Skip to content

Commit

Permalink
Restructure code to let linker perform deadcode elimination step
Browse files Browse the repository at this point in the history
Cobra, in its default configuration, will execute a template to generate
help, usage and version outputs. Text/template execution calls MethodByName
and MethodByName disables dead code elimination in the Go linker, therefore
all programs that make use of cobra will be linked with dead code
elimination disabled, even if they end up replacing the default usage, help
and version formatters with a custom function and no actual text/template
evaluations are ever made at runtime.

Dead code elimination in the linker helps reduce disk space and memory
utilization of programs. For example, for the simple example program used by
TestDeadcodeElimination 40% of the final executable size is dead code. For a
more realistic example, 12% of the size of Delve's executable is deadcode.

This PR changes Cobra so that, in its default configuration, it does not
automatically inhibit deadcode elimination by:

1. changing Cobra's default behavior to emit output for usage and help using
   simple Go functions instead of template execution
2. quarantining all calls to template execution into SetUsageTemplate,
   SetHelpTemplate and SetVersionTemplate so that the linker can statically
   determine if they are reachable
  • Loading branch information
aarzilli committed Feb 10, 2024
1 parent bcfcff7 commit 8159848
Show file tree
Hide file tree
Showing 3 changed files with 236 additions and 56 deletions.
16 changes: 10 additions & 6 deletions cobra.go
Original file line number Diff line number Diff line change
Expand Up @@ -176,12 +176,16 @@ func rpad(s string, padding int) string {
return fmt.Sprintf(formattedString, s)
}

// tmpl executes the given template text on data, writing the result to w.
func tmpl(w io.Writer, text string, data interface{}) error {
t := template.New("top")
t.Funcs(templateFuncs)
template.Must(t.Parse(text))
return t.Execute(w, data)
func tmpl(text string) *tmplFunc {
return &tmplFunc{
tmpl: text,
fn: func(w io.Writer, data interface{}) error {
t := template.New("top")
t.Funcs(templateFuncs)
template.Must(t.Parse(text))
return t.Execute(w, data)
},
}
}

// ld compares two strings and returns the levenshtein distance between them.
Expand Down
58 changes: 58 additions & 0 deletions cobra_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,10 @@
package cobra

import (
"os"
"os/exec"
"path/filepath"
"strings"
"testing"
"text/template"
)
Expand Down Expand Up @@ -222,3 +226,57 @@ func TestRpad(t *testing.T) {
})
}
}

func TestDeadcodeElimination(t *testing.T) {
// check that a simple program using cobra in its default configuration is
// linked with deadcode elimination enabled.
const (
dirname = "test_deadcode"
progname = "test_deadcode_elimination"
)
os.Mkdir(dirname, 0770)
filename := filepath.Join(dirname, progname+".go")
err := os.WriteFile(filename, []byte(`package main
import (
"fmt"
"os"
"github.com/spf13/cobra"
)
var rootCmd = &cobra.Command{
Version: "1.0",
Use: "example_program",
Short: "example_program - test fixture to check that deadcode elimination is allowed",
Run: func(cmd *cobra.Command, args []string) {
fmt.Println("hello world")
},
Aliases: []string{"alias1", "alias2"},
Example: "stringer --help",
}
func main() {
if err := rootCmd.Execute(); err != nil {
fmt.Fprintf(os.Stderr, "Whoops. There was an error while executing your CLI '%s'", err)
os.Exit(1)
}
}
`), 0660)
if err != nil {
t.Fatalf("could not write test program: %v", err)
}
defer os.RemoveAll(dirname)
buf, err := exec.Command("go", "build", filename).CombinedOutput()
if err != nil {
t.Fatalf("could not compile test program: %s", string(buf))
}
defer os.Remove(progname)
buf, err = exec.Command("go", "tool", "nm", progname).CombinedOutput()
if err != nil {
t.Fatalf("could not run go tool nm: %v", err)
}
if strings.Contains(string(buf), "MethodByName") {
t.Error("compiled programs contains MethodByName symbol")
}
}
Loading

0 comments on commit 8159848

Please sign in to comment.