[ruff] Add assert-with-print-message rule (#11974)

[denwong47]

Summary

Addresses #11974 to add a RUF rule to replace print expressions in assert statements with the inner message.

An autofix is available, but is considered unsafe as it changes behaviour of the execution, notably:

• removal of the printout in stdout, and
• AssertionError instance containing a different message.

While the detection of the condition is a straightforward matter, deciding how to resolve the print arguments into a string literal can be a relatively subjective matter. The implementation of this PR chooses to be as tolerant as possible, and will attempt to reformat any number of print arguments containing single or concatenated strings or variables into either a string literal, or a f-string if any variables or placeholders are detected.

Test Plan

cargo test.

Examples

For ease of discussion, this is the diff for the tests:

 # Standard Case
 # Expects:
 # - single StringLiteral
-assert True, print("This print is not intentional.")
+assert True, "This print is not intentional."
 
 # Concatenated string literals
 # Expects:
 # - single StringLiteral
-assert True, print("This print" " is not intentional.")
+assert True, "This print is not intentional."
 
 # Positional arguments, string literals
 # Expects:
 # - single StringLiteral concatenated with " "
-assert True, print("This print", "is not intentional")
+assert True, "This print is not intentional"
 
 # Concatenated string literals combined with Positional arguments
 # Expects:
 # - single stringliteral concatenated with " " only between `print` and `is`
-assert True, print("This " "print", "is not intentional.")
+assert True, "This print is not intentional."
 
 # Positional arguments, string literals with a variable
 # Expects:
 # - single FString concatenated with " "
-assert True, print("This", print.__name__, "is not intentional.")
+assert True, f"This {print.__name__} is not intentional."

 # Mixed brackets string literals
 # Expects:
 # - single StringLiteral concatenated with " "
-assert True, print("This print", 'is not intentional', """and should be removed""")
+assert True, "This print is not intentional and should be removed"
 
 # Mixed brackets with other brackets inside
 # Expects:
 # - single StringLiteral concatenated with " " and escaped brackets
-assert True, print("This print", 'is not "intentional"', """and "should" be 'removed'""")
+assert True, "This print is not \"intentional\" and \"should\" be 'removed'"
 
 # Positional arguments, string literals with a separator
 # Expects:
 # - single StringLiteral concatenated with "|"
-assert True, print("This print", "is not intentional", sep="|")
+assert True, "This print|is not intentional"
 
 # Positional arguments, string literals with None as separator
 # Expects:
 # - single StringLiteral concatenated with " "
-assert True, print("This print", "is not intentional", sep=None)
+assert True, "This print is not intentional"
 
 # Positional arguments, string literals with variable as separator, needs f-string
 # Expects:
 # - single FString concatenated with "{U00A0}"
-assert True, print("This print", "is not intentional", sep=U00A0)
+assert True, f"This print{U00A0}is not intentional"
 
 # Unnecessary f-string
 # Expects:
 # - single StringLiteral
-assert True, print(f"This f-string is just a literal.")
+assert True, "This f-string is just a literal."
 
 # Positional arguments, string literals and f-strings
 # Expects:
 # - single FString concatenated with " "
-assert True, print("This print", f"is not {'intentional':s}")
+assert True, f"This print is not {'intentional':s}"
 
 # Positional arguments, string literals and f-strings with a separator
 # Expects:
 # - single FString concatenated with "|"
-assert True, print("This print", f"is not {'intentional':s}", sep="|")
+assert True, f"This print|is not {'intentional':s}"
 
 # A single f-string
 # Expects:
 # - single FString
-assert True, print(f"This print is not {'intentional':s}")
+assert True, f"This print is not {'intentional':s}"
 
 # A single f-string with a redundant separator
 # Expects:
 # - single FString
-assert True, print(f"This print is not {'intentional':s}", sep="|")
+assert True, f"This print is not {'intentional':s}"
 
 # Complex f-string with variable as separator
 # Expects:
 # - single FString concatenated with "{U00A0}", all placeholders preserved
 condition = "True is True"
 maintainer = "John Doe"
-assert True, print("Unreachable due to", condition, f", ask {maintainer} for advice", sep=U00A0)
+assert True, f"Unreachable due to{U00A0}{condition}{U00A0}, ask {maintainer} for advice"
 
 # Empty print
 # Expects:
 # - `msg` entirely removed from assertion
-assert True, print()
+assert True
 
 # Empty print with separator
 # Expects:
 # - `msg` entirely removed from assertion
-assert True, print(sep=" ")
+assert True
 
 # Custom print function that actually returns a string
 # Expects:
@@ -100,4 +100,4 @@
 # Use of `builtins.print`
 # Expects:
 # - single StringLiteral
-assert True, builtins.print("This print should be removed.")
+assert True, "This print should be removed."

Known Issues

The current implementation resolves all arguments and separators of the print expression into a single string, be it StringLiteralValue::single or a FStringValue::single. This:

• potentially joins together strings well beyond the ideal character limit for each line, and
• does not preserve multi-line strings in their original format, in favour of a single line "...\n...\n..." format.

These are purely formatting issues only occurring in unusual scenarios.

Additionally, the autofix will tolerate print calls that were previously invalid:

assert True, print("this", "should not be allowed", sep=42)

This will be transformed into

assert True, f"this{42}should not be allowed"

which some could argue is an alteration of behaviour.

[charliermarsh]

Thanks! I will review.

[charliermarsh]

This is excellent work, nicely done.

[MichaReiser]

I think I would rename the rule to assert-with-print-message, it's otherwise unclear if it also captures assert print("test")

[charliermarsh]

Makes sense to me.