Prevent EnsureProviderValid from mutating

This function has caused repeated test failures with concurrent map mutations, the most
recent of which is
https://github.com/pulumi/pulumi-terraform-bridge/actions/runs/12772071950/job/35600764628?pr=2832. This
commit converts the function to return a copy instead of mutating.

pkg/internal/tests/pulcheck/pulcheck.go

@@ -52,8 +52,39 @@ func resourceNeedsUpdate(res *schema.Resource) bool {
 	return false
 }
 
+func copyMap[K comparable, V any](m map[K]V, cp func(V) V) map[K]V {
+	dst := make(map[K]V, len(m))
+	for k, v := range m {
+		dst[k] = cp(v)
+	}
+	return dst
+}
+
+// WithValidProvider returns a copy of tfp, with all required fields filled with default
+// values.
+//
 // This is an experimental API.
-func EnsureProviderValid(t T, tfp *schema.Provider) {
+func WithValidProvider(t T, tfp *schema.Provider) *schema.Provider {
+	if tfp == nil {
+		return nil
+	}
+
+	// Copy tfp as deep as we will mutate.
+	{
+		dst := *tfp // memcopy
+		dst.ResourcesMap = copyMap(tfp.ResourcesMap, func(v *schema.Resource) *schema.Resource {
+			cp := *v // memcopy
+			cp.Schema = copyMap(v.Schema, func(s *schema.Schema) *schema.Schema {
+				cp := *s
+				return &cp
+			})
+			return &cp
+		})
+		tfp = &dst
+	}
+
+	// Now ensure that tfp is valid
+
 	for _, r := range tfp.ResourcesMap {
 		if r.Schema["id"] == nil {
 			r.Schema["id"] = &schema.Schema{
@@ -108,6 +139,8 @@ func EnsureProviderValid(t T, tfp *schema.Provider) {
 		}
 	}
 	require.NoError(t, tfp.InternalValidate())
+
+	return tfp
 }
 
 func ProviderServerFromInfo(
@@ -206,7 +239,7 @@ func BridgedProvider(t T, providerName string, tfp *schema.Provider, opts ...Bri
 		opt(&options)
 	}
 
-	EnsureProviderValid(t, tfp)
+	tfp = WithValidProvider(t, tfp)
 
 	// If the PULUMI_ACCURATE_BRIDGE_PREVIEWS environment variable is set, use it to enable
 	// accurate bridge previews.

pkg/tests/tfcheck/tfcheck.go

@@ -76,7 +76,7 @@ func NewTfDriver(t pulcheck.T, dir, providerName string, prov any) *TFDriver {
 }
 
 func newTfDriverSDK(t pulcheck.T, dir, providerName string, prov *schema.Provider) *TFDriver {
-	pulcheck.EnsureProviderValid(t, prov)
+	prov = pulcheck.WithValidProvider(t, prov)
 	v6server, err := tf5to6server.UpgradeServer(context.Background(),
 		func() tfprotov5.ProviderServer { return prov.GRPCProvider() })
 	require.NoError(t, err)