feat: Allow merging lock dependencies to tolerate a nil. This enables use of -safe-init and -intput=false; can write a dep lock file when init stops after downloading config-derived providers only.

internal/command/meta_dependencies.go

@@ -79,10 +79,20 @@ func (m *Meta) replaceLockedDependencies(new *depsfile.Locks) tfdiags.Diagnostic
 // This method supports downloading providers in 2 steps, and is used during the second download step and
 // while updating the dependency lock file.
 func (m *Meta) mergeLockedDependencies(baseLocks, additionalLocks *depsfile.Locks) *depsfile.Locks {
+	if baseLocks == nil && additionalLocks == nil {
+		return depsfile.NewLocks() // empty locks
+	}
+	if additionalLocks == nil {
+		return baseLocks
+	}
+	if baseLocks == nil {
+		return additionalLocks
+	}
 
-	mergedLocks := baseLocks.DeepCopy()
+	// Here we know that there are two sets of locks to combine and return
 
 	// Append locks derived from the state to locks derived from config.
+	mergedLocks := baseLocks.DeepCopy()
 	for _, lock := range additionalLocks.AllProviders() {
 		match := mergedLocks.Provider(lock.Provider())
 		if match != nil {

internal/command/meta_dependencies_test.go

@@ -17,7 +17,6 @@ import (
 // This tests combining locks from config and state. Locks derived from state are always unconstrained, i.e. no version constraint data,
 // so this test
 func Test_mergeLockedDependencies_config_and_state(t *testing.T) {
-
 	providerA := tfaddr.NewProvider(tfaddr.DefaultProviderRegistryHost, "my-org", "providerA")
 	providerB := tfaddr.NewProvider(tfaddr.DefaultProviderRegistryHost, "my-org", "providerB")
 	v1_0_0 := providerreqs.MustParseVersion("1.0.0")
@@ -38,6 +37,37 @@ func Test_mergeLockedDependencies_config_and_state(t *testing.T) {
 			stateLocks:    depsfile.NewLocks(),
 			expectedLocks: depsfile.NewLocks(),
 		},
+		"nil config locks": {
+			configLocks: nil,
+			stateLocks: func() *depsfile.Locks {
+				configLocks := depsfile.NewLocks()
+				configLocks.SetProvider(providerA, v1_0_0, versionConstraintv1, hashesProviderA)
+				return configLocks
+			}(),
+			expectedLocks: func() *depsfile.Locks {
+				combinedLocks := depsfile.NewLocks()
+				combinedLocks.SetProvider(providerA, v1_0_0, versionConstraintv1, hashesProviderA)
+				return combinedLocks
+			}(),
+		},
+		"nil state locks": {
+			configLocks: func() *depsfile.Locks {
+				configLocks := depsfile.NewLocks()
+				configLocks.SetProvider(providerA, v1_0_0, versionConstraintv1, hashesProviderA)
+				return configLocks
+			}(),
+			stateLocks: nil,
+			expectedLocks: func() *depsfile.Locks {
+				combinedLocks := depsfile.NewLocks()
+				combinedLocks.SetProvider(providerA, v1_0_0, versionConstraintv1, hashesProviderA)
+				return combinedLocks
+			}(),
+		},
+		"all nil locks": {
+			configLocks:   nil,
+			stateLocks:    nil,
+			expectedLocks: depsfile.NewLocks(),
+		},
 		"when provider only described in config, output locks have matching constraints": {
 			configLocks: func() *depsfile.Locks {
 				configLocks := depsfile.NewLocks()