Accept variables (NameExpr) in loguru calls

Partially fixes kornicameister#49

Note that mypy _cannot_ type-check a format expression if it is not Final.
E.g.:

```python
from loguru import logger
from typing import Final

foo: Final = "bar"
logger.info(foo, 1)  # error: Not all arguments converted during string formatting
foo = "bar"
logger.info(foo, 1)  # no error (and will fail at runtime)
```

This is a limitation with mypy and I don't think we can do much about it

loguru_mypy/__init__.py

@@ -52,7 +52,10 @@ class Opts(t.NamedTuple):
 }  # type: te.Final
 
 
-def _check_str_format_call(log_msg_expr: StrExpr, ctx: MethodContext) -> None:
+def _check_str_format_call(
+    log_msg_expr: t.Union[StrExpr, NameExpr],
+    ctx: MethodContext,
+) -> None:
     """ Taps into mypy to typecheck something like this:
 
         ```py
@@ -98,7 +101,7 @@ def _loguru_logger_call_handler(
     log_msg_expr = ctx.args[0][0]
     logger_opts = loggers.get(ctx.type) or DEFAULT_OPTS
 
-    if isinstance(log_msg_expr, StrExpr):
+    if isinstance(log_msg_expr, (StrExpr, NameExpr)):
         _check_str_format_call(log_msg_expr, ctx)
     elif isinstance(log_msg_expr, (IntExpr, FloatExpr)):
         # nothing to be done, this is valid log

typesafety/test_issue_49.yml

@@ -7,3 +7,35 @@
     logger.debug(123.3)
     logger.trace(1)
     logger.error(.3)
+- case: variables
+  main: |
+    from loguru import logger
+
+    foo = "bar"
+    logger.info(foo)
+    logger.debug(foo)
+    logger.trace(foo)
+    logger.error(foo)
+- case: variables__type-checked__wrong
+  main: |
+    from loguru import logger
+    from typing import Final
+
+    foo: Final = "bar"
+    logger.info(foo, 1)
+  out: |
+    main:5: error: Not all arguments converted during string formatting  [str-format]
+- case: variables__type-checked__correct
+  main: |
+    from loguru import logger
+    from typing import Final
+
+    foo: Final = "bar {}"
+    logger.info(foo, 1)
+- case: variables__mypy_cant_tell
+  main: |
+    from loguru import logger
+    from typing import Final
+
+    foo = "bar"
+    logger.info(foo, 1)  # This is wrong but mypy is at a loss