codegen: Lambda improvements (#1476)

* Use #line directives in generated C++ code for lambdas

The #line directive in gcc is meant specifically for pieces of imported
code included in generated code, exactly what happens with lambdas in
the yaml files: https://gcc.gnu.org/onlinedocs/cpp/Line-Control.html

With this change, if I add the following at line 165 of kithen.yaml:
    - lambda: undefined_var == 5;

then "$ esphome kitchen.yaml compile" shows the following:

INFO Reading configuration kitchen.yaml...
INFO Generating C++ source...
INFO Compiling app...
INFO Running:  platformio run -d kitchen
<...>
Compiling .pioenvs/kitchen/src/main.cpp.o
kitchen.yaml: In lambda function:
kitchen.yaml:165:7: error: 'undefined_var' was not declared in this scope
*** [.pioenvs/kitchen/src/main.cpp.o] Error 1
== [FAILED] Took 2.37 seconds ==

* Silence gcc warning on multiline macros in lambdas

When the \ is used at the end of the C++ source in a lambda (line
continuation, often used in preprocessor macros), esphome will copy that
into main.cpp once as code and once as a // commment.  gcc will complain
about the multiline commment:

Compiling .pioenvs/kitchen/src/main.cpp.o
kitchen.yaml:640:3: warning: multi-line comment [-Wcomment]

Try to replace the \ with a "<cont>" for lack of a better idea.

esphome/config_validation.py

@@ -17,9 +17,10 @@ from esphome.const import ALLOWED_NAME_CHARS, CONF_AVAILABILITY, CONF_COMMAND_TO
     CONF_HOUR, CONF_MINUTE, CONF_SECOND, CONF_VALUE, CONF_UPDATE_INTERVAL, CONF_TYPE_ID, \
     CONF_TYPE, CONF_PACKAGES
 from esphome.core import CORE, HexInt, IPAddress, Lambda, TimePeriod, TimePeriodMicroseconds, \
-    TimePeriodMilliseconds, TimePeriodSeconds, TimePeriodMinutes
+    TimePeriodMilliseconds, TimePeriodSeconds, TimePeriodMinutes, DocumentLocation
 from esphome.helpers import list_starts_with, add_class_to_obj
 from esphome.voluptuous_schema import _Schema
+from esphome.yaml_util import ESPHomeDataBase
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -982,7 +983,11 @@ LAMBDA_ENTITY_ID_PROG = re.compile(r'id\(\s*([a-zA-Z0-9_]+\.[.a-zA-Z0-9_]+)\s*\)
 def lambda_(value):
     """Coerce this configuration option to a lambda."""
     if not isinstance(value, Lambda):
-        value = Lambda(string_strict(value))
+        start_mark = None
+        if isinstance(value, ESPHomeDataBase) and value.esp_range is not None:
+            start_mark = DocumentLocation.copy(value.esp_range.start_mark)
+            start_mark.line += value.content_offset
+        value = Lambda(string_strict(value), start_mark)
     entity_id_parts = re.split(LAMBDA_ENTITY_ID_PROG, value.value)
     if len(entity_id_parts) != 1:
         entity_ids = ' '.join("'{}'".format(entity_id_parts[i])