Move VerboseFileReads into Methods lint pass

Author: Jarcho

clippy_lints/src/lib.register_lints.rs

@@ -370,6 +370,7 @@ store.register_lints(&[
     methods::UNWRAP_USED,
     methods::USELESS_ASREF,
     methods::VEC_RESIZE_TO_ZERO,
+    methods::VERBOSE_FILE_READS,
     methods::WRONG_SELF_CONVENTION,
     methods::ZST_OFFSET,
     minmax::MIN_MAX,
@@ -564,7 +565,6 @@ store.register_lints(&[
     useless_conversion::USELESS_CONVERSION,
     vec::USELESS_VEC,
     vec_init_then_push::VEC_INIT_THEN_PUSH,
-    verbose_file_reads::VERBOSE_FILE_READS,
     wildcard_imports::ENUM_GLOB_USE,
     wildcard_imports::WILDCARD_IMPORTS,
     write::PRINTLN_EMPTY_STRING,

clippy_lints/src/lib.register_restriction.rs

@@ -39,6 +39,7 @@ store.register_group(true, "clippy::restriction", Some("clippy_restriction"), ve
     LintId::of(methods::GET_UNWRAP),
     LintId::of(methods::MAP_ERR_IGNORE),
     LintId::of(methods::UNWRAP_USED),
+    LintId::of(methods::VERBOSE_FILE_READS),
     LintId::of(misc::FLOAT_CMP_CONST),
     LintId::of(misc_early::SEPARATED_LITERAL_SUFFIX),
     LintId::of(misc_early::UNNEEDED_FIELD_PATTERN),
@@ -75,7 +76,6 @@ store.register_group(true, "clippy::restriction", Some("clippy_restriction"), ve
     LintId::of(unicode::NON_ASCII_LITERAL),
     LintId::of(unnecessary_self_imports::UNNECESSARY_SELF_IMPORTS),
     LintId::of(unwrap_in_result::UNWRAP_IN_RESULT),
-    LintId::of(verbose_file_reads::VERBOSE_FILE_READS),
     LintId::of(write::PRINT_STDERR),
     LintId::of(write::PRINT_STDOUT),
     LintId::of(write::USE_DEBUG),

clippy_lints/src/lib.rs

@@ -394,7 +394,6 @@ mod use_self;
 mod useless_conversion;
 mod vec;
 mod vec_init_then_push;
-mod verbose_file_reads;
 mod wildcard_imports;
 mod write;
 mod zero_div_zero;
@@ -773,7 +772,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_early_pass(|| Box::new(option_env_unwrap::OptionEnvUnwrap));
     let warn_on_all_wildcard_imports = conf.warn_on_all_wildcard_imports;
     store.register_late_pass(move || Box::new(wildcard_imports::WildcardImports::new(warn_on_all_wildcard_imports)));
-    store.register_late_pass(|| Box::new(verbose_file_reads::VerboseFileReads));
     store.register_late_pass(|| Box::new(redundant_pub_crate::RedundantPubCrate::default()));
     store.register_late_pass(|| Box::new(unnamed_address::UnnamedAddress));
     store.register_late_pass(|| Box::new(dereference::Dereferencing::default()));

clippy_lints/src/methods/mod.rs

@@ -89,6 +89,7 @@ mod unwrap_used;
 mod useless_asref;
 mod utils;
 mod vec_resize_to_zero;
+mod verbose_file_reads;
 mod wrong_self_convention;
 mod zst_offset;
 
@@ -2783,6 +2784,33 @@ declare_clippy_lint! {
     "emptying a vector with `resize(0, an_int)` instead of `clear()` is probably an argument inversion mistake"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for use of File::read_to_end and File::read_to_string.
+    ///
+    /// ### Why is this bad?
+    /// `fs::{read, read_to_string}` provide the same functionality when `buf` is empty with fewer imports and no intermediate values.
+    /// See also: [fs::read docs](https://doc.rust-lang.org/std/fs/fn.read.html), [fs::read_to_string docs](https://doc.rust-lang.org/std/fs/fn.read_to_string.html)
+    ///
+    /// ### Example
+    /// ```rust,no_run
+    /// # use std::io::Read;
+    /// # use std::fs::File;
+    /// let mut f = File::open("foo.txt").unwrap();
+    /// let mut bytes = Vec::new();
+    /// f.read_to_end(&mut bytes).unwrap();
+    /// ```
+    /// Can be written more concisely as
+    /// ```rust,no_run
+    /// # use std::fs;
+    /// let mut bytes = fs::read("foo.txt").unwrap();
+    /// ```
+    #[clippy::version = "1.44.0"]
+    pub VERBOSE_FILE_READS,
+    restriction,
+    "use of `File::read_to_end` or `File::read_to_string`"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Option<RustcVersion>,
@@ -2900,6 +2928,7 @@ impl_lint_pass!(Methods => [
     UNIT_HASH,
     UNNECESSARY_SORT_BY,
     VEC_RESIZE_TO_ZERO,
+    VERBOSE_FILE_READS,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -3287,6 +3316,12 @@ impl Methods {
                 ("push", [arg]) => {
                     path_buf_push_overwrite::check(cx, expr, arg);
                 },
+                ("read_to_end", []) => {
+                    verbose_file_reads::check(cx, expr, recv, verbose_file_reads::READ_TO_END_MSG);
+                },
+                ("read_to_string", []) => {
+                    verbose_file_reads::check(cx, expr, recv, verbose_file_reads::READ_TO_STRING_MSG);
+                },
                 ("repeat", [arg]) => {
                     repeat_once::check(cx, expr, recv, arg);
                 },

clippy_lints/src/methods/verbose_file_reads.rs

@@ -0,0 +1,28 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::is_trait_method;
+use clippy_utils::ty::is_type_diagnostic_item;
+use rustc_hir::{Expr, ExprKind, QPath};
+use rustc_lint::LateContext;
+use rustc_span::sym;
+
+use super::VERBOSE_FILE_READS;
+
+pub(super) const READ_TO_END_MSG: (&str, &str) = ("use of `File::read_to_end`", "consider using `fs::read` instead");
+pub(super) const READ_TO_STRING_MSG: (&str, &str) = (
+    "use of `File::read_to_string`",
+    "consider using `fs::read_to_string` instead",
+);
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    recv: &'tcx Expr<'_>,
+    (msg, help): (&str, &str),
+) {
+    if is_trait_method(cx, expr, sym::IoRead)
+        && matches!(recv.kind, ExprKind::Path(QPath::Resolved(None, _)))
+        && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty_adjusted(recv).peel_refs(), sym::File)
+    {
+        span_lint_and_help(cx, VERBOSE_FILE_READS, expr.span, msg, None, help);
+    }
+}