From dbfbd0e77fd12a46ac81d0ec6fca4012aad0ea2d Mon Sep 17 00:00:00 2001 From: Samuel Tardieu Date: Mon, 19 Feb 2024 23:30:17 +0100 Subject: [PATCH 1/5] feat: add `const_is_empty` lint --- CHANGELOG.md | 1 + clippy_lints/src/declared_lints.rs | 1 + clippy_lints/src/methods/is_empty.rs | 40 +++++++++ clippy_lints/src/methods/mod.rs | 35 +++++++- tests/ui/const_is_empty.rs | 52 +++++++++++ tests/ui/const_is_empty.stderr | 124 +++++++++++++++++++++++++++ 6 files changed, 252 insertions(+), 1 deletion(-) create mode 100644 clippy_lints/src/methods/is_empty.rs create mode 100644 tests/ui/const_is_empty.rs create mode 100644 tests/ui/const_is_empty.stderr diff --git a/CHANGELOG.md b/CHANGELOG.md index 26dce1f92657..9182e61f6d66 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -5109,6 +5109,7 @@ Released 2018-09-13 [`collection_is_never_read`]: https://rust-lang.github.io/rust-clippy/master/index.html#collection_is_never_read [`comparison_chain`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_chain [`comparison_to_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#comparison_to_empty +[`const_is_empty`]: https://rust-lang.github.io/rust-clippy/master/index.html#const_is_empty [`const_static_lifetime`]: https://rust-lang.github.io/rust-clippy/master/index.html#const_static_lifetime [`copy_iterator`]: https://rust-lang.github.io/rust-clippy/master/index.html#copy_iterator [`crate_in_macro_def`]: https://rust-lang.github.io/rust-clippy/master/index.html#crate_in_macro_def diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs index b6a35bb3e032..fe9bc77ce556 100644 --- a/clippy_lints/src/declared_lints.rs +++ b/clippy_lints/src/declared_lints.rs @@ -350,6 +350,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[ crate::methods::CLONE_ON_COPY_INFO, crate::methods::CLONE_ON_REF_PTR_INFO, crate::methods::COLLAPSIBLE_STR_REPLACE_INFO, + crate::methods::CONST_IS_EMPTY_INFO, crate::methods::DRAIN_COLLECT_INFO, crate::methods::ERR_EXPECT_INFO, crate::methods::EXPECT_FUN_CALL_INFO, diff --git a/clippy_lints/src/methods/is_empty.rs b/clippy_lints/src/methods/is_empty.rs new file mode 100644 index 000000000000..4713c99d33b5 --- /dev/null +++ b/clippy_lints/src/methods/is_empty.rs @@ -0,0 +1,40 @@ +use clippy_utils::diagnostics::span_lint_and_note; +use clippy_utils::expr_or_init; +use rustc_ast::LitKind; +use rustc_hir::{Expr, ExprKind}; +use rustc_lint::{LateContext, LintContext}; +use rustc_middle::lint::in_external_macro; +use rustc_span::source_map::Spanned; + +use super::CONST_IS_EMPTY; + +pub(super) fn check(cx: &LateContext<'_>, expr: &'_ Expr<'_>, receiver: &Expr<'_>) { + if in_external_macro(cx.sess(), expr.span) || !receiver.span.eq_ctxt(expr.span) { + return; + } + let init_expr = expr_or_init(cx, receiver); + if let Some(init_is_empty) = is_empty(init_expr) + && init_expr.span.eq_ctxt(receiver.span) + { + span_lint_and_note( + cx, + CONST_IS_EMPTY, + expr.span, + &format!("this expression always evaluates to {init_is_empty:?}"), + Some(init_expr.span), + "because its initialization value is constant", + ); + } +} + +fn is_empty(expr: &'_ rustc_hir::Expr<'_>) -> Option { + if let ExprKind::Lit(Spanned { node, .. }) = expr.kind { + match node { + LitKind::Str(sym, _) => Some(sym.is_empty()), + LitKind::ByteStr(value, _) | LitKind::CStr(value, _) => Some(value.is_empty()), + _ => None, + } + } else { + None + } +} diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs index 820f4c858906..b6894971acc3 100644 --- a/clippy_lints/src/methods/mod.rs +++ b/clippy_lints/src/methods/mod.rs @@ -36,6 +36,7 @@ mod inefficient_to_string; mod inspect_for_each; mod into_iter_on_ref; mod is_digit_ascii_radix; +mod is_empty; mod iter_cloned_collect; mod iter_count; mod iter_filter; @@ -4041,6 +4042,31 @@ declare_clippy_lint! { "calling `.get().is_some()` or `.get().is_none()` instead of `.contains()` or `.contains_key()`" } +declare_clippy_lint! { + /// ### What it does + /// It identifies calls to `.is_empty()` on constant values. + /// + /// ### Why is this bad? + /// String literals and constant values are known at compile time. Checking if they + /// are empty will always return the same value. This might not be the intention of + /// the expression. + /// + /// ### Example + /// ```no_run + /// let value = ""; + /// if value.is_empty() { + /// println!("the string is empty"); + /// } + /// ``` + /// Use instead: + /// ```no_run + /// println!("the string is empty"); + /// ``` + #[clippy::version = "1.78.0"] + pub CONST_IS_EMPTY, + suspicious, + "is_empty() called on strings known at compile time" +} pub struct Methods { avoid_breaking_exported_api: bool, msrv: Msrv, @@ -4089,6 +4115,7 @@ impl_lint_pass!(Methods => [ CLONE_ON_COPY, CLONE_ON_REF_PTR, COLLAPSIBLE_STR_REPLACE, + CONST_IS_EMPTY, ITER_OVEREAGER_CLONED, CLONED_INSTEAD_OF_COPIED, FLAT_MAP_OPTION, @@ -4442,7 +4469,7 @@ impl Methods { ("as_deref" | "as_deref_mut", []) => { needless_option_as_deref::check(cx, expr, recv, name); }, - ("as_bytes" | "is_empty", []) => { + ("as_bytes", []) => { if let Some(("as_str", recv, [], as_str_span, _)) = method_call(recv) { redundant_as_str::check(cx, expr, recv, as_str_span, span); } @@ -4616,6 +4643,12 @@ impl Methods { ("hash", [arg]) => { unit_hash::check(cx, expr, recv, arg); }, + ("is_empty", []) => { + if let Some(("as_str", recv, [], as_str_span, _)) = method_call(recv) { + redundant_as_str::check(cx, expr, recv, as_str_span, span); + } + is_empty::check(cx, expr, recv); + }, ("is_file", []) => filetype_is_file::check(cx, expr, recv), ("is_digit", [radix]) => is_digit_ascii_radix::check(cx, expr, recv, radix, &self.msrv), ("is_none", []) => check_is_some_is_none(cx, expr, recv, call_span, false), diff --git a/tests/ui/const_is_empty.rs b/tests/ui/const_is_empty.rs new file mode 100644 index 000000000000..d61cdbb04249 --- /dev/null +++ b/tests/ui/const_is_empty.rs @@ -0,0 +1,52 @@ +#![warn(clippy::const_is_empty)] + +fn test_literal() { + if "".is_empty() { + //~^ERROR: this expression always evaluates to true + } + if "foobar".is_empty() { + //~^ERROR: this expression always evaluates to false + } +} + +fn test_byte_literal() { + if b"".is_empty() { + //~^ERROR: this expression always evaluates to true + } + if b"foobar".is_empty() { + //~^ERROR: this expression always evaluates to false + } +} + +fn test_no_mut() { + let mut empty = ""; + if empty.is_empty() { + // No lint because it is mutable + } +} + +fn test_propagated() { + let empty = ""; + let non_empty = "foobar"; + let empty2 = empty; + let non_empty2 = non_empty; + if empty2.is_empty() { + //~^ERROR: this expression always evaluates to true + } + if non_empty2.is_empty() { + //~^ERROR: this expression always evaluates to false + } +} + +fn main() { + let value = "foobar"; + let _ = value.is_empty(); + //~^ ERROR: this expression always evaluates to false + let x = value; + let _ = x.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = "".is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = b"".is_empty(); + //~^ ERROR: this expression always evaluates to true +} diff --git a/tests/ui/const_is_empty.stderr b/tests/ui/const_is_empty.stderr new file mode 100644 index 000000000000..5a89e686242d --- /dev/null +++ b/tests/ui/const_is_empty.stderr @@ -0,0 +1,124 @@ +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:4:8 + | +LL | if "".is_empty() { + | ^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:4:8 + | +LL | if "".is_empty() { + | ^^ + = note: `-D clippy::const-is-empty` implied by `-D warnings` + = help: to override `-D warnings` add `#[allow(clippy::const_is_empty)]` + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:7:8 + | +LL | if "foobar".is_empty() { + | ^^^^^^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:7:8 + | +LL | if "foobar".is_empty() { + | ^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:13:8 + | +LL | if b"".is_empty() { + | ^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:13:8 + | +LL | if b"".is_empty() { + | ^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:16:8 + | +LL | if b"foobar".is_empty() { + | ^^^^^^^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:16:8 + | +LL | if b"foobar".is_empty() { + | ^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:33:8 + | +LL | if empty2.is_empty() { + | ^^^^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:29:17 + | +LL | let empty = ""; + | ^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:36:8 + | +LL | if non_empty2.is_empty() { + | ^^^^^^^^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:30:21 + | +LL | let non_empty = "foobar"; + | ^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:43:13 + | +LL | let _ = value.is_empty(); + | ^^^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:42:17 + | +LL | let value = "foobar"; + | ^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:46:13 + | +LL | let _ = x.is_empty(); + | ^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:42:17 + | +LL | let value = "foobar"; + | ^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:48:13 + | +LL | let _ = "".is_empty(); + | ^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:48:13 + | +LL | let _ = "".is_empty(); + | ^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:50:13 + | +LL | let _ = b"".is_empty(); + | ^^^^^^^^^^^^^^ + | +note: because its initialization value is constant + --> tests/ui/const_is_empty.rs:50:13 + | +LL | let _ = b"".is_empty(); + | ^^^ + +error: aborting due to 10 previous errors + From 89b334d47cf3326af349e2a6a747e707f47bdd30 Mon Sep 17 00:00:00 2001 From: Samuel Tardieu Date: Sun, 18 Feb 2024 15:39:34 +0100 Subject: [PATCH 2/5] chore: update some tests to allow `const_is_empty` --- tests/ui/bool_assert_comparison.fixed | 2 +- tests/ui/bool_assert_comparison.rs | 2 +- tests/ui/len_zero.fixed | 8 ++++- tests/ui/len_zero.rs | 8 ++++- tests/ui/len_zero.stderr | 46 +++++++++++++-------------- tests/ui/needless_bitwise_bool.fixed | 1 + tests/ui/needless_bitwise_bool.rs | 1 + tests/ui/needless_bitwise_bool.stderr | 2 +- tests/ui/redundant_as_str.fixed | 1 + tests/ui/redundant_as_str.rs | 1 + tests/ui/redundant_as_str.stderr | 4 +-- 11 files changed, 46 insertions(+), 30 deletions(-) diff --git a/tests/ui/bool_assert_comparison.fixed b/tests/ui/bool_assert_comparison.fixed index 63b8e27e1c6c..b05166a055ee 100644 --- a/tests/ui/bool_assert_comparison.fixed +++ b/tests/ui/bool_assert_comparison.fixed @@ -1,4 +1,4 @@ -#![allow(unused, clippy::assertions_on_constants)] +#![allow(unused, clippy::assertions_on_constants, clippy::const_is_empty)] #![warn(clippy::bool_assert_comparison)] use std::ops::Not; diff --git a/tests/ui/bool_assert_comparison.rs b/tests/ui/bool_assert_comparison.rs index 58f81fedb795..dc51fcf1d36b 100644 --- a/tests/ui/bool_assert_comparison.rs +++ b/tests/ui/bool_assert_comparison.rs @@ -1,4 +1,4 @@ -#![allow(unused, clippy::assertions_on_constants)] +#![allow(unused, clippy::assertions_on_constants, clippy::const_is_empty)] #![warn(clippy::bool_assert_comparison)] use std::ops::Not; diff --git a/tests/ui/len_zero.fixed b/tests/ui/len_zero.fixed index 745fc7e1a8b3..c16d7a266161 100644 --- a/tests/ui/len_zero.fixed +++ b/tests/ui/len_zero.fixed @@ -1,5 +1,11 @@ #![warn(clippy::len_zero)] -#![allow(dead_code, unused, clippy::needless_if, clippy::len_without_is_empty)] +#![allow( + dead_code, + unused, + clippy::needless_if, + clippy::len_without_is_empty, + clippy::const_is_empty +)] extern crate core; use core::ops::Deref; diff --git a/tests/ui/len_zero.rs b/tests/ui/len_zero.rs index 048ad2f4fd34..5c49a5abf812 100644 --- a/tests/ui/len_zero.rs +++ b/tests/ui/len_zero.rs @@ -1,5 +1,11 @@ #![warn(clippy::len_zero)] -#![allow(dead_code, unused, clippy::needless_if, clippy::len_without_is_empty)] +#![allow( + dead_code, + unused, + clippy::needless_if, + clippy::len_without_is_empty, + clippy::const_is_empty +)] extern crate core; use core::ops::Deref; diff --git a/tests/ui/len_zero.stderr b/tests/ui/len_zero.stderr index b1f04c94de66..dd07a85d62ca 100644 --- a/tests/ui/len_zero.stderr +++ b/tests/ui/len_zero.stderr @@ -1,5 +1,5 @@ error: length comparison to zero - --> tests/ui/len_zero.rs:82:8 + --> tests/ui/len_zero.rs:88:8 | LL | if x.len() == 0 { | ^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `x.is_empty()` @@ -8,13 +8,13 @@ LL | if x.len() == 0 { = help: to override `-D warnings` add `#[allow(clippy::len_zero)]` error: length comparison to zero - --> tests/ui/len_zero.rs:86:8 + --> tests/ui/len_zero.rs:92:8 | LL | if "".len() == 0 {} | ^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `"".is_empty()` error: comparison to empty slice - --> tests/ui/len_zero.rs:95:20 + --> tests/ui/len_zero.rs:101:20 | LL | println!("{}", *s1 == ""); | ^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `s1.is_empty()` @@ -23,121 +23,121 @@ LL | println!("{}", *s1 == ""); = help: to override `-D warnings` add `#[allow(clippy::comparison_to_empty)]` error: comparison to empty slice - --> tests/ui/len_zero.rs:96:20 + --> tests/ui/len_zero.rs:102:20 | LL | println!("{}", **s2 == ""); | ^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `s2.is_empty()` error: comparison to empty slice - --> tests/ui/len_zero.rs:97:20 + --> tests/ui/len_zero.rs:103:20 | LL | println!("{}", ***s3 == ""); | ^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `s3.is_empty()` error: comparison to empty slice - --> tests/ui/len_zero.rs:98:20 + --> tests/ui/len_zero.rs:104:20 | LL | println!("{}", ****s4 == ""); | ^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `s4.is_empty()` error: comparison to empty slice - --> tests/ui/len_zero.rs:99:20 + --> tests/ui/len_zero.rs:105:20 | LL | println!("{}", *****s5 == ""); | ^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `s5.is_empty()` error: comparison to empty slice - --> tests/ui/len_zero.rs:100:20 + --> tests/ui/len_zero.rs:106:20 | LL | println!("{}", ******(s6) == ""); | ^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `(s6).is_empty()` error: comparison to empty slice - --> tests/ui/len_zero.rs:103:20 + --> tests/ui/len_zero.rs:109:20 | LL | println!("{}", &**d2s == ""); | ^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `(**d2s).is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:118:8 + --> tests/ui/len_zero.rs:124:8 | LL | if has_is_empty.len() == 0 { | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:121:8 + --> tests/ui/len_zero.rs:127:8 | LL | if has_is_empty.len() != 0 { | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:124:8 + --> tests/ui/len_zero.rs:130:8 | LL | if has_is_empty.len() > 0 { | ^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to one - --> tests/ui/len_zero.rs:127:8 + --> tests/ui/len_zero.rs:133:8 | LL | if has_is_empty.len() < 1 { | ^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()` error: length comparison to one - --> tests/ui/len_zero.rs:130:8 + --> tests/ui/len_zero.rs:136:8 | LL | if has_is_empty.len() >= 1 { | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:141:8 + --> tests/ui/len_zero.rs:147:8 | LL | if 0 == has_is_empty.len() { | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:144:8 + --> tests/ui/len_zero.rs:150:8 | LL | if 0 != has_is_empty.len() { | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:147:8 + --> tests/ui/len_zero.rs:153:8 | LL | if 0 < has_is_empty.len() { | ^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to one - --> tests/ui/len_zero.rs:150:8 + --> tests/ui/len_zero.rs:156:8 | LL | if 1 <= has_is_empty.len() { | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to one - --> tests/ui/len_zero.rs:153:8 + --> tests/ui/len_zero.rs:159:8 | LL | if 1 > has_is_empty.len() { | ^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:167:8 + --> tests/ui/len_zero.rs:173:8 | LL | if with_is_empty.len() == 0 { | ^^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `with_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:179:6 + --> tests/ui/len_zero.rs:185:6 | LL | (has_is_empty.len() > 0).then(|| println!("This can happen.")); | ^^^^^^^^^^^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:180:6 + --> tests/ui/len_zero.rs:186:6 | LL | (has_is_empty.len() == 0).then(|| println!("Or this!")); | ^^^^^^^^^^^^^^^^^^^^^^^ help: using `is_empty` is clearer and more explicit: `has_is_empty.is_empty()` error: length comparison to zero - --> tests/ui/len_zero.rs:184:8 + --> tests/ui/len_zero.rs:190:8 | LL | if b.len() != 0 {} | ^^^^^^^^^^^^ help: using `!is_empty` is clearer and more explicit: `!b.is_empty()` diff --git a/tests/ui/needless_bitwise_bool.fixed b/tests/ui/needless_bitwise_bool.fixed index 201f8a4c19de..a8176618c1f2 100644 --- a/tests/ui/needless_bitwise_bool.fixed +++ b/tests/ui/needless_bitwise_bool.fixed @@ -1,4 +1,5 @@ #![warn(clippy::needless_bitwise_bool)] +#![allow(clippy::const_is_empty)] fn returns_bool() -> bool { true diff --git a/tests/ui/needless_bitwise_bool.rs b/tests/ui/needless_bitwise_bool.rs index b0e5014b74b7..f190eb2b76e7 100644 --- a/tests/ui/needless_bitwise_bool.rs +++ b/tests/ui/needless_bitwise_bool.rs @@ -1,4 +1,5 @@ #![warn(clippy::needless_bitwise_bool)] +#![allow(clippy::const_is_empty)] fn returns_bool() -> bool { true diff --git a/tests/ui/needless_bitwise_bool.stderr b/tests/ui/needless_bitwise_bool.stderr index f29d4492540f..9f14646c3e5a 100644 --- a/tests/ui/needless_bitwise_bool.stderr +++ b/tests/ui/needless_bitwise_bool.stderr @@ -1,5 +1,5 @@ error: use of bitwise operator instead of lazy operator between booleans - --> tests/ui/needless_bitwise_bool.rs:22:8 + --> tests/ui/needless_bitwise_bool.rs:23:8 | LL | if y & !x { | ^^^^^^ help: try: `y && !x` diff --git a/tests/ui/redundant_as_str.fixed b/tests/ui/redundant_as_str.fixed index 4185b402226c..708a1cc91506 100644 --- a/tests/ui/redundant_as_str.fixed +++ b/tests/ui/redundant_as_str.fixed @@ -1,4 +1,5 @@ #![warn(clippy::redundant_as_str)] +#![allow(clippy::const_is_empty)] fn main() { let string = "Hello, world!".to_owned(); diff --git a/tests/ui/redundant_as_str.rs b/tests/ui/redundant_as_str.rs index 7a74d8a55ded..257af591ceff 100644 --- a/tests/ui/redundant_as_str.rs +++ b/tests/ui/redundant_as_str.rs @@ -1,4 +1,5 @@ #![warn(clippy::redundant_as_str)] +#![allow(clippy::const_is_empty)] fn main() { let string = "Hello, world!".to_owned(); diff --git a/tests/ui/redundant_as_str.stderr b/tests/ui/redundant_as_str.stderr index f086de5fedeb..f5379d701db8 100644 --- a/tests/ui/redundant_as_str.stderr +++ b/tests/ui/redundant_as_str.stderr @@ -1,5 +1,5 @@ error: this `as_str` is redundant and can be removed as the method immediately following exists on `String` too - --> tests/ui/redundant_as_str.rs:7:29 + --> tests/ui/redundant_as_str.rs:8:29 | LL | let _redundant = string.as_str().as_bytes(); | ^^^^^^^^^^^^^^^^^ help: try: `as_bytes` @@ -8,7 +8,7 @@ LL | let _redundant = string.as_str().as_bytes(); = help: to override `-D warnings` add `#[allow(clippy::redundant_as_str)]` error: this `as_str` is redundant and can be removed as the method immediately following exists on `String` too - --> tests/ui/redundant_as_str.rs:8:29 + --> tests/ui/redundant_as_str.rs:9:29 | LL | let _redundant = string.as_str().is_empty(); | ^^^^^^^^^^^^^^^^^ help: try: `is_empty` From 288497093b3bba07d8ab994913135ad6b0cccbc8 Mon Sep 17 00:00:00 2001 From: Samuel Tardieu Date: Mon, 19 Feb 2024 23:52:09 +0100 Subject: [PATCH 3/5] feat: extend `const_is_empty` with many kinds of constants --- clippy_lints/src/methods/is_empty.rs | 49 +++++---- clippy_utils/src/consts.rs | 96 +++++++++++++++-- tests/ui/const_is_empty.rs | 49 +++++++++ tests/ui/const_is_empty.stderr | 153 ++++++++++++++++----------- 4 files changed, 259 insertions(+), 88 deletions(-) diff --git a/clippy_lints/src/methods/is_empty.rs b/clippy_lints/src/methods/is_empty.rs index 4713c99d33b5..7fe66062251b 100644 --- a/clippy_lints/src/methods/is_empty.rs +++ b/clippy_lints/src/methods/is_empty.rs @@ -1,40 +1,49 @@ -use clippy_utils::diagnostics::span_lint_and_note; -use clippy_utils::expr_or_init; -use rustc_ast::LitKind; -use rustc_hir::{Expr, ExprKind}; +use clippy_utils::consts::constant_is_empty; +use clippy_utils::diagnostics::span_lint; +use clippy_utils::{find_binding_init, path_to_local}; +use rustc_hir::{Expr, HirId}; use rustc_lint::{LateContext, LintContext}; use rustc_middle::lint::in_external_macro; -use rustc_span::source_map::Spanned; +use rustc_span::sym; use super::CONST_IS_EMPTY; +/// Expression whose initialization depend on a constant conditioned by a `#[cfg(…)]` directive will +/// not trigger the lint. pub(super) fn check(cx: &LateContext<'_>, expr: &'_ Expr<'_>, receiver: &Expr<'_>) { if in_external_macro(cx.sess(), expr.span) || !receiver.span.eq_ctxt(expr.span) { return; } let init_expr = expr_or_init(cx, receiver); - if let Some(init_is_empty) = is_empty(init_expr) - && init_expr.span.eq_ctxt(receiver.span) - { - span_lint_and_note( + if !receiver.span.eq_ctxt(init_expr.span) { + return; + } + if let Some(init_is_empty) = constant_is_empty(cx, init_expr) { + span_lint( cx, CONST_IS_EMPTY, expr.span, &format!("this expression always evaluates to {init_is_empty:?}"), - Some(init_expr.span), - "because its initialization value is constant", ); } } -fn is_empty(expr: &'_ rustc_hir::Expr<'_>) -> Option { - if let ExprKind::Lit(Spanned { node, .. }) = expr.kind { - match node { - LitKind::Str(sym, _) => Some(sym.is_empty()), - LitKind::ByteStr(value, _) | LitKind::CStr(value, _) => Some(value.is_empty()), - _ => None, - } - } else { - None +fn is_under_cfg(cx: &LateContext<'_>, id: HirId) -> bool { + cx.tcx + .hir() + .parent_id_iter(id) + .any(|id| cx.tcx.hir().attrs(id).iter().any(|attr| attr.has_name(sym::cfg))) +} + +/// Similar to [`clippy_utils::expr_or_init`], but does not go up the chain if the initialization +/// value depends on a `#[cfg(…)]` directive. +fn expr_or_init<'a, 'b, 'tcx: 'b>(cx: &LateContext<'tcx>, mut expr: &'a Expr<'b>) -> &'a Expr<'b> { + while let Some(init) = path_to_local(expr) + .and_then(|id| find_binding_init(cx, id)) + .filter(|init| cx.typeck_results().expr_adjustments(init).is_empty()) + .filter(|init| !is_under_cfg(cx, init.hir_id)) + { + expr = init; } + expr } diff --git a/clippy_utils/src/consts.rs b/clippy_utils/src/consts.rs index 79c691992a85..774f3f99d46f 100644 --- a/clippy_utils/src/consts.rs +++ b/clippy_utils/src/consts.rs @@ -10,6 +10,7 @@ use rustc_hir::{BinOp, BinOpKind, Block, ConstBlock, Expr, ExprKind, HirId, Item use rustc_lexer::tokenize; use rustc_lint::LateContext; use rustc_middle::mir::interpret::{alloc_range, Scalar}; +use rustc_middle::mir::ConstValue; use rustc_middle::ty::{self, EarlyBinder, FloatTy, GenericArgsRef, IntTy, List, ScalarInt, Ty, TyCtxt, UintTy}; use rustc_middle::{bug, mir, span_bug}; use rustc_span::symbol::{Ident, Symbol}; @@ -303,6 +304,12 @@ impl ConstantSource { } } +/// Attempts to check whether the expression is a constant representing an empty slice, str, array, +/// etc… +pub fn constant_is_empty(lcx: &LateContext<'_>, e: &Expr<'_>) -> Option { + ConstEvalLateContext::new(lcx, lcx.typeck_results()).expr_is_empty(e) +} + /// Attempts to evaluate the expression as a constant. pub fn constant<'tcx>( lcx: &LateContext<'tcx>, @@ -402,7 +409,13 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> { match e.kind { ExprKind::ConstBlock(ConstBlock { body, .. }) => self.expr(self.lcx.tcx.hir().body(body).value), ExprKind::DropTemps(e) => self.expr(e), - ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id, self.typeck_results.expr_ty(e)), + ExprKind::Path(ref qpath) => { + self.fetch_path_and_apply(qpath, e.hir_id, self.typeck_results.expr_ty(e), |this, result| { + let result = mir_to_const(this.lcx, result)?; + this.source = ConstantSource::Constant; + Some(result) + }) + }, ExprKind::Block(block, _) => self.block(block), ExprKind::Lit(lit) => { if is_direct_expn_of(e.span, "cfg").is_some() { @@ -468,6 +481,39 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> { } } + /// Simple constant folding to determine if an expression is an empty slice, str, array, … + pub fn expr_is_empty(&mut self, e: &Expr<'_>) -> Option { + match e.kind { + ExprKind::ConstBlock(ConstBlock { body, .. }) => self.expr_is_empty(self.lcx.tcx.hir().body(body).value), + ExprKind::DropTemps(e) => self.expr_is_empty(e), + ExprKind::Path(ref qpath) => { + self.fetch_path_and_apply(qpath, e.hir_id, self.typeck_results.expr_ty(e), |this, result| { + mir_is_empty(this.lcx, result) + }) + }, + ExprKind::Lit(lit) => { + if is_direct_expn_of(e.span, "cfg").is_some() { + None + } else { + match &lit.node { + LitKind::Str(is, _) => Some(is.is_empty()), + LitKind::ByteStr(s, _) | LitKind::CStr(s, _) => Some(s.is_empty()), + _ => None, + } + } + }, + ExprKind::Array(vec) => self.multi(vec).map(|v| v.is_empty()), + ExprKind::Repeat(..) => { + if let ty::Array(_, n) = self.typeck_results.expr_ty(e).kind() { + Some(n.try_eval_target_usize(self.lcx.tcx, self.lcx.param_env)? == 0) + } else { + span_bug!(e.span, "typeck error"); + } + }, + _ => None, + } + } + #[expect(clippy::cast_possible_wrap)] fn constant_not(&self, o: &Constant<'tcx>, ty: Ty<'_>) -> Option> { use self::Constant::{Bool, Int}; @@ -515,8 +561,11 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> { vec.iter().map(|elem| self.expr(elem)).collect::>() } - /// Lookup a possibly constant expression from an `ExprKind::Path`. - fn fetch_path(&mut self, qpath: &QPath<'_>, id: HirId, ty: Ty<'tcx>) -> Option> { + /// Lookup a possibly constant expression from an `ExprKind::Path` and apply a function on it. + fn fetch_path_and_apply(&mut self, qpath: &QPath<'_>, id: HirId, ty: Ty<'tcx>, f: F) -> Option + where + F: FnOnce(&mut Self, rustc_middle::mir::Const<'tcx>) -> Option, + { let res = self.typeck_results.qpath_res(qpath, id); match res { Res::Def(DefKind::Const | DefKind::AssocConst, def_id) => { @@ -549,9 +598,7 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> { .const_eval_resolve(self.param_env, mir::UnevaluatedConst::new(def_id, args), None) .ok() .map(|val| rustc_middle::mir::Const::from_value(val, ty))?; - let result = mir_to_const(self.lcx, result)?; - self.source = ConstantSource::Constant; - Some(result) + f(self, result) }, _ => None, } @@ -742,7 +789,6 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> { } pub fn mir_to_const<'tcx>(lcx: &LateContext<'tcx>, result: mir::Const<'tcx>) -> Option> { - use rustc_middle::mir::ConstValue; let mir::Const::Val(val, _) = result else { // We only work on evaluated consts. return None; @@ -788,6 +834,42 @@ pub fn mir_to_const<'tcx>(lcx: &LateContext<'tcx>, result: mir::Const<'tcx>) -> } } +fn mir_is_empty<'tcx>(lcx: &LateContext<'tcx>, result: mir::Const<'tcx>) -> Option { + let mir::Const::Val(val, _) = result else { + // We only work on evaluated consts. + return None; + }; + match (val, result.ty().kind()) { + (_, ty::Ref(_, inner_ty, _)) => match inner_ty.kind() { + ty::Str | ty::Slice(_) => { + if let ConstValue::Indirect { alloc_id, offset } = val { + // Get the length from the slice, using the same formula as + // [`ConstValue::try_get_slice_bytes_for_diagnostics`]. + let a = lcx.tcx.global_alloc(alloc_id).unwrap_memory().inner(); + let ptr_size = lcx.tcx.data_layout.pointer_size; + if a.size() < offset + 2 * ptr_size { + // (partially) dangling reference + return None; + } + let len = a + .read_scalar(&lcx.tcx, alloc_range(offset + ptr_size, ptr_size), false) + .ok()? + .to_target_usize(&lcx.tcx) + .ok()?; + Some(len == 0) + } else { + None + } + }, + ty::Array(_, len) => Some(len.try_to_target_usize(lcx.tcx)? == 0), + _ => None, + }, + (ConstValue::Indirect { .. }, ty::Array(_, len)) => Some(len.try_to_target_usize(lcx.tcx)? == 0), + (ConstValue::ZeroSized, _) => Some(true), + _ => None, + } +} + fn field_of_struct<'tcx>( adt_def: ty::AdtDef<'tcx>, lcx: &LateContext<'tcx>, diff --git a/tests/ui/const_is_empty.rs b/tests/ui/const_is_empty.rs index d61cdbb04249..bd7e3a7c5d5b 100644 --- a/tests/ui/const_is_empty.rs +++ b/tests/ui/const_is_empty.rs @@ -38,6 +38,55 @@ fn test_propagated() { } } +const EMPTY_STR: &str = ""; +const NON_EMPTY_STR: &str = "foo"; +const EMPTY_BSTR: &[u8] = b""; +const NON_EMPTY_BSTR: &[u8] = b"foo"; +const EMPTY_U8_SLICE: &[u8] = &[]; +const NON_EMPTY_U8_SLICE: &[u8] = &[1, 2]; +const EMPTY_SLICE: &[u32] = &[]; +const NON_EMPTY_SLICE: &[u32] = &[1, 2]; +const NON_EMPTY_SLICE_REPEAT: &[u32] = &[1; 2]; +const EMPTY_ARRAY: [u32; 0] = []; +const EMPTY_ARRAY_REPEAT: [u32; 0] = [1; 0]; +const NON_EMPTY_ARRAY: [u32; 2] = [1, 2]; +const NON_EMPTY_ARRAY_REPEAT: [u32; 2] = [1; 2]; +const EMPTY_REF_ARRAY: &[u32; 0] = &[]; +const NON_EMPTY_REF_ARRAY: &[u32; 3] = &[1, 2, 3]; + +fn test_from_const() { + let _ = EMPTY_STR.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = NON_EMPTY_STR.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = EMPTY_BSTR.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = NON_EMPTY_BSTR.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = EMPTY_ARRAY.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = EMPTY_ARRAY_REPEAT.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = EMPTY_U8_SLICE.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = NON_EMPTY_U8_SLICE.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = NON_EMPTY_ARRAY.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = NON_EMPTY_ARRAY_REPEAT.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = EMPTY_REF_ARRAY.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = NON_EMPTY_REF_ARRAY.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = EMPTY_SLICE.is_empty(); + //~^ ERROR: this expression always evaluates to true + let _ = NON_EMPTY_SLICE.is_empty(); + //~^ ERROR: this expression always evaluates to false + let _ = NON_EMPTY_SLICE_REPEAT.is_empty(); + //~^ ERROR: this expression always evaluates to false +} + fn main() { let value = "foobar"; let _ = value.is_empty(); diff --git a/tests/ui/const_is_empty.stderr b/tests/ui/const_is_empty.stderr index 5a89e686242d..ef5aa556e6a0 100644 --- a/tests/ui/const_is_empty.stderr +++ b/tests/ui/const_is_empty.stderr @@ -4,11 +4,6 @@ error: this expression always evaluates to true LL | if "".is_empty() { | ^^^^^^^^^^^^^ | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:4:8 - | -LL | if "".is_empty() { - | ^^ = note: `-D clippy::const-is-empty` implied by `-D warnings` = help: to override `-D warnings` add `#[allow(clippy::const_is_empty)]` @@ -17,108 +12,144 @@ error: this expression always evaluates to false | LL | if "foobar".is_empty() { | ^^^^^^^^^^^^^^^^^^^ - | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:7:8 - | -LL | if "foobar".is_empty() { - | ^^^^^^^^ error: this expression always evaluates to true --> tests/ui/const_is_empty.rs:13:8 | LL | if b"".is_empty() { | ^^^^^^^^^^^^^^ - | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:13:8 - | -LL | if b"".is_empty() { - | ^^^ error: this expression always evaluates to false --> tests/ui/const_is_empty.rs:16:8 | LL | if b"foobar".is_empty() { | ^^^^^^^^^^^^^^^^^^^^ - | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:16:8 - | -LL | if b"foobar".is_empty() { - | ^^^^^^^^^ error: this expression always evaluates to true --> tests/ui/const_is_empty.rs:33:8 | LL | if empty2.is_empty() { | ^^^^^^^^^^^^^^^^^ - | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:29:17 - | -LL | let empty = ""; - | ^^ error: this expression always evaluates to false --> tests/ui/const_is_empty.rs:36:8 | LL | if non_empty2.is_empty() { | ^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:58:13 | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:30:21 +LL | let _ = EMPTY_STR.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:60:13 | -LL | let non_empty = "foobar"; - | ^^^^^^^^ +LL | let _ = NON_EMPTY_STR.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:62:13 + | +LL | let _ = EMPTY_BSTR.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:43:13 + --> tests/ui/const_is_empty.rs:64:13 | -LL | let _ = value.is_empty(); - | ^^^^^^^^^^^^^^^^ +LL | let _ = NON_EMPTY_BSTR.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:66:13 + | +LL | let _ = EMPTY_ARRAY.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:68:13 | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:42:17 +LL | let _ = EMPTY_ARRAY_REPEAT.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:70:13 | -LL | let value = "foobar"; - | ^^^^^^^^ +LL | let _ = EMPTY_U8_SLICE.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:46:13 + --> tests/ui/const_is_empty.rs:72:13 | -LL | let _ = x.is_empty(); - | ^^^^^^^^^^^^ +LL | let _ = NON_EMPTY_U8_SLICE.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:74:13 | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:42:17 +LL | let _ = NON_EMPTY_ARRAY.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:76:13 | -LL | let value = "foobar"; - | ^^^^^^^^ +LL | let _ = NON_EMPTY_ARRAY_REPEAT.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:48:13 + --> tests/ui/const_is_empty.rs:78:13 | -LL | let _ = "".is_empty(); - | ^^^^^^^^^^^^^ +LL | let _ = EMPTY_REF_ARRAY.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:80:13 + | +LL | let _ = NON_EMPTY_REF_ARRAY.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:82:13 + | +LL | let _ = EMPTY_SLICE.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:84:13 + | +LL | let _ = NON_EMPTY_SLICE.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:86:13 | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:48:13 +LL | let _ = NON_EMPTY_SLICE_REPEAT.is_empty(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:92:13 + | +LL | let _ = value.is_empty(); + | ^^^^^^^^^^^^^^^^ + +error: this expression always evaluates to false + --> tests/ui/const_is_empty.rs:95:13 + | +LL | let _ = x.is_empty(); + | ^^^^^^^^^^^^ + +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:97:13 | LL | let _ = "".is_empty(); - | ^^ + | ^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:50:13 + --> tests/ui/const_is_empty.rs:99:13 | LL | let _ = b"".is_empty(); | ^^^^^^^^^^^^^^ - | -note: because its initialization value is constant - --> tests/ui/const_is_empty.rs:50:13 - | -LL | let _ = b"".is_empty(); - | ^^^ -error: aborting due to 10 previous errors +error: aborting due to 25 previous errors From 1159e2c00fdc97dede1dca0464d57750283ac3df Mon Sep 17 00:00:00 2001 From: Samuel Tardieu Date: Tue, 20 Feb 2024 00:05:59 +0100 Subject: [PATCH 4/5] feat: add more tests for the `const_is_empty` lint Suggested by @xFredNet and @matthiaskrgr. --- tests/ui/const_is_empty.rs | 68 ++++++++++++++++++++++++++++++++++ tests/ui/const_is_empty.stderr | 58 ++++++++++++++++------------- 2 files changed, 100 insertions(+), 26 deletions(-) diff --git a/tests/ui/const_is_empty.rs b/tests/ui/const_is_empty.rs index bd7e3a7c5d5b..df7817e4b5fe 100644 --- a/tests/ui/const_is_empty.rs +++ b/tests/ui/const_is_empty.rs @@ -1,4 +1,6 @@ +#![feature(inline_const)] #![warn(clippy::const_is_empty)] +#![allow(clippy::needless_late_init, unused_must_use)] fn test_literal() { if "".is_empty() { @@ -99,3 +101,69 @@ fn main() { let _ = b"".is_empty(); //~^ ERROR: this expression always evaluates to true } + +fn str_from_arg(var: &str) { + var.is_empty(); + // Do not lint, we know nothiny about var +} + +fn update_str() { + let mut value = "duck"; + value = "penguin"; + + let _ = value.is_empty(); + // Do not lint since value is mutable +} + +fn macros() { + // Content from Macro + let file = include_str!("const_is_empty.rs"); + let _ = file.is_empty(); + // No lint because initializer comes from a macro result + + let var = env!("PATH"); + let _ = var.is_empty(); + // No lint because initializer comes from a macro result +} + +fn conditional_value() { + let value; + + if true { + value = "hey"; + } else { + value = "hej"; + } + + let _ = value.is_empty(); + // Do not lint, current constant folding is too simple to detect this +} + +fn cfg_conditioned() { + #[cfg(test)] + let val = ""; + #[cfg(not(test))] + let val = "foo"; + + let _ = val.is_empty(); + // Do not lint, value depend on a #[cfg(…)] directive +} + +fn not_cfg_conditioned() { + let val = ""; + #[cfg(not(target_os = "inexistent"))] + let _ = val.is_empty(); + //~^ ERROR: this expression always evaluates to true +} + +const fn const_rand() -> &'static str { + "17" +} + +fn const_expressions() { + let _ = const { if true { "1" } else { "2" } }.is_empty(); + // Do not lint, we do not recurse into boolean expressions + + let _ = const_rand().is_empty(); + // Do not lint, we do not recurse into functions +} diff --git a/tests/ui/const_is_empty.stderr b/tests/ui/const_is_empty.stderr index ef5aa556e6a0..0e09da77bb46 100644 --- a/tests/ui/const_is_empty.stderr +++ b/tests/ui/const_is_empty.stderr @@ -1,5 +1,5 @@ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:4:8 + --> tests/ui/const_is_empty.rs:6:8 | LL | if "".is_empty() { | ^^^^^^^^^^^^^ @@ -8,148 +8,154 @@ LL | if "".is_empty() { = help: to override `-D warnings` add `#[allow(clippy::const_is_empty)]` error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:7:8 + --> tests/ui/const_is_empty.rs:9:8 | LL | if "foobar".is_empty() { | ^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:13:8 + --> tests/ui/const_is_empty.rs:15:8 | LL | if b"".is_empty() { | ^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:16:8 + --> tests/ui/const_is_empty.rs:18:8 | LL | if b"foobar".is_empty() { | ^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:33:8 + --> tests/ui/const_is_empty.rs:35:8 | LL | if empty2.is_empty() { | ^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:36:8 + --> tests/ui/const_is_empty.rs:38:8 | LL | if non_empty2.is_empty() { | ^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:58:13 + --> tests/ui/const_is_empty.rs:60:13 | LL | let _ = EMPTY_STR.is_empty(); | ^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:60:13 + --> tests/ui/const_is_empty.rs:62:13 | LL | let _ = NON_EMPTY_STR.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:62:13 + --> tests/ui/const_is_empty.rs:64:13 | LL | let _ = EMPTY_BSTR.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:64:13 + --> tests/ui/const_is_empty.rs:66:13 | LL | let _ = NON_EMPTY_BSTR.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:66:13 + --> tests/ui/const_is_empty.rs:68:13 | LL | let _ = EMPTY_ARRAY.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:68:13 + --> tests/ui/const_is_empty.rs:70:13 | LL | let _ = EMPTY_ARRAY_REPEAT.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:70:13 + --> tests/ui/const_is_empty.rs:72:13 | LL | let _ = EMPTY_U8_SLICE.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:72:13 + --> tests/ui/const_is_empty.rs:74:13 | LL | let _ = NON_EMPTY_U8_SLICE.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:74:13 + --> tests/ui/const_is_empty.rs:76:13 | LL | let _ = NON_EMPTY_ARRAY.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:76:13 + --> tests/ui/const_is_empty.rs:78:13 | LL | let _ = NON_EMPTY_ARRAY_REPEAT.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:78:13 + --> tests/ui/const_is_empty.rs:80:13 | LL | let _ = EMPTY_REF_ARRAY.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:80:13 + --> tests/ui/const_is_empty.rs:82:13 | LL | let _ = NON_EMPTY_REF_ARRAY.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:82:13 + --> tests/ui/const_is_empty.rs:84:13 | LL | let _ = EMPTY_SLICE.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:84:13 + --> tests/ui/const_is_empty.rs:86:13 | LL | let _ = NON_EMPTY_SLICE.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:86:13 + --> tests/ui/const_is_empty.rs:88:13 | LL | let _ = NON_EMPTY_SLICE_REPEAT.is_empty(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:92:13 + --> tests/ui/const_is_empty.rs:94:13 | LL | let _ = value.is_empty(); | ^^^^^^^^^^^^^^^^ error: this expression always evaluates to false - --> tests/ui/const_is_empty.rs:95:13 + --> tests/ui/const_is_empty.rs:97:13 | LL | let _ = x.is_empty(); | ^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:97:13 + --> tests/ui/const_is_empty.rs:99:13 | LL | let _ = "".is_empty(); | ^^^^^^^^^^^^^ error: this expression always evaluates to true - --> tests/ui/const_is_empty.rs:99:13 + --> tests/ui/const_is_empty.rs:101:13 | LL | let _ = b"".is_empty(); | ^^^^^^^^^^^^^^ -error: aborting due to 25 previous errors +error: this expression always evaluates to true + --> tests/ui/const_is_empty.rs:155:13 + | +LL | let _ = val.is_empty(); + | ^^^^^^^^^^^^^^ + +error: aborting due to 26 previous errors From 898ed8825d610d4f441ccb7c84c770261ce45ded Mon Sep 17 00:00:00 2001 From: Samuel Tardieu Date: Mon, 26 Feb 2024 09:47:13 +0100 Subject: [PATCH 5/5] feat: make `const_is_empty` lint ignore external constants --- clippy_utils/src/consts.rs | 11 +++++++++++ tests/ui/const_is_empty.rs | 5 +++++ 2 files changed, 16 insertions(+) diff --git a/clippy_utils/src/consts.rs b/clippy_utils/src/consts.rs index 774f3f99d46f..a4cb4ee93caa 100644 --- a/clippy_utils/src/consts.rs +++ b/clippy_utils/src/consts.rs @@ -13,6 +13,7 @@ use rustc_middle::mir::interpret::{alloc_range, Scalar}; use rustc_middle::mir::ConstValue; use rustc_middle::ty::{self, EarlyBinder, FloatTy, GenericArgsRef, IntTy, List, ScalarInt, Ty, TyCtxt, UintTy}; use rustc_middle::{bug, mir, span_bug}; +use rustc_span::def_id::DefId; use rustc_span::symbol::{Ident, Symbol}; use rustc_span::SyntaxContext; use rustc_target::abi::Size; @@ -482,11 +483,21 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> { } /// Simple constant folding to determine if an expression is an empty slice, str, array, … + /// `None` will be returned if the constness cannot be determined, or if the resolution + /// leaves the local crate. pub fn expr_is_empty(&mut self, e: &Expr<'_>) -> Option { match e.kind { ExprKind::ConstBlock(ConstBlock { body, .. }) => self.expr_is_empty(self.lcx.tcx.hir().body(body).value), ExprKind::DropTemps(e) => self.expr_is_empty(e), ExprKind::Path(ref qpath) => { + if !self + .typeck_results + .qpath_res(qpath, e.hir_id) + .opt_def_id() + .is_some_and(DefId::is_local) + { + return None; + } self.fetch_path_and_apply(qpath, e.hir_id, self.typeck_results.expr_ty(e), |this, result| { mir_is_empty(this.lcx, result) }) diff --git a/tests/ui/const_is_empty.rs b/tests/ui/const_is_empty.rs index df7817e4b5fe..ae37a82e4f93 100644 --- a/tests/ui/const_is_empty.rs +++ b/tests/ui/const_is_empty.rs @@ -167,3 +167,8 @@ fn const_expressions() { let _ = const_rand().is_empty(); // Do not lint, we do not recurse into functions } + +fn constant_from_external_crate() { + let _ = std::env::consts::EXE_EXTENSION.is_empty(); + // Do not lint, `exe_ext` comes from the `std` crate +}