Merge pull request #12942 from hashicorp/jbardin/GH-12905

merge config.Terraform fields in config.Append

config/append.go

@@ -35,8 +35,13 @@ func Append(c1, c2 *Config) (*Config, error) {
 		c.Atlas = c2.Atlas
 	}
 
-	c.Terraform = c1.Terraform
+	// merge Terraform blocks
-	if c2.Terraform != nil {
+	if c1.Terraform != nil {
+		c.Terraform = c1.Terraform
+		if c2.Terraform != nil {
+			c.Terraform.Merge(c2.Terraform)
+		}
+	} else {
 		c.Terraform = c2.Terraform
 	}
 

config/append_test.go

@@ -118,6 +118,31 @@ func TestAppend(t *testing.T) {
 			},
 			false,
 		},
+
+		// appending configs merges terraform blocks
+		{
+			&Config{
+				Terraform: &Terraform{
+					RequiredVersion: "A",
+				},
+			},
+			&Config{
+				Terraform: &Terraform{
+					Backend: &Backend{
+						Type: "test",
+					},
+				},
+			},
+			&Config{
+				Terraform: &Terraform{
+					RequiredVersion: "A",
+					Backend: &Backend{
+						Type: "test",
+					},
+				},
+			},
+			false,
+		},
 	}
 
 	for i, tc := range cases {

config/config_terraform.go

@@ -47,6 +47,18 @@ func (t *Terraform) Validate() []error {
 	return errs
 }
 
+// Merge t with t2.
+// Any conflicting fields are overwritten by t2.
+func (t *Terraform) Merge(t2 *Terraform) {
+	if t2.RequiredVersion != "" {
+		t.RequiredVersion = t2.RequiredVersion
+	}
+
+	if t2.Backend != nil {
+		t.Backend = t2.Backend
+	}
+}
+
 // Backend is the configuration for the "backend" to use with Terraform.
 // A backend is responsible for all major behavior of Terraform's core.
 // The abstraction layer above the core (the "backend") allows for behavior

config/merge.go

@@ -32,9 +32,13 @@ func Merge(c1, c2 *Config) (*Config, error) {
 		c.Atlas = c2.Atlas
 	}
 
-	// Merge the Terraform configuration, which is a complete overwrite.
+	// Merge the Terraform configuration
-	c.Terraform = c1.Terraform
+	if c1.Terraform != nil {
-	if c2.Terraform != nil {
+		c.Terraform = c1.Terraform
+		if c2.Terraform != nil {
+			c.Terraform.Merge(c2.Terraform)
+		}
+	} else {
 		c.Terraform = c2.Terraform
 	}
 

config/merge_test.go

@@ -434,6 +434,31 @@ func TestMerge(t *testing.T) {
 			},
 			false,
 		},
+
+		// terraform blocks are merged, not overwritten
+		{
+			&Config{
+				Terraform: &Terraform{
+					RequiredVersion: "A",
+				},
+			},
+			&Config{
+				Terraform: &Terraform{
+					Backend: &Backend{
+						Type: "test",
+					},
+				},
+			},
+			&Config{
+				Terraform: &Terraform{
+					RequiredVersion: "A",
+					Backend: &Backend{
+						Type: "test",
+					},
+				},
+			},
+			false,
+		},
 	}
 
 	for i, tc := range cases {