Add Runner.Backend()

Closes #46.

This allows rulesets developed as plugins to add lint rules based on the
configuration of the state backend.

Author: pd

terraform/configs.go

@@ -69,6 +69,16 @@ type Connection struct {
 	DeclRange hcl.Range
 }
 
+// Backend is an alternative representation of configs.Backend.
+// https://github.com/hashicorp/terraform/blob/v0.12.26/configs/backend.go#L12-L18
+type Backend struct {
+	Type        string
+	Config      hcl.Body
+	ConfigRange hcl.Range
+	TypeRange   hcl.Range
+	DeclRange   hcl.Range
+}
+
 // ProvisionerWhen is an alternative representation of configs.ProvisionerWhen.
 // https://github.com/hashicorp/terraform/blob/v0.12.26/configs/provisioner.go#L172-L181
 type ProvisionerWhen int

tflint/client/client.go

@@ -103,6 +103,26 @@ func (c *Client) WalkResources(resource string, walker func(*terraform.Resource)
 	return nil
 }
 
+// Backend calls the server-side Backend method and returns the backend configuration.
+func (c *Client) Backend() (*terraform.Backend, error) {
+	log.Printf("[DEBUG] Backend")
+
+	var response BackendResponse
+	if err := c.rpcClient.Call("Plugin.Backend", BackendRequest{}, &response); err != nil {
+		return nil, err
+	}
+	if response.Err != nil {
+		return nil, response.Err
+	}
+
+	backend, diags := decodeBackend(response.Backend)
+	if diags.HasErrors() {
+		return nil, diags
+	}
+
+	return backend, nil
+}
+
 // EvaluateExpr calls the server-side EvalExpr method and reflects the response
 // in the passed argument.
 func (c *Client) EvaluateExpr(expr hcl.Expression, ret interface{}) error {

tflint/client/client_test.go

@@ -85,6 +85,17 @@ func (*mockServer) Resources(req *ResourcesRequest, resp *ResourcesResponse) err
 	return nil
 }
 
+func (*mockServer) Backend(req *BackendRequest, resp *BackendResponse) error {
+	*resp = BackendResponse{Backend: &Backend{
+		Type:        "example",
+		Config:      []byte(`storage = "cloud"`),
+		ConfigRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 5}, End: hcl.Pos{Line: 3, Column: 22}},
+		DeclRange:   hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 2, Column: 3}, End: hcl.Pos{Line: 2, Column: 22}},
+		TypeRange:   hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 2, Column: 11}, End: hcl.Pos{Line: 2, Column: 19}},
+	}, Err: nil}
+	return nil
+}
+
 func (*mockServer) EvalExpr(req *EvalExprRequest, resp *EvalExprResponse) error {
 	*resp = EvalExprResponse{Val: cty.StringVal("1"), Err: nil}
 	return nil
@@ -150,6 +161,53 @@ func Test_WalkResourceAttributes(t *testing.T) {
 	}
 }
 
+func Test_Backend(t *testing.T) {
+	client, server := startMockServer(t)
+	defer server.Listener.Close()
+
+	expected := &terraform.Backend{
+		Type: "example",
+		Config: &hclsyntax.Body{
+			Attributes: hclsyntax.Attributes{
+				"storage": {
+					Name: "storage",
+					Expr: &hclsyntax.TemplateExpr{
+						Parts: []hclsyntax.Expression{
+							&hclsyntax.LiteralValueExpr{
+								SrcRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 16}, End: hcl.Pos{Line: 3, Column: 21}},
+							},
+						},
+						SrcRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 15}, End: hcl.Pos{Line: 3, Column: 22}},
+					},
+					SrcRange:    hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 5}, End: hcl.Pos{Line: 3, Column: 22}},
+					NameRange:   hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 5}, End: hcl.Pos{Line: 3, Column: 12}},
+					EqualsRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 13}, End: hcl.Pos{Line: 3, Column: 14}},
+				},
+			},
+			Blocks:   hclsyntax.Blocks{},
+			SrcRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 5}, End: hcl.Pos{Line: 3, Column: 22}},
+			EndRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 22}, End: hcl.Pos{Line: 3, Column: 22}},
+		},
+		ConfigRange: hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 3, Column: 5}, End: hcl.Pos{Line: 3, Column: 22}},
+		DeclRange:   hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 2, Column: 3}, End: hcl.Pos{Line: 2, Column: 22}},
+		TypeRange:   hcl.Range{Filename: "example.tf", Start: hcl.Pos{Line: 2, Column: 11}, End: hcl.Pos{Line: 2, Column: 19}},
+	}
+
+	backend, err := client.Backend()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	opts := []cmp.Option{
+		cmpopts.IgnoreUnexported(hclsyntax.Body{}),
+		cmpopts.IgnoreFields(hclsyntax.LiteralValueExpr{}, "Val"),
+		cmpopts.IgnoreFields(hcl.Pos{}, "Byte"),
+	}
+	if !cmp.Equal(expected, backend, opts...) {
+		t.Fatalf("Diff: %s", cmp.Diff(expected, backend, opts...))
+	}
+}
+
 func Test_WalkResourceBlocks(t *testing.T) {
 	client, server := startMockServer(t)
 	defer server.Listener.Close()

tflint/client/decode.go

@@ -165,6 +165,34 @@ func decodeManagedResource(resource *ManagedResource) (*terraform.ManagedResourc
 	}, nil
 }
 
+// Backend is an intermediate representation of terraform.Backend.
+type Backend struct {
+	Type        string
+	Config      []byte
+	ConfigRange hcl.Range
+	TypeRange   hcl.Range
+	DeclRange   hcl.Range
+}
+
+func decodeBackend(backend *Backend) (*terraform.Backend, hcl.Diagnostics) {
+	if backend == nil {
+		return nil, nil
+	}
+
+	file, diags := parseConfig(backend.Config, backend.ConfigRange.Filename, backend.ConfigRange.Start)
+	if diags.HasErrors() {
+		return nil, diags
+	}
+
+	return &terraform.Backend{
+		Type:        backend.Type,
+		Config:      file.Body,
+		TypeRange:   backend.TypeRange,
+		DeclRange:   backend.DeclRange,
+		ConfigRange: backend.ConfigRange,
+	}, nil
+}
+
 // Connection is an intermediate representation of terraform.Connection.
 type Connection struct {
 	Config      []byte

tflint/client/rpc.go

@@ -17,6 +17,15 @@ type AttributesResponse struct {
 	Err        error
 }
 
+// BackendRequest is a request to the server-side Backend method.
+type BackendRequest struct{}
+
+// BackendResponse is a response to the server-side Backend method.
+type BackendResponse struct {
+	Backend *Backend
+	Err     error
+}
+
 // BlocksRequest is a request to the server-side Blocks method.
 type BlocksRequest struct {
 	Resource  string

tflint/interface.go

@@ -20,6 +20,9 @@ type Runner interface {
 	// You must pass a resource type as the first argument.
 	WalkResources(string, func(*terraform.Resource) error) error
 
+	// Backend returns the backend configuration, if any.
+	Backend() (*terraform.Backend, error)
+
 	// EvaluateExpr evaluates the passed expression and reflects the result in ret.
 	// Since this function returns an application error, it is expected to use the EnsureNoError
 	// to determine whether to continue processing.

tflint/server/server.go

@@ -7,6 +7,7 @@ type Server interface {
 	Attributes(*client.AttributesRequest, *client.AttributesResponse) error
 	Blocks(*client.BlocksRequest, *client.BlocksResponse) error
 	Resources(*client.ResourcesRequest, *client.ResourcesResponse) error
+	Backend(*client.BackendRequest, *client.BackendResponse) error
 	EvalExpr(*client.EvalExprRequest, *client.EvalExprResponse) error
 	EmitIssue(*client.EmitIssueRequest, *interface{}) error
 }