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‎404.html‎

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‎CNAME‎

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flow.org

‎_src/cli/apply-code-action.md‎

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---
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title: Apply Code Action
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slug: /cli/apply-code-action
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description: "Apply LSP code actions like autofixes and code transformations from the command line, useful for scripting and batch-fixing."
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---
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The `apply-code-action` command exposes LSP code actions via the CLI, allowing you to apply autofixes and code transformations without an editor. This is useful for scripting, CI pipelines, or batch-fixing files from the command line.
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## Usage {#toc-usage}
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```sh
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flow apply-code-action SUBCOMMAND [OPTIONS]... FILE
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```
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The command requires a running Flow server. If one is not already running, it will be started automatically.
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## Subcommands {#toc-subcommands}
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### `experimental.quickfix` {#toc-experimental-quickfix}
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Applies all safe quickfixes to a file. These are the same quickfixes that your editor shows via LSP code actions, such as adding suppression comments or replacing deprecated syntax.
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```sh
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flow apply-code-action 'experimental.quickfix' [OPTIONS] FILE
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```
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By default, only safe quickfixes are applied. You can optionally include one additional best-effort fix using the `--include-best-effort-fix` flag. Best-effort fixes may change the runtime semantics of your program (for example, adding a type annotation to a variable declaration to satisfy a type error).
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**Options:**
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- `--in-place`: Overwrite the input file with the result. Without this flag, the transformed file contents are printed to stdout.
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- `--include-best-effort-fix`: Include one additional best-effort quickfix beyond the safe fixes.
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**Example:**
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```sh
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# Print the file with all safe quickfixes applied
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flow apply-code-action 'experimental.quickfix' src/app.js
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# Apply safe quickfixes and overwrite the file
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flow apply-code-action 'experimental.quickfix' --in-place src/app.js
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# Also apply one best-effort fix
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flow apply-code-action 'experimental.quickfix' --include-best-effort-fix src/app.js
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```
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### `source.addMissingImports` {#toc-source-add-missing-imports}
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Adds missing import statements for unresolved references in a file. Flow resolves each unbound name to an export in your project and inserts the appropriate `import` statement.
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```sh
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flow apply-code-action 'source.addMissingImports' [OPTIONS] FILE
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```
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**Options:**
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- `--in-place`: Overwrite the input file with the result. Without this flag, the transformed file contents are printed to stdout.
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**Example:**
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Given a file `app.js` that references `OtherModule` without importing it:
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```js
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// @flow
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OtherModule;
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```
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Running the command:
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```sh
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flow apply-code-action 'source.addMissingImports' app.js
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```
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produces output with the import added:
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```js
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// @flow
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import OtherModule from "./OtherModule";
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OtherModule;
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```
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To update the file in place:
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```sh
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flow apply-code-action 'source.addMissingImports' --in-place app.js
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```
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### `suggestImports` {#toc-suggest-imports}
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Lists import suggestions for all unbound names in a file, ranked by usage. Unlike the other subcommands, this does not modify the file. Instead, it outputs a JSON object describing the available import code actions for each unresolved name.
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```sh
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flow apply-code-action suggestImports [OPTIONS] FILE
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```
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**Options:**
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- `--json`: Output results in JSON format (default behavior for this subcommand).
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- `--pretty`: Pretty-print the JSON output.
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**Example:**
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```sh
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flow apply-code-action suggestImports --pretty src/app.js
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```
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The output is a JSON object keyed by unbound name, where each value is an array of possible import actions:
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```json
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{
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"OtherModule": [
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{
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"title": "Import default from ./OtherModule",
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"kind": "quickfix",
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"edit": {
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"changes": {
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"file:///path/to/app.js": [
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{
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"newText": "import OtherModule from \"./OtherModule\";\n\n",
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"range": {
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"start": { "character": 0, "line": 1 },
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"end": { "character": 0, "line": 1 }
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}
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}
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]
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}
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}
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}
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]
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}
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```
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When multiple modules export the same name, all candidates are listed so you can choose the appropriate one.
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## See Also {#toc-see-also}
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- [Editor Setup](../editors/index.md) — IDE integrations that provide code actions interactively

‎_src/cli/coverage.md‎

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---
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title: Flow Coverage
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slug: /cli/coverage
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description: "Measure how much of your code is covered by Flow's type checking, based on the presence of the any type in inferred expressions."
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---
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The coverage command provides a metric of the amount of checking that Flow has
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performed on each part of your code. A program with high Flow coverage should
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increase your confidence that Flow has detected any potential runtime errors.
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The determining factor for this is the presence of [`any`](../types/any.md) in the
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inferred type of each expression. An expression whose inferred type is `any` is
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considered *uncovered*, otherwise it is considered *covered*.
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To see why this metric was chosen for determining Flow's effectiveness, consider
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the example
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```js flow-check
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const one: any = 1;
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one();
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```
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This code leads to a runtime type error, since we are attempting to perform a call
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on a number. Flow, however, does not flag an error here, because we have annotated
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variable `one` as `any`. Flow's checking is effectively turned off whenever `any`
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is involved, so it will silently allow the call. The use of this *unsafe* type has
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rendered the type checker ineffective, and the coverage metric is here to surface
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this, by reporting all instances of `one` as uncovered.
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## Design Space {#toc-design-space}
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**Which types should be "covered"?**
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What was described above is a rather coarse grained way to determine coverage. One
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could imagine a criterion that flags expressions as uncovered if *any* part of their
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type includes `any`, for example `Array<any>`. While there is value in a metric like
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this, the "uncovered" part of the type will typically be uncovered through various
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operations on values of this type. For example, in the code
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```js flow-check
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declare const arr: Array<any>;
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arr.forEach(x => {});
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```
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the parameter `x` will be flagged as uncovered. Also, in practice, a strict criterion
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like this would be too noisy and rather expensive to compute on the fly.
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**Union types**
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An exception to this principle are union types: the type `number | any` is considered
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*uncovered*, even though technically `any` is not the top-level constructor.
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Unions merely encode an option among *a set of* other types. In that sense we are
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conservatively viewing an expression as uncovered, when at least one possible type
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of that expression causes limited checking. For example, in the code
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```js flow-check
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let x: number | any = 1;
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x = "a";
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```
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Flow will let you assign anything to `x`, which reduces confidence in the use
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of `x` as a number. Thus `x` is considered uncovered.
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**The empty type**
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An interesting type from a coverage perspective is the [`empty`](../types/empty.md) type.
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This type roughly corresponds to *dead code*. As such checking around expressions with
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type `empty` is more relaxed, but for a good reason: this code will not be executed at
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runtime. Since it is a common practice to clean up such code, Flow coverage will
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also report code whose type is inferred to be `empty`, but distinguishes it from
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the case of `any`.
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## Command Line Use {#toc-command-line-use}
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To find out the coverage of a file foo.js with the following contents
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```js flow-check
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function add(one: any, two: any): number {
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return one + two;
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}
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add(1, 2);
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```
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you can issue the following command
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```
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$ flow coverage file.js
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Covered: 50.00% (5 of 10 expressions)
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```
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This output means that 5 out of the 10 nodes of this program were inferred to have type
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`any`. To see exactly which parts are uncovered you can also pass one of the following
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flags:
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* `--color`: This will print foo.js on the terminal with the uncovered locations in
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red color. E.g. `flow coverage --color file.js`
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* `--json`: This will list out all location spans that are uncovered under
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the tag `"uncovered_locs"`. E.g. `flow coverage --json file.js`
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Finally, as an example of dead code, consider the code:
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```js flow-check
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function f(x: 'a' | 'b') {
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if (x === 'a') {
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// ...
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} else if (x === 'b') {
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// ...
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} else {
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x;
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}
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}
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```
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The final `else` clause should never be reached, as we've already checked for both members of the union.
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Because of this, `x` is inferred to have the type `empty` in that branch.
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In the colored version of this command, these parts appear in blue color,
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and in the JSON version they are under the field `"empty_locs"`.
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**Use on multiple files**
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If you want to check coverage of multiple files at once, Flow offers the
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`batch-coverage` command:
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```
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$ flow batch-coverage dir/
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```
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will report coverage statistics for each file under `dir/`, as well as aggregate
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results.
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Note that `batch-coverage` requires a non-lazy Flow server.
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## See Also {#toc-see-also}
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- [Any](../types/any.md) — the type that reduces coverage, and how to avoid it
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- [Unknown](../types/unknown.md) — the safe alternative to `any` that maintains coverage

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