Truncate integer division and remainder in Python and JavaScript

[matt-edmondson]

Fixes #114

Problem

The AST means / and % on two integers the way C, C++, C#, Go and Rust do: the quotient truncates toward zero and the remainder takes the dividend's sign. Python's and JavaScript's / are true division, and Python's % floors. So -7 / 2 came out as -3.5 in both targets (a float from a function annotated -> int), and Python gave 1 for -7 % 2 instead of -1.

Change

• StandardLanguageGenerator now has a GenerateBinary hook, an IsIntegerArithmetic check built on the existing StaticType inference, and an OpenStaticTypeScope guard.
• Python and JavaScript now open the static-type scope that Go already uses, in functions and in methods, and register typed locals. That way parameters and locals are known to be integers.
• Python, when both operands are statically integers:
  • Division is written as int(a / b). It isn't //, which floors.
  • Remainder is written as (a - b * int(a / b)). If an operand is anything other than a literal or a variable, it goes through (lambda a, b: …)(x, y) so it is evaluated only once. math.fmod isn't used because an expression can be generated outside a file that could carry the import.
• JavaScript: division is written as Math.trunc(a / b). JavaScript's % already truncates, so it is unchanged.
• If an operand's type is unknown or not an integer, the output is unchanged.

Tests

• IntegerDivisionTests generates functions that divide integer parameters, integer literals, a typed local, and a call operand. It runs them under real python3 and node with negative and mixed-sign operands, and compares the results with C#'s / and %.
• The Python test also checks that the result is an int and that the call operand runs exactly once.
• A third test pins that non-integer division and division with unknown types are left as is.
• With the generator changes reverted, both runtime tests fail. Full suite: 1092 passed, 0 failed. The build has 0 warnings.

Not covered here: compound assignment (x /= 2 on an int) has the same mismatch in Python. It goes through AssignmentStatement rather than BinaryExpression, and is left for a follow-up.

🤖 Generated with Claude Code

https://claude.ai/code/session_01AXWSrf4nXKEZF5xVNTiVV5

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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