Bug/missing AllowRoot panics no context methods

[nilsolofsson]

If you setup otelsql without passing otelsql.AllowRoot() any calls to a "No Context" variant of the query methods will cause a panic in the runtime.

This PR solves this by making sure that methodTracer isn't null before applying the queryTrace function to the middlewares.

[nhatthm]

Hi, I don't get the problem. Could you please elaborate?

any calls to a "No Context" variant of the query

[nilsolofsson]

Yeah sorry, should have a personal proof reader 😄
The issue is specifically (atleast from my investigation) happening for prepared statements. But if you create a prepared statement and call any "non-context" query method there will be a nil-pointer panic, due to the current makeQueryerContextMiddlewares adding a middleware that references a nil interface.

To clarify here's an example that produces the panic without this PR.

	drivername, err := otelsql.Register("postgres",
		// uncomment to allow otelsql to create root spans
		// otelsql.AllowRoot(),
		otelsql.TraceQueryWithoutArgs(),
		otelsql.TraceRowsAffected(),
		otelsql.TraceLastInsertID(),
	)
	if err != nil {
		panic(err)
	}

	sqlDB, err := sql.Open(drivername, dataSourceName)
	if err != nil {
		return err
	}
	sqlxDB := sqlx.NewDb(sqlDB, "postgres")

	stmt, err := sqlxDB.Prepare("SELECT 1")
	if err != nil {
		return err
	}

	_, err = stmt.Query() // <--- This will result in a panic due to nil pointers
	if err != nil {
		return err	
	}

[nhatthm]

Cool! Thanks for the example ❤️

[codecov]

Codecov Report

Merging #227 (0c5693b) into master (3e506ca) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #227   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         1217      1219    +2     
=========================================
+ Hits          1217      1219    +2     

Flag	Coverage Δ
unittests-Linux-X64	100.00% <100.00%> (ø)
unittests-Windows-X64	100.00% <100.00%> (ø)
unittests-macOS-X64	100.00% <100.00%> (ø)

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Files Changed	Coverage Δ
query.go	100.00% <100.00%> (ø)

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