[Fix] Reject workspace_id with a leading zero in provider_config

NEXT_CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Bug Fixes
 
 * Expand the "workspace-level resource requires a workspace_id" error to list all sources checked (resource `provider_config`, provider `workspace_id`, the configured profile, and the `DATABRICKS_WORKSPACE_ID` environment variable) so users know where to set it ([#5763](https://github.com/databricks/terraform-provider-databricks/pull/5763)).
+* Reject `workspace_id` values with a leading zero (e.g. `0470576644108500`) in `provider_config` so the literal value is no longer written to state where it would not match the canonical numeric workspace ID returned by the API ([#5764](https://github.com/databricks/terraform-provider-databricks/pull/5764)).
 
 ### Documentation
 

common/unified_provider.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"strconv"
+	"strings"
 
 	"github.com/databricks/databricks-sdk-go"
 	"github.com/databricks/databricks-sdk-go/client"
@@ -30,8 +31,31 @@ type ProviderConfig struct {
 // workspaceIDValidateFunc is used to validate the workspace ID for the provider configuration.
 // Accepts either a classic numeric workspace ID or a connection ID that the platform gateway
 // can disambiguate via the X-Databricks-Workspace-Id header.
+//
+// All-digit values are treated as classic numeric workspace IDs and must be in
+// canonical form: a leading zero (e.g. "0470576644108500") is rejected. Although
+// strconv.ParseInt tolerates leading zeros and the resource would still be created
+// in the correct workspace, the literal value is written verbatim to Terraform
+// state, where it no longer matches the canonical numeric form returned by the API.
+// That mismatch poisons every downstream string comparison (perpetual diffs,
+// failed workspace_id reconciliation). Non-numeric connection IDs are left
+// untouched so the platform gateway can disambiguate them server-side.
 func workspaceIDValidateFunc() func(interface{}, string) ([]string, []error) {
-	return validation.StringIsNotEmpty
+	return func(i interface{}, k string) ([]string, []error) {
+		if warnings, errs := validation.StringIsNotEmpty(i, k); len(errs) > 0 {
+			return warnings, errs
+		}
+		v := i.(string)
+		// Only constrain all-digit values; connection IDs (containing non-digit
+		// characters) are passed through unchanged.
+		if isNumericWorkspaceID(v) && len(v) > 1 && v[0] == '0' {
+			return nil, []error{fmt.Errorf(
+				"expected %s to be a numeric workspace ID without a leading zero, got %q; "+
+					"use the canonical numeric form (e.g. %q)",
+				k, v, strings.TrimLeft(v, "0"))}
+		}
+		return nil, nil
+	}
 }
 
 // AddNamespaceInSchema adds the provider_config schema to the given schema map.

common/unified_provider_test.go

@@ -47,15 +47,30 @@ func TestWorkspaceIDValidateFunc(t *testing.T) {
 			expectError: false,
 		},
 		{
-			name:        "value with leading zero now accepted",
+			name:        "numeric value with leading zero rejected",
 			input:       "0123",
+			expectError: true,
+		},
+		{
+			name:        "numeric value with leading zero rejected - long form",
+			input:       "0470576644108500",
+			expectError: true,
+		},
+		{
+			name:        "single zero accepted",
+			input:       "0",
 			expectError: false,
 		},
 		{
 			name:        "valid arbitrary non-empty string",
 			input:       "abc123",
 			expectError: false,
 		},
+		{
+			name:        "connection ID with leading zero accepted",
+			input:       "0abc-def-123",
+			expectError: false,
+		},
 		{
 			name:        "invalid empty string",
 			input:       "",