chore: improve dynamic parameter validation errors (#18501)

`BuildError` response from `wsbuilder` does not support rich errors from validation. Changed this to use the `Validations` block of codersdk responses to return all errors for invalid parameters.

coderd/httpapi/httperror/doc.go

@@ -0,0 +1,4 @@
+// Package httperror handles formatting and writing some sentinel errors returned
+// within coder to the API.
+// This package exists outside httpapi to avoid some cyclic dependencies
+package httperror

coderd/httpapi/httperror/wsbuild.go

@@ -0,0 +1,91 @@
+package httperror
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"sort"
+
+	"github.com/hashicorp/hcl/v2"
+
+	"github.com/coder/coder/v2/coderd/dynamicparameters"
+	"github.com/coder/coder/v2/coderd/httpapi"
+	"github.com/coder/coder/v2/coderd/wsbuilder"
+	"github.com/coder/coder/v2/codersdk"
+)
+
+func WriteWorkspaceBuildError(ctx context.Context, rw http.ResponseWriter, err error) {
+	var buildErr wsbuilder.BuildError
+	if errors.As(err, &buildErr) {
+		if httpapi.IsUnauthorizedError(err) {
+			buildErr.Status = http.StatusForbidden
+		}
+
+		httpapi.Write(ctx, rw, buildErr.Status, codersdk.Response{
+			Message: buildErr.Message,
+			Detail:  buildErr.Error(),
+		})
+		return
+	}
+
+	var parameterErr *dynamicparameters.ResolverError
+	if errors.As(err, &parameterErr) {
+		resp := codersdk.Response{
+			Message:     "Unable to validate parameters",
+			Validations: nil,
+		}
+
+		// Sort the parameter names so that the order is consistent.
+		sortedNames := make([]string, 0, len(parameterErr.Parameter))
+		for name := range parameterErr.Parameter {
+			sortedNames = append(sortedNames, name)
+		}
+		sort.Strings(sortedNames)
+
+		for _, name := range sortedNames {
+			diag := parameterErr.Parameter[name]
+			resp.Validations = append(resp.Validations, codersdk.ValidationError{
+				Field:  name,
+				Detail: DiagnosticsErrorString(diag),
+			})
+		}
+
+		if parameterErr.Diagnostics.HasErrors() {
+			resp.Detail = DiagnosticsErrorString(parameterErr.Diagnostics)
+		}
+
+		httpapi.Write(ctx, rw, http.StatusBadRequest, resp)
+		return
+	}
+
+	httpapi.Write(ctx, rw, http.StatusInternalServerError, codersdk.Response{
+		Message: "Internal error creating workspace build.",
+		Detail:  err.Error(),
+	})
+}
+
+func DiagnosticError(d *hcl.Diagnostic) string {
+	return fmt.Sprintf("%s; %s", d.Summary, d.Detail)
+}
+
+func DiagnosticsErrorString(d hcl.Diagnostics) string {
+	count := len(d)
+	switch {
+	case count == 0:
+		return "no diagnostics"
+	case count == 1:
+		return DiagnosticError(d[0])
+	default:
+		for _, d := range d {
+			// Render the first error diag.
+			// If there are warnings, do not priority them over errors.
+			if d.Severity == hcl.DiagError {
+				return fmt.Sprintf("%s, and %d other diagnostic(s)", DiagnosticError(d), count-1)
+			}
+		}
+
+		// All warnings? ok...
+		return fmt.Sprintf("%s, and %d other diagnostic(s)", DiagnosticError(d[0]), count-1)
+	}
+}