[edusperoni]

Description

Stacked on #2096 (base perf/primitive-callback-returns). That PR added a spec pinning how a JS callback's result converts to each primitive return type, and the spec exposed real crashes, fixed here.

A callback result only reached Java when the generic converter happened to produce exactly the declared wrapper type, which is all the generated binding's cast accepts. So these all threw ClassCastException, a crash when it happens on an Android callback:

• a double callback returning a whole number (return 1);
• a float callback returning a negative or whole number;
• a byte/short callback returning any plain number;
• a char callback returning a string.

New rule: a result converts whenever the declared type can hold it.

Return type	Accepted
byte / short / int / long	whole numbers in the type's range
float	0, NaN, ±Infinity, or a magnitude within float range
double	any number
char	a one-character string
boolean	booleans, and Boolean objects by their value

Number objects follow the same rules as numbers.

Values the type can't hold still throw, matching the deliberate specs in numericConversionTests.js (an out-of-range long for int, 1e-40 for float):

• non-whole or out-of-range numbers for integer types;
• float underflow or overflow;
• strings for numeric types;
• numbers for boolean/char.

null/undefined/{} still become the default value, and cast markers behave as before.

Behavior changes: 35 cells of the 33×8 matrix go from throwing to a value, and one value changes: new Boolean(false) returned true and now returns false. Nothing that converted before now throws.

Every changed cell

JS value	return type	before	after
0	byte	throws ClassCastException	0
0	short	throws ClassCastException	0
0	float	throws ClassCastException	0.0
0	double	throws ClassCastException	0.0
1	byte	throws ClassCastException	1
1	short	throws ClassCastException	1
1	float	throws ClassCastException	1.0
1	double	throws ClassCastException	1.0
-1	byte	throws ClassCastException	-1
-1	short	throws ClassCastException	-1
-1	float	throws ClassCastException	-1.0
-1	double	throws ClassCastException	-1.0
-0	byte	throws ClassCastException	0
-0	short	throws ClassCastException	0
-0	float	throws ClassCastException	-0.0
-0	double	throws ClassCastException	-0.0
2^31	float	throws ClassCastException	2.1474836E9
2^31	double	throws ClassCastException	2.147483648E9
-2^31-1	float	throws ClassCastException	-2.1474836E9
-2^31-1	double	throws ClassCastException	-2.147483649E9
2^40	float	throws ClassCastException	1.0995116E12
2^40	double	throws ClassCastException	1.099511627776E12
2^60	float	throws ClassCastException	1.1529215E18
2^60	double	throws ClassCastException	1.152921504606847E18
-1.5	float	throws ClassCastException	-1.5
NaN	float	throws ClassCastException	NaN
Infinity	float	throws ClassCastException	Infinity
-Infinity	float	throws ClassCastException	-Infinity
-2.5	float	throws ClassCastException	-2.5
'1'	char	throws ClassCastException	49
'a'	char	throws ClassCastException	97
Number(5)	byte	throws ClassCastException	5
Number(5)	short	throws ClassCastException	5
Number(5)	float	throws ClassCastException	5.0
Number(5)	double	throws ClassCastException	5.0
Boolean(false)	boolean	true	false

Does your pull request have unit tests?

Yes. testPrimitiveCallbackReturns.js is updated to the new matrix. numericConversionTests.js is unchanged and still passes, including its exception cases. Full suite: 1484 specs, 0 failures.

Summary by CodeRabbit

• New Features
  • JavaScript callbacks now support more return-value conversions for Java primitive types, including booleans, characters, and numeric values. Primitive and boxed values are handled where supported, with range and format checks applied to integral returns.
  • Float and double results now preserve clearer formatting for special values and decimal precision.

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Walkthrough

The runtime converts JavaScript values for Java primitive callback return types and handles raw-bit results for all primitive types. The callback tests update their expected conversion results and float and double formatting.

Changes: Primitive callback return conversion

Layer / File(s)	Summary
Native conversion rules test-app/runtime/src/main/cpp/Runtime.cpp	TryGetPrimitiveReturnBits adds direct conversion for Boolean, char, and numeric returns from primitive or boxed values, subject to type-specific acceptance rules.
Java primitive result handling test-app/runtime/src/main/java/com/tns/Runtime.java	Runtime allocates raw-bit result buffers for all primitive type IDs and converts char, byte, and short results.
Callback return test expectations test-app/app/src/main/java/com/tns/tests/PrimitiveReturnTest.java, test-app/app/src/main/assets/app/tests/testPrimitiveCallbackReturns.js	The Java test formats float and double values with specified precision. The JavaScript expectation matrix changes to match the callback conversion results.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Suggested reviewers: nathanwalker

Merge Risk: Minimal · previous review 189bf

This change fixes ClassCastException crashes when JavaScript callbacks return values for primitive Java return types. No actionable merge-blocking risk remains after the review.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title "fix: convert callback results the return type can hold" matches the main change. The PR changes the conversion of JavaScript callback results to Java primitive return types so that values t…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title "fix: convert callback results the return type can hold" matches the main change. The PR changes the conversion of JavaScript callback results to Java primitive return types so that values the declared type can hold are accepted (for example, in-range integers, floats within range, one-character strings for char, and Boolean objects). The raw summary shows changes in Runtime.cpp, Runtime.java, PrimitiveReturnTest.java, and testPrimitiveCallbackReturns.js, all of which fit this title. The title is short, specific, and uses a conventional fix: prefix.

Full details: Docstring Coverage

Explanation

Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 5 functions across 4 files.

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Write docstrings for the functions missing them to satisfy the coverage threshold.

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_{A rabbit checks each value's path,
And counts the bits from first to last.
A char hops in, one unit wide,
While floats round neatly as they glide.
The tests now mark what conversions cast.}

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Failed pre-merge checks:
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Write docstrings for the functions missing them to satisfy the coverage
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Commits

Reviewing files that changed from the base of the PR and between a494cbb and 189bf5a.

Files selected for processing: 4

• test-app/app/src/main/assets/app/tests/testPrimitiveCallbackReturns.js
• test-app/app/src/main/java/com/tns/tests/PrimitiveReturnTest.java
• test-app/runtime/src/main/cpp/Runtime.cpp
• test-app/runtime/src/main/java/com/tns/Runtime.java

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