feat: config file

[mickamy]

No description provided.

[Copilot]

Pull request overview

Adds YAML-based configuration support for sql-tapd, allowing runtime settings to be loaded from a config file and overridden by CLI flags.

Changes:

• Introduces a config package with defaults and a YAML loader (with unknown-field detection).
• Updates sql-tapd to load config from .sql-tap.yaml (or -config) and apply CLI overrides only for explicitly-set flags.
• Extends golangci-lint tag style rules to enforce yaml tags as snake_case.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
config/config.go	New config model, defaults, and YAML loader with KnownFields(true) to catch typos.
config/config_test.go	Unit tests for defaults, explicit/implicit loading behavior, partial overrides, and invalid/unknown YAML.
cmd/sql-tapd/main.go	Wires config loading into sql-tapd, implements “explicit flag overrides config” semantics, and refactors run signature.
.golangci.yaml	Enforces snake_case for YAML struct tags via tagliatelle.

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[Copilot]

The flag descriptions for -driver/-listen/-upstream still say "(required)", but this PR also allows providing those values via the config file. Consider updating the help text to reflect that they are only required when not set in the config (e.g., "required unless provided by -config / .sql-tap.yaml").

Suggested change

	driver := fs.String("driver", "", "database driver: postgres, mysql, tidb (required)")
	listen := fs.String("listen", "", "client listen address (required)")
	upstream := fs.String("upstream", "", "upstream database address (required)")
	driver := fs.String("driver", "", "database driver: postgres, mysql, tidb (required unless provided by -config / .sql-tap.yaml)")
	listen := fs.String("listen", "", "client listen address (required unless provided by -config / .sql-tap.yaml)")
	upstream := fs.String("upstream", "", "upstream database address (required unless provided by -config / .sql-tap.yaml)")

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

cmd/sql-tapd/main.go:141

• explainDriver is left as the zero value when cfg.Driver is not one of mysql/tidb/postgres, which maps to explain.Postgres (Driver iota=0). That means an unsupported driver can incorrectly initialize the EXPLAIN client as Postgres before later failing in the proxy switch. Consider adding a default case that returns an error (or validating cfg.Driver once up-front) so unsupported drivers don’t silently fall back to Postgres behavior.

		var explainDriver explain.Driver
		switch cfg.Driver {
		case "mysql":
			explainDriver = explain.MySQL
		case "tidb":
			explainDriver = explain.TiDB
		case "postgres":
			explainDriver = explain.Postgres
		}
		explainClient = explain.NewClient(db, explainDriver)

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