Update all tests to comply with clippy::manual_empty_string_creations

Author: Guilherme-Vasconcelos

clippy_dev/src/new_lint.rs

@@ -155,7 +155,7 @@ fn to_camel_case(name: &str) -> String {
     name.split('_')
         .map(|s| {
             if s.is_empty() {
-                String::from("")
+                String::new()
             } else {
                 [&s[0..1].to_uppercase(), &s[1..]].concat()
             }

clippy_lints/src/manual_async_fn.rs

@@ -192,7 +192,7 @@ fn suggested_ret(cx: &LateContext<'_>, output: &Ty<'_>) -> Option<(&'static str,
     match output.kind {
         TyKind::Tup(tys) if tys.is_empty() => {
             let sugg = "remove the return type";
-            Some((sugg, "".into()))
+            Some((sugg, String::new()))
         },
         _ => {
             let sugg = "return the output of the future directly";

clippy_lints/src/methods/option_map_unwrap_or.rs

@@ -78,7 +78,7 @@ pub(super) fn check<'tcx>(
                     map_span,
                     String::from(if unwrap_snippet_none { "and_then" } else { "map_or" }),
                 ),
-                (expr.span.with_lo(unwrap_recv.span.hi()), String::from("")),
+                (expr.span.with_lo(unwrap_recv.span.hi()), String::new()),
             ];
 
             if !unwrap_snippet_none {

clippy_lints/src/misc_early/unneeded_wildcard_pattern.rs

@@ -46,7 +46,7 @@ fn span_lint(cx: &EarlyContext<'_>, span: Span, only_one: bool) {
             "these patterns are unneeded as the `..` pattern can match those elements"
         },
         if only_one { "remove it" } else { "remove them" },
-        "".to_string(),
+        String::new(),
         Applicability::MachineApplicable,
     );
 }

clippy_lints/src/unnecessary_wraps.rs

@@ -130,7 +130,7 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryWraps {
                         (
                             ret_expr.span,
                             if inner_type.is_unit() {
-                                "".to_string()
+                                String::new()
                             } else {
                                 snippet(cx, arg.span.source_callsite(), "..").to_string()
                             }

tests/ui/case_sensitive_file_extension_comparisons.rs

@@ -14,31 +14,31 @@ fn is_rust_file(filename: &str) -> bool {
 
 fn main() {
     // std::string::String and &str should trigger the lint failure with .ext12
-    let _ = String::from("").ends_with(".ext12");
+    let _ = String::new().ends_with(".ext12");
     let _ = "str".ends_with(".ext12");
 
     // The test struct should not trigger the lint failure with .ext12
     TestStruct {}.ends_with(".ext12");
 
     // std::string::String and &str should trigger the lint failure with .EXT12
-    let _ = String::from("").ends_with(".EXT12");
+    let _ = String::new().ends_with(".EXT12");
     let _ = "str".ends_with(".EXT12");
 
     // The test struct should not trigger the lint failure with .EXT12
     TestStruct {}.ends_with(".EXT12");
 
     // Should not trigger the lint failure with .eXT12
-    let _ = String::from("").ends_with(".eXT12");
+    let _ = String::new().ends_with(".eXT12");
     let _ = "str".ends_with(".eXT12");
     TestStruct {}.ends_with(".eXT12");
 
     // Should not trigger the lint failure with .EXT123 (too long)
-    let _ = String::from("").ends_with(".EXT123");
+    let _ = String::new().ends_with(".EXT123");
     let _ = "str".ends_with(".EXT123");
     TestStruct {}.ends_with(".EXT123");
 
     // Shouldn't fail if it doesn't start with a dot
-    let _ = String::from("").ends_with("a.ext");
+    let _ = String::new().ends_with("a.ext");
     let _ = "str".ends_with("a.extA");
     TestStruct {}.ends_with("a.ext");
 }

tests/ui/case_sensitive_file_extension_comparisons.stderr

@@ -8,10 +8,10 @@ LL |     filename.ends_with(".rs")
    = help: consider using a case-insensitive comparison instead
 
 error: case-sensitive file extension comparison
-  --> $DIR/case_sensitive_file_extension_comparisons.rs:17:30
+  --> $DIR/case_sensitive_file_extension_comparisons.rs:17:27
    |
-LL |     let _ = String::from("").ends_with(".ext12");
-   |                              ^^^^^^^^^^^^^^^^^^^
+LL |     let _ = String::new().ends_with(".ext12");
+   |                           ^^^^^^^^^^^^^^^^^^^
    |
    = help: consider using a case-insensitive comparison instead
 
@@ -24,10 +24,10 @@ LL |     let _ = "str".ends_with(".ext12");
    = help: consider using a case-insensitive comparison instead
 
 error: case-sensitive file extension comparison
-  --> $DIR/case_sensitive_file_extension_comparisons.rs:24:30
+  --> $DIR/case_sensitive_file_extension_comparisons.rs:24:27
    |
-LL |     let _ = String::from("").ends_with(".EXT12");
-   |                              ^^^^^^^^^^^^^^^^^^^
+LL |     let _ = String::new().ends_with(".EXT12");
+   |                           ^^^^^^^^^^^^^^^^^^^
    |
    = help: consider using a case-insensitive comparison instead
 

tests/ui/format.fixed

@@ -33,7 +33,7 @@ fn main() {
     format!("foo {}", "bar");
     format!("{} bar", "foo");
 
-    let arg: String = "".to_owned();
+    let arg = String::new();
     arg.to_string();
     format!("{:?}", arg); // Don't warn about debug.
     format!("{:8}", arg);

tests/ui/format.rs

@@ -35,7 +35,7 @@ fn main() {
     format!("foo {}", "bar");
     format!("{} bar", "foo");
 
-    let arg: String = "".to_owned();
+    let arg = String::new();
     format!("{}", arg);
     format!("{:?}", arg); // Don't warn about debug.
     format!("{:8}", arg);

tests/ui/identity_op.fixed

@@ -68,7 +68,7 @@ fn main() {
     &x;
     x;
 
-    let mut a = A("".into());
+    let mut a = A(String::new());
     let b = a << 0; // no error: non-integer
 
     1 * Meter; // no error: non-integer

tests/ui/identity_op.rs

@@ -68,7 +68,7 @@ fn main() {
     &x >> 0;
     x >> &0;
 
-    let mut a = A("".into());
+    let mut a = A(String::new());
     let b = a << 0; // no error: non-integer
 
     1 * Meter; // no error: non-integer

tests/ui/manual_empty_string_creations.fixed

@@ -7,7 +7,7 @@ macro_rules! create_strings_from_macro {
     ($some_str:expr) => {
         let _: String = $some_str.into();
         let _ = $some_str.to_string();
-    }
+    };
 }
 
 fn main() {

tests/ui/or_fun_call.fixed

@@ -90,8 +90,8 @@ fn or_fun_call() {
     let mut btree_vec = BTreeMap::<u64, Vec<i32>>::new();
     btree_vec.entry(42).or_insert(vec![]);
 
-    let stringy = Some(String::from(""));
-    let _ = stringy.unwrap_or_else(|| "".to_owned());
+    let stringy = Some(String::new());
+    let _ = stringy.unwrap_or_default();
 
     let opt = Some(1);
     let hello = "Hello";

tests/ui/or_fun_call.rs

@@ -90,8 +90,8 @@ fn or_fun_call() {
     let mut btree_vec = BTreeMap::<u64, Vec<i32>>::new();
     btree_vec.entry(42).or_insert(vec![]);
 
-    let stringy = Some(String::from(""));
-    let _ = stringy.unwrap_or("".to_owned());
+    let stringy = Some(String::new());
+    let _ = stringy.unwrap_or(String::new());
 
     let opt = Some(1);
     let hello = "Hello";

tests/ui/or_fun_call.stderr

@@ -66,11 +66,11 @@ error: use of `unwrap_or` followed by a function call
 LL |     without_default.unwrap_or(Foo::new());
    |                     ^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(Foo::new)`
 
-error: use of `unwrap_or` followed by a function call
+error: use of `unwrap_or` followed by a call to `new`
   --> $DIR/or_fun_call.rs:94:21
    |
-LL |     let _ = stringy.unwrap_or("".to_owned());
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_else(|| "".to_owned())`
+LL |     let _ = stringy.unwrap_or(String::new());
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `unwrap_or_default()`
 
 error: use of `unwrap_or` followed by a function call
   --> $DIR/or_fun_call.rs:102:21

tests/ui/string_add.rs

@@ -7,13 +7,13 @@ extern crate macro_rules;
 #[allow(clippy::string_add_assign, unused)]
 fn main() {
     // ignores assignment distinction
-    let mut x = "".to_owned();
+    let mut x = String::new();
 
     for _ in 1..3 {
         x = x + ".";
     }
 
-    let y = "".to_owned();
+    let y = String::new();
     let z = y + "...";
 
     assert_eq!(&x, &z);

tests/ui/string_add_assign.fixed

@@ -4,13 +4,13 @@
 #[warn(clippy::string_add_assign)]
 fn main() {
     // ignores assignment distinction
-    let mut x = "".to_owned();
+    let mut x = String::new();
 
     for _ in 1..3 {
         x += ".";
     }
 
-    let y = "".to_owned();
+    let y = String::new();
     let z = y + "...";
 
     assert_eq!(&x, &z);

tests/ui/string_add_assign.rs

@@ -4,13 +4,13 @@
 #[warn(clippy::string_add_assign)]
 fn main() {
     // ignores assignment distinction
-    let mut x = "".to_owned();
+    let mut x = String::new();
 
     for _ in 1..3 {
         x = x + ".";
     }
 
-    let y = "".to_owned();
+    let y = String::new();
     let z = y + "...";
 
     assert_eq!(&x, &z);

tests/ui/unnecessary_owned_empty_strings.fixed

@@ -12,6 +12,7 @@ fn main() {
     ref_str_argument("");
 
     // should be linted
+    #[allow(clippy::manual_empty_string_creations)]
     ref_str_argument("");
 
     // should not be linted

tests/ui/unnecessary_owned_empty_strings.rs

@@ -12,6 +12,7 @@ fn main() {
     ref_str_argument(&String::new());
 
     // should be linted
+    #[allow(clippy::manual_empty_string_creations)]
     ref_str_argument(&String::from(""));
 
     // should not be linted

tests/ui/unnecessary_owned_empty_strings.stderr

@@ -7,7 +7,7 @@ LL |     ref_str_argument(&String::new());
    = note: `-D clippy::unnecessary-owned-empty-strings` implied by `-D warnings`
 
 error: usage of `&String::from("")` for a function expecting a `&str` argument
-  --> $DIR/unnecessary_owned_empty_strings.rs:15:22
+  --> $DIR/unnecessary_owned_empty_strings.rs:16:22
    |
 LL |     ref_str_argument(&String::from(""));
    |                      ^^^^^^^^^^^^^^^^^ help: try: `""`

tests/ui/useless_conversion_try.rs

@@ -29,10 +29,10 @@ fn main() {
     let _ = String::try_from("foo".to_string()).unwrap();
     let _ = String::try_from(format!("A: {:04}", 123)).unwrap();
     let _: String = format!("Hello {}", "world").try_into().unwrap();
-    let _: String = "".to_owned().try_into().unwrap();
+    let _: String = String::new().try_into().unwrap();
     let _: String = match String::from("_").try_into() {
         Ok(a) => a,
-        Err(_) => "".into(),
+        Err(_) => String::new(),
     };
     // FIXME this is a false negative
     #[allow(clippy::cmp_owned)]

tests/ui/useless_conversion_try.stderr

@@ -62,7 +62,7 @@ LL |     let _: String = format!("Hello {}", "world").try_into().unwrap();
 error: useless conversion to the same type: `std::string::String`
   --> $DIR/useless_conversion_try.rs:32:21
    |
-LL |     let _: String = "".to_owned().try_into().unwrap();
+LL |     let _: String = String::new().try_into().unwrap();
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider removing `.try_into()`