Return error if additional args passed to campaigns command

CHANGELOG.md

@@ -17,6 +17,7 @@ All notable changes to `src-cli` are documented in this file.
 
 ### Fixed
 
+- `src campaign [validate|apply|preview]` now print an error and usage information if a user accidentally provides an additional argument. [#384](https://github.com/sourcegraph/src-cli/pull/384)
 - Fix a regression that was introduced by [#361](https://github.com/sourcegraph/src-cli/pull/361) and caused the "Resolving repositories" step of `src campaign [apply|preview]` to crash when the search query in the campaign spec yielded file matches and repository matches from the same repository.
 
 ### Removed

cmd/src/campaigns_apply.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 
@@ -57,6 +58,10 @@ Examples:
 			return err
 		}
 
+		if len(flagSet.Args()) != 0 {
+			return &usageError{errors.New("additional arguments not allowed")}
+		}
+
 		out := output.NewOutput(flagSet.Output(), output.OutputOpts{Verbose: *verbose})
 
 		ctx, cancel := contextCancelOnInterrupt(context.Background())

cmd/src/campaigns_preview.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 
@@ -32,6 +33,10 @@ Examples:
 			return err
 		}
 
+		if len(flagSet.Args()) != 0 {
+			return &usageError{errors.New("additional arguments not allowed")}
+		}
+
 		out := output.NewOutput(flagSet.Output(), output.OutputOpts{Verbose: *verbose})
 
 		ctx, cancel := contextCancelOnInterrupt(context.Background())

cmd/src/campaigns_validate.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 
@@ -30,6 +31,10 @@ Examples:
 			return err
 		}
 
+		if len(flagSet.Args()) != 0 {
+			return &usageError{errors.New("additional arguments not allowed")}
+		}
+
 		specFile, err := campaignsOpenFileFlag(fileFlag)
 		if err != nil {
 			return err

cmd/src/cmd.go

@@ -93,7 +93,7 @@ func (c commander) run(flagSet *flag.FlagSet, cmdName, usageText string, args []
 		// Execute the subcommand.
 		if err := cmd.handler(flagSet.Args()[1:]); err != nil {
 			if _, ok := err.(*usageError); ok {
-				log.Println(err)
+				log.Printf("error: %s\n\n", err)
 				cmd.flagSet.Usage()
 				os.Exit(2)
 			}