From cffca13504822be81dcf86e597d2d1cec16dd930 Mon Sep 17 00:00:00 2001
From: Jan Schlosser <jan.schlosser@bmw.de>
Date: Thu, 8 Oct 2026 14:54:36 +0200
Subject: [PATCH] Fix RULE-15-1-3 false positives for lambda conversion
 operators

The closure type of a captureless lambda has a compiler-generated
conversion operator to a function pointer. It is implicit by definition
and cannot be declared explicit, so reporting it is a false positive.

Exclude conversion operators declared by a Closure and add regression
tests for captureless, generic and capturing lambdas.
---
 ...6-10-08-fix-fp-rule-15-1-3-lambda-conversion.md |  4 ++++
 .../RULE-15-1-3/NonExplicitConversionMember.ql     |  3 +++
 cpp/misra/test/rules/RULE-15-1-3/test.cpp          | 14 +++++++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 change_notes/2026-10-08-fix-fp-rule-15-1-3-lambda-conversion.md

diff --git a/change_notes/2026-10-08-fix-fp-rule-15-1-3-lambda-conversion.md b/change_notes/2026-10-08-fix-fp-rule-15-1-3-lambda-conversion.md
new file mode 100644
index 0000000000..122b028451
--- /dev/null
+++ b/change_notes/2026-10-08-fix-fp-rule-15-1-3-lambda-conversion.md
@@ -0,0 +1,4 @@
+- `RULE-15-1-3` - `NonExplicitConversionMember.ql`:
+   - Fixed false positives on the compiler-generated conversion operator of a
+     captureless lambda's closure type (conversion to a function pointer). This
+     operator is implicit by definition and cannot be declared `explicit`.
diff --git a/cpp/misra/src/rules/RULE-15-1-3/NonExplicitConversionMember.ql b/cpp/misra/src/rules/RULE-15-1-3/NonExplicitConversionMember.ql
index c85e0d259c..7d6594c4c2 100644
--- a/cpp/misra/src/rules/RULE-15-1-3/NonExplicitConversionMember.ql
+++ b/cpp/misra/src/rules/RULE-15-1-3/NonExplicitConversionMember.ql
@@ -42,6 +42,9 @@ where
     exists(ConversionOperator co |
       x = co and
       not co.isExplicit() and
+      // The conversion to a function pointer of a captureless lambda is
+      // compiler-generated and cannot be declared explicit.
+      not co.getDeclaringType() instanceof Closure and
       message = "Conversion operator shall be explicit."
     )
   )
diff --git a/cpp/misra/test/rules/RULE-15-1-3/test.cpp b/cpp/misra/test/rules/RULE-15-1-3/test.cpp
index c1470de113..41145356f5 100644
--- a/cpp/misra/test/rules/RULE-15-1-3/test.cpp
+++ b/cpp/misra/test/rules/RULE-15-1-3/test.cpp
@@ -44,4 +44,16 @@ class TestClass7 {
   operator double() const;          // NON_COMPLIANT
   operator const char *() const;    // NON_COMPLIANT
   explicit operator void *() const; // COMPLIANT
-};
\ No newline at end of file
+};
+
+void test_lambdas() {
+  // The conversion to a function pointer of a captureless lambda's closure
+  // type is compiler-generated and cannot be declared explicit.
+  auto l1 = [](std::int32_t a) { return a; }; // COMPLIANT
+  auto l2 = [](auto a) { return a; };         // COMPLIANT
+  l2(1);
+  std::int32_t captured = 0;
+  auto l3 = [captured](std::int32_t a) { return a + captured; }; // COMPLIANT
+  (void)l1;
+  (void)l3;
+}