Add option to require @prettier or @format pragma (#2772)

* Add option to require @prettier or @format pragma

Fixes #2397.

Inspired by `eslint-plugin-prettier` and the discussion in #2397, this
implements requiring a special comment pragma to be present in a file's
first comment in order to be formatted.

This will help large codebases gradually transition to prettier over
time without tons of churn or large code reviews.

I implemented this as a standard prettier "option", not just a typical
`argv` flag, as it is relevant in both the cli and the api. This way it
can be provided programmatically, on the command line, or standardized
in a prettierrc file so like the style options, every user can use this
setting consistently and only apply prettier to relevant files, no
mattier their editor integration.

This requires the pragma begin with `@` (in fact it's inserted if the
user doesn't provide it). Currently the usage implies it must be
"prettier" or "format", but it can technically be any value other than
"none", which is similar to the `trailingCommas` option.

cc @vjeux

* Don't quote anything in runPrettier; this is usually handled by a shell

* Make --require-pragma a boolean option

* Use jest-docblock to find pragmas without parsing the ast

* Clarify docs

* includes -> indexOf

* Move test out of integration

README.md

@@ -274,6 +274,17 @@ you can pass `--no-config` instead.
 
 Path to a file containing patterns that describe files to ignore.  By default, prettier looks for `./.prettierignore`.
 
+#### `--require-pragma`
+
+Require a special comment, called a pragma, to be present in the file's first docblock comment in order for prettier to format it.
+```js
+/**
+ * @prettier
+ */
+```
+
+Valid pragmas are `@prettier` and `@format`.
+
 #### `--list-different`
 
 Another useful flag is `--list-different` (or `-l`) which prints the filenames of files that are different from Prettier formatting. If there are differences the script errors out, which is useful in a CI scenario.
@@ -288,7 +299,7 @@ Do not look for a configuration file.  The default settings will be used.
 
 #### `--config-precedence`
 
-Defines how config file should be evaluated in combination of CLI options. 
+Defines how config file should be evaluated in combination of CLI options.
 
 **cli-override (default)**
 

docs/options.md

@@ -133,3 +133,26 @@ Default | CLI Override | API Override
 --------|--------------|-------------
 None | `--stdin-filepath <string>` | `filepath: "<string>"`
 
+## Require pragma
+Prettier can restrict itself to only format files that contain a special comment, called a pragma, at the top of the file. This is very useful
+when gradually transitioning large, unformatted codebases to prettier.
+
+For example, a file with the following as its first comment will be formatted when `--require-pragma` is supplied:
+
+```js
+/**
+ * @prettier
+ */
+```
+
+or
+
+```js
+/**
+ * @format
+ */
+```
+
+Default | CLI Override | API Override
+--------|--------------|-------------
+None | `--require-pragma` | `requirePragma`

index.js

@@ -10,6 +10,7 @@ const normalizeOptions = require("./src/options").normalize;
 const parser = require("./src/parser");
 const printDocToDebug = require("./src/doc-debug").printDocToDebug;
 const config = require("./src/resolve-config");
+const docblock = require("jest-docblock");
 
 function guessLineEnding(text) {
   const index = text.indexOf("\n");
@@ -30,6 +31,11 @@ function attachComments(text, ast, opts) {
   return astComments;
 }
 
+function hasPragma(text) {
+  const pragmas = Object.keys(docblock.parse(docblock.extract(text)));
+  return pragmas.indexOf("prettier") !== -1 || pragmas.indexOf("format") !== -1;
+}
+
 function ensureAllCommentsPrinted(astComments) {
   if (!astComments) {
     return;
@@ -56,6 +62,10 @@ function ensureAllCommentsPrinted(astComments) {
 }
 
 function formatWithCursor(text, opts, addAlignmentSize) {
+  if (opts.requirePragma && !hasPragma(text)) {
+    return { formatted: text };
+  }
+
   text = stripBom(text);
   addAlignmentSize = addAlignmentSize || 0;
 

package.json

@@ -23,6 +23,7 @@
     "globby": "^6.1.0",
     "graphql": "0.10.1",
     "ignore": "^3.3.3",
+    "jest-docblock": "^21.0.2",
     "jest-validate": "20.0.3",
     "minimatch": "3.0.4",
     "minimist": "1.2.0",

src/cli-constant.js

@@ -7,7 +7,8 @@ const booleanOptionNames = [
   "bracket-spacing",
   "jsx-bracket-same-line",
   // Deprecated in 0.0.10
-  "flow-parser"
+  "flow-parser",
+  "require-pragma"
 ];
 
 const stringOptionNames = [
@@ -86,6 +87,8 @@ Available options:
                            Finds and prints the path to a configuration file for a given input file.
   --ignore-path <path>     Path to a file containing patterns that describe files to ignore.
                            Defaults to ./.prettierignore.
+  --require-pragma
+                           Require either '@prettier' or '@format' to be present in the file's first docblock comment in order for it to be formatted.
   --stdin                  Read input from stdin.
   --stdin-filepath         Path to the file used to read from stdin.
   --print-width <int>      Specify the length of line that the printer will wrap on. Defaults to 80.

src/cli-util.js

@@ -25,6 +25,7 @@ function getOptions(argv) {
     printWidth: getIntOption(argv, "print-width"),
     tabWidth: getIntOption(argv, "tab-width"),
     bracketSpacing: argv["bracket-spacing"],
+    requirePragma: argv["require-pragma"],
     singleQuote: argv["single-quote"],
     jsxBracketSameLine: argv["jsx-bracket-same-line"],
     filepath: argv["stdin-filepath"],

src/options.js

@@ -15,6 +15,7 @@ const defaults = {
   bracketSpacing: true,
   jsxBracketSameLine: false,
   parser: "babylon",
+  requirePragma: false,
   semi: true
 };
 

tests/require-pragma/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,59 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`module-with-pragma.js 1`] = `
+/**
+ * @flow
+ * @format
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ * @format
+ */
+
+function foo(bar) {
+  return bar + 3 + 4;
+}
+
+`;
+
+exports[`module-without-pragma.js 1`] = `
+/**
+ * @flow
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
+
+`;

tests/require-pragma/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, { requirePragma: true });

tests/require-pragma/module-with-pragma.js

@@ -0,0 +1,14 @@
+/**
+ * @flow
+ * @format
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}

tests/require-pragma/module-without-pragma.js

@@ -0,0 +1,13 @@
+/**
+ * @flow
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}

tests_integration/__tests__/__snapshots__/early-exit.js.snap

@@ -19,6 +19,8 @@ Available options:
                            Finds and prints the path to a configuration file for a given input file.
   --ignore-path <path>     Path to a file containing patterns that describe files to ignore.
                            Defaults to ./.prettierignore.
+  --require-pragma
+                           Require either '@prettier' or '@format' to be present in the file's first docblock comment in order for it to be formatted.
   --stdin                  Read input from stdin.
   --stdin-filepath         Path to the file used to read from stdin.
   --print-width <int>      Specify the length of line that the printer will wrap on. Defaults to 80.

yarn.lock

@@ -2258,6 +2258,10 @@ jest-docblock@^20.0.1, jest-docblock@^20.0.3:
   version "20.0.3"
   resolved "https://registry.yarnpkg.com/jest-docblock/-/jest-docblock-20.0.3.tgz#17bea984342cc33d83c50fbe1545ea0efaa44712"
 
+jest-docblock@^21.0.2:
+  version "21.0.2"
+  resolved "https://registry.yarnpkg.com/jest-docblock/-/jest-docblock-21.0.2.tgz#66f69ddb440799fc32f91d0ac3d8d35e99e2032f"
+
 jest-environment-jsdom@^20.0.3:
   version "20.0.3"
   resolved "https://registry.yarnpkg.com/jest-environment-jsdom/-/jest-environment-jsdom-20.0.3.tgz#048a8ac12ee225f7190417713834bb999787de99"