add two lints to string module

clippy_lints/src/lib.rs

@@ -306,8 +306,6 @@ mod shadow;
 mod single_component_path_imports;
 mod slow_vector_initialization;
 mod stable_sort_primitive;
-mod str_to_string;
-mod string_to_string;
 mod strings;
 mod suspicious_trait_impl;
 mod swap;
@@ -829,12 +827,12 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS,
         &slow_vector_initialization::SLOW_VECTOR_INITIALIZATION,
         &stable_sort_primitive::STABLE_SORT_PRIMITIVE,
-        &str_to_string::STR_TO_STRING,
-        &string_to_string::STRING_TO_STRING,
         &strings::STRING_ADD,
         &strings::STRING_ADD_ASSIGN,
         &strings::STRING_FROM_UTF8_AS_BYTES,
         &strings::STRING_LIT_AS_BYTES,
+        &strings::STRING_TO_STRING,
+        &strings::STR_TO_STRING,
         &suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL,
         &suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL,
         &swap::ALMOST_SWAPPED,
@@ -1169,8 +1167,8 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_early_pass(|| box asm_syntax::InlineAsmX86AttSyntax);
     store.register_early_pass(|| box asm_syntax::InlineAsmX86IntelSyntax);
     store.register_late_pass(|| box undropped_manually_drops::UndroppedManuallyDrops);
-    store.register_late_pass(|| box str_to_string::StrToString);
-    store.register_late_pass(|| box string_to_string::StringToString);
+    store.register_late_pass(|| box strings::StrToString);
+    store.register_late_pass(|| box strings::StringToString);
 
 
     store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
@@ -1212,9 +1210,9 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&pattern_type_mismatch::PATTERN_TYPE_MISMATCH),
         LintId::of(&shadow::SHADOW_REUSE),
         LintId::of(&shadow::SHADOW_SAME),
-        LintId::of(&str_to_string::STR_TO_STRING),
-        LintId::of(&string_to_string::STRING_TO_STRING),
         LintId::of(&strings::STRING_ADD),
+        LintId::of(&strings::STRING_TO_STRING),
+        LintId::of(&strings::STR_TO_STRING),
         LintId::of(&types::RC_BUFFER),
         LintId::of(&unwrap_in_result::UNWRAP_IN_RESULT),
         LintId::of(&verbose_file_reads::VERBOSE_FILE_READS),

clippy_lints/src/strings.rs

@@ -2,6 +2,7 @@ use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, LangItem, QPath};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Spanned;
 use rustc_span::sym;
@@ -11,7 +12,7 @@ use if_chain::if_chain;
 use crate::utils::SpanlessEq;
 use crate::utils::{
     get_parent_expr, is_allowed, is_type_diagnostic_item, match_function_call, method_calls, paths, span_lint,
-    span_lint_and_sugg,
+    span_lint_and_help, span_lint_and_sugg,
 };
 
 declare_clippy_lint! {
@@ -289,3 +290,98 @@ impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
         }
     }
 }
+
+declare_clippy_lint! {
+    /// **What it does:** This lint checks for `.to_string()` method calls on values of type `&str`.
+    ///
+    /// **Why is this bad?** This does a multitude of things to just clone a string. Using `.to_owned()` is more specific.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// // example code where clippy issues a warning
+    /// let _ = "str".to_string();
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// // example code which does not raise clippy warning
+    /// let _ = "str".to_owned();
+    /// ```
+    pub STR_TO_STRING,
+    restriction,
+    "using `to_string()` on a `&str`, which should be `to_owned()`"
+}
+
+declare_lint_pass!(StrToString => [STR_TO_STRING]);
+
+impl LateLintPass<'_> for StrToString {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
+        if_chain! {
+            if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
+            if path.ident.name == sym!(to_string);
+            let ty = cx.typeck_results().expr_ty(&args[0]);
+            if let ty::Ref(_, ty, ..) = ty.kind();
+            if *ty.kind() == ty::Str;
+            then {
+                span_lint_and_help(
+                    cx,
+                    STR_TO_STRING,
+                    expr.span,
+                    "`to_string()` does a multitude of things to just clone a `&str`",
+                    None,
+                    "consider using `.to_owned()`",
+                );
+            }
+        }
+    }
+}
+
+declare_clippy_lint! {
+    /// **What it does:** This lint checks for `.to_string()` method calls on values of type `String`.
+    ///
+    /// **Why is this bad?** This does a multitude of things to just clone a string. Using `.clone()` is more specific.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// // example code where clippy issues a warning
+    /// let msg = String::from("Hello World");
+    /// let _ = msg.to_string();
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// // example code which does not raise clippy warning
+    /// let msg = String::from("Hello World");
+    /// let _ = msg.clone();
+    /// ```
+    pub STRING_TO_STRING,
+    restriction,
+    "using `to_string()` on a `String`, which should be `clone()`"
+}
+
+declare_lint_pass!(StringToString => [STRING_TO_STRING]);
+
+impl LateLintPass<'_> for StringToString {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
+        if_chain! {
+            if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
+            if path.ident.name == sym!(to_string);
+            let ty = cx.typeck_results().expr_ty(&args[0]);
+            if is_type_diagnostic_item(cx, ty, sym!(string_type));
+            then {
+                span_lint_and_help(
+                    cx,
+                    STRING_TO_STRING,
+                    expr.span,
+                    "`to_string()` does a multitude of things to just clone a `String`",
+                    None,
+                    "consider using `.clone()`",
+                );
+            }
+        }
+    }
+}

src/lintlist/mod.rs

@@ -2242,7 +2242,7 @@ vec![
         group: "restriction",
         desc: "using `to_string()` on a `&str`, which should be `to_owned()`",
         deprecation: None,
-        module: "str_to_string",
+        module: "strings",
     },
     Lint {
         name: "string_add",
@@ -2284,7 +2284,7 @@ vec![
         group: "restriction",
         desc: "using `to_string()` on a `String`, which should be `clone()`",
         deprecation: None,
-        module: "string_to_string",
+        module: "strings",
     },
     Lint {
         name: "struct_excessive_bools",