fix(alertgroups): add expression validator to detect new lines on expressions (#807)

stackit/internal/services/observability/alertgroup/resource.go

@@ -207,6 +207,10 @@ func (a *alertGroupResource) Schema(_ context.Context, _ resource.SchemaRequest,
 							Required:    true,
 							Validators: []validator.String{
 								stringvalidator.LengthBetween(1, 600),
+								// The API currently accepts expressions with trailing newlines but does not return them,
+								// leading to inconsistent Terraform results. This issue has been reported to the Obs team.
+								// Until it is resolved, we proactively notify users if their input contains a trailing newline.
+								validate.ValidNoTrailingNewline(),
 							},
 						},
 						"for": schema.StringAttribute{

stackit/internal/services/observability/log-alertgroup/resource.go

@@ -207,6 +207,10 @@ func (l *logAlertGroupResource) Schema(_ context.Context, _ resource.SchemaReque
 							Required:    true,
 							Validators: []validator.String{
 								stringvalidator.LengthBetween(1, 600),
+								// The API currently accepts expressions with trailing newlines but does not return them,
+								// leading to inconsistent Terraform results. This issue has been reported to the Obs team.
+								// Until it is resolved, we proactively notify users if their input contains a trailing newline.
+								validate.ValidNoTrailingNewline(),
 							},
 						},
 						"for": schema.StringAttribute{

stackit/internal/services/ske/cluster/resource.go

@@ -997,7 +997,7 @@ func toNodepoolsPayload(ctx context.Context, m *Model, availableMachineVersions
 			if v.IsNull() || v.IsUnknown() {
 				continue
 			}
-			s, err := conversion.ToString(context.TODO(), v)
+			s, err := conversion.ToString(ctx, v)
 			if err != nil {
 				continue
 			}

stackit/internal/validate/validate.go

@@ -313,3 +313,34 @@ func ValidDurationString() *Validator {
 		},
 	}
 }
+
+// ValidNoTrailingNewline returns a Validator that checks if the input string has no trailing newline
+// character ("\n" or "\r\n"). If a trailing newline is present, a diagnostic error will be appended.
+func ValidNoTrailingNewline() *Validator {
+	description := `The value must not have a trailing newline character ("\n" or "\r\n"). You can remove a trailing newline by using Terraform's built-in chomp() function.`
+
+	return &Validator{
+		description: description,
+		validate: func(_ context.Context, req validator.StringRequest, resp *validator.StringResponse) {
+			val := req.ConfigValue.ValueString()
+			if val == "" {
+				return
+			}
+			if len(val) >= 2 && val[len(val)-2:] == "\r\n" {
+				resp.Diagnostics.Append(validatordiag.InvalidAttributeValueDiagnostic(
+					req.Path,
+					description,
+					val,
+				))
+				return
+			}
+			if val[len(val)-1] == '\n' {
+				resp.Diagnostics.Append(validatordiag.InvalidAttributeValueDiagnostic(
+					req.Path,
+					description,
+					val,
+				))
+			}
+		},
+	}
+}

stackit/internal/validate/validate_test.go

@@ -845,3 +845,74 @@ func TestValidTtlDuration(t *testing.T) {
 		})
 	}
 }
+
+func TestValidNoTrailingNewline(t *testing.T) {
+	tests := []struct {
+		description string
+		input       string
+		isValid     bool
+	}{
+		{
+			"string with no trailing newline",
+			"abc",
+			true,
+		},
+		{
+			"string with trailing \\n",
+			"abc\n",
+			false,
+		},
+		{
+			"string with trailing \\r\\n",
+			"abc\r\n",
+			false,
+		},
+		{
+			"string with internal newlines but not trailing",
+			"abc\ndef\nghi",
+			true,
+		},
+		{
+			"empty string",
+			"",
+			true,
+		},
+		{
+			"string that is just \\n",
+			"\n",
+			false,
+		},
+		{
+			"string that is just \\r\\n",
+			"\r\n",
+			false,
+		},
+		{
+			"string with multiple newlines, trailing",
+			"abc\n\n",
+			false,
+		},
+		{
+			"string with newlines but ends with character",
+			"abc\ndef\n",
+			false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.description, func(t *testing.T) {
+			r := validator.StringResponse{}
+			va := ValidNoTrailingNewline()
+			va.ValidateString(context.Background(), validator.StringRequest{
+				ConfigValue: types.StringValue(tt.input),
+			}, &r)
+
+			if !tt.isValid && !r.Diagnostics.HasError() {
+				t.Fatalf("Expected validation to fail for input: %q", tt.input)
+			}
+			if tt.isValid && r.Diagnostics.HasError() {
+				t.Fatalf("Expected validation to succeed for input: %q, but got errors: %v", tt.input, r.Diagnostics.Errors())
+			}
+		})
+	}
+}