Add Fw::Optional type for C++14 environments

[devin-ai-integration]

Related Issue(s)	nasa#4986
Has Unit Tests (y/n)	y
Documentation Included (y/n)	n (Doxygen-style comments in header)
Generative AI was used in this contribution (y/n)	AI

---

Change Description

Adds Fw::Optional<T> — a lightweight, C++14-compatible optional type — to Fw/Types/.

namespace Fw {
struct Absent { constexpr explicit Absent() {} };
constexpr Absent ABSENT = Absent();

template <typename T>
class Optional {
    // union-based storage, bool engaged flag
    constexpr Optional();            // empty
    constexpr Optional(const T& t);  // engaged
    bool has_value() const;
    T& value();                      // asserts engaged
    const T& value_or(const T& default_value) const;
    void reset();
    Optional& operator=(const T& t);
    Optional& operator=(const Absent&);
    bool operator==(const Optional&) const;
    // ...
};
}

Key design choices vs. the fprime-vorago original:

• Lives in Fw namespace (not Va416x0Types)
• Member naming follows F' convention (m_ prefix)
• Adds value_or(), copy assignment, and Optional-to-Optional equality
• Comparison operators are const-correct
• Only supports trivially-destructible T (documented, destructor is defaulted)

Rationale

std::optional is unavailable in C++14, yet the pattern is extremely useful for expressing nullable values safely. An Optional was already proven useful in fprime-vorago; this promotes it to the core framework so all F' projects can use it.

Testing/Review Recommendations

• Unit tests in Fw/Types/test/ut/OptionalTest.cpp cover: default/value/copy construction, assignment, reset(), value_or(), ABSENT comparisons, struct and floating-point payloads, constexpr usage.
• Verify the union-based approach compiles cleanly on target toolchains (ARM, etc.) with -std=c++14.
• Confirm FW_ASSERT fires on value() access when empty (death tests not included — framework assert handling varies).

Future Work

• Consider adding emplace() for in-place construction.
• Consider serialization support (Fw::Serializable integration) if needed for telemetry.

AI Usage (see policy)

AI (Devin) was used for the full implementation: code generation, test authoring, and PR creation. The design is based on the existing fprime-vorago Optional.hpp by @celskeggs.

IAMAI

Link to Devin session: https://nasa-jpl-demo.devinenterprise.com/sessions/a3fd7acb122e42c8bf59b31bf2d4ae35

---

[devin-ai-integration]

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[devin-ai-integration]

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[github-actions]

Coverage report — base devel

No baseline branch coverage/devel found. This run becomes the seed once it lands on devel.

Overall (line): 81.26% (no baseline)
Regression threshold: 0.50% (line).

Regressions

(none over threshold)

Modules changed

(no measurable change)

New modules

Module	Line	Function	Branch
CFDP/Checksum	71.15	57.14	53.85
Drv/AsyncByteStreamBufferAdapter	100.00	100.00	100.00
Drv/ByteStreamBufferAdapter	100.00	100.00	100.00
Drv/Ip	44.32	57.38	25.36
Drv/TcpClient	75.00	100.00	47.37
Drv/TcpServer	84.72	100.00	60.00
Drv/Udp	68.09	90.91	42.86
Fw/Buffer	81.25	89.47	58.62
Fw/DataStructures	98.48	96.95	83.21
Fw/Dp	94.83	96.67	95.95
Fw/FilePacket	75.24	89.06	54.30
Fw/Log	71.43	72.41	60.00
Fw/Logger	100.00	100.00	100.00
Fw/SerializableFile	90.00	100.00	79.41
Fw/Time	88.62	85.48	86.84
Fw/Tlm	53.76	60.00	37.50
Fw/Types	55.85	60.06	36.31
Os	18.07	19.52	14.52
Os/Generic	89.10	96.30	67.18
Os/Generic/Types	92.45	91.67	82.14
Os/Posix	62.40	84.21	44.10
Svc/ActiveRateGroup	100.00	100.00	92.31
Svc/ActiveTextLogger	79.05	90.00	71.23
Svc/AssertFatalAdapter	94.74	100.00	86.67
Svc/BufferAccumulator	88.00	94.12	74.49
Svc/BufferLogger	92.62	86.96	80.46
Svc/BufferManager	99.05	100.00	83.64
Svc/BufferRepeater	91.67	100.00	75.00
Svc/ChronoTime	100.00	100.00	100.00
Svc/CmdDispatcher	96.97	91.67	91.75
Svc/CmdSequencer	93.89	97.12	84.63
Svc/CmdSplitter	100.00	100.00	100.00
Svc/ComLogger	97.37	91.67	83.91
Svc/ComSplitter	100.00	100.00	100.00
Svc/ComStub	98.51	100.00	85.19
Svc/DpCatalog	78.00	100.00	66.27
Svc/DpManager	97.44	100.00	100.00
Svc/DpWriter	97.58	90.00	97.22
Svc/FileDownlink	84.15	90.91	71.90
Svc/FileManager	88.41	93.33	82.44
Svc/FileUplink	92.35	96.55	80.95
Svc/FileWorker	90.29	100.00	84.87
Svc/FprimeDeframer	100.00	100.00	97.92
Svc/FprimeFramer	100.00	100.00	95.45
Svc/FprimeRouter	88.89	100.00	78.26
Svc/FpySequencer	86.76	99.04	76.89
Svc/GenericHub	100.00	100.00	85.64
Svc/Health	100.00	100.00	88.66
Svc/LinuxTimer	97.06	100.00	82.35
Svc/OsTime	70.00	83.33	60.98
Svc/PassiveRateGroup	100.00	100.00	89.47
Svc/PolyDb	100.00	100.00	53.57
Svc/PosixTime	100.00	100.00	75.00
Svc/PrmDb	92.75	89.47	88.24
Svc/RateGroupDriver	100.00	100.00	68.75
Svc/SeqDispatcher	73.08	80.00	71.05
Svc/StaticMemory	100.00	100.00	100.00
Svc/SystemResources	98.63	100.00	76.19
Svc/TlmChan	77.59	85.71	63.03
Svc/TlmPacketizer	92.49	100.00	77.45
Svc/Version	96.10	100.00	86.96
Utils	20.04	26.44	24.07
Utils/Types	92.11	95.83	77.08

Modules without UTs

CFDP/Checksum/GTest, Drv/ByteStreamDriverModel, Drv/Interfaces, Drv/LinuxGpioDriver, Drv/LinuxI2cDriver, Drv/LinuxSpiDriver, Drv/LinuxUartDriver, Drv/Ports, Drv/Ports/DataTypes, FppTestProject/FppTest/interfaces, FppTestProject/FppTest/topology/async, FppTestProject/FppTest/topology/components/Comp, FppTestProject/FppTest/topology/components/Framework, FppTestProject/FppTest/topology/components/Receiver, FppTestProject/FppTest/topology/components/Sender, FppTestProject/FppTest/topology/guarded, FppTestProject/FppTest/topology/ports, FppTestProject/FppTest/topology/sync, FppTestProject/FppTest/topology/top_ports, FppTestProject/FppTest/topology/types, Fw/Cmd, Fw/Com, Fw/Comp, Fw/FilePacket/GTest, Fw/Fpy, Fw/Interfaces, Fw/Obj, Fw/Port, Fw/Ports/CompletionStatus, Fw/Ports/Ready, Fw/Ports/Signal, Fw/Ports/SuccessCondition, Fw/Prm, Fw/SerializableFile/test/TestSerializable, Fw/Sm, Fw/Test, Fw/Types/GTest, Os/Models, Svc/Cycle, Svc/DpPorts, Svc/Fatal, Svc/FatalHandler, Svc/FileDownlinkPorts, Svc/FprimeProtocol, Svc/Interfaces, Svc/PassiveConsoleTextLogger, Svc/Ping, Svc/PolyIf, Svc/Ports/CommsPorts, Svc/Ports/FilePorts, Svc/Ports/OsTimeEpoch, Svc/Ports/TlmPacketizerPorts, Svc/Ports/VersionPorts, Svc/Sched, Svc/Seq, Svc/Subtopologies/CdhCore, Svc/Subtopologies/ComCcsds, Svc/Subtopologies/ComFprime, Svc/Subtopologies/ComLoggerTee, Svc/Subtopologies/DataProducts, Svc/Subtopologies/FileHandling, Svc/Types/TlmPacketizerTypes, Svc/WatchDog, TestDeploymentsProject/Ref/PingReceiver, TestDeploymentsProject/Ref/RecvBuffApp, TestDeploymentsProject/Ref/SendBuffApp, TestDeploymentsProject/Ref/Top, TestDeploymentsProject/Ref/TypeDemo, cmake/test/data/TestDeployment/TestBuildAutocoder, cmake/test/data/TestDeployment/TestChainedAutocoder, cmake/test/data/TestDeployment/TestHeaderAutocoder, cmake/test/data/TestDeployment/TestTargetAutocoder, cmake/test/data/test-fprime-library/TestLibrary/TestComponent, cmake/test/data/test-fprime-library2/TestLibrary2/TestComponent