improved string_add/string_add_assign messages, Allow-by-default string_add_assign

README.md

@@ -29,7 +29,7 @@ Lints included in this crate:
  - `inline_always`: Warns on `#[inline(always)]`, because in most cases it is a bad idea
  - `collapsible_if`: Warns on cases where two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` can be written as `if x && y { foo() }`
  - `zero_width_space`: Warns on encountering a unicode zero-width space
- - `string_add_assign`: Warns on `x = x + ..` where `x` is a `String` and suggests using `push_str(..)` instead.
+ - `string_add_assign`: Warns on `x = x + ..` where `x` is a `String` and suggests using `push_str(..)` instead. Allowed by default.
  - `string_add`: Matches `x + ..` where `x` is a `String` and where `string_add_assign` doesn't warn. Allowed by default.
  - `needless_return`: Warns on using `return expr;` when a simple `expr` would suffice.
  - `let_and_return`: Warns on doing `let x = expr; x` at the end of a function.

src/strings.rs

@@ -13,14 +13,15 @@ use utils::{match_def_path, span_lint, walk_ptrs_ty, get_parent_expr};
 
 declare_lint! {
     pub STRING_ADD_ASSIGN,
-    Warn,
-    "Warn on `x = x + ..` where x is a `String`"
+    Allow,
+    "expressions of the form `x = x + ..` where x is a `String`"
 }
 
 declare_lint! {
     pub STRING_ADD,
     Allow,
-    "Warn on `x + ..` where x is a `String`"
+    "expressions of the form `x + ..` where x is a `String` \
+     unless `string_add_assign` matches"
 }
 
 #[derive(Copy, Clone)]