configs: fix panic with provider aliases

addProviderRequirements() was incorrectly using the map keys from the module
provider configs when looking up the provider FQN. The map keys include
alias, so this resulted in a panic. Update addProviderRequirements() to
use the provider's name (only) when looking up the FQN.

configs/config.go

@@ -222,8 +222,8 @@ func (c *Config) addProviderRequirements(reqs getproviders.Requirements) hcl.Dia
 	}
 
 	// "provider" block can also contain version constraints
-	for name, provider := range c.Module.ProviderConfigs {
-		fqn := c.Module.ProviderForLocalConfig(addrs.LocalProviderConfig{LocalName: name})
+	for _, provider := range c.Module.ProviderConfigs {
+		fqn := c.Module.ProviderForLocalConfig(addrs.LocalProviderConfig{LocalName: provider.Name})
 		if _, ok := reqs[fqn]; !ok {
 			// We'll at least have an unconstrained dependency then, but might
 			// add to this in the loop below.

configs/config_test.go

@@ -162,3 +162,14 @@ func TestConfigProviderForConfigAddr(t *testing.T) {
 		t.Errorf("wrong result\ngot:  %s\nwant: %s", got, want)
 	}
 }
+
+func TestConfigAddProviderRequirements(t *testing.T) {
+	cfg, diags := testModuleConfigFromFile("testdata/valid-files/providers-explicit-implied.tf")
+	assertNoDiagnostics(t, diags)
+
+	reqs := getproviders.Requirements{
+		addrs.NewDefaultProvider("null"): nil,
+	}
+	diags = cfg.addProviderRequirements(reqs)
+	assertNoDiagnostics(t, diags)
+}