feat: Augment schema parser error messages

[tbkr]

Description

Augment schema parser error messages. Now showing in which step of the schema file parsing the error is occurring.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌈🌦️📖🚧 Documentation FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/fdb/pull-requests/PR-277

[Copilot]

Pull request overview

This PR aims to improve diagnosability of FDB schema parsing failures by adding higher-level context (which parsing phase failed) to schema parser error handling, and introduces a small test suite + fixtures to exercise broken schema inputs.

Changes:

• Add parsing-stage context around schema parsing exceptions (types parsing vs rules parsing).
• Wrap schema-load parsing errors with additional file-path context.
• Add a new parsing test target with schema fixtures (valid schema and several intentionally broken schemas).

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
src/fdb5/rules/SchemaParser.cc	Adds try/catch blocks and logging to annotate errors during type/rule parsing phases.
src/fdb5/rules/Schema.cc	Wraps StreamParser::Error to add schema path context when load fails.
tests/fdb/CMakeLists.txt	Registers the new parsing test subdirectory.
tests/fdb/parsing/CMakeLists.txt	Adds a new unit test target and copies parsing fixtures into the build tree.
tests/fdb/parsing/test_schema_parsing.cc	Adds unit tests intended to exercise broken/valid schema inputs.
tests/fdb/parsing/data/schema	Adds a valid schema fixture.
tests/fdb/parsing/data/schema_incomplete_rule	Adds a broken schema fixture (missing closing bracket).
tests/fdb/parsing/data/broken_schema_no_rule	Adds a fixture with only type definitions and no rules.
tests/fdb/parsing/data/broken_types_missing_semicolon	Adds a broken types fixture (missing semicolon).
tests/fdb/parsing/data/broken_types_no_name	Adds a broken types fixture (missing name).
tests/fdb/parsing/data/broken_types_no_type	Adds a broken types fixture (missing type).

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.44970% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.63%. Comparing base (e5a5a47) to head (10b8bb0).

Files with missing lines	Patch %	Lines
src/fdb5/rules/SchemaParser.cc	93.05%	5 Missing ⚠️
tests/fdb/parsing/test_schema_parsing.cc	98.86%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #277      +/-   ##
===========================================
+ Coverage    77.51%   77.63%   +0.12%     
===========================================
  Files          411      412       +1     
  Lines        27553    27677     +124     
  Branches      2769     2771       +2     
===========================================
+ Hits         21358    21488     +130     
+ Misses        6195     6189       -6     

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[tbkr]

The fix from #276 should be merged first.

[caraghbiner]

I agree that 0 rules should be an error.

[tbkr]

ecmwf/eckit#293 needs to be merged first.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 11 comments.

[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (6)

src/fdb5/rules/SchemaParser.cc:46

• Grammar in this error message is incorrect ("character which are"). Also, adding a newline via std::endl ends up in what() and makes matching/printing noisier.

        std::stringstream buf;
        buf << "Schema file contained non-ASCII character which are not supported." << std::endl;
        throw SchemaParser::Error(buf.str(), parser_.line() + 1);

src/fdb5/rules/SchemaParser.cc:312

• Most parser errors use parser_.line() + 1, but this throws with parser_.line() which is inconsistent and likely off-by-one.

    if (result.size() == 0) {
        std::stringstream buf;
        buf << "SchemaParser::parse: Empty rule list. Didn't find any rule in the provided schema file." << std::endl;
        throw Error(buf.str(), parser_.line());
    }

src/fdb5/rules/Schema.cc:206

• This wrapper rethrows a fresh SchemaParser::Error without preserving the original error's line number (it will default to 0). It would be more useful to keep the line information from the underlying parse error when rethrowing (if the exception exposes it).

        std::stringstream buf;
        buf << "Error loading FDB schema file: " << path << ". Underlying issue: " << spe.what();
        throw SchemaParser::Error(buf.str());
    }

src/fdb5/rules/SchemaParser.h:41

• SchemaParser previously initialised the underlying eckit::StreamParser with the (in, true) constructor; the new member initialisation drops that boolean flag, which may change parsing behaviour. If the intent is only to improve error messages, keep the constructor arguments consistent.

    SchemaParser(std::istream& in) : parser_(eckit::StreamParser(in)) {}

src/fdb5/rules/SchemaParser.cc:305

• Most parser errors use parser_.line() + 1, but this one uses parser_.line() directly, which is likely to report an off-by-one line number compared to other failures.

This issue also appears on line 308 of the same file.

    if (c) {
        throw Error(std::string("SchemaParser::parse: Error parsing rules: remaining char: ") + c, parser_.line());
    }

src/fdb5/rules/Schema.cc:202

• Catch parser exceptions by const reference (no mutation intended, and it allows catching const exceptions).

    catch (SchemaParser::Error& spe) {