cli: fmt -check should return early on diff

The `nomad fmt -check` command incorrectly writes to file because we didn't
return before writing the file on a diff. The docstring for the `-list` and
`-write` flags is also unclear and can be easily misread to be the opposite of
the actual behavior. Clarify this and fix up the docs to match.

command/fmt.go

@@ -47,27 +47,30 @@ func (*FormatCommand) Help() string {
 	helpText := `
 Usage: nomad fmt [flags] paths ...
 
-	Formats Nomad agent configuration and job file to a canonical format.
-	If a path is a directory, it will recursively format all files
-	with .nomad and .hcl extensions in the directory.
-	
-	If you provide a single dash (-) as argument, fmt will read from standard
-	input (STDIN) and output the processed output to standard output (STDOUT).
+  Formats Nomad agent configuration and job file to a canonical format.
+  If a path is a directory, it will recursively format all files
+  with .nomad and .hcl extensions in the directory.
+
+  If you provide a single dash (-) as argument, fmt will read from standard
+  input (STDIN) and output the processed output to standard output (STDOUT).
 
 Format Options:
 
-	-list=false
-		Don't list the files, which contain formatting inconsistencies.
+  -check
+	Check if the files are valid HCL files. If not, exit status of the
+	command will be 1 and the incorrect files will not be formatted. This
+    flag overrides any -write flag value.
 
-	-check
-		Check if the files are valid HCL files. If not, exit status of the command
-		will be 1 and the incorrect files will not be formatted.
+  -list
+	List the files which contain formatting inconsistencies. Defaults
+	to -list=true.
 
-	-write=false
-		Don't overwrite the input files.
+  -recursive
+	Process files in subdirectories. By default only the given (or current)
+	directory is processed.
 
-	-recursive
-		Process also files in subdirectories. By default only the given (or current) directory is processed.
+  -write
+	Overwrite the input files. Defaults to -write=true.
 `
 
 	return strings.TrimSpace(helpText)
@@ -251,16 +254,18 @@ func (f *FormatCommand) processFile(path string, r io.Reader) {
 			f.Ui.Output(path)
 		}
 
+		if f.check {
+			f.checkSuccess = false
+			return
+		}
+
 		if f.write {
 			if err := os.WriteFile(path, out, 0644); err != nil {
 				f.appendError(fmt.Errorf("Failed to write file %s: %w", path, err))
 				return
 			}
 		}
 
-		if f.check {
-			f.checkSuccess = false
-		}
 	}
 
 	if !f.list && !f.write {

website/content/docs/commands/fmt.mdx

@@ -26,16 +26,19 @@ If you provide a single dash (-) as argument, fmt will read from standard input
 
 ## Format Options:
 
-- `-list=false` :	Don't list the files, which contain formatting inconsistencies.
-- `-check` : Check if the files are valid HCL files. If not, exit status of the command
-    will be 1 and the incorrect files will not be formatted.
-- `-write=false` : Don't overwrite the input files.
-- `-recursive` : Process also files in subdirectories. By default only the given (or current) directory is processed.
+- `-check`: Check if the files are valid HCL files. If not, exit status of the
+  command will be 1 and the incorrect files will not be formatted. This flag
+  overrides any `-write` flag value.
+- `-list`: List the files which contain formatting inconsistencies. Defaults to
+  `-list=true`.
+- `-recursive`: Process files in subdirectories. By default only the given (or
+	current) directory is processed.
+- `-write`: Overwrite the input files. Defaults to `-write=true`.
 
 ## Examples
 
 ```shell-session
-$ cat agent.hcl 
+$ cat agent.hcl
 server {
     enabled = true
   bootstrap_expect = 1
@@ -46,9 +49,9 @@ client {
 }
 
 $ nomad fmt
-
 agent.hcl
-$ cat agent.hcl 
+
+$ cat agent.hcl
 server {
   enabled          = true
   bootstrap_expect = 1