Add a has_parameter function to check if a document appears to be using parameters

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: quarto
 Title: R Interface to 'Quarto' Markdown Publishing System
-Version: 1.4.4.9027
+Version: 1.4.4.9028
 Authors@R: c(
     person("JJ", "Allaire", , "jj@posit.co", role = "aut",
            comment = c(ORCID = "0000-0003-0174-9868")),

NAMESPACE

@@ -5,6 +5,7 @@ export(check_newer_version)
 export(detect_bookdown_crossrefs)
 export(find_project_root)
 export(get_running_project_root)
+export(has_parameters)
 export(is_using_quarto)
 export(new_blog_post)
 export(project_path)

NEWS.md

@@ -2,6 +2,8 @@
 
 - Package is now licenced MIT like Quarto CLI.
 
+- Added `has_parameters()` function to detect whether Quarto documents use parameters. The function works with both knitr and Jupyter engines: for knitr documents (.qmd), it checks for a "params" field in the document metadata; for Jupyter notebooks (.ipynb), it detects cells tagged with "parameters" using papermill convention. This enables programmatic identification of parameterized documents for automated workflows and document processing (#245).
+
 - Added `detect_bookdown_crossrefs()` function to help users migrate from bookdown to Quarto by identifying cross-references that need manual conversion. The function scans R Markdown or Quarto files to detect bookdown-specific cross-reference syntax (like `\@ref(fig:label)` and `(\#eq:label)`) and provides detailed guidance on converting them to Quarto syntax (like `@fig-label` and `{#eq-label}`). It offers both compact and verbose reporting modes, with context-aware warnings that only show syntax patterns actually found in your files.
 
 - Added `project_path()`, `get_running_project_root()`, and `find_project_root()` functions for Quarto-aware project path construction. These functions provide a consistent way to reference files relative to the project root, working both during Quarto rendering (using `QUARTO_PROJECT_ROOT` environment variables) and in interactive sessions (using intelligent project detection). The `project_path()` function is particularly useful in Quarto document cells where you need to reference data files or scripts from the project root regardless of the document's location in subdirectories (#180).0).

R/parameters.R

@@ -0,0 +1,107 @@
+#' Check if a Quarto document uses parameters
+#'
+#' Determines whether a Quarto document uses parameters by examining the document
+#' structure and metadata. This function works with both knitr and Jupyter engines,
+#' using different detection methods for each:
+#'
+#' - **Knitr engine (.qmd files)**: Checks for a "params" field in the document's
+#'   YAML metadata using `quarto_inspect()`
+#' - **Jupyter engine (.ipynb files)**: Looks for code cells tagged with "parameters"
+#'   following the papermill convention. For .ipynb files, the function parses the
+#'   notebook JSON directly due to limitations in `quarto inspect`.
+#'
+#' @param input Path to the Quarto document (.qmd or .ipynb file) to inspect.
+#'
+#' @return Logical. `TRUE` if the document uses parameters, `FALSE` otherwise.
+#'
+#' @details
+#' Parameters in Quarto enable creating dynamic, reusable documents. This function
+#' helps identify parameterized documents programmatically, which is useful for:
+#'
+#' - Document processing workflows
+#' - Automated report generation
+#' - Parameter validation before rendering
+#' - Project analysis and organization
+#'
+#' For more information about using parameters in Quarto, see
+#' <https://quarto.org/docs/computations/parameters.html>
+#'
+#' @examples
+#' \dontrun{
+#' # Check if a document uses parameters
+#' has_parameters("my-document.qmd")
+#'
+#' # Check a parameterized report
+#' has_parameters("parameterized-report.qmd")
+#'
+#' # Check a Jupyter notebook
+#' has_parameters("analysis.ipynb")
+#'
+#' # Use in a workflow
+#' if (has_parameters("report.qmd")) {
+#'   message("This document accepts parameters")
+#' }
+#' }
+#'
+#' @export
+has_parameters <- function(input) {
+  if (!file.exists(input)) {
+    cli::cli_abort(
+      c(
+        "File {.file {input}} does not exist.",
+        ">" = "Please provide a valid Quarto document."
+      ),
+      call = rlang::caller_env()
+    )
+  }
+
+  # Check for Jupyter engine: look for cells with "parameters" tag
+  # Note: quarto_inspect() has limitations with Jupyter notebooks and may not
+  # detect code cells properly, so we fall back to direct JSON parsing for .ipynb files
+  if (identical(fs::path_ext(input), "ipynb")) {
+    return(has_parameters_jupyter_direct(input))
+  }
+
+  inspect <- quarto::quarto_inspect(input)
+
+  if (identical(inspect$engines, "jupyter")) {
+    return(
+      "parameters" %in% inspect$fileInformation[[input]]$codeCells$metadata$tags
+    )
+  } else if (identical(inspect$engines, "knitr")) {
+    return(
+      "params" %in% names(inspect$fileInformation[[input]]$metadata)
+    )
+  } else {
+    return(FALSE)
+  }
+}
+
+# Helper function to directly parse Jupyter notebook JSON for parameters
+# This is needed because quarto_inspect() has limitations with detecting
+# code cells in Jupyter notebooks
+has_parameters_jupyter_direct <- function(notebook_path) {
+  tryCatch(
+    {
+      # Read and parse the notebook JSON with simplifyDataFrame = FALSE
+      # to preserve the original structure
+      notebook_json <- jsonlite::fromJSON(
+        notebook_path,
+        simplifyDataFrame = FALSE
+      )
+
+      # Check if there are cells
+      if (length(notebook_json$cells) == 0) {
+        return(FALSE)
+      }
+      # Look through cells for parameters tag
+      any(sapply(notebook_json$cells, function(cell) {
+        "parameters" %in% cell$metadata$tags
+      }))
+    },
+    error = function(e) {
+      # If JSON parsing fails, return FALSE
+      return(FALSE)
+    }
+  )
+}

_pkgdown.yml

@@ -45,6 +45,7 @@ reference:
     for Quarto documents and projects:
   contents:
   - quarto_inspect
+  - has_parameters
   - quarto_path
   - quarto_version
   - quarto_available

tests/testthat/resources/test-no-parameters.ipynb

@@ -0,0 +1,47 @@
+{
+ "cells": [
+  {
+   "cell_type": "raw",
+   "id": "cell-0",
+   "metadata": {},
+   "source": [
+    "---\n",
+    "title: \"Test Notebook without Parameters\"\n",
+    "format: html\n",
+    "---"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "cell-1",
+   "metadata": {},
+   "source": [
+    "## Test Notebook\n",
+    "\n",
+    "This notebook does not use parameters."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "cell-2",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(\"Hello World!\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "name": "python"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}

tests/testthat/resources/test-with-parameters.ipynb

@@ -0,0 +1,63 @@
+{
+ "cells": [
+  {
+   "cell_type": "raw",
+   "id": "cell-0",
+   "metadata": {},
+   "source": [
+    "---\n",
+    "title: \"Test Notebook with Parameters\"\n",
+    "format: html\n",
+    "---"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "cell-1",
+   "metadata": {
+    "tags": [
+     "parameters"
+    ]
+   },
+   "outputs": [],
+   "source": [
+    "# Parameters cell\n",
+    "name = \"John\"\n",
+    "age = 30"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "cell-2",
+   "metadata": {},
+   "source": [
+    "## Test Notebook\n",
+    "\n",
+    "This notebook uses parameters defined in the cell above."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "cell-3",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "print(f\"Hello {name}, you are {age} years old!\")"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "name": "python"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}

tests/testthat/test-parameters.R

@@ -0,0 +1,58 @@
+test_that("has_parameters() works with knitr engine", {
+  skip_if_no_quarto()
+
+  # Create a .qmd file with params in metadata
+  qmd_with_params <- local_qmd_file(
+    "---",
+    "title: Test Document",
+    "params:",
+    "  name: John",
+    "---",
+    "",
+    "# Test Document",
+    "",
+    "This is a test document with parameters.",
+    "```{r}",
+    "params$name",
+    "```"
+  )
+
+  # Create a .qmd file without params
+  qmd_no_params <- local_qmd_file(
+    "---",
+    "title: Test Document",
+    "---",
+    "",
+    "# Test Document",
+    "",
+    "This is a test document without parameters."
+  )
+
+  expect_true(has_parameters(qmd_with_params))
+  expect_false(has_parameters(qmd_no_params))
+})
+
+test_that("has_parameters() works with Jupyter engine", {
+  skip_if_no_quarto()
+
+  # Test with notebook that has parameters cell
+  expect_true(has_parameters(resources_path("test-with-parameters.ipynb")))
+
+  # Test with notebook that doesn't have parameters
+  expect_false(has_parameters(resources_path("test-no-parameters.ipynb")))
+})
+
+test_that("has_parameters() handles non-existent files", {
+  expect_error(
+    has_parameters("non-existent-file.qmd"),
+    class = "rlang_error"
+  )
+})
+
+test_that("has_parameters() works with existing test files", {
+  skip_if_no_quarto()
+
+  # Test with existing test files that don't have parameters
+  expect_false(has_parameters(test_path("test.qmd")))
+  expect_false(has_parameters(test_path("test.ipynb")))
+})