Executable scripts must have shebang (#!) line to be effectively
executable on most Unix-like systems. Enforce this, and conversely
enforce that files with a shebang line are executable.

Check that the specified interperter is consistent with the file
extension.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Add enough type annotations to pass mypy 0.782 with Python 3.5. The
source code will still run normally under older Python versions.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

This makes the code cleaner.

As a bonus, mypy no longer gets confused.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Since no typing stubs are available for mbed_host_tests.py, mypy
errors out on mbedtls_test.py with

    error: Skipping analyzing 'mbed_host_tests': found module but no type hints or library stubs

Ignore this import to get at least some benefit from mypy without
spending significant effort to write stubs.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Allow Python scripts in tests/scripts to import modules located in the
scripts directory. To do this, use
```
import scripts_path # pylint: disable=unused-import
```

Declare the scripts directory to pylint and to mypy.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Generalize the very ad hoc run_c function into a function to generate
a C program to print the value of a list of expressions. Refactor the
code into several functions to make it more manageable.

No intended behavior change.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Create a directory mbedtls_dev intended to contain various Python
module for use by Python scripts located anywhere in the Mbed TLS
source tree.

Move get_c_expression_values and its auxiliary functions into a new
Python module mbedtls_dev.c_build_helper.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Tell mypy to support packages without an __init__.py (PEP 420
namespace packages). Python 3.3 and (modern) Pylint support them out
of the box, but mypy needs to be told to support them.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

With just the option --can-pylint or --can-mypy, check whether the
requisite tool is available with an acceptable version and exit.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

This reduces dependencies, doesn't require maintainers to know awk,
and makes the version parsing more robust.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

As indicated in the comments in the can_mypy function, we don't just
need a mypy executable to be present, we need it to work.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

Make sure to run mypy with the desired Python version.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

`tests/scripts/all.sh check_python_files` now runs mypy (in addition
to pylint) if it's available. So install mypy.

Install mypy 0.780, which is the earliest version that works on our
code at this time.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>