Feat: Implement better location reporting (Issue #158)

[miker2]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @miker2, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the debugging and traceability of configuration values within the system. It introduces a comprehensive mechanism to track the full lineage of a configuration item, providing a detailed history of how it was derived through various processing steps like references, variable substitutions, and expression evaluations. This enhancement provides much richer context for understanding the provenance of any given configuration value.

Highlights

• Enhanced Location Tracking: I've introduced an origins vector to the ConfigBase class to track the lineage of configuration values. This allows the loc() method to report not just the immediate source file and line, but also a chain of where the value originated from (e.g., through references, variable substitutions, or expressions).
• Propagation of Origin Information: I've modified several key helper functions in src/config_helpers.cpp (structFromReference, replaceProtoVar, resolveVarRefs, evaluateExpression) to correctly populate and propagate the new origins vector. This ensures that as configuration values are created, cloned, or transformed, their full derivation history is preserved.
• New Test Case for Location Reporting: I've added a new LocationReporting test case to tests/config_parse_test.cpp. This test specifically verifies that the enhanced loc() functionality correctly outputs the detailed origin chain, confirming the feature works as intended.

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[gemini-code-assist]

Code Review

This pull request introduces an important feature for better location reporting, which will be very helpful for debugging configurations. I've identified a few critical issues related to state modification of shared objects and test portability that need to be addressed. There's also a high-severity issue with how origins are added to expressions, which could lead to confusing location reports.

[gemini-code-assist]

Modifying the origins of a value object retrieved from the configuration map via getConfigValue can lead to incorrect origin information for other references, representing a state corruption bug.

[gemini-code-assist]

The test LocationReporting uses hardcoded absolute paths in EXPECT_THAT. This will cause the test to fail on any other machine or in a CI environment where the project path is different. Please use the baseDir() helper to construct the expected paths dynamically.

Suggested change

	EXPECT_THAT(output, testing::HasSubstr("var_ref1 = \"test\" # /Users/michael/repos/flexi_config_reader/examples/env/env_example1.cfg:1 (from /Users/michael/repos/flexi_config_reader/examples/config_example13.cfg:5)"));
	EXPECT_THAT(output, testing::HasSubstr("var_ref2 = \"test\" # /Users/michael/repos/flexi_config_reader/examples/env/env_example2.cfg:2 (from /Users/michael/repos/flexi_config_reader/examples/config_example13.cfg:6)"));
	const auto base_path = baseDir();
	const auto expected_loc1 = (base_path / "env/env_example1.cfg").string();
	const auto config_path = (base_path / "config_example13.cfg").string();
	const auto expected_loc3 = (base_path / "env/env_example2.cfg").string();
	EXPECT_THAT(output, testing::HasSubstr(fmt::format("var_ref1 = \"test\" # {}:1 (from {}:5)", expected_loc1, config_path)));
	EXPECT_THAT(output, testing::HasSubstr(fmt::format("var_ref2 = \"test\" # {}:2 (from {}:6)", expected_loc3, config_path)));

[gemini-code-assist]

This loop adds all variables from ref_vars to the new expression's origins. However, the expression may only use a subset of these variables, leading to inaccurate location information.

[gemini-code-assist]

This loop for constructing the origin string can be made more concise and potentially more efficient by using fmt::join with a range view. This avoids manual handling of separators and string concatenation in a loop.

    s += " (from ";
    auto origin_locs = origins | ranges::views::transform([](const auto& o) {
      return fmt::format("{}:{}", o->source, o->line);
    });
    s += fmt::join(origin_locs, " <- ");
    s += ")";