#21017 Invalid/unused `pants: ...` directives like `no-infer-dep` are silently ignored Issue created by huonw Describe the bug Someone can currently write a

# pants: no-infer-dep

line that does nothing and receives no prompt for this. This may lead to users shipping code with unintended dependencies. For instance, maybe one has a

use_bar

function in

foo.py

that does a lazy import of some chunky library

bar

. The default Pants behaviour will infer a dependency from

foo

to

bar

. However, if

bar

is chunky (or has chunky deps) one might not want to pull it in for all users of

foo

, only those that call

use_bar

(and those specific consumers can annotate the dependency manually).

# foo.py
def use_bar():
    import bar

One might make various mistakes that mean Pants still infers a dependency on `bar`:

def use_bar():
    # pants: no-infer-dep
    import bar

(The correct syntax is

import bar # pants: no-infer-dep

on one line. (Experienced Python users may know this is the usual convention, but other ecosystems have different conventions for this sort of comment, so may be tripped up.)

def use_bar():
    import bar # pants: no-infer

(Spelled incorrectly, lots of other variations of mistake too

pants: no-dep

or

pants: no-inefr-dep

.) A user "should" validate that their code does what's expected, but we can help when it seems obviously-wrong. (And it's definitely possible to end up with this accidentally, e.g. add a correct comment, then a year later, apply a code-formatter that makes a large number of changes and happens to moves the comments: only a super-hero would remember to check the

pants: no-infer-dep

comments.) Suggestion Emit errors/warnings about

pants: ...

comments that don't apply, either because: • directive not understood • directive not attached to an appropriate element Reproducer

cd $(mktemp -d)

cat > pants.toml <<EOF
[GLOBAL]
pants_version = "2.22.0a0"
backend_packages = ["pants.backend.python"]

[python]
interpreter_constraints = ["==3.10.*"]
EOF

echo 'python_sources(name="src")' > BUILD

cat > foo.py <<EOF
def use_bar():
    # pants: no-infer-dep
    import bar
EOF

touch bar.py

# BUG: no errors/warnings, only output is: //bar.py:src
pants dependencies foo.py

Pants version 2.21.0 OS macOS Additional info #20207 is related, in that the subtleties of placing a

no-infer-dep

correctly matter less if Pants will at least guide users. pantsbuild/pants