Add TOML language formatting support to Prettier

per1234 · per1234 · commit e6a8ef7b2e5b · 2025-06-17T23:46:06.000-07:00
Projects may use data files written in the TOML language. A common example of such is the `pyproject.toml` file present
in projects that use the Poetry Python package management tool (either for project code dependencies, or development
tools).

In cases where the TOML content is edited directly by human contributors, it will be useful to provide code formatting
infrastructure for TOML files, and to enforce consistent formatting. This is easily accomplished by adding TOML support
to the existing code formatting infrastructure via the "prettier-plugin-toml" plugin for the Prettier formatting tool.

Poetry's `poetry.lock` file is also written in the TOML language. This file is automatically generated and never
manually edited. In this case, the automatically generated content is accepted as-is. So Prettier is configured to
exclude the `poetry.lock` file from formatting.
diff --git a/.github/workflows/check-prettier-formatting-task.yml b/.github/workflows/check-prettier-formatting-task.yml
@@ -90,6 +90,13 @@ on:
       - "**.mkdn?"
       - "**.ronn"
       - "**.workbook"
+      # TOML
+      - "**/Cargo.lock"
+      - "**/Cargo.toml.orig"
+      - "**/Gopkg.lock"
+      - "**/Pipfile"
+      - "**/pdm.lock"
+      - "**.toml"
       # YAML
       - "**/.clang-format"
       - "**/.clang-tidy"
@@ -189,6 +196,13 @@ on:
       - "**.mkdn?"
       - "**.ronn"
       - "**.workbook"
+      # TOML
+      - "**/Cargo.lock"
+      - "**/Cargo.toml.orig"
+      - "**/Gopkg.lock"
+      - "**/Pipfile"
+      - "**/pdm.lock"
+      - "**.toml"
       # YAML
       - "**/.clang-format"
       - "**/.clang-tidy"
diff --git a/.prettierignore b/.prettierignore
@@ -4,3 +4,4 @@ node_modules/
 /other/clang-format-configuration/testdata/golden/samples/
 /other/clang-format-configuration/testdata/input/samples/
 /other/clang-format-configuration/.clang-format
+poetry.lock
diff --git a/.prettierrc.yml b/.prettierrc.yml
@@ -0,0 +1,3 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-prettier-formatting/toml/.prettierrc.yml
+plugins:
+  - prettier-plugin-toml
diff --git a/Taskfile.yml b/Taskfile.yml
@@ -351,6 +351,7 @@ tasks:
       - |
         cp \
           "{{.WORKFLOW_TEMPLATE_ASSETS_PATH}}/check-javascript/.eslintrc.yml" \
+          "{{.WORKFLOW_TEMPLATE_ASSETS_PATH}}/check-prettier-formatting/toml/.prettierrc.yml" \
           "{{.WORKFLOW_TEMPLATE_ASSETS_PATH}}/general/.editorconfig" \
           "{{.WORKFLOW_TEMPLATE_ASSETS_PATH}}/check-python/.flake8" \
           "{{.WORKFLOW_TEMPLATE_ASSETS_PATH}}/check-markdown/.markdownlint.yml" \
diff --git a/package-lock.json b/package-lock.json
diff --git a/package.json b/package.json
@@ -9,7 +9,8 @@
     "github-label-sync": "3.0.0",
     "markdown-link-check": "^3.13.7",
     "markdownlint-cli": "^0.45.0",
-    "prettier": "^3.5.3"
+    "prettier": "^3.5.3",
+    "prettier-plugin-toml": "^2.0.5"
   },
   "dependencies": {
     "js-yaml": "^4.1.0"
diff --git a/workflow-templates/assets/check-prettier-formatting/.prettierignore b/workflow-templates/assets/check-prettier-formatting/.prettierignore
@@ -1,3 +1,4 @@
 .licenses/
 __pycache__/
 node_modules/
+poetry.lock
diff --git a/workflow-templates/assets/check-prettier-formatting/toml/.prettierrc.yml b/workflow-templates/assets/check-prettier-formatting/toml/.prettierrc.yml
@@ -0,0 +1,3 @@
+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-prettier-formatting/toml/.prettierrc.yml
+plugins:
+  - prettier-plugin-toml
diff --git a/workflow-templates/check-prettier-formatting-task.md b/workflow-templates/check-prettier-formatting-task.md
@@ -8,6 +8,7 @@ Use [Prettier](https://prettier.io/docs/en/index.html) to check formatting. Supp
 - HTML
 - JSON
 - Markdown
+- TOML ([via plugin](#toml-support-optional))
 - YAML
 
 This is the version of the workflow for projects using the [Task](https://taskfile.dev/#/) task runner tool.
@@ -72,6 +73,25 @@ Add the following to [`/.gitignore`](https://git-scm.com/docs/gitignore):
 /node_modules/
 ```
 
+### TOML Support (Optional)
+
+If the project contains manually maintained [TOML](https://toml.io/) language files, some additional configuration is needed to add support to Prettier for this language.
+
+#### Assets
+
+- [`.prettierrc.yml`](assets/check-prettier-formatting/toml/.prettierrc.yml) - Prettier configuration file
+  - Install to: repository root.
+
+#### Dependencies
+
+Add the TOML support dependencies by running this command:
+
+```text
+npm install --save-dev prettier-plugin-toml@^2.0.2
+```
+
+Commit the resulting changes to the `package.json` and `package-lock.json` files.
+
 ### Readme badge
 
 Markdown badge:
diff --git a/workflow-templates/check-prettier-formatting-task.yml b/workflow-templates/check-prettier-formatting-task.yml
@@ -90,6 +90,13 @@ on:
       - "**.mkdn?"
       - "**.ronn"
       - "**.workbook"
+      # TOML
+      - "**/Cargo.lock"
+      - "**/Cargo.toml.orig"
+      - "**/Gopkg.lock"
+      - "**/Pipfile"
+      - "**/pdm.lock"
+      - "**.toml"
       # YAML
       - "**/.clang-format"
       - "**/.clang-tidy"
@@ -189,6 +196,13 @@ on:
       - "**.mkdn?"
       - "**.ronn"
       - "**.workbook"
+      # TOML
+      - "**/Cargo.lock"
+      - "**/Cargo.toml.orig"
+      - "**/Gopkg.lock"
+      - "**/Pipfile"
+      - "**/pdm.lock"
+      - "**.toml"
       # YAML
       - "**/.clang-format"
       - "**/.clang-tidy"

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+# Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-prettier-formatting/toml/.prettierrc.yml`
	`2`	`+plugins:`
	`3`	`+ - prettier-plugin-toml`