From 7192297c2878b22e44ca5bc58f5f7544b33cdf4a Mon Sep 17 00:00:00 2001
From: Max Baumann <max@bmn.dev>
Date: Sun, 27 Mar 2022 19:58:23 +0200
Subject: [PATCH] additional checks for conditionally compiled code

---
 clippy_lints/src/unit_like_struct_brackets.rs | 56 +++++++++++++++++--
 tests/ui/unit_like_struct_brackets.fixed      | 11 +++-
 tests/ui/unit_like_struct_brackets.rs         | 11 +++-
 3 files changed, 70 insertions(+), 8 deletions(-)

diff --git a/clippy_lints/src/unit_like_struct_brackets.rs b/clippy_lints/src/unit_like_struct_brackets.rs
index c4623df46bda..cb6e2a44afbe 100644
--- a/clippy_lints/src/unit_like_struct_brackets.rs
+++ b/clippy_lints/src/unit_like_struct_brackets.rs
@@ -1,8 +1,10 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::{diagnostics::span_lint_and_sugg, source::snippet_opt};
 use rustc_ast::ast::{Item, ItemKind, VariantData};
 use rustc_errors::Applicability;
+use rustc_lexer::TokenKind;
 use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::Span;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -28,9 +30,9 @@ declare_lint_pass!(UnitLikeStructBrackets => [UNIT_LIKE_STRUCT_BRACKETS]);
 
 impl EarlyLintPass for UnitLikeStructBrackets {
     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
-        if let ItemKind::Struct(var_data, _) = &item.kind && has_no_fields(var_data) {
-            let span_after_ident = item.span.with_lo(item.ident.span.hi());
+        let span_after_ident = item.span.with_lo(item.ident.span.hi());
 
+        if let ItemKind::Struct(var_data, _) = &item.kind && has_no_fields(cx, var_data, span_after_ident) {
             span_lint_and_sugg(
                 cx,
                 UNIT_LIKE_STRUCT_BRACKETS,
@@ -44,9 +46,51 @@ impl EarlyLintPass for UnitLikeStructBrackets {
     }
 }
 
-fn has_no_fields(var_data: &VariantData) -> bool {
+fn has_fields_in_hir(var_data: &VariantData) -> bool {
     match var_data {
-        VariantData::Struct(defs, _) | VariantData::Tuple(defs, _) => defs.is_empty(),
-        VariantData::Unit(_) => false,
+        VariantData::Struct(defs, _) | VariantData::Tuple(defs, _) => !defs.is_empty(),
+        VariantData::Unit(_) => true,
+    }
+}
+
+fn has_no_ident_token(braces_span_str: &str) -> bool {
+    !rustc_lexer::tokenize(braces_span_str).any(|t| t.kind == TokenKind::Ident)
+}
+
+fn has_no_fields(cx: &EarlyContext<'_>, var_data: &VariantData, braces_span: Span) -> bool {
+    if has_fields_in_hir(var_data) {
+        return false;
+    }
+
+    // there might still be field declarations hidden from HIR
+    // (conditionaly compiled code using #[cfg(..)])
+
+    let Some(braces_span_str) = snippet_opt(cx, braces_span) else {
+        return false;
+    };
+
+    has_no_ident_token(braces_span_str.as_ref())
+}
+
+#[cfg(test)]
+mod unit_test {
+    use super::*;
+
+    #[test]
+    fn test_has_no_ident_token() {
+        let input = "{ field: u8 }";
+        assert!(!has_no_ident_token(input));
+
+        let input = "(u8, String);";
+        assert!(!has_no_ident_token(input));
+
+        let input = " {
+                // test = 5
+        }
+        ";
+        assert!(has_no_ident_token(input));
+
+        let input = " ();";
+        assert!(has_no_ident_token(input));
     }
 }
diff --git a/tests/ui/unit_like_struct_brackets.fixed b/tests/ui/unit_like_struct_brackets.fixed
index e6cf4a0c0b46..78764337ec0f 100644
--- a/tests/ui/unit_like_struct_brackets.fixed
+++ b/tests/ui/unit_like_struct_brackets.fixed
@@ -5,8 +5,17 @@
 pub struct MyEmptyStruct; // should trigger lint
 struct MyEmptyTupleStruct; // should trigger lint
 
+// should not trigger lint
+struct MyCfgStruct {
+    #[cfg(feature = "thisisneverenabled")]
+    field: u8,
+}
+
+// should not trigger lint
+struct MyCfgTupleStruct(#[cfg(feature = "thisisneverenabled")] u8);
+
+// should not trigger lint
 struct MyStruct {
-    // should not trigger lint
     field: u8,
 }
 struct MyTupleStruct(usize, String); // should not trigger lint
diff --git a/tests/ui/unit_like_struct_brackets.rs b/tests/ui/unit_like_struct_brackets.rs
index 306e4c207d85..c43f97adfe90 100644
--- a/tests/ui/unit_like_struct_brackets.rs
+++ b/tests/ui/unit_like_struct_brackets.rs
@@ -5,8 +5,17 @@
 pub struct MyEmptyStruct {} // should trigger lint
 struct MyEmptyTupleStruct(); // should trigger lint
 
+// should not trigger lint
+struct MyCfgStruct {
+    #[cfg(feature = "thisisneverenabled")]
+    field: u8,
+}
+
+// should not trigger lint
+struct MyCfgTupleStruct(#[cfg(feature = "thisisneverenabled")] u8);
+
+// should not trigger lint
 struct MyStruct {
-    // should not trigger lint
     field: u8,
 }
 struct MyTupleStruct(usize, String); // should not trigger lint