feat: add version-file input to read kubectl version from .tool-versions

README.md

@@ -11,6 +11,27 @@ Acceptable values are latest or any semantic version string like `v1.15.0`. Use
   id: install
 ```
 
+Alternatively, read the kubectl version from an
+[asdf/mise `.tool-versions` file](https://asdf-vm.com/manage/configuration.html):
+
+```yaml
+- uses: azure/setup-kubectl@v5
+  with:
+     version-file: '.tool-versions'
+  id: install
+```
+
+The kubectl entry may use `major.minor`, `major.minor.patch`, an optional `v`
+prefix, or `latest`:
+
+```text
+kubectl 1.31.2
+```
+
+When both inputs are set, a specific `version` other than `latest` takes
+precedence and the action emits a warning. The default `version: latest` allows
+`version-file` to select the version.
+
 Refer to the action metadata file for details about all the inputs https://github.com/Azure/setup-kubectl/blob/main/action.yml
 
 # Contributing

action.yml

@@ -3,8 +3,11 @@ description: 'Install a specific version of kubectl binary. Acceptable values ar
 inputs:
    version:
       description: 'Version of kubectl'
-      required: true
+      required: false
       default: 'latest'
+   version-file:
+      description: 'Path to a .tool-versions (asdf/mise) file to read the kubectl version from. A specific version other than latest takes precedence.'
+      required: false
    downloadBaseURL:
       description: 'Base URL to download kubectl from (https only). Use for private mirrors.'
       required: false

src/helpers.ts

@@ -304,3 +304,72 @@ export function getExecutableExtension(): string {
    }
    return ''
 }
+
+export function parseToolVersionsFile(filePath: string): string {
+   const maxBytes = 64 * 1024
+   const pathStats = fs.lstatSync(filePath, {bigint: true})
+   if (pathStats.isSymbolicLink() || !pathStats.isFile()) {
+      throw new Error(
+         `The version-file '${filePath}' must be a regular file and not a symbolic link.`
+      )
+   }
+   if (pathStats.size > BigInt(maxBytes)) {
+      throw new Error(
+         `The version-file '${filePath}' exceeds the ${maxBytes}-byte size limit.`
+      )
+   }
+
+   const noFollow = fs.constants.O_NOFOLLOW ?? 0
+   // A FIFO swapped in after lstat must not block open before fstat can reject it.
+   // O_NONBLOCK has no effect on regular files; these flags are POSIX-only.
+   const nonBlock = fs.constants.O_NONBLOCK ?? 0
+   const fd = fs.openSync(filePath, fs.constants.O_RDONLY | noFollow | nonBlock)
+   let content: string
+   try {
+      const fileStats = fs.fstatSync(fd, {bigint: true})
+      if (!fileStats.isFile()) {
+         throw new Error(
+            `The version-file '${filePath}' must be a regular file and not a symbolic link.`
+         )
+      }
+      if (pathStats.dev !== fileStats.dev || pathStats.ino !== fileStats.ino) {
+         throw new Error(
+            `The version-file '${filePath}' changed while it was being opened.`
+         )
+      }
+
+      const buffer = Buffer.alloc(maxBytes + 1)
+      let bytesRead = 0
+      while (bytesRead < buffer.length) {
+         const count = fs.readSync(
+            fd,
+            buffer,
+            bytesRead,
+            buffer.length - bytesRead,
+            null
+         )
+         if (count === 0) break
+         bytesRead += count
+      }
+      if (bytesRead > maxBytes) {
+         throw new Error(
+            `The version-file '${filePath}' exceeds the ${maxBytes}-byte size limit.`
+         )
+      }
+      content = buffer.toString('utf8', 0, bytesRead)
+   } finally {
+      fs.closeSync(fd)
+   }
+
+   for (const line of content.split('\n')) {
+      const trimmed = line.trim()
+      if (trimmed.startsWith('#') || trimmed === '') continue
+      const [tool, version] = trimmed.split(/\s+/)
+      if (tool === 'kubectl' && version) {
+         return version
+      }
+   }
+   throw new Error(
+      `Could not find a kubectl entry in tool-versions file: ${filePath}`
+   )
+}