Merge pull request #2004 from sunfishcode/master

When suggesting `from(x)` for lossless casts, strip parens from `x`.

clippy_lints/src/types.rs

@@ -10,7 +10,7 @@ use syntax::ast::{FloatTy, IntTy, UintTy};
 use syntax::attr::IntType;
 use syntax::codemap::Span;
 use utils::{comparisons, higher, in_external_macro, in_macro, last_path_segment, match_def_path, match_path,
-            opt_def_id, snippet, span_help_and_lint, span_lint, span_lint_and_sugg, type_size};
+            opt_def_id, snippet, snippet_opt, span_help_and_lint, span_lint, span_lint_and_sugg, type_size};
 use utils::paths;
 
 /// Handles all the linting of funky types
@@ -580,14 +580,36 @@ fn span_precision_loss_lint(cx: &LateContext, expr: &Expr, cast_from: Ty, cast_t
     );
 }
 
+fn should_strip_parens(op: &Expr, snip: &str) -> bool {
+    if let ExprBinary(_, _, _) = op.node {
+        if snip.starts_with('(') && snip.ends_with(')') {
+            return true;
+        }
+    }
+    false
+}
+
 fn span_lossless_lint(cx: &LateContext, expr: &Expr, op: &Expr, cast_from: Ty, cast_to: Ty) {
+    // The suggestion is to use a function call, so if the original expression
+    // has parens on the outside, they are no longer needed.
+    let opt = snippet_opt(cx, op.span);
+    let sugg = if let Some(ref snip) = opt {
+        if should_strip_parens(op, snip) {
+            &snip[1..snip.len()-1]
+        } else {
+            snip.as_str()
+        }
+    } else {
+        ".."
+    };
+
     span_lint_and_sugg(
         cx,
         CAST_LOSSLESS,
         expr.span,
         &format!("casting {} to {} may become silently lossy if types change", cast_from, cast_to),
         "try",
-        format!("{}::from({})", cast_to, &snippet(cx, op.span, "..")),
+        format!("{}::from({})", cast_to, sugg),
     );
 }
 

tests/ui/cast.rs

@@ -57,6 +57,8 @@ fn main() {
     1u32 as f64;
     // Test cast_lossless with casts from floating-point types
     1.0f32 as f64;
+    // Test cast_lossless with an expression wrapped in parens
+    (1u8 + 1u8) as u16;
     // Test cast_sign_loss
     1i32 as u32;
     1isize as usize;

tests/ui/cast.stderr

@@ -308,151 +308,157 @@ error: casting f32 to f64 may become silently lossy if types change
 59 |     1.0f32 as f64;
    |     ^^^^^^^^^^^^^ help: try: `f64::from(1.0f32)`
 
-error: casting i32 to u32 may lose the sign of the value
+error: casting u8 to u16 may become silently lossy if types change
   --> $DIR/cast.rs:61:5
    |
-61 |     1i32 as u32;
+61 |     (1u8 + 1u8) as u16;
+   |     ^^^^^^^^^^^^^^^^^^ help: try: `u16::from(1u8 + 1u8)`
+
+error: casting i32 to u32 may lose the sign of the value
+  --> $DIR/cast.rs:63:5
+   |
+63 |     1i32 as u32;
    |     ^^^^^^^^^^^
 
 error: casting isize to usize may lose the sign of the value
-  --> $DIR/cast.rs:62:5
+  --> $DIR/cast.rs:64:5
    |
-62 |     1isize as usize;
+64 |     1isize as usize;
    |     ^^^^^^^^^^^^^^^
 
 error: casting isize to i8 may truncate the value
-  --> $DIR/cast.rs:65:5
+  --> $DIR/cast.rs:67:5
    |
-65 |     1isize as i8;
+67 |     1isize as i8;
    |     ^^^^^^^^^^^^
 
 error: casting isize to f64 causes a loss of precision on targets with 64-bit wide pointers (isize is 64 bits wide, but f64's mantissa is only 52 bits wide)
-  --> $DIR/cast.rs:66:5
+  --> $DIR/cast.rs:68:5
    |
-66 |     1isize as f64;
+68 |     1isize as f64;
    |     ^^^^^^^^^^^^^
 
 error: casting usize to f64 causes a loss of precision on targets with 64-bit wide pointers (usize is 64 bits wide, but f64's mantissa is only 52 bits wide)
-  --> $DIR/cast.rs:67:5
+  --> $DIR/cast.rs:69:5
    |
-67 |     1usize as f64;
+69 |     1usize as f64;
    |     ^^^^^^^^^^^^^
 
 error: casting isize to f32 causes a loss of precision (isize is 32 or 64 bits wide, but f32's mantissa is only 23 bits wide)
-  --> $DIR/cast.rs:68:5
+  --> $DIR/cast.rs:70:5
    |
-68 |     1isize as f32;
+70 |     1isize as f32;
    |     ^^^^^^^^^^^^^
 
 error: casting usize to f32 causes a loss of precision (usize is 32 or 64 bits wide, but f32's mantissa is only 23 bits wide)
-  --> $DIR/cast.rs:69:5
+  --> $DIR/cast.rs:71:5
    |
-69 |     1usize as f32;
+71 |     1usize as f32;
    |     ^^^^^^^^^^^^^
 
 error: casting isize to i32 may truncate the value on targets with 64-bit wide pointers
-  --> $DIR/cast.rs:70:5
+  --> $DIR/cast.rs:72:5
    |
-70 |     1isize as i32;
+72 |     1isize as i32;
    |     ^^^^^^^^^^^^^
 
 error: casting isize to u32 may lose the sign of the value
-  --> $DIR/cast.rs:71:5
+  --> $DIR/cast.rs:73:5
    |
-71 |     1isize as u32;
+73 |     1isize as u32;
    |     ^^^^^^^^^^^^^
 
 error: casting isize to u32 may truncate the value on targets with 64-bit wide pointers
-  --> $DIR/cast.rs:71:5
+  --> $DIR/cast.rs:73:5
    |
-71 |     1isize as u32;
+73 |     1isize as u32;
    |     ^^^^^^^^^^^^^
 
 error: casting usize to u32 may truncate the value on targets with 64-bit wide pointers
-  --> $DIR/cast.rs:72:5
+  --> $DIR/cast.rs:74:5
    |
-72 |     1usize as u32;
+74 |     1usize as u32;
    |     ^^^^^^^^^^^^^
 
 error: casting usize to i32 may truncate the value on targets with 64-bit wide pointers
-  --> $DIR/cast.rs:73:5
+  --> $DIR/cast.rs:75:5
    |
-73 |     1usize as i32;
+75 |     1usize as i32;
    |     ^^^^^^^^^^^^^
 
 error: casting usize to i32 may wrap around the value on targets with 32-bit wide pointers
-  --> $DIR/cast.rs:73:5
+  --> $DIR/cast.rs:75:5
    |
-73 |     1usize as i32;
+75 |     1usize as i32;
    |     ^^^^^^^^^^^^^
 
 error: casting i64 to isize may truncate the value on targets with 32-bit wide pointers
-  --> $DIR/cast.rs:75:5
+  --> $DIR/cast.rs:77:5
    |
-75 |     1i64 as isize;
+77 |     1i64 as isize;
    |     ^^^^^^^^^^^^^
 
 error: casting i64 to usize may lose the sign of the value
-  --> $DIR/cast.rs:76:5
+  --> $DIR/cast.rs:78:5
    |
-76 |     1i64 as usize;
+78 |     1i64 as usize;
    |     ^^^^^^^^^^^^^
 
 error: casting i64 to usize may truncate the value on targets with 32-bit wide pointers
-  --> $DIR/cast.rs:76:5
+  --> $DIR/cast.rs:78:5
    |
-76 |     1i64 as usize;
+78 |     1i64 as usize;
    |     ^^^^^^^^^^^^^
 
 error: casting u64 to isize may truncate the value on targets with 32-bit wide pointers
-  --> $DIR/cast.rs:77:5
+  --> $DIR/cast.rs:79:5
    |
-77 |     1u64 as isize;
+79 |     1u64 as isize;
    |     ^^^^^^^^^^^^^
 
 error: casting u64 to isize may wrap around the value on targets with 64-bit wide pointers
-  --> $DIR/cast.rs:77:5
+  --> $DIR/cast.rs:79:5
    |
-77 |     1u64 as isize;
+79 |     1u64 as isize;
    |     ^^^^^^^^^^^^^
 
 error: casting u64 to usize may truncate the value on targets with 32-bit wide pointers
-  --> $DIR/cast.rs:78:5
+  --> $DIR/cast.rs:80:5
    |
-78 |     1u64 as usize;
+80 |     1u64 as usize;
    |     ^^^^^^^^^^^^^
 
 error: casting u32 to isize may wrap around the value on targets with 32-bit wide pointers
-  --> $DIR/cast.rs:79:5
+  --> $DIR/cast.rs:81:5
    |
-79 |     1u32 as isize;
+81 |     1u32 as isize;
    |     ^^^^^^^^^^^^^
 
 error: casting i32 to usize may lose the sign of the value
-  --> $DIR/cast.rs:82:5
+  --> $DIR/cast.rs:84:5
    |
-82 |     1i32 as usize;
+84 |     1i32 as usize;
    |     ^^^^^^^^^^^^^
 
 error: casting to the same type is unnecessary (`i32` -> `i32`)
-  --> $DIR/cast.rs:84:5
+  --> $DIR/cast.rs:86:5
    |
-84 |     1i32 as i32;
+86 |     1i32 as i32;
    |     ^^^^^^^^^^^
    |
    = note: `-D unnecessary-cast` implied by `-D warnings`
 
 error: casting to the same type is unnecessary (`f32` -> `f32`)
-  --> $DIR/cast.rs:85:5
+  --> $DIR/cast.rs:87:5
    |
-85 |     1f32 as f32;
+87 |     1f32 as f32;
    |     ^^^^^^^^^^^
 
 error: casting to the same type is unnecessary (`bool` -> `bool`)
-  --> $DIR/cast.rs:86:5
+  --> $DIR/cast.rs:88:5
    |
-86 |     false as bool;
+88 |     false as bool;
    |     ^^^^^^^^^^^^^
 
-error: aborting due to 74 previous errors
+error: aborting due to 75 previous errors