terraform: fix ProviderConfigTransformer

The ProviderConfigTransformer was using only the provider FQN to attach
a provider configuration to the provider, but what it needs to do is
find the local name for the given provider FQN (which may not match the
type name) and use that when searching for matching provider
configuration.

Fixes #26556

This will also be backported to the v0.13 branch.

terraform/context_validate_test.go

@@ -650,6 +650,38 @@ func TestContext2Validate_providerConfig_good(t *testing.T) {
 	}
 }
 
+// In this test there is a mismatch between the provider's fqn (hashicorp/test)
+// and it's local name set in required_providers (arbitrary).
+func TestContext2Validate_requiredProviderConfig(t *testing.T) {
+	m := testModule(t, "validate-required-provider-config")
+	p := testProvider("aws")
+
+	p.GetSchemaReturn = &ProviderSchema{
+		Provider: &configschema.Block{
+			Attributes: map[string]*configschema.Attribute{
+				"required_attribute": {Type: cty.String, Required: true},
+			},
+		},
+		ResourceTypes: map[string]*configschema.Block{
+			"aws_instance": {
+				Attributes: map[string]*configschema.Attribute{},
+			},
+		},
+	}
+
+	c := testContext2(t, &ContextOpts{
+		Config: m,
+		Providers: map[addrs.Provider]providers.Factory{
+			addrs.NewDefaultProvider("aws"): testProviderFuncFixed(p),
+		},
+	})
+
+	diags := c.Validate()
+	if diags.HasErrors() {
+		t.Fatalf("unexpected error: %s", diags.Err())
+	}
+}
+
 func TestContext2Validate_provisionerConfig_bad(t *testing.T) {
 	m := testModule(t, "validate-bad-prov-conf")
 	p := testProvider("aws")

terraform/testdata/validate-required-provider-config/main.tf

@@ -0,0 +1,20 @@
+# This test verifies that the provider local name, local config and fqn map
+# together properly when the local name does not match the type.
+
+terraform {
+  required_providers {
+    arbitrary = {
+      source = "hashicorp/aws"
+    }
+  }
+}
+
+# hashicorp/test has required provider config attributes. This "arbitrary"
+# provider configuration block should map to hashicorp/test.
+provider "arbitrary" {
+  required_attribute = "bloop"
+}
+
+resource "aws_instance" "test" {
+  provider = "arbitrary"
+}

terraform/transform_provider.go

@@ -721,9 +721,12 @@ func (t *ProviderConfigTransformer) attachProviderConfigs(g *Graph) error {
 			continue
 		}
 
+		// Find the localName for the provider fqn
+		localName := mc.Module.LocalNameForProvider(addr.Provider)
+
 		// Go through the provider configs to find the matching config
 		for _, p := range mc.Module.ProviderConfigs {
-			if p.Name == addr.Provider.Type && p.Alias == addr.Alias {
+			if p.Name == localName && p.Alias == addr.Alias {
 				log.Printf("[TRACE] ProviderConfigTransformer: attaching to %q provider configuration from %s", dag.VertexName(v), p.DeclRange)
 				apn.AttachProvider(p)
 				break