Fix a race condition when evaluating on the root context

[wata727]

Fixes #2094

#1944 parallelized the inspection of child modules, but did not take into account side effects that the child modules could cause on the root module. These are unsafe because the root module is shared by each child module (goroutine).

tflint/cmd/inspect.go

Lines 162 to 174 in 90494f3

	// Run checks for module calls are performed in parallel.
	// The rootRunner is shared between goroutines but read-only, so this is goroutine-safe.
	// Note that checks against the rootRunner are not parallelized, as autofix may cause the module to be rebuilt.
	ch := make(chan error, len(moduleRunners))
	for _, runner := range moduleRunners {
	if opts.NoParallelRunners {
	ch <- ruleset.Check(plugin.NewGRPCServer(runner, rootRunner, cli.loader.Files(), sdkVersions[name]))
	} else {
	go func(runner *tflint.Runner) {
	ch <- ruleset.Check(plugin.NewGRPCServer(runner, rootRunner, cli.loader.Files(), sdkVersions[name]))
	}(runner)
	}
	}

The side effect reported in #2094 was the call stack. TFLint detects loops while building the call stack to prevent infinite loops when evaluating local values ​​with circular references. This call stack was shared per Runner (Evaluator).

tflint/terraform/evaluator.go

Lines 76 to 82 in a7ebc9b

	type Evaluator struct {
	Meta *ContextMeta
	ModulePath addrs.ModuleInstance
	Config *Config
	VariableValues map[string]map[string]cty.Value
	CallStack *CallStack
	}

This means that the call stack with side effects is shared between goroutines.

To prevent this, we moved the call stack into a scope instead of the evaluator. The scope is initialized per evaluation and therefore is not shared between goroutines. As a result, the race condition is fixed.

tflint/terraform/evaluator.go

Lines 84 to 90 in a7ebc9b

	// EvaluateExpr takes the given HCL expression and evaluates it to produce a value.
	func (e *Evaluator) EvaluateExpr(expr hcl.Expression, wantType cty.Type) (cty.Value, hcl.Diagnostics) {
	if e == nil {
	panic("evaluator must not be nil")
	}
	return e.scope().EvalExpr(expr, wantType)
	}

To prevent such bugs, we added a test case to run with go test --race. In general, this tends to slow down compilation speed, so we only run some tests with --race, and we expect to increase the number of tests if similar bugs are found.