Declare lint.

CHANGELOG.md

@@ -1093,6 +1093,7 @@ Released 2018-09-13
 [`extend_from_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#extend_from_slice
 [`extra_unused_lifetimes`]: https://rust-lang.github.io/rust-clippy/master/index.html#extra_unused_lifetimes
 [`fallible_impl_from`]: https://rust-lang.github.io/rust-clippy/master/index.html#fallible_impl_from
+[`filetype_is_file`]: https://rust-lang.github.io/rust-clippy/master/index.html#filetype_is_file
 [`filter_map`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_map
 [`filter_map_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_map_next
 [`filter_next`]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_next

clippy_lints/src/lib.rs

@@ -612,6 +612,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         &methods::CLONE_ON_COPY,
         &methods::CLONE_ON_REF_PTR,
         &methods::EXPECT_FUN_CALL,
+        &methods::FILETYPE_IS_FILE,
         &methods::FILTER_MAP,
         &methods::FILTER_MAP_NEXT,
         &methods::FILTER_NEXT,
@@ -1199,6 +1200,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&methods::CLONE_DOUBLE_REF),
         LintId::of(&methods::CLONE_ON_COPY),
         LintId::of(&methods::EXPECT_FUN_CALL),
+        LintId::of(&methods::FILETYPE_IS_FILE),
         LintId::of(&methods::FILTER_NEXT),
         LintId::of(&methods::FLAT_MAP_IDENTITY),
         LintId::of(&methods::INEFFICIENT_TO_STRING),
@@ -1384,6 +1386,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&mem_replace::MEM_REPLACE_OPTION_WITH_NONE),
         LintId::of(&mem_replace::MEM_REPLACE_WITH_DEFAULT),
         LintId::of(&methods::CHARS_LAST_CMP),
+        LintId::of(&methods::FILETYPE_IS_FILE),
         LintId::of(&methods::INTO_ITER_ON_REF),
         LintId::of(&methods::ITER_CLONED_COLLECT),
         LintId::of(&methods::ITER_NTH_ZERO),

clippy_lints/src/methods/mod.rs

@@ -1130,6 +1130,40 @@ declare_clippy_lint! {
     "Check for offset calculations on raw pointers to zero-sized types"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for `FileType::is_file()`.
+    ///
+    /// **Why is this bad?** When people testing a file type with `FileType::is_file`
+    /// they are testing whether a path is something they can get bytes from. But
+    /// `is_file` doesn't cover special file types in unix-like systems. and not covering
+    /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust,ignore
+    /// let metadata = std::fs::metadata("foo.txt")?;
+    /// let filetype = metadata.file_type();
+    ///
+    /// if filetype.is_file() {
+    ///     // read file
+    /// }
+    /// ```
+    ///
+    /// should be writing as:
+    ///
+    /// ```rust,ignore
+    /// let metadata = std::fs::metadata("foo.txt")?;
+    /// let filetype = metadata.file_type();
+    ///
+    /// if !filetype.is_dir() {
+    ///     // read file
+    /// }
+    /// ```
+    pub FILETYPE_IS_FILE,
+    style,
+    "`FileType::is_file` is not recommended to test for readable file type."
+}
+
 declare_lint_pass!(Methods => [
     OPTION_UNWRAP_USED,
     RESULT_UNWRAP_USED,
@@ -1177,6 +1211,7 @@ declare_lint_pass!(Methods => [
     UNINIT_ASSUMED_INIT,
     MANUAL_SATURATING_ARITHMETIC,
     ZST_OFFSET,
+    FILETYPE_IS_FILE,
 ]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {

src/lintlist/mod.rs

@@ -560,6 +560,13 @@ pub const ALL_LINTS: [Lint; 346] = [
         deprecation: None,
         module: "fallible_impl_from",
     },
+    Lint {
+        name: "filetype_is_file",
+        group: "style",
+        desc: "`FileType::is_file` is not recommended to test for readable file type.",
+        deprecation: None,
+        module: "methods",
+    },
     Lint {
         name: "filter_map",
         group: "pedantic",