fix: collapsible_else_if FP on conditionally compiled stmt

Author: profetia

clippy_lints/src/collapsible_if.rs

@@ -2,12 +2,13 @@ use clippy_config::Conf;
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
 use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::{IntoSpan as _, SpanRangeExt, snippet, snippet_block, snippet_block_with_applicability};
+use clippy_utils::span_contains_non_comment;
 use rustc_ast::BinOpKind;
 use rustc_errors::Applicability;
 use rustc_hir::{Block, Expr, ExprKind, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::impl_lint_pass;
-use rustc_span::Span;
+use rustc_span::{BytePos, Span};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -96,6 +97,8 @@ impl CollapsibleIf {
             && cx.tcx.hir_attrs(else_.hir_id).is_empty()
             && !else_.span.from_expansion()
             && let ExprKind::If(..) = else_.kind
+            && let up_to_if = else_block.span.until(else_.span)
+            && !span_contains_non_comment(cx, up_to_if.with_lo(BytePos(up_to_if.lo().0 + 1)))
         {
             // Prevent "elseif"
             // Check that the "else" is followed by whitespace
@@ -141,7 +144,7 @@ impl CollapsibleIf {
                     let then_open_bracket = then.span.split_at(1).0.with_leading_whitespace(cx).into_span();
                     let then_closing_bracket = {
                         let end = then.span.shrink_to_hi();
-                        end.with_lo(end.lo() - rustc_span::BytePos(1))
+                        end.with_lo(end.lo() - BytePos(1))
                             .with_leading_whitespace(cx)
                             .into_span()
                     };

clippy_utils/src/lib.rs

@@ -122,7 +122,7 @@ use rustc_span::hygiene::{ExpnKind, MacroKind};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{Ident, Symbol, kw};
 use rustc_span::{InnerSpan, Span};
-use source::walk_span_to_context;
+use source::{SpanRangeExt, walk_span_to_context};
 use visitors::{Visitable, for_each_unconsumed_temporary};
 
 use crate::consts::{ConstEvalCtxt, Constant, mir_to_const};
@@ -2788,6 +2788,16 @@ pub fn span_contains_comment(sm: &SourceMap, span: Span) -> bool {
     });
 }
 
+/// Checks whether a given span has any non-comment token. This checks for all types of token other
+/// than line comment "//", block comment "/**", doc "///" "//!" and whitespace
+/// This is useful to determine if there are any actual code tokens in the span that are omitted in
+/// the late pass, such as platform-specific code.
+pub fn span_contains_non_comment(cx: &impl source::HasSession, span: Span) -> bool {
+    matches!(span.get_source_text(cx), Some(snippet) if tokenize_with_text(&snippet).any(|(token, _, _)| {
+        !matches!(token, TokenKind::LineComment { .. } | TokenKind::BlockComment { .. } | TokenKind::Whitespace)
+    }))
+}
+
 /// Returns all the comments a given span contains
 ///
 /// Comments are returned wrapped with their relevant delimiters

tests/ui/collapsible_else_if.fixed

@@ -86,3 +86,21 @@ fn issue_7318() {
     }else if false {}
     //~^^^ collapsible_else_if
 }
+
+fn issue14799() {
+    use std::ops::ControlFlow;
+
+    let c: ControlFlow<_, ()> = ControlFlow::Break(Some(42));
+    if let ControlFlow::Break(Some(_)) = c {
+        todo!();
+    } else {
+        #[cfg(target_os = "freebsd")]
+        todo!();
+
+        if let ControlFlow::Break(None) = c {
+            todo!();
+        } else {
+            todo!();
+        }
+    }
+}

tests/ui/collapsible_else_if.rs

@@ -102,3 +102,21 @@ fn issue_7318() {
     }
     //~^^^ collapsible_else_if
 }
+
+fn issue14799() {
+    use std::ops::ControlFlow;
+
+    let c: ControlFlow<_, ()> = ControlFlow::Break(Some(42));
+    if let ControlFlow::Break(Some(_)) = c {
+        todo!();
+    } else {
+        #[cfg(target_os = "freebsd")]
+        todo!();
+
+        if let ControlFlow::Break(None) = c {
+            todo!();
+        } else {
+            todo!();
+        }
+    }
+}