add tests for crazy edge cases

esphome/components/api/user_services.h

@@ -51,14 +51,13 @@ template<typename... Ts> class UserServiceBase : public UserServiceDescriptor {
       return false;
     if (req.args.size() != sizeof...(Ts))
       return false;
-    this->execute_(req.args, std::make_index_sequence<sizeof...(Ts)>{});
+    this->execute_(req.args, typename gens<sizeof...(Ts)>::type());
     return true;
   }
 
  protected:
   virtual void execute(Ts... x) = 0;
-  template<typename ArgsContainer, size_t... S>
-  void execute_(const ArgsContainer &args, std::index_sequence<S...> type) {
+  template<typename ArgsContainer, int... S> void execute_(const ArgsContainer &args, seq<S...> type) {
     this->execute((get_execute_arg_value<Ts>(args[S]))...);
   }
 
@@ -96,14 +95,13 @@ template<typename... Ts> class UserServiceDynamic : public UserServiceDescriptor
       return false;
     if (req.args.size() != sizeof...(Ts))
       return false;
-    this->execute_(req.args, std::make_index_sequence<sizeof...(Ts)>{});
+    this->execute_(req.args, typename gens<sizeof...(Ts)>::type());
     return true;
   }
 
  protected:
   virtual void execute(Ts... x) = 0;
-  template<typename ArgsContainer, size_t... S>
-  void execute_(const ArgsContainer &args, std::index_sequence<S...> type) {
+  template<typename ArgsContainer, int... S> void execute_(const ArgsContainer &args, seq<S...> type) {
     this->execute((get_execute_arg_value<Ts>(args[S]))...);
   }
 

esphome/components/script/script.h

@@ -46,14 +46,14 @@ template<typename... Ts> class Script : public ScriptLogger, public Trigger<Ts..
 
   // execute this script using a tuple that contains the arguments
   void execute_tuple(const std::tuple<Ts...> &tuple) {
-    this->execute_tuple_(tuple, std::make_index_sequence<sizeof...(Ts)>{});
+    this->execute_tuple_(tuple, typename gens<sizeof...(Ts)>::type());
   }
 
   // Internal function to give scripts readable names.
   void set_name(const LogString *name) { name_ = name; }
 
  protected:
-  template<size_t... S> void execute_tuple_(const std::tuple<Ts...> &tuple, std::index_sequence<S...> /*unused*/) {
+  template<int... S> void execute_tuple_(const std::tuple<Ts...> &tuple, seq<S...> /*unused*/) {
     this->execute(std::get<S>(tuple)...);
   }
 
@@ -157,7 +157,7 @@ template<typename... Ts> class QueueingScript : public Script<Ts...>, public Com
       const size_t queue_capacity = static_cast<size_t>(this->max_runs_ - 1);
       auto tuple_ptr = std::move(this->var_queue_[this->queue_front_]);
       this->queue_front_ = (this->queue_front_ + 1) % queue_capacity;
-      this->trigger_tuple_(*tuple_ptr, std::make_index_sequence<sizeof...(Ts)>{});
+      this->trigger_tuple_(*tuple_ptr, typename gens<sizeof...(Ts)>::type());
     }
   }
 
@@ -174,7 +174,7 @@ template<typename... Ts> class QueueingScript : public Script<Ts...>, public Com
     }
   }
 
-  template<size_t... S> void trigger_tuple_(const std::tuple<Ts...> &tuple, std::index_sequence<S...> /*unused*/) {
+  template<int... S> void trigger_tuple_(const std::tuple<Ts...> &tuple, seq<S...> /*unused*/) {
     this->trigger(std::get<S>(tuple)...);
   }
 
@@ -305,7 +305,7 @@ template<class C, typename... Ts> class ScriptWaitAction : public Action<Ts...>,
 
     while (!this->param_queue_.empty()) {
       auto &params = this->param_queue_.front();
-      this->play_next_tuple_(params, std::make_index_sequence<sizeof...(Ts)>{});
+      this->play_next_tuple_(params, typename gens<sizeof...(Ts)>::type());
       this->param_queue_.pop_front();
     }
     // Queue is now empty - disable loop until next play_complex
@@ -321,7 +321,7 @@ template<class C, typename... Ts> class ScriptWaitAction : public Action<Ts...>,
   }
 
  protected:
-  template<size_t... S> void play_next_tuple_(const std::tuple<Ts...> &tuple, std::index_sequence<S...> /*unused*/) {
+  template<int... S> void play_next_tuple_(const std::tuple<Ts...> &tuple, seq<S...> /*unused*/) {
     this->play_next_(std::get<S>(tuple)...);
   }
 

esphome/core/automation.h

@@ -11,26 +11,10 @@
 
 namespace esphome {
 
-// C++20 std::index_sequence is now used for tuple unpacking
-// Legacy seq<>/gens<> pattern deprecated but kept for backwards compatibility
 // https://stackoverflow.com/questions/7858817/unpacking-a-tuple-to-call-a-matching-function-pointer/7858971#7858971
-// Remove before 2026.6.0
-// NOLINTBEGIN(readability-identifier-naming)
-#if defined(__GNUC__) || defined(__clang__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-#endif
-
-template<int...> struct ESPDEPRECATED("Use std::index_sequence instead. Removed in 2026.6.0", "2025.12.0") seq {};
-template<int N, int... S>
-struct ESPDEPRECATED("Use std::make_index_sequence instead. Removed in 2026.6.0", "2025.12.0") gens
-    : gens<N - 1, N - 1, S...> {};
-template<int... S> struct gens<0, S...> { using type = seq<S...>; };
-
-#if defined(__GNUC__) || defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
-// NOLINTEND(readability-identifier-naming)
+template<int...> struct seq {};                                       // NOLINT
+template<int N, int... S> struct gens : gens<N - 1, N - 1, S...> {};  // NOLINT
+template<int... S> struct gens<0, S...> { using type = seq<S...>; };  // NOLINT
 
 #define TEMPLATABLE_VALUE_(type, name) \
  protected: \
@@ -168,11 +152,11 @@ template<typename... Ts> class Condition {
 
   /// Call check with a tuple of values as parameter.
   bool check_tuple(const std::tuple<Ts...> &tuple) {
-    return this->check_tuple_(tuple, std::make_index_sequence<sizeof...(Ts)>{});
+    return this->check_tuple_(tuple, typename gens<sizeof...(Ts)>::type());
   }
 
  protected:
-  template<size_t... S> bool check_tuple_(const std::tuple<Ts...> &tuple, std::index_sequence<S...> /*unused*/) {
+  template<int... S> bool check_tuple_(const std::tuple<Ts...> &tuple, seq<S...> /*unused*/) {
     return this->check(std::get<S>(tuple)...);
   }
 };
@@ -247,11 +231,11 @@ template<typename... Ts> class Action {
       }
     }
   }
-  template<size_t... S> void play_next_tuple_(const std::tuple<Ts...> &tuple, std::index_sequence<S...> /*unused*/) {
+  template<int... S> void play_next_tuple_(const std::tuple<Ts...> &tuple, seq<S...> /*unused*/) {
     this->play_next_(std::get<S>(tuple)...);
   }
   void play_next_tuple_(const std::tuple<Ts...> &tuple) {
-    this->play_next_tuple_(tuple, std::make_index_sequence<sizeof...(Ts)>{});
+    this->play_next_tuple_(tuple, typename gens<sizeof...(Ts)>::type());
   }
 
   virtual void stop() {}
@@ -293,9 +277,7 @@ template<typename... Ts> class ActionList {
     if (this->actions_begin_ != nullptr)
       this->actions_begin_->play_complex(x...);
   }
-  void play_tuple(const std::tuple<Ts...> &tuple) {
-    this->play_tuple_(tuple, std::make_index_sequence<sizeof...(Ts)>{});
-  }
+  void play_tuple(const std::tuple<Ts...> &tuple) { this->play_tuple_(tuple, typename gens<sizeof...(Ts)>::type()); }
   void stop() {
     if (this->actions_begin_ != nullptr)
       this->actions_begin_->stop_complex();
@@ -316,7 +298,7 @@ template<typename... Ts> class ActionList {
   }
 
  protected:
-  template<size_t... S> void play_tuple_(const std::tuple<Ts...> &tuple, std::index_sequence<S...> /*unused*/) {
+  template<int... S> void play_tuple_(const std::tuple<Ts...> &tuple, seq<S...> /*unused*/) {
     this->play(std::get<S>(tuple)...);
   }
 

esphome/cpp_generator.py

@@ -19,11 +19,21 @@ from esphome.core import (
     TimePeriodNanoseconds,
     TimePeriodSeconds,
 )
+from esphome.coroutine import CoroPriority, coroutine_with_priority
 from esphome.helpers import cpp_string_escape, indent_all_but_first_and_last
 from esphome.types import Expression, SafeExpType, TemplateArgsType
 from esphome.util import OrderedDict
 from esphome.yaml_util import ESPHomeDataBase
 
+# Keys for lambda deduplication storage in CORE.data
+_KEY_LAMBDA_DEDUP = "lambda_dedup"
+_KEY_LAMBDA_DEDUP_DECLARATIONS = "lambda_dedup_declarations"
+
+# Regex patterns for static variable detection (compiled once)
+_RE_CPP_SINGLE_LINE_COMMENT = re.compile(r"//.*?$", re.MULTILINE)
+_RE_CPP_MULTI_LINE_COMMENT = re.compile(r"/\*.*?\*/", re.DOTALL)
+_RE_STATIC_VARIABLE = re.compile(r"\bstatic\s+(?!cast|assert|pointer_cast)\w+\s+\w+")
+
 
 class RawExpression(Expression):
     __slots__ = ("text",)
@@ -188,7 +198,7 @@ class LambdaExpression(Expression):
 
     def __init__(
         self, parts, parameters, capture: str = "=", return_type=None, source=None
-    ):
+    ) -> None:
         self.parts = parts
         if not isinstance(parameters, ParameterListExpression):
             parameters = ParameterListExpression(*parameters)
@@ -197,16 +207,21 @@ class LambdaExpression(Expression):
         self.capture = capture
         self.return_type = safe_exp(return_type) if return_type is not None else None
 
-    def __str__(self):
+    def format_body(self) -> str:
+        """Format the lambda body with source directive and content."""
+        body = ""
+        if self.source is not None:
+            body += f"{self.source.as_line_directive}\n"
+        body += self.content
+        return body
+
+    def __str__(self) -> str:
         # Stateless lambdas (empty capture) implicitly convert to function pointers
         # when assigned to function pointer types - no unary + needed
         cpp = f"[{self.capture}]({self.parameters})"
         if self.return_type is not None:
             cpp += f" -> {self.return_type}"
-        cpp += " {\n"
-        if self.source is not None:
-            cpp += f"{self.source.as_line_directive}\n"
-        cpp += f"{self.content}\n}}"
+        cpp += f" {{\n{self.format_body()}\n}}"
         return indent_all_but_first_and_last(cpp)
 
     @property
@@ -214,6 +229,37 @@ class LambdaExpression(Expression):
         return "".join(str(part) for part in self.parts)
 
 
+class SharedFunctionLambdaExpression(LambdaExpression):
+    """A lambda expression that references a shared deduplicated function.
+
+    This class wraps a function pointer but maintains the LambdaExpression
+    interface so calling code works unchanged.
+    """
+
+    __slots__ = ("_func_name",)
+
+    def __init__(
+        self,
+        func_name: str,
+        parameters: TemplateArgsType,
+        return_type: SafeExpType | None = None,
+    ) -> None:
+        # Initialize parent with empty parts since we're just a function reference
+        super().__init__(
+            [], parameters, capture="", return_type=return_type, source=None
+        )
+        self._func_name = func_name
+
+    def __str__(self) -> str:
+        # Just return the function name - it's already a function pointer
+        return self._func_name
+
+    @property
+    def content(self) -> str:
+        # No content, just a function reference
+        return ""
+
+
 # pylint: disable=abstract-method
 class Literal(Expression, metaclass=abc.ABCMeta):
     __slots__ = ()
@@ -583,6 +629,25 @@ def add_global(expression: SafeExpType | Statement, prepend: bool = False):
     CORE.add_global(expression, prepend)
 
 
+@coroutine_with_priority(CoroPriority.FINAL)
+async def flush_lambda_dedup_declarations() -> None:
+    """Flush all deferred lambda deduplication declarations to global scope.
+
+    This is a coroutine that runs with FINAL priority (after all components)
+    to ensure all referenced variables are declared before the shared
+    lambda functions that use them.
+    """
+    if _KEY_LAMBDA_DEDUP_DECLARATIONS not in CORE.data:
+        return
+
+    declarations = CORE.data[_KEY_LAMBDA_DEDUP_DECLARATIONS]
+    for func_declaration in declarations:
+        add_global(RawStatement(func_declaration))
+
+    # Clear the list so we don't add them again
+    CORE.data[_KEY_LAMBDA_DEDUP_DECLARATIONS] = []
+
+
 def add_library(name: str, version: str | None, repository: str | None = None):
     """Add a library to the codegen library storage.
 
@@ -656,6 +721,93 @@ async def get_variable_with_full_id(id_: ID) -> tuple[ID, "MockObj"]:
     return await CORE.get_variable_with_full_id(id_)
 
 
+def _has_static_variables(code: str) -> bool:
+    """Check if code contains static variable definitions.
+
+    Static variables in lambdas should not be deduplicated because each lambda
+    instance should have its own static variable state.
+
+    Args:
+        code: The lambda body code to check
+
+    Returns:
+        True if code contains static variable definitions
+    """
+    # Remove C++ comments to avoid false positives
+    # Remove single-line comments (// ...)
+    code_no_comments = _RE_CPP_SINGLE_LINE_COMMENT.sub("", code)
+    # Remove multi-line comments (/* ... */)
+    code_no_comments = _RE_CPP_MULTI_LINE_COMMENT.sub("", code_no_comments)
+
+    # Match: static <type> <identifier>
+    # But not: static_cast, static_assert, static_pointer_cast
+    return bool(_RE_STATIC_VARIABLE.search(code_no_comments))
+
+
+def _get_shared_lambda_name(lambda_expr: LambdaExpression) -> str | None:
+    """Get the shared function name for a lambda expression.
+
+    If an identical lambda was already generated, returns the existing shared
+    function name. Otherwise, creates a new shared function and returns its name.
+
+    Lambdas with static variables are not deduplicated to preserve their
+    independent state.
+
+    Args:
+        lambda_expr: The lambda expression to deduplicate
+
+    Returns:
+        The name of the shared function for this lambda (either existing or newly created),
+        or None if the lambda should not be deduplicated (e.g., contains static variables)
+    """
+    # Create a unique key from the lambda content, parameters, and return type
+    content = lambda_expr.content
+
+    # Don't deduplicate lambdas with static variables - each instance needs its own state
+    if _has_static_variables(content):
+        return None
+    param_str = str(lambda_expr.parameters)
+    return_str = (
+        str(lambda_expr.return_type) if lambda_expr.return_type is not None else "void"
+    )
+
+    # Use tuple of (content, params, return_type) as key
+    lambda_key = (content, param_str, return_str)
+
+    # Initialize deduplication storage in CORE.data if not exists
+    if _KEY_LAMBDA_DEDUP not in CORE.data:
+        CORE.data[_KEY_LAMBDA_DEDUP] = {}
+        # Register the flush job to run after all components (FINAL priority)
+        # This ensures all variables are declared before shared lambda functions
+        CORE.add_job(flush_lambda_dedup_declarations)
+
+    lambda_cache = CORE.data[_KEY_LAMBDA_DEDUP]
+
+    # Check if we've seen this lambda before
+    if lambda_key in lambda_cache:
+        # Return name of existing shared function
+        return lambda_cache[lambda_key]
+
+    # First occurrence - create a shared function
+    # Use the cache size as the function number
+    func_name = f"shared_lambda_{len(lambda_cache)}"
+
+    # Build the function declaration using lambda's body formatting
+    func_declaration = (
+        f"{return_str} {func_name}({param_str}) {{\n{lambda_expr.format_body()}\n}}"
+    )
+
+    # Store the declaration to be added later (after all variable declarations)
+    # We can't add it immediately because it might reference variables not yet declared
+    CORE.data.setdefault(_KEY_LAMBDA_DEDUP_DECLARATIONS, []).append(func_declaration)
+
+    # Store in cache
+    lambda_cache[lambda_key] = func_name
+
+    # Return the function name (this is the first occurrence, but we still generate shared function)
+    return func_name
+
+
 async def process_lambda(
     value: Lambda,
     parameters: TemplateArgsType,
@@ -713,6 +865,19 @@ async def process_lambda(
         location.line += value.content_offset
     else:
         location = None
+
+    # Lambda deduplication: Only deduplicate stateless lambdas (empty capture).
+    # Stateful lambdas cannot be shared as they capture different contexts.
+    # Lambdas with static variables are also not deduplicated to preserve independent state.
+    if capture == "":
+        lambda_expr = LambdaExpression(
+            parts, parameters, capture, return_type, location
+        )
+        func_name = _get_shared_lambda_name(lambda_expr)
+        if func_name is not None:
+            # Return a shared function reference instead of inline lambda
+            return SharedFunctionLambdaExpression(func_name, parameters, return_type)
+
     return LambdaExpression(parts, parameters, capture, return_type, location)
 
 

tests/component_tests/text/test_text.py

@@ -1,4 +1,6 @@
-"""Tests for the binary sensor component."""
+"""Tests for the text component."""
+
+from esphome.core import CORE
 
 
 def test_text_is_setup(generate_main):
@@ -56,15 +58,22 @@ def test_text_config_value_mode_set(generate_main):
     assert "it_3->traits.set_mode(text::TEXT_MODE_PASSWORD);" in main_cpp
 
 
-def test_text_config_lamda_is_set(generate_main):
+def test_text_config_lambda_is_set(generate_main) -> None:
     """
-    Test if lambda is set for lambda mode (optimized with stateless lambda)
+    Test if lambda is set for lambda mode (optimized with stateless lambda and deduplication)
     """
     # Given
 
     # When
     main_cpp = generate_main("tests/component_tests/text/test_text.yaml")
 
+    # Get both global and main sections to find the shared lambda definition
+    full_cpp = CORE.cpp_global_section + main_cpp
+
     # Then
-    assert "it_4->set_template([]() -> esphome::optional<std::string> {" in main_cpp
-    assert 'return std::string{"Hello"};' in main_cpp
+    # Lambda is deduplicated into a shared function (reference in main section)
+    assert "it_4->set_template(shared_lambda_" in main_cpp
+    # Lambda body should be in the code somewhere
+    assert 'return std::string{"Hello"};' in full_cpp
+    # Verify the shared lambda function is defined (in global section)
+    assert "esphome::optional<std::string> shared_lambda_" in full_cpp

tests/unit_tests/test_lambda_dedup.py

@@ -0,0 +1,279 @@
+"""Tests for lambda deduplication in cpp_generator."""
+
+from esphome import cpp_generator as cg
+from esphome.core import CORE
+
+
+def test_deduplicate_identical_lambdas() -> None:
+    """Test that identical stateless lambdas are deduplicated."""
+    # Create two identical lambda expressions
+    lambda1 = cg.LambdaExpression(
+        parts=["return 42;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    lambda2 = cg.LambdaExpression(
+        parts=["return 42;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    # Try to deduplicate them
+    func_name1 = cg._get_shared_lambda_name(lambda1)
+    func_name2 = cg._get_shared_lambda_name(lambda2)
+
+    # Both should get the same function name (deduplication happened)
+    assert func_name1 == func_name2
+    assert func_name1 == "shared_lambda_0"
+
+
+def test_different_lambdas_not_deduplicated() -> None:
+    """Test that different lambdas get different function names."""
+    lambda1 = cg.LambdaExpression(
+        parts=["return 42;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    lambda2 = cg.LambdaExpression(
+        parts=["return 24;"],  # Different content
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    func_name1 = cg._get_shared_lambda_name(lambda1)
+    func_name2 = cg._get_shared_lambda_name(lambda2)
+
+    # Different lambdas should get different function names
+    assert func_name1 != func_name2
+    assert func_name1 == "shared_lambda_0"
+    assert func_name2 == "shared_lambda_1"
+
+
+def test_different_return_types_not_deduplicated() -> None:
+    """Test that lambdas with different return types are not deduplicated."""
+    lambda1 = cg.LambdaExpression(
+        parts=["return 42;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    lambda2 = cg.LambdaExpression(
+        parts=["return 42;"],  # Same content
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("float"),  # Different return type
+    )
+
+    func_name1 = cg._get_shared_lambda_name(lambda1)
+    func_name2 = cg._get_shared_lambda_name(lambda2)
+
+    # Different return types = different functions
+    assert func_name1 != func_name2
+
+
+def test_different_parameters_not_deduplicated() -> None:
+    """Test that lambdas with different parameters are not deduplicated."""
+    lambda1 = cg.LambdaExpression(
+        parts=["return x;"],
+        parameters=[("int", "x")],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    lambda2 = cg.LambdaExpression(
+        parts=["return x;"],  # Same content
+        parameters=[("float", "x")],  # Different parameter type
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    func_name1 = cg._get_shared_lambda_name(lambda1)
+    func_name2 = cg._get_shared_lambda_name(lambda2)
+
+    # Different parameters = different functions
+    assert func_name1 != func_name2
+
+
+def test_flush_lambda_dedup_declarations() -> None:
+    """Test that deferred declarations are properly stored for later flushing."""
+    # Create a lambda which will create a deferred declaration
+    lambda1 = cg.LambdaExpression(
+        parts=["return 42;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    cg._get_shared_lambda_name(lambda1)
+
+    # Check that declaration was stored
+    assert cg._KEY_LAMBDA_DEDUP_DECLARATIONS in CORE.data
+    assert len(CORE.data[cg._KEY_LAMBDA_DEDUP_DECLARATIONS]) == 1
+
+    # Verify the declaration content is correct
+    declaration = CORE.data[cg._KEY_LAMBDA_DEDUP_DECLARATIONS][0]
+    assert "shared_lambda_0" in declaration
+    assert "return 42;" in declaration
+
+    # Note: The actual flushing happens via CORE.add_job with FINAL priority
+    # during real code generation, so we don't test that here
+
+
+def test_shared_function_lambda_expression() -> None:
+    """Test SharedFunctionLambdaExpression behaves correctly."""
+    shared_lambda = cg.SharedFunctionLambdaExpression(
+        func_name="shared_lambda_0",
+        parameters=[],
+        return_type=cg.RawExpression("int"),
+    )
+
+    # Should output just the function name
+    assert str(shared_lambda) == "shared_lambda_0"
+
+    # Should have empty capture (stateless)
+    assert shared_lambda.capture == ""
+
+    # Should have empty content (just a reference)
+    assert shared_lambda.content == ""
+
+
+def test_lambda_deduplication_counter() -> None:
+    """Test that lambda counter increments correctly."""
+    # Create 3 different lambdas
+    for i in range(3):
+        lambda_expr = cg.LambdaExpression(
+            parts=[f"return {i};"],
+            parameters=[],
+            capture="",
+            return_type=cg.RawExpression("int"),
+        )
+        func_name = cg._get_shared_lambda_name(lambda_expr)
+        assert func_name == f"shared_lambda_{i}"
+
+
+def test_lambda_format_body() -> None:
+    """Test that format_body correctly formats lambda body with source."""
+    # Without source
+    lambda1 = cg.LambdaExpression(
+        parts=["return 42;"],
+        parameters=[],
+        capture="",
+        return_type=None,
+        source=None,
+    )
+    assert lambda1.format_body() == "return 42;"
+
+    # With source would need a proper source object, skip for now
+
+
+def test_stateful_lambdas_not_deduplicated() -> None:
+    """Test that stateful lambdas (non-empty capture) are not deduplicated."""
+    # _get_shared_lambda_name is only called for stateless lambdas (capture == "")
+    # Stateful lambdas bypass deduplication entirely in process_lambda
+
+    # Verify that a stateful lambda would NOT get deduplicated
+    # by checking it's not in the stateless dedup cache
+    stateful_lambda = cg.LambdaExpression(
+        parts=["return x + y;"],
+        parameters=[],
+        capture="=",  # Non-empty capture means stateful
+        return_type=cg.RawExpression("int"),
+    )
+
+    # Stateful lambdas should NOT be passed to _get_shared_lambda_name
+    # This is enforced by the `if capture == ""` check in process_lambda
+    # We verify the lambda has a non-empty capture
+    assert stateful_lambda.capture != ""
+    assert stateful_lambda.capture == "="
+
+
+def test_static_variable_detection() -> None:
+    """Test detection of static variables in lambda code."""
+    # Should detect static variables
+    assert cg._has_static_variables("static int counter = 0;")
+    assert cg._has_static_variables("static bool flag = false; return flag;")
+    assert cg._has_static_variables("  static  float  value  =  1.0;  ")
+
+    # Should NOT detect static_cast, static_assert, etc. (with underscores)
+    assert not cg._has_static_variables("return static_cast<int>(value);")
+    assert not cg._has_static_variables("static_assert(sizeof(int) == 4);")
+    assert not cg._has_static_variables("auto ptr = static_pointer_cast<Foo>(bar);")
+
+    # Edge case: 'cast', 'assert', 'pointer_cast' are NOT C++ keywords
+    # Someone could use them as type names, but we should NOT flag them
+    # because they're not actually static variables with state
+    # NOTE: These are valid C++ but extremely unlikely in ESPHome lambdas
+    assert not cg._has_static_variables("static cast obj;")  # 'cast' as type name
+    assert not cg._has_static_variables("static assert value;")  # 'assert' as type name
+    assert not cg._has_static_variables(
+        "static pointer_cast ptr;"
+    )  # 'pointer_cast' as type
+
+    # Should NOT detect in comments
+    assert not cg._has_static_variables("// static int x = 0;\nreturn 42;")
+    assert not cg._has_static_variables("/* static int y = 0; */ return 42;")
+
+    # Should detect even with comments elsewhere
+    assert cg._has_static_variables("// comment\nstatic int x = 0;\nreturn x;")
+
+    # Should NOT detect non-static code
+    assert not cg._has_static_variables("int counter = 0; return counter++;")
+    assert not cg._has_static_variables("return 42;")
+
+
+def test_lambdas_with_static_not_deduplicated() -> None:
+    """Test that lambdas with static variables are not deduplicated."""
+    # Two identical lambdas with static variables
+    lambda1 = cg.LambdaExpression(
+        parts=["static int counter = 0; return counter++;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    lambda2 = cg.LambdaExpression(
+        parts=["static int counter = 0; return counter++;"],
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    # Should return None (not deduplicated)
+    func_name1 = cg._get_shared_lambda_name(lambda1)
+    func_name2 = cg._get_shared_lambda_name(lambda2)
+
+    assert func_name1 is None
+    assert func_name2 is None
+
+
+def test_lambdas_without_static_still_deduplicated() -> None:
+    """Test that lambdas without static variables are still deduplicated."""
+    # Two identical lambdas WITHOUT static variables
+    lambda1 = cg.LambdaExpression(
+        parts=["int counter = 0; return counter++;"],  # No static
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    lambda2 = cg.LambdaExpression(
+        parts=["int counter = 0; return counter++;"],  # No static
+        parameters=[],
+        capture="",
+        return_type=cg.RawExpression("int"),
+    )
+
+    # Should be deduplicated (same function name)
+    func_name1 = cg._get_shared_lambda_name(lambda1)
+    func_name2 = cg._get_shared_lambda_name(lambda2)
+
+    assert func_name1 is not None
+    assert func_name2 is not None
+    assert func_name1 == func_name2