Added suggestion for conversion with is_ok.

clippy_lints/src/checked_conversions.rs

@@ -4,9 +4,9 @@ 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::{span_lint, SpanlessEq};
+use crate::utils::{span_lint_and_sugg, snippet_with_applicability, SpanlessEq};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for explicit bounds checking when casting.
@@ -54,16 +54,26 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CheckedConversions {
             }
         };
 
-        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_else(|| "IntegerType".to_string()),
-                ),
-            );
+        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
+                );
+            }
         }
     }
 }

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

@@ -1,5 +1,9 @@
+// run-rustfix
+
 #![warn(clippy::checked_conversions)]
 #![allow(clippy::cast_lossless)]
+#![allow(dead_code)]
+use std::convert::TryFrom;
 
 // Positive tests
 

tests/ui/checked_conversions.stderr

@@ -1,52 +1,52 @@
-error: Checked cast can be simplified: `u32::try_from`
-  --> $DIR/checked_conversions.rs:9:8
+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: `u16::try_from`
-  --> $DIR/checked_conversions.rs:17:8
+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: `u8::try_from`
-  --> $DIR/checked_conversions.rs:25:8
+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: `i32::try_from`
-  --> $DIR/checked_conversions.rs:35:8
+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: `i16::try_from`
-  --> $DIR/checked_conversions.rs:43:8
+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: `i32::try_from`
-  --> $DIR/checked_conversions.rs:53:8
+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: `isize::try_from`
-  --> $DIR/checked_conversions.rs:61:8
+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: `u16::try_from`
-  --> $DIR/checked_conversions.rs:69:8
+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