Minor additions to the guide about access to source code of functions.

PiperOrigin-RevId: 349276476
Change-Id: I2b93bf77e0942134f4c651e802ce29ff55b44dc5

tensorflow/python/autograph/g3doc/reference/common_errors.md

@@ -10,6 +10,11 @@ This warning is output when AutoGraph could not convert a function, for an
 unexpected reason. The error message contains the reason why the function could
 not be converted, as well as guidance on how to proceed next.
 
+The exact error message may vary from version to version but in general, the
+cause of the failure appears somewhere in the text, for example as
+"Cause: could not get source code" or "Original error: could not get source
+code".
+
 Note: AutoGraph does not always output a warning. For example, constructors
 are silently called without conversion.
 
@@ -24,6 +29,16 @@ Note: the warning is output to the [abseil](https://github.com/abseil/abseil-py)
 logger, with `WARNING` severity. To direct these warnings to `stdout`, use
 `tf.autograph.set_verbosity(0, True)`.
 
+### "Unable to locate the source code" or "Source not found" errors
+
+Newer versions of AutoGraph raise a `ConversionError`. Older versions print a
+warning. In both cases, a similar message about finding the source code is
+included.
+
+These errors are raised when AutoGraph is unable to find the source code of
+functions it needs to transform. See [Limitations](limitations.md) for more
+details.
+
 ### "WARNING: Large unrolled loop detected"
 
 This warning is output when AutoGraph detects a `for` or `while` loop that

tensorflow/python/autograph/g3doc/reference/limitations.md

@@ -693,12 +693,25 @@ exceptions exist:
  * functions created dynamically, using `exec` or `eval`
 
 Use
-[inspect.getsource](https://docs.python.org/3/library/inspect.html#inspect.getsource)
+[inspect.findsource](https://docs.python.org/3/library/inspect.html#inspect.findsource)
 to quickly diagnose whether the source code is available for a function.
 
+For example:
+
+```
+import inspect
+
+def simple_function():
+  return 1
+
+# If this raises an error, then AutoGraph prints a warning.
+# If it returns source code, then AutoGraph should work as well.
+inspect.findsource(simple_function)
+```
+
 #### Source code of lambda functions
 
-##### Changes in TF 2.4
+##### TF 2.4 and newer
 
 Key Point: When nesting lambda functions, use distinguishing argument names
 to avoid parse errors.
@@ -726,7 +739,7 @@ use distinct argument names:
 l = lambda outer_x: lambda inner_x: inner_x + 1
 ```
 
-##### TF 2.3 and older
+##### Before TF 2.3 and older
 
 In older versions of TensorFlow, the loading code for lambda functions is not
 robust. Follow the guidance below to avoid errors.