fix(collapsible{,_else}_if): respect #[expect] on inner if (#15647)

Fixes https://github.com/rust-lang/rust-clippy/issues/13365

Pretty much the exact approach described in
https://github.com/rust-lang/rust-clippy/issues/13365#issuecomment-2344850167,
thank you @Jarcho!
r? @Jarcho

changelog: [`collapsible_if`]: respect `#[expect]` on inner `if`
changelog: [`collapsible_else_if`]: respect `#[expect]` on inner `if`

clippy_lints/src/collapsible_if.rs

@@ -1,16 +1,16 @@
 use clippy_config::Conf;
-use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::diagnostics::span_lint_hir_and_then;
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::{IntoSpan as _, SpanRangeExt, snippet, snippet_block_with_applicability};
-use clippy_utils::{span_contains_non_whitespace, tokenize_with_text};
-use rustc_ast::BinOpKind;
+use clippy_utils::{span_contains_non_whitespace, sym, tokenize_with_text};
+use rustc_ast::{BinOpKind, MetaItemInner};
 use rustc_errors::Applicability;
 use rustc_hir::{Block, Expr, ExprKind, StmtKind};
 use rustc_lexer::TokenKind;
-use rustc_lint::{LateContext, LateLintPass};
+use rustc_lint::{LateContext, LateLintPass, Level};
 use rustc_session::impl_lint_pass;
 use rustc_span::source_map::SourceMap;
-use rustc_span::{BytePos, Span};
+use rustc_span::{BytePos, Span, Symbol};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -95,14 +95,14 @@ impl CollapsibleIf {
 
     fn check_collapsible_else_if(&self, cx: &LateContext<'_>, then_span: Span, else_block: &Block<'_>) {
         if let Some(else_) = expr_block(else_block)
-            && cx.tcx.hir_attrs(else_.hir_id).is_empty()
             && !else_.span.from_expansion()
             && let ExprKind::If(else_if_cond, ..) = else_.kind
-            && !block_starts_with_significant_tokens(cx, else_block, else_, self.lint_commented_code)
+            && self.check_significant_tokens_and_expect_attrs(cx, else_block, else_, sym::collapsible_else_if)
         {
-            span_lint_and_then(
+            span_lint_hir_and_then(
                 cx,
                 COLLAPSIBLE_ELSE_IF,
+                else_.hir_id,
                 else_block.span,
                 "this `else { if .. }` block can be collapsed",
                 |diag| {
@@ -166,15 +166,15 @@ impl CollapsibleIf {
 
     fn check_collapsible_if_if(&self, cx: &LateContext<'_>, expr: &Expr<'_>, check: &Expr<'_>, then: &Block<'_>) {
         if let Some(inner) = expr_block(then)
-            && cx.tcx.hir_attrs(inner.hir_id).is_empty()
             && let ExprKind::If(check_inner, _, None) = &inner.kind
             && self.eligible_condition(cx, check_inner)
             && expr.span.eq_ctxt(inner.span)
-            && !block_starts_with_significant_tokens(cx, then, inner, self.lint_commented_code)
+            && self.check_significant_tokens_and_expect_attrs(cx, then, inner, sym::collapsible_if)
         {
-            span_lint_and_then(
+            span_lint_hir_and_then(
                 cx,
                 COLLAPSIBLE_IF,
+                inner.hir_id,
                 expr.span,
                 "this `if` statement can be collapsed",
                 |diag| {
@@ -219,6 +219,45 @@ impl CollapsibleIf {
         !matches!(cond.kind, ExprKind::Let(..))
             || (cx.tcx.sess.edition().at_least_rust_2024() && self.msrv.meets(cx, msrvs::LET_CHAINS))
     }
+
+    // Check that nothing significant can be found between the initial `{` of `inner_if` and
+    // the beginning of `inner_if_expr`...
+    //
+    // Unless it's only an `#[expect(clippy::collapsible{,_else}_if)]` attribute, in which case we
+    // _do_ need to lint, in order to actually fulfill its expectation (#13365)
+    fn check_significant_tokens_and_expect_attrs(
+        &self,
+        cx: &LateContext<'_>,
+        inner_if: &Block<'_>,
+        inner_if_expr: &Expr<'_>,
+        expected_lint_name: Symbol,
+    ) -> bool {
+        match cx.tcx.hir_attrs(inner_if_expr.hir_id) {
+            [] => {
+                // There aren't any attributes, so just check for significant tokens
+                let span = inner_if.span.split_at(1).1.until(inner_if_expr.span);
+                !span_contains_non_whitespace(cx, span, self.lint_commented_code)
+            },
+
+            [attr]
+                if matches!(Level::from_attr(attr), Some((Level::Expect, _)))
+                    && let Some(metas) = attr.meta_item_list()
+                    && let Some(MetaItemInner::MetaItem(meta_item)) = metas.first()
+                    && let [tool, lint_name] = meta_item.path.segments.as_slice()
+                    && tool.ident.name == sym::clippy
+                    && [expected_lint_name, sym::style, sym::all].contains(&lint_name.ident.name) =>
+            {
+                // There is an `expect` attribute -- check that there is no _other_ significant text
+                let span_before_attr = inner_if.span.split_at(1).1.until(attr.span());
+                let span_after_attr = attr.span().between(inner_if_expr.span);
+                !span_contains_non_whitespace(cx, span_before_attr, self.lint_commented_code)
+                    && !span_contains_non_whitespace(cx, span_after_attr, self.lint_commented_code)
+            },
+
+            // There are other attributes, which are significant tokens -- check failed
+            _ => false,
+        }
+    }
 }
 
 impl_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
@@ -242,18 +281,6 @@ impl LateLintPass<'_> for CollapsibleIf {
     }
 }
 
-// Check that nothing significant can be found but whitespaces between the initial `{` of `block`
-// and the beginning of `stop_at`.
-fn block_starts_with_significant_tokens(
-    cx: &LateContext<'_>,
-    block: &Block<'_>,
-    stop_at: &Expr<'_>,
-    lint_commented_code: bool,
-) -> bool {
-    let span = block.span.split_at(1).1.until(stop_at.span);
-    span_contains_non_whitespace(cx, span, lint_commented_code)
-}
-
 /// If `block` is a block with either one expression or a statement containing an expression,
 /// return the expression. We don't peel blocks recursively, as extra blocks might be intentional.
 fn expr_block<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {

clippy_utils/src/sym.rs

@@ -111,6 +111,8 @@ generate! {
     clone_into,
     cloned,
     cognitive_complexity,
+    collapsible_else_if,
+    collapsible_if,
     collect,
     const_ptr,
     contains,

tests/ui-toml/collapsible_if/collapsible_else_if.fixed

@@ -1,7 +1,7 @@
 #![allow(clippy::eq_op, clippy::nonminimal_bool)]
+#![warn(clippy::collapsible_if)]
 
 #[rustfmt::skip]
-#[warn(clippy::collapsible_if)]
 fn main() {
     let (x, y) = ("hello", "world");
 
@@ -48,3 +48,20 @@ fn main() {
         }
     //~^^^^^^ collapsible_else_if
 }
+
+fn issue_13365() {
+    // the comments don't stop us from linting, so the the `expect` *will* be fulfilled
+    if true {
+    } else {
+        // some other text before
+        #[expect(clippy::collapsible_else_if)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(clippy::collapsible_else_if)]
+        // some other text after
+        if false {}
+    }
+}

tests/ui-toml/collapsible_if/collapsible_else_if.rs

@@ -1,7 +1,7 @@
 #![allow(clippy::eq_op, clippy::nonminimal_bool)]
+#![warn(clippy::collapsible_if)]
 
 #[rustfmt::skip]
-#[warn(clippy::collapsible_if)]
 fn main() {
     let (x, y) = ("hello", "world");
 
@@ -53,3 +53,20 @@ fn main() {
     }
     //~^^^^^^ collapsible_else_if
 }
+
+fn issue_13365() {
+    // the comments don't stop us from linting, so the the `expect` *will* be fulfilled
+    if true {
+    } else {
+        // some other text before
+        #[expect(clippy::collapsible_else_if)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(clippy::collapsible_else_if)]
+        // some other text after
+        if false {}
+    }
+}

tests/ui/collapsible_else_if.fixed

@@ -87,6 +87,33 @@ fn issue_7318() {
     //~^^^ collapsible_else_if
 }
 
+fn issue_13365() {
+    // all the `expect`s that we should fulfill
+    if true {
+    } else {
+        #[expect(clippy::collapsible_else_if)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(clippy::style)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(clippy::all)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(warnings)]
+        if false {}
+    }
+}
+
 fn issue14799() {
     use std::ops::ControlFlow;
 

tests/ui/collapsible_else_if.rs

@@ -103,6 +103,33 @@ fn issue_7318() {
     //~^^^ collapsible_else_if
 }
 
+fn issue_13365() {
+    // all the `expect`s that we should fulfill
+    if true {
+    } else {
+        #[expect(clippy::collapsible_else_if)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(clippy::style)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(clippy::all)]
+        if false {}
+    }
+
+    if true {
+    } else {
+        #[expect(warnings)]
+        if false {}
+    }
+}
+
 fn issue14799() {
     use std::ops::ControlFlow;
 

tests/ui/collapsible_else_if.stderr

@@ -151,7 +151,7 @@ LL | |     }
    | |_____^ help: collapse nested if block: `if false {}`
 
 error: this `else { if .. }` block can be collapsed
-  --> tests/ui/collapsible_else_if.rs:130:12
+  --> tests/ui/collapsible_else_if.rs:157:12
    |
 LL |       } else {
    |  ____________^

tests/ui/collapsible_else_if_unfixable.rs

@@ -0,0 +1,22 @@
+//@no-rustfix
+#![warn(clippy::collapsible_else_if)]
+
+fn issue_13365() {
+    // in the following examples, we won't lint because of the comments,
+    // so the the `expect` will be unfulfilled
+    if true {
+    } else {
+        // some other text before
+        #[expect(clippy::collapsible_else_if)]
+        if false {}
+    }
+    //~^^^ ERROR: this lint expectation is unfulfilled
+
+    if true {
+    } else {
+        #[expect(clippy::collapsible_else_if)]
+        // some other text after
+        if false {}
+    }
+    //~^^^^ ERROR: this lint expectation is unfulfilled
+}

tests/ui/collapsible_else_if_unfixable.stderr

@@ -0,0 +1,17 @@
+error: this lint expectation is unfulfilled
+  --> tests/ui/collapsible_else_if_unfixable.rs:10:18
+   |
+LL |         #[expect(clippy::collapsible_else_if)]
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D unfulfilled-lint-expectations` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(unfulfilled_lint_expectations)]`
+
+error: this lint expectation is unfulfilled
+  --> tests/ui/collapsible_else_if_unfixable.rs:17:18
+   |
+LL |         #[expect(clippy::collapsible_else_if)]
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+

tests/ui/collapsible_if.fixed

@@ -144,6 +144,24 @@ fn layout_check() -> u32 {
     //~^^^^^ collapsible_if
 }
 
+fn issue13365() {
+    // all the `expect`s that we should fulfill
+    if true {
+        #[expect(clippy::collapsible_if)]
+        if true {}
+    }
+
+    if true {
+        #[expect(clippy::style)]
+        if true {}
+    }
+
+    if true {
+        #[expect(clippy::all)]
+        if true {}
+    }
+}
+
 fn issue14722() {
     let x = if true {
         Some(1)

tests/ui/collapsible_if.rs

@@ -154,6 +154,24 @@ fn layout_check() -> u32 {
     //~^^^^^ collapsible_if
 }
 
+fn issue13365() {
+    // all the `expect`s that we should fulfill
+    if true {
+        #[expect(clippy::collapsible_if)]
+        if true {}
+    }
+
+    if true {
+        #[expect(clippy::style)]
+        if true {}
+    }
+
+    if true {
+        #[expect(clippy::all)]
+        if true {}
+    }
+}
+
 fn issue14722() {
     let x = if true {
         Some(1)

tests/ui/collapsible_if.stderr

@@ -191,7 +191,7 @@ LL ~     ; 3
    |
 
 error: this `if` statement can be collapsed
-  --> tests/ui/collapsible_if.rs:178:5
+  --> tests/ui/collapsible_if.rs:196:5
    |
 LL | /     if true {
 LL | |         (if true {

tests/ui/collapsible_if_unfixable.rs

@@ -0,0 +1,20 @@
+//@ no-rustfix
+#![warn(clippy::collapsible_if)]
+
+fn issue13365() {
+    // in the following examples, we won't lint because of the comments,
+    // so the the `expect` will be unfulfilled
+    if true {
+        // don't collapsible because of this comment
+        #[expect(clippy::collapsible_if)]
+        if true {}
+    }
+    //~^^^ ERROR: this lint expectation is unfulfilled
+
+    if true {
+        #[expect(clippy::collapsible_if)]
+        // don't collapsible because of this comment
+        if true {}
+    }
+    //~^^^^ ERROR: this lint expectation is unfulfilled
+}

tests/ui/collapsible_if_unfixable.stderr

@@ -0,0 +1,17 @@
+error: this lint expectation is unfulfilled
+  --> tests/ui/collapsible_if_unfixable.rs:9:18
+   |
+LL |         #[expect(clippy::collapsible_if)]
+   |                  ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D unfulfilled-lint-expectations` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(unfulfilled_lint_expectations)]`
+
+error: this lint expectation is unfulfilled
+  --> tests/ui/collapsible_if_unfixable.rs:15:18
+   |
+LL |         #[expect(clippy::collapsible_if)]
+   |                  ^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+