feat: add validation warnings for 5-field cron expressions

- Detect when users provide Unix 5-field cron format
- Provide helpful warning with suggested 6-field conversion
- Maintain backwards compatibility - expressions still work
- Add comprehensive tests for validation function

This helps users avoid confusion where '*/5 * * * *' (intended for
every 5 minutes) actually runs every 5 seconds due to the missing
seconds field.

Author: blink-so[bot]

provider/script.go

@@ -3,6 +3,7 @@ package provider
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/google/uuid"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/diag"
@@ -13,6 +14,32 @@ import (
 
 var ScriptCRONParser = cron.NewParser(cron.Second | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.DowOptional | cron.Descriptor)
 
+// ValidateCronExpression validates a cron expression and provides helpful warnings for common mistakes
+func ValidateCronExpression(cronExpr string) (warnings []string, errors []error) {
+	// Check if it looks like a 5-field Unix cron expression
+	fields := strings.Fields(cronExpr)
+	if len(fields) == 5 {
+		// Try to parse as standard Unix cron (without seconds)
+		unixParser := cron.NewParser(cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.DowOptional | cron.Descriptor)
+		if _, err := unixParser.Parse(cronExpr); err == nil {
+			// It's a valid 5-field expression, provide a helpful warning
+			warnings = append(warnings, fmt.Sprintf(
+				"The cron expression '%s' appears to be in Unix 5-field format. "+
+					"Coder uses 6-field format (seconds minutes hours day month day-of-week). "+
+					"Consider prefixing with '0 ' to run at the start of each minute: '0 %s'",
+				cronExpr, cronExpr))
+		}
+	}
+
+	// Validate with the actual 6-field parser
+	_, err := ScriptCRONParser.Parse(cronExpr)
+	if err != nil {
+		errors = append(errors, fmt.Errorf("%s is not a valid cron expression: %w", cronExpr, err))
+	}
+
+	return warnings, errors
+}
+
 func scriptResource() *schema.Resource {
 	return &schema.Resource{
 		SchemaVersion: 1,
@@ -78,11 +105,7 @@ func scriptResource() *schema.Resource {
 					if !ok {
 						return []string{}, []error{fmt.Errorf("got type %T instead of string", i)}
 					}
-					_, err := ScriptCRONParser.Parse(v)
-					if err != nil {
-						return []string{}, []error{fmt.Errorf("%s is not a valid cron expression: %w", v, err)}
-					}
-					return nil, nil
+					return ValidateCronExpression(v)
 				},
 			},
 			"start_blocks_login": {

provider/script_test.go

@@ -8,6 +8,8 @@ import (
 
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/resource"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/terraform"
+
+	"github.com/coder/terraform-provider-coder/v2/provider"
 )
 
 func TestScript(t *testing.T) {
@@ -124,3 +126,73 @@ func TestScriptStartBlocksLoginRequiresRunOnStart(t *testing.T) {
 		}},
 	})
 }
+
+func TestValidateCronExpression(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name           string
+		cronExpr       string
+		expectWarnings bool
+		expectErrors   bool
+		warningContains string
+	}{
+		{
+			name:           "valid 6-field expression",
+			cronExpr:       "0 0 22 * * *",
+			expectWarnings: false,
+			expectErrors:   false,
+		},
+		{
+			name:           "valid 6-field expression with seconds",
+			cronExpr:       "30 0 9 * * 1-5",
+			expectWarnings: false,
+			expectErrors:   false,
+		},
+		{
+			name:            "5-field Unix format - should warn",
+			cronExpr:        "0 22 * * *",
+			expectWarnings:  true,
+			expectErrors:    false,
+			warningContains: "appears to be in Unix 5-field format",
+		},
+		{
+			name:            "5-field every 5 minutes - should warn",
+			cronExpr:        "*/5 * * * *",
+			expectWarnings:  true,
+			expectErrors:    false,
+			warningContains: "Consider prefixing with '0 '",
+		},
+		{
+			name:         "invalid expression",
+			cronExpr:     "invalid",
+			expectErrors: true,
+		},
+		{
+			name:         "too many fields",
+			cronExpr:     "0 0 0 0 0 0 0",
+			expectErrors: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			warnings, errors := provider.ValidateCronExpression(tt.cronExpr)
+
+			if tt.expectWarnings {
+				require.NotEmpty(t, warnings, "Expected warnings but got none")
+				if tt.warningContains != "" {
+					require.Contains(t, warnings[0], tt.warningContains)
+				}
+			} else {
+				require.Empty(t, warnings, "Expected no warnings but got: %v", warnings)
+			}
+
+			if tt.expectErrors {
+				require.NotEmpty(t, errors, "Expected errors but got none")
+			} else {
+				require.Empty(t, errors, "Expected no errors but got: %v", errors)
+			}
+		})
+	}
+}