Auto merge of #9667 - dorublanzeanu:master, r=giraffate

add new lint `seek_to_start_instead_of_rewind `

changelog: `seek_to_start_instead_of_rewind`: new lint to suggest using `rewind` instead of `seek` to start

Resolve #8600

10 files changed, 406 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b5a1d194794..7e91365c69a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4200,6 +4200,7 @@ Released 2018-09-13
 [`same_item_push`]: https://rust-lang.github.io/rust-clippy/master/index.html#same_item_push
 [`same_name_method`]: https://rust-lang.github.io/rust-clippy/master/index.html#same_name_method
 [`search_is_some`]: https://rust-lang.github.io/rust-clippy/master/index.html#search_is_some
+[`seek_to_start_instead_of_rewind`]: https://rust-lang.github.io/rust-clippy/master/index.html#seek_to_start_instead_of_rewind
 [`self_assignment`]: https://rust-lang.github.io/rust-clippy/master/index.html#self_assignment
 [`self_named_constructors`]: https://rust-lang.github.io/rust-clippy/master/index.html#self_named_constructors
 [`self_named_module_files`]: https://rust-lang.github.io/rust-clippy/master/index.html#self_named_module_files
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 2bb8dfee152..a903d46b2a4 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -363,6 +363,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::REPEAT_ONCE_INFO,
     crate::methods::RESULT_MAP_OR_INTO_OPTION_INFO,
     crate::methods::SEARCH_IS_SOME_INFO,
+    crate::methods::SEEK_TO_START_INSTEAD_OF_REWIND_INFO,
     crate::methods::SHOULD_IMPLEMENT_TRAIT_INFO,
     crate::methods::SINGLE_CHAR_ADD_STR_INFO,
     crate::methods::SINGLE_CHAR_PATTERN_INFO,
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index fb92779be2a..4fd1e3e54ae 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -69,6 +69,7 @@ mod path_buf_push_overwrite;
 mod range_zip_with_len;
 mod repeat_once;
 mod search_is_some;
+mod seek_to_start_instead_of_rewind;
 mod single_char_add_str;
 mod single_char_insert_string;
 mod single_char_pattern;
@@ -3066,6 +3067,37 @@ declare_clippy_lint! {
     "iterating on map using `iter` when `keys` or `values` would do"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// Checks for jumps to the start of a stream that implements `Seek`
+    /// and uses the `seek` method providing `Start` as parameter.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Readability. There is a specific method that was implemented for
+    /// this exact scenario.
+    ///
+    /// ### Example
+    /// ```rust
+    /// # use std::io;
+    /// fn foo<T: io::Seek>(t: &mut T) {
+    ///     t.seek(io::SeekFrom::Start(0));
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// # use std::io;
+    /// fn foo<T: io::Seek>(t: &mut T) {
+    ///     t.rewind();
+    /// }
+    /// ```
+    #[clippy::version = "1.66.0"]
+    pub SEEK_TO_START_INSTEAD_OF_REWIND,
+    complexity,
+    "jumping to the start of stream using `seek` method"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -3190,6 +3222,7 @@ impl_lint_pass!(Methods => [
     VEC_RESIZE_TO_ZERO,
     VERBOSE_FILE_READS,
     ITER_KV_MAP,
+    SEEK_TO_START_INSTEAD_OF_REWIND,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -3604,6 +3637,11 @@ impl Methods {
                 ("resize", [count_arg, default_arg]) => {
                     vec_resize_to_zero::check(cx, expr, count_arg, default_arg, span);
                 },
+                ("seek", [arg]) => {
+                    if meets_msrv(self.msrv, msrvs::SEEK_REWIND) {
+                        seek_to_start_instead_of_rewind::check(cx, expr, recv, arg, span);
+                    }
+                },
                 ("sort", []) => {
                     stable_sort_primitive::check(cx, expr, recv);
                 },
diff --git a/clippy_lints/src/methods/seek_to_start_instead_of_rewind.rs b/clippy_lints/src/methods/seek_to_start_instead_of_rewind.rs
new file mode 100644
index 00000000000..7e3bed1e41a
--- /dev/null
+++ b/clippy_lints/src/methods/seek_to_start_instead_of_rewind.rs
@@ -0,0 +1,45 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::ty::implements_trait;
+use clippy_utils::{get_trait_def_id, match_def_path, paths};
+use rustc_ast::ast::{LitIntType, LitKind};
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_span::Span;
+
+use super::SEEK_TO_START_INSTEAD_OF_REWIND;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    recv: &'tcx Expr<'_>,
+    arg: &'tcx Expr<'_>,
+    name_span: Span,
+) {
+    // Get receiver type
+    let ty = cx.typeck_results().expr_ty(recv).peel_refs();
+
+    if let Some(seek_trait_id) = get_trait_def_id(cx, &paths::STD_IO_SEEK) &&
+        implements_trait(cx, ty, seek_trait_id, &[]) &&
+        let ExprKind::Call(func, args1) = arg.kind &&
+        let ExprKind::Path(ref path) = func.kind &&
+        let Some(def_id) = cx.qpath_res(path, func.hir_id).opt_def_id() &&
+        match_def_path(cx, def_id, &paths::STD_IO_SEEKFROM_START) &&
+        args1.len() == 1 &&
+        let ExprKind::Lit(ref lit) = args1[0].kind &&
+        let LitKind::Int(0, LitIntType::Unsuffixed) = lit.node
+    {
+        let method_call_span = expr.span.with_lo(name_span.lo());
+        span_lint_and_then(
+            cx,
+            SEEK_TO_START_INSTEAD_OF_REWIND,
+            method_call_span,
+            "used `seek` to go to the start of the stream",
+            |diag| {
+                let app = Applicability::MachineApplicable;
+
+                diag.span_suggestion(method_call_span, "replace with", "rewind()", app);
+            },
+        );
+    }
+}
diff --git a/clippy_utils/src/msrvs.rs b/clippy_utils/src/msrvs.rs
index 9780794fa99..04b504d044d 100644
--- a/clippy_utils/src/msrvs.rs
+++ b/clippy_utils/src/msrvs.rs
@@ -38,4 +38,5 @@ msrv_aliases! {
     1,18,0 { HASH_MAP_RETAIN, HASH_SET_RETAIN }
     1,17,0 { FIELD_INIT_SHORTHAND, STATIC_IN_CONST, EXPECT_ERR }
     1,16,0 { STR_REPEAT }
+    1,55,0 { SEEK_REWIND }
 }
diff --git a/clippy_utils/src/paths.rs b/clippy_utils/src/paths.rs
index bc851473430..e37c7e34c0c 100644
--- a/clippy_utils/src/paths.rs
+++ b/clippy_utils/src/paths.rs
@@ -115,6 +115,8 @@ pub const STDERR: [&str; 4] = ["std", "io", "stdio", "stderr"];
 pub const STDOUT: [&str; 4] = ["std", "io", "stdio", "stdout"];
 pub const CONVERT_IDENTITY: [&str; 3] = ["core", "convert", "identity"];
 pub const STD_FS_CREATE_DIR: [&str; 3] = ["std", "fs", "create_dir"];
+pub const STD_IO_SEEK: [&str; 3] = ["std", "io", "Seek"];
+pub const STD_IO_SEEKFROM_START: [&str; 4] = ["std", "io", "SeekFrom", "Start"];
 pub const STRING_AS_MUT_STR: [&str; 4] = ["alloc", "string", "String", "as_mut_str"];
 pub const STRING_AS_STR: [&str; 4] = ["alloc", "string", "String", "as_str"];
 pub const STRING_NEW: [&str; 4] = ["alloc", "string", "String", "new"];
diff --git a/src/docs/seek_to_start_instead_of_rewind.txt b/src/docs/seek_to_start_instead_of_rewind.txt
new file mode 100644
index 00000000000..bef11b2312a
--- /dev/null
+++ b/src/docs/seek_to_start_instead_of_rewind.txt
@@ -0,0 +1,22 @@
+### What it does
+
+Checks for jumps to the start of a stream that implements `Seek`
+and uses the `seek` method providing `Start` as parameter.
+
+### Why is this bad?
+
+Readability. There is a specific method that was implemented for
+this exact scenario.
+
+### Example
+```
+fn foo<T: io::Seek>(t: &mut T) {
+    t.seek(io::SeekFrom::Start(0));
+}
+```
+Use instead:
+```
+fn foo<T: io::Seek>(t: &mut T) {
+    t.rewind();
+}
+```
\ No newline at end of file
diff --git a/tests/ui/seek_to_start_instead_of_rewind.fixed b/tests/ui/seek_to_start_instead_of_rewind.fixed
new file mode 100644
index 00000000000..464b6cdef63
--- /dev/null
+++ b/tests/ui/seek_to_start_instead_of_rewind.fixed
@@ -0,0 +1,137 @@
+// run-rustfix
+#![allow(unused)]
+#![feature(custom_inner_attributes)]
+#![warn(clippy::seek_to_start_instead_of_rewind)]
+
+use std::fs::OpenOptions;
+use std::io::{Read, Seek, SeekFrom, Write};
+
+struct StructWithSeekMethod {}
+
+impl StructWithSeekMethod {
+    fn seek(&mut self, from: SeekFrom) {}
+}
+
+trait MySeekTrait {
+    fn seek(&mut self, from: SeekFrom) {}
+}
+
+struct StructWithSeekTrait {}
+impl MySeekTrait for StructWithSeekTrait {}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_method(t: &mut StructWithSeekMethod) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_method_owned_false<T>(mut t: StructWithSeekMethod) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_trait(t: &mut StructWithSeekTrait) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_trait_owned<T>(mut t: StructWithSeekTrait) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_trait_bound<T: MySeekTrait>(t: &mut T) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should trigger clippy warning
+fn seek_to_start<T: Seek>(t: &mut T) {
+    t.rewind();
+}
+
+// This should trigger clippy warning
+fn owned_seek_to_start<T: Seek>(mut t: T) {
+    t.rewind();
+}
+
+// This should NOT trigger clippy warning because
+// it does not seek to start
+fn seek_to_5<T: Seek>(t: &mut T) {
+    t.seek(SeekFrom::Start(5));
+}
+
+// This should NOT trigger clippy warning because
+// it does not seek to start
+fn seek_to_end<T: Seek>(t: &mut T) {
+    t.seek(SeekFrom::End(0));
+}
+
+fn main() {
+    let mut f = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .create(true)
+        .open("foo.txt")
+        .unwrap();
+
+    let mut my_struct_trait = StructWithSeekTrait {};
+    seek_to_start_false_trait_bound(&mut my_struct_trait);
+
+    let hello = "Hello!\n";
+    write!(f, "{hello}").unwrap();
+    seek_to_5(&mut f);
+    seek_to_end(&mut f);
+    seek_to_start(&mut f);
+
+    let mut buf = String::new();
+    f.read_to_string(&mut buf).unwrap();
+
+    assert_eq!(&buf, hello);
+}
+
+fn msrv_1_54() {
+    #![clippy::msrv = "1.54"]
+
+    let mut f = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .create(true)
+        .open("foo.txt")
+        .unwrap();
+
+    let hello = "Hello!\n";
+    write!(f, "{hello}").unwrap();
+
+    f.seek(SeekFrom::Start(0));
+
+    let mut buf = String::new();
+    f.read_to_string(&mut buf).unwrap();
+
+    assert_eq!(&buf, hello);
+}
+
+fn msrv_1_55() {
+    #![clippy::msrv = "1.55"]
+
+    let mut f = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .create(true)
+        .open("foo.txt")
+        .unwrap();
+
+    let hello = "Hello!\n";
+    write!(f, "{hello}").unwrap();
+
+    f.rewind();
+
+    let mut buf = String::new();
+    f.read_to_string(&mut buf).unwrap();
+
+    assert_eq!(&buf, hello);
+}
diff --git a/tests/ui/seek_to_start_instead_of_rewind.rs b/tests/ui/seek_to_start_instead_of_rewind.rs
new file mode 100644
index 00000000000..68e09bd7c1f
--- /dev/null
+++ b/tests/ui/seek_to_start_instead_of_rewind.rs
@@ -0,0 +1,137 @@
+// run-rustfix
+#![allow(unused)]
+#![feature(custom_inner_attributes)]
+#![warn(clippy::seek_to_start_instead_of_rewind)]
+
+use std::fs::OpenOptions;
+use std::io::{Read, Seek, SeekFrom, Write};
+
+struct StructWithSeekMethod {}
+
+impl StructWithSeekMethod {
+    fn seek(&mut self, from: SeekFrom) {}
+}
+
+trait MySeekTrait {
+    fn seek(&mut self, from: SeekFrom) {}
+}
+
+struct StructWithSeekTrait {}
+impl MySeekTrait for StructWithSeekTrait {}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_method(t: &mut StructWithSeekMethod) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_method_owned_false<T>(mut t: StructWithSeekMethod) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_trait(t: &mut StructWithSeekTrait) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_trait_owned<T>(mut t: StructWithSeekTrait) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// StructWithSeekMethod does not implement std::io::Seek;
+fn seek_to_start_false_trait_bound<T: MySeekTrait>(t: &mut T) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should trigger clippy warning
+fn seek_to_start<T: Seek>(t: &mut T) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should trigger clippy warning
+fn owned_seek_to_start<T: Seek>(mut t: T) {
+    t.seek(SeekFrom::Start(0));
+}
+
+// This should NOT trigger clippy warning because
+// it does not seek to start
+fn seek_to_5<T: Seek>(t: &mut T) {
+    t.seek(SeekFrom::Start(5));
+}
+
+// This should NOT trigger clippy warning because
+// it does not seek to start
+fn seek_to_end<T: Seek>(t: &mut T) {
+    t.seek(SeekFrom::End(0));
+}
+
+fn main() {
+    let mut f = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .create(true)
+        .open("foo.txt")
+        .unwrap();
+
+    let mut my_struct_trait = StructWithSeekTrait {};
+    seek_to_start_false_trait_bound(&mut my_struct_trait);
+
+    let hello = "Hello!\n";
+    write!(f, "{hello}").unwrap();
+    seek_to_5(&mut f);
+    seek_to_end(&mut f);
+    seek_to_start(&mut f);
+
+    let mut buf = String::new();
+    f.read_to_string(&mut buf).unwrap();
+
+    assert_eq!(&buf, hello);
+}
+
+fn msrv_1_54() {
+    #![clippy::msrv = "1.54"]
+
+    let mut f = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .create(true)
+        .open("foo.txt")
+        .unwrap();
+
+    let hello = "Hello!\n";
+    write!(f, "{hello}").unwrap();
+
+    f.seek(SeekFrom::Start(0));
+
+    let mut buf = String::new();
+    f.read_to_string(&mut buf).unwrap();
+
+    assert_eq!(&buf, hello);
+}
+
+fn msrv_1_55() {
+    #![clippy::msrv = "1.55"]
+
+    let mut f = OpenOptions::new()
+        .write(true)
+        .read(true)
+        .create(true)
+        .open("foo.txt")
+        .unwrap();
+
+    let hello = "Hello!\n";
+    write!(f, "{hello}").unwrap();
+
+    f.seek(SeekFrom::Start(0));
+
+    let mut buf = String::new();
+    f.read_to_string(&mut buf).unwrap();
+
+    assert_eq!(&buf, hello);
+}
diff --git a/tests/ui/seek_to_start_instead_of_rewind.stderr b/tests/ui/seek_to_start_instead_of_rewind.stderr
new file mode 100644
index 00000000000..de0eec5d909
--- /dev/null
+++ b/tests/ui/seek_to_start_instead_of_rewind.stderr
@@ -0,0 +1,22 @@
+error: used `seek` to go to the start of the stream
+  --> $DIR/seek_to_start_instead_of_rewind.rs:54:7
+   |
+LL |     t.seek(SeekFrom::Start(0));
+   |       ^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `rewind()`
+   |
+   = note: `-D clippy::seek-to-start-instead-of-rewind` implied by `-D warnings`
+
+error: used `seek` to go to the start of the stream
+  --> $DIR/seek_to_start_instead_of_rewind.rs:59:7
+   |
+LL |     t.seek(SeekFrom::Start(0));
+   |       ^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `rewind()`
+
+error: used `seek` to go to the start of the stream
+  --> $DIR/seek_to_start_instead_of_rewind.rs:131:7
+   |
+LL |     f.seek(SeekFrom::Start(0));
+   |       ^^^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `rewind()`
+
+error: aborting due to 3 previous errors
+