Improve the overall speed and memory use of libCellML

[agarny]

Fixes #1368.

[Copilot]

Pull request overview

This PR focuses on improving libCellML performance and memory usage by removing some regex usage, reducing copying/allocations, adding caches/sets for faster lookups, and switching several internal containers to unordered variants. It also updates tests to cover new XML/Printer and Generator edge cases.

Changes:

• Replace regex-heavy logic with simpler string/character operations and pre-reserve strings/vectors to reduce allocations.
• Introduce caching and set/unordered_set-based membership checks to reduce repeated linear scans during analysis/validation/printing.
• Change a large portion of the public C++ API to return const std::string& / const std::vector<...>&, and update build settings (C++20 + macOS deployment target).

Reviewed changes

Copilot reviewed 55 out of 56 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/printer/printer.cpp	Adds Printer tests for XML processing-instruction/malformed XML in Math.
tests/coverage/coverage.cpp	Adds coverage tests for generator version strings and Printer math edge case.
src/xmlnode.h	Replaces hasAttribute() with rawName() API.
src/xmlnode.cpp	Optimises element checks; adds rawName(); streamlines attribute access.
src/xmldoc.cpp	Removes regex in error callback; uses std::replace for newline cleanup.
src/xmlattribute.cpp	Avoids string allocations for namespace comparisons; adds nullptr namespace handling.
src/variable.cpp	Reduces lambda captures; removes unnecessary captures; returns string refs for some getters.
src/validator.cpp	Replaces repeated linear searches with (un)ordered sets; uses std::format; reduces copies.
src/utilities.h	Changes analyserVariables() to return by reference.
src/utilities.cpp	Adds reserve() calls; speeds equivalent-variable traversal with a seen set; uses std::format.
src/units.cpp	Avoids temporary copies when reading/updating unit definitions.
src/reset.cpp	Changes getters to return const std::string& to avoid copies.
src/printer.cpp	Removes regex from math printing and connection de-duplication; reduces allocations; adds sets.
src/parser.cpp	Reduces copies in namespace validation; adds string reserve for issue text.
src/namedentity.cpp	Changes name() to return const std::string&.
src/model.cpp	Uses unordered_set to de-dupe import requirements; reduces lambda captures.
src/issue.cpp	Changes description() to return const std::string&.
src/internaltypes.h	Switches several internal maps to unordered variants (incl. ConnectionMap).
src/importsource.cpp	Changes url() to return const std::string&.
src/importer.cpp	Speeds library lookups with find/emplace; uses unordered_set for name checks.
src/importedentity.cpp	Changes importReference() to return const std::string&.
src/generatorvariabletracker.cpp	Avoids intermediate vector copies; reserves result capacity.
src/generatorprofiletools.cpp	Reserves profile string buffer.
src/generatorprofile.cpp	Changes many getters to return const std::string&.
src/generator_p.h	Updates Generator impl APIs and switches dependency tracking to unordered sets.
src/entity.cpp	Changes id() to return const std::string&.
src/debug.cpp	Reserves output buffer for AST printing.
src/componententity.cpp	Reduces lambda captures; changes encapsulationId getter to string ref.
src/component.cpp	Reduces lambda captures; changes math getter to string ref.
src/commonutils.cpp	Simplifies owningModel traversal using parent chain.
src/api/libcellml/variable.h	Public API: returns string refs for initialValue/interfaceType.
src/api/libcellml/reset.h	Public API: returns string refs for reset/test values and IDs.
src/api/libcellml/namedentity.h	Public API: returns string ref for name().
src/api/libcellml/issue.h	Public API: returns string ref for description().
src/api/libcellml/importsource.h	Public API: returns string ref for url().
src/api/libcellml/importedentity.h	Public API: returns string ref for importReference().
src/api/libcellml/generatorprofile.h	Public API: returns string refs for many profile strings.
src/api/libcellml/entity.h	Public API: returns string ref for id().
src/api/libcellml/componententity.h	Public API: returns string ref for encapsulationId().
src/api/libcellml/component.h	Public API: returns string ref for math().
src/api/libcellml/analysermodel.h	Public API: returns vector refs for model collections.
src/api/libcellml/analyserexternalvariable.h	Public API: returns vector ref for dependencies.
src/api/libcellml/analyserequationast.h	Public API: returns string ref for AST value.
src/api/libcellml/analyserequation.h	Public API: returns vector refs for equation collections.
src/annotator.cpp	Uses std::format; reduces repeated lookups; reserves buffers for hashing.
src/analyservariable.cpp	Reserves vector capacity when materialising weakptr lists.
src/analysermodel_p.h	Adds analyser-variable and equivalence caching structures.
src/analysermodel.cpp	Returns vectors by ref; adds analyser-variable cache; updates equivalence cache keying.
src/analyserexternalvariable.cpp	Reduces lambda captures; returns dependencies by ref.
src/analyserequationast.cpp	Returns AST value by ref.
src/analyserequation.cpp	Reserves capacities; returns various vectors by ref.
src/analyser_p.h	Adds caches and sets for membership; switches maps to unordered variants.
src/analyser.cpp	Removes repeated linear scans via sets/caches; uses raw XML names for faster MathML dispatch.
CMakeLists.txt	Sets C++20 and raises macOS deployment target.
.github/workflows/deploy-on-release.yml	Updates macOS deployment target used for release builds.

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