+        u_8 -= 1;
     }
 
-    match end {
+    match end_8 {
         10 => {
-            if i > 0 {
-                i -= 1;
+            // Lint
+            if u_8 > 0 {
+                u_8 -= 1;
             }
         },
-        11 => i += 1,
-        _ => i = 0,
+        11 => u_8 += 1,
+        _ => u_8 = 0,
+    }
+
+    let end_16: u16 = 35;
+    let start_16: u16 = 40;
+
+    let mut u_16: u16 = end_16 - start_16;
+
+    // Lint
+    if u_16 > 0 {
+        u_16 -= 1;
+    }
+
+    let mut end_32: u32 = 7000;
+    let mut start_32: u32 = 7010;
+
+    let mut u_32: u32 = end_32 - start_32;
+
+    // Lint
+    if u_32 != 0 {
+        u_32 -= 1;
+    }
+
+    // No Lint
+    if u_32 > 0 {
+        u_16 += 1;
+    }
+
+    // No Lint
+    if u_32 != 0 {
+        end_32 -= 1;
+        start_32 += 1;
+    }
+
+    let mut end_64: u64 = 75001;
+    let mut start_64: u64 = 75000;
+
+    let mut u_64: u64 = end_64 - start_64;
+
+    // Lint
+    if u_64 > 0 {
+        u_64 -= 1;
+    }
+
+    // Lint
+    if 0 < u_64 {
+        u_64 -= 1;
+    }
+
+    // Lint
+    if 0 != u_64 {
+        u_64 -= 1;
+    }
+
+    // No Lint
+    if u_64 >= 1 {
+        u_64 -= 1;
+    }
+
+    // No Lint
+    if u_64 > 0 {
+        end_64 -= 1;
+    }
+
+    // Tests for usize
+    let end_usize: usize = 8054;
+    let start_usize: usize = 8050;
+
+    let mut u_usize: usize = end_usize - start_usize;
+
+    // Lint
+    if u_usize > 0 {
+        u_usize -= 1;
+    }
+
+    // Tests for signed integers
+
+    let endi_8: i8 = 10;
+    let starti_8: i8 = 50;
+
+    let mut i_8: i8 = endi_8 - starti_8;
+
+    // Lint
+    if i_8 > i8::MIN {
+        i_8 -= 1;
+    }
+
+    // Lint
+    if i_8 > i8::min_value() {
+        i_8 -= 1;
+    }
+
+    // Lint
+    if i_8 != i8::MIN {
+        i_8 -= 1;
+    }
+
+    // Lint
+    if i_8 != i8::min_value() {
+        i_8 -= 1;
+    }
+
+    let endi_16: i16 = 45;
+    let starti_16: i16 = 44;
+
+    let mut i_16: i16 = endi_16 - starti_16;
+
+    // Lint
+    if i_16 > i16::MIN {
+        i_16 -= 1;
+    }
+
+    // Lint
+    if i_16 > i16::min_value() {
+        i_16 -= 1;
+    }
+
+    // Lint
+    if i_16 != i16::MIN {
+        i_16 -= 1;
+    }
+
+    // Lint
+    if i_16 != i16::min_value() {
+        i_16 -= 1;
+    }
+
+    let endi_32: i32 = 45;
+    let starti_32: i32 = 44;
+
+    let mut i_32: i32 = endi_32 - starti_32;
+
+    // Lint
+    if i_32 > i32::MIN {
+        i_32 -= 1;
+    }
+
+    // Lint
+    if i_32 > i32::min_value() {
+        i_32 -= 1;
+    }
+
+    // Lint
+    if i_32 != i32::MIN {
+        i_32 -= 1;
+    }
+
+    // Lint
+    if i_32 != i32::min_value() {
+        i_32 -= 1;
+    }
+
+    let endi_64: i64 = 45;
+    let starti_64: i64 = 44;
+
+    let mut i_64: i64 = endi_64 - starti_64;
+
+    // Lint
+    if i64::min_value() < i_64 {
+        i_64 -= 1;
+    }
+
+    // Lint
+    if i64::MIN != i_64 {
+        i_64 -= 1;
+    }
+
+    // Lint
+    if i64::MIN < i_64 {
+        i_64 -= 1;
+    }
+
+    // No Lint
+    if i_64 > 0 {
+        i_64 -= 1;
+    }
+
+    // No Lint
+    if i_64 != 0 {
+        i_64 -= 1;
     }
 }

tests/ui/implicit_saturating_sub.stderr

@@ -0,0 +1,188 @@
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:13:5
+   |
+LL | /     if u_8 > 0 {
+LL | |         u_8 -= 1;
+LL | |     }
+   | |_____^ help: try: `u_8 = u_8.saturating_sub(1);`
+   |
+   = note: `-D clippy::implicit-saturating-sub` implied by `-D warnings`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:20:13
+   |
+LL | /             if u_8 > 0 {
+LL | |                 u_8 -= 1;
+LL | |             }
+   | |_____________^ help: try: `u_8 = u_8.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:34:5
+   |
+LL | /     if u_16 > 0 {
+LL | |         u_16 -= 1;
+LL | |     }
+   | |_____^ help: try: `u_16 = u_16.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:44:5
+   |
+LL | /     if u_32 != 0 {
+LL | |         u_32 -= 1;
+LL | |     }
+   | |_____^ help: try: `u_32 = u_32.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:65:5
+   |
+LL | /     if u_64 > 0 {
+LL | |         u_64 -= 1;
+LL | |     }
+   | |_____^ help: try: `u_64 = u_64.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:70:5
+   |
+LL | /     if 0 < u_64 {
+LL | |         u_64 -= 1;
+LL | |     }
+   | |_____^ help: try: `u_64 = u_64.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:75:5
+   |
+LL | /     if 0 != u_64 {
+LL | |         u_64 -= 1;
+LL | |     }
+   | |_____^ help: try: `u_64 = u_64.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:96:5
+   |
+LL | /     if u_usize > 0 {
+LL | |         u_usize -= 1;
+LL | |     }
+   | |_____^ help: try: `u_usize = u_usize.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:108:5
+   |
+LL | /     if i_8 > i8::MIN {
+LL | |         i_8 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_8 = i_8.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:113:5
+   |
+LL | /     if i_8 > i8::min_value() {
+LL | |         i_8 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_8 = i_8.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:118:5
+   |
+LL | /     if i_8 != i8::MIN {
+LL | |         i_8 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_8 = i_8.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:123:5
+   |
+LL | /     if i_8 != i8::min_value() {
+LL | |         i_8 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_8 = i_8.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:133:5
+   |
+LL | /     if i_16 > i16::MIN {
+LL | |         i_16 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_16 = i_16.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:138:5
+   |
+LL | /     if i_16 > i16::min_value() {
+LL | |         i_16 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_16 = i_16.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:143:5
+   |
+LL | /     if i_16 != i16::MIN {
+LL | |         i_16 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_16 = i_16.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:148:5
+   |
+LL | /     if i_16 != i16::min_value() {
+LL | |         i_16 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_16 = i_16.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:158:5
+   |
+LL | /     if i_32 > i32::MIN {
+LL | |         i_32 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_32 = i_32.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:163:5
+   |
+LL | /     if i_32 > i32::min_value() {
+LL | |         i_32 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_32 = i_32.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:168:5
+   |
+LL | /     if i_32 != i32::MIN {
+LL | |         i_32 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_32 = i_32.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:173:5
+   |
+LL | /     if i_32 != i32::min_value() {
+LL | |         i_32 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_32 = i_32.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:183:5
+   |
+LL | /     if i64::min_value() < i_64 {
+LL | |         i_64 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_64 = i_64.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:188:5
+   |
+LL | /     if i64::MIN != i_64 {
+LL | |         i_64 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_64 = i_64.saturating_sub(1);`
+
+error: Implicitly performing saturating subtraction
+  --> $DIR/implicit_saturating_sub.rs:193:5
+   |
+LL | /     if i64::MIN < i_64 {
+LL | |         i_64 -= 1;
+LL | |     }
+   | |_____^ help: try: `i_64 = i_64.saturating_sub(1);`
+
+error: aborting due to 23 previous errors
+