Fix negative integer parsing with JSON_NO_INT64

[fzlzjerry]

Fixes #1341.

OurReader::decodeNumber() subtracts a Value::UInt last digit from a LargestInt expression. With JSON_NO_INT64, both have the same width, so the usual arithmetic conversions make the subtraction unsigned. For example, -1 becomes a uintValue containing 4294967295; even -0 gets the wrong stored type.

Keep the last digit signed. The existing quotient/remainder calculation still handles the minimum signed value without negating it directly.

Making the affected configuration testable

Current master first fails to compile with JSON_NO_INT64 on GCC/Clang because the private integerToDouble(Json::UInt64) overload refers to a disabled type. The patch guards that overload, along with 64-bit-only test helpers and API checks. The existing no-int64 floating-point assertions are updated to the current 17-digit formatting.

The reader/writer fixtures that contain 64-bit limits still run. The test driver reads the executable's existing --json-config output and selects explicit floating-point expectations for those three inputs when integer storage is limited to 32 bits. All other expectations, and all default-configuration expectations, stay unchanged; no fixture is skipped. Invalid configuration output fails the test run.

Added regression tests cover negative zero, digit boundaries, signed limits, scalar/array/object contexts, unsigned limits, and the existing out-of-range floating-point fallback. A separate Linux CMake job exercises the complete no-int64 CTest suite so the configuration stays covered. It pins checkout to a full commit, limits permissions to read-only contents, and disables persisted checkout credentials.

There are no public-header changes. This does not add sign-only-token validation; that is covered separately by #1703. The verified reproduction is a Linux build with the library and consumer both compiled with JSON_NO_INT64, rather than a reproduction of the original MSVC 2015 environment.

Validation

• Pristine master: the default build passes all 3 CTests; the no-int64 build fails at the unguarded overload. With only that prerequisite guard applied, all 8 negative CharReader consumer cases fail while the 8 legacy Reader controls pass. Both readers pass all 16 cases after the fix.
• GCC 14 and Clang 19 × C++11/17/20 × default/no-int64: all 12 configurations pass all 3 CTests with the repository's normal warning settings. Both integer configurations pass all 133 C++ unit tests.
• Meson 1.5.1, Clang 19, C++11, shared/static libraries and werror=true: all 3 test suites pass in both configurations.
• Full no-int64 CTest run passes with AddressSanitizer, UndefinedBehaviorSanitizer and LeakSanitizer enabled.
• 21 configuration/real-CLI scenarios check configuration errors, expected-file selection, missing variants, and deliberately corrupted expectations.
• C++11 amalgamated builds and installed-library consumers built with Clang C++17/C++23 pass in both configurations. The default Linux dynamic export set is unchanged (1,905 symbols).
• clang-format 18 over src, include and example, actionlint, and git diff --check pass.

An additional warnings-as-errors stress run encounters pre-existing GCC C++20 implicit-this capture and Clang C++17/20 signed-size warnings. Those failures were reproduced on pristine master; the unrelated source lines are unchanged.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[greptile-apps]

Greptile Summary

This PR fixes signed negative-integer decoding when JsonCpp is built with JSON_NO_INT64 and makes that configuration continuously testable.

• Keeps the final digit signed during negative integer reconstruction, preserving signed values and the intValue type.
• Guards code and test helpers that require 64-bit integer aliases.
• Adds boundary and container-context regression coverage.
• Selects configuration-specific corpus expectations through validated --json-config output.
• Adds a least-privilege CMake CI job for the no-int64 configuration.

Confidence Score: 5/5

The PR appears safe to merge; no outstanding correctness, security, or repository-rule issue remains.

The signed reconstruction now preserves negative integer values and types under JSON_NO_INT64, while out-of-range values retain their floating-point fallback. The previous workflow-security finding was manually resolved after the checkout action was pinned and the job was hardened.

Important Files Changed

Filename	Overview
src/lib_json/json_reader.cpp	Preserves signed arithmetic while reconstructing negative integers, including the minimum configured signed value.
src/lib_json/json_value.cpp	Excludes the unavailable UInt64-specific conversion overload when 64-bit integer support is disabled.
src/test_lib_json/main.cpp	Makes unit tests configuration-aware and adds comprehensive negative-integer and numeric-boundary regressions.
test/runjsontests.py	Validates the executable’s integer configuration and selects matching expected corpus output.
.github/workflows/cmake.yml	Adds a hardened CI job that builds and runs the complete no-int64 CTest suite.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A["JSON numeric token"] --> B["OurReader::decodeNumber"]
    B --> C{"Within configured integer range?"}
    C -->|Negative| D["Signed LargestInt reconstruction"]
    C -->|Non-negative| E["Signed or unsigned Value"]
    C -->|Out of range| F["Floating-point fallback"]
    D --> G["Json::Value tree"]
    E --> G
    F --> G
    G --> H["Unit and corpus round-trip tests"]

Loading

_{Reviews (2): Last reviewed commit: "Pin checkout and limit permissions in th..." | Re-trigger Greptile}