backend/remote: fix an error that prevents checking constraints

backend/remote/backend.go

@@ -224,7 +224,7 @@ func (b *Remote) Configure(obj cty.Value) tfdiags.Diagnostics {
 	}
 
 	// Check any retrieved constraints to make sure we are compatible.
-	if constraints == nil {
+	if constraints != nil {
 		diags = diags.Append(b.checkConstraints(constraints))
 	}
 

backend/remote/backend_test.go

@@ -128,6 +128,84 @@ func TestRemote_config(t *testing.T) {
 	}
 }
 
+func TestRemote_versionConstraints(t *testing.T) {
+	cases := map[string]struct {
+		config     cty.Value
+		prerelease string
+		version    string
+		result     string
+	}{
+		"compatible version": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"hostname":     cty.NullVal(cty.String),
+				"organization": cty.StringVal("hashicorp"),
+				"token":        cty.NullVal(cty.String),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name":   cty.StringVal("prod"),
+					"prefix": cty.NullVal(cty.String),
+				}),
+			}),
+			version: "0.11.1",
+		},
+		"version too old": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"hostname":     cty.NullVal(cty.String),
+				"organization": cty.StringVal("hashicorp"),
+				"token":        cty.NullVal(cty.String),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name":   cty.StringVal("prod"),
+					"prefix": cty.NullVal(cty.String),
+				}),
+			}),
+			version: "0.10.1",
+			result:  "upgrade Terraform to >= 0.11.8",
+		},
+		"version too new": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"hostname":     cty.NullVal(cty.String),
+				"organization": cty.StringVal("hashicorp"),
+				"token":        cty.NullVal(cty.String),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name":   cty.StringVal("prod"),
+					"prefix": cty.NullVal(cty.String),
+				}),
+			}),
+			version: "0.12.0",
+			result:  "downgrade Terraform to <= 0.11.11",
+		},
+	}
+
+	// Save and restore the actual version.
+	p := version.Prerelease
+	v := version.Version
+	defer func() {
+		version.Prerelease = p
+		version.Version = v
+	}()
+
+	for name, tc := range cases {
+		s := testServer(t)
+		b := New(testDisco(s))
+
+		// Set the version for this test.
+		version.Prerelease = tc.prerelease
+		version.Version = tc.version
+
+		// Validate
+		valDiags := b.ValidateConfig(tc.config)
+		if valDiags.HasErrors() {
+			t.Fatalf("%s: unexpected validation result: %v", name, valDiags.Err())
+		}
+
+		// Configure
+		confDiags := b.Configure(tc.config)
+		if (confDiags.Err() != nil || tc.result != "") &&
+			(confDiags.Err() == nil || !strings.Contains(confDiags.Err().Error(), tc.result)) {
+			t.Fatalf("%s: unexpected configure result: %v", name, confDiags.Err())
+		}
+	}
+}
+
 func TestRemote_localBackend(t *testing.T) {
 	b := testBackendDefault(t)
 
@@ -323,7 +401,16 @@ func TestRemote_checkConstraints(t *testing.T) {
 		},
 	}
 
+	// Save and restore the actual version.
+	p := version.Prerelease
+	v := version.Version
+	defer func() {
+		version.Prerelease = p
+		version.Version = v
+	}()
+
 	for name, tc := range cases {
+		// Set the version for this test.
 		version.Prerelease = tc.prerelease
 		version.Version = tc.version
 

backend/remote/testing.go

@@ -181,7 +181,21 @@ func testServer(t *testing.T) *httptest.Server {
 	// Respond to service discovery calls.
 	mux.HandleFunc("/well-known/terraform.json", func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
-		io.WriteString(w, `{"tfe.v2.1":"/api/v2/"}`)
+		io.WriteString(w, `{
+  "tfe.v2.1": "/api/v2/",
+  "versions.v1": "/v1/versions/"
+}`)
+	})
+
+	// Respond to service version constraints calls.
+	mux.HandleFunc("/v1/versions/", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		io.WriteString(w, `{
+  "service": "tfe.v2.1",
+  "product": "terraform",
+	"minimum": "0.11.8",
+	"maximum": "0.11.11"
+}`)
 	})
 
 	// Respond to the initial query to read the hashicorp org entitlements.
@@ -243,7 +257,8 @@ func testServer(t *testing.T) *httptest.Server {
 // localhost to a local test server.
 func testDisco(s *httptest.Server) *disco.Disco {
 	services := map[string]interface{}{
-		"tfe.v2.1": fmt.Sprintf("%s/api/v2/", s.URL),
+		"tfe.v2.1":    fmt.Sprintf("%s/api/v2/", s.URL),
+		"versions.v1": fmt.Sprintf("%s/v1/versions/", s.URL),
 	}
 	d := disco.NewWithCredentialsSource(credsSrc)