Let the commands store flagComp functions internally (and avoid global state)

bash_completions.go

@@ -534,9 +534,10 @@ func writeLocalNonPersistentFlag(buf io.StringWriter, flag *pflag.Flag) {
 
 // prepareCustomAnnotationsForFlags setup annotations for go completions for registered flags
 func prepareCustomAnnotationsForFlags(cmd *Command) {
-	flagCompletionMutex.RLock()
-	defer flagCompletionMutex.RUnlock()
-	for flag := range flagCompletionFunctions {
+	cmd.initializeCompletionStorage()
+	cmd.flagCompletionMutex.RLock()
+	defer cmd.flagCompletionMutex.RUnlock()
+	for flag := range cmd.flagCompletionFunctions {
 		// Make sure the completion script calls the __*_go_custom_completion function for
 		// every registered flag.  We need to do this here (and not when the flag was registered
 		// for completion) so that we can know the root command name for the prefix
@@ -644,6 +645,7 @@ func writeCmdAliases(buf io.StringWriter, cmd *Command) {
 	WriteStringAndCheck(buf, `    fi`)
 	WriteStringAndCheck(buf, "\n")
 }
+
 func writeArgAliases(buf io.StringWriter, cmd *Command) {
 	WriteStringAndCheck(buf, "    noun_aliases=()\n")
 	sort.Strings(cmd.ArgAliases)

command.go

@@ -26,6 +26,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"sync"
 
 	flag "github.com/spf13/pflag"
 )
@@ -163,6 +164,13 @@ type Command struct {
 	// that we can use on every pflag set and children commands
 	globNormFunc func(f *flag.FlagSet, name string) flag.NormalizedName
 
+	// flagsCompletions contrains completions for arbitrary lists of flags.
+	// Those flags may or may not actually strictly belong to the command in the function,
+	// but registering completions for them through the command allows for garbage-collecting.
+	flagCompletionFunctions map[*flag.Flag]func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective)
+	// lock for reading and writing from flagCompletionFunctions
+	flagCompletionMutex *sync.RWMutex
+
 	// usageFunc is usage func defined by user.
 	usageFunc func(*Command) error
 	// usageTemplate is usage template defined by user.

completions.go

@@ -32,12 +32,6 @@ const (
 	ShellCompNoDescRequestCmd = "__completeNoDesc"
 )
 
-// Global map of flag completion functions. Make sure to use flagCompletionMutex before you try to read and write from it.
-var flagCompletionFunctions = map[*pflag.Flag]func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective){}
-
-// lock for reading and writing from flagCompletionFunctions
-var flagCompletionMutex = &sync.RWMutex{}
-
 // ShellCompDirective is a bit map representing the different behaviors the shell
 // can be instructed to have once completions have been provided.
 type ShellCompDirective int
@@ -135,23 +129,41 @@ func (c *Command) RegisterFlagCompletionFunc(flagName string, f func(cmd *Comman
 	if flag == nil {
 		return fmt.Errorf("RegisterFlagCompletionFunc: flag '%s' does not exist", flagName)
 	}
-	flagCompletionMutex.Lock()
-	defer flagCompletionMutex.Unlock()
+	// Ensure none of our relevant fields are nil.
+	c.initializeCompletionStorage()
 
-	if _, exists := flagCompletionFunctions[flag]; exists {
+	c.flagCompletionMutex.Lock()
+	defer c.flagCompletionMutex.Unlock()
+
+	// And attempt to bind the completion.
+	if _, exists := c.flagCompletionFunctions[flag]; exists {
 		return fmt.Errorf("RegisterFlagCompletionFunc: flag '%s' already registered", flagName)
 	}
-	flagCompletionFunctions[flag] = f
+	c.flagCompletionFunctions[flag] = f
 	return nil
 }
 
 // GetFlagCompletion returns the completion function for the given flag, if available.
-func GetFlagCompletion(flag *pflag.Flag) (func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective), bool) {
-	flagCompletionMutex.RLock()
-	defer flagCompletionMutex.RUnlock()
+func (c *Command) GetFlagCompletion(flag *pflag.Flag) (func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective), bool) {
+	c.initializeCompletionStorage()
+
+	c.flagCompletionMutex.RLock()
+	defer c.flagCompletionMutex.RUnlock()
+
+	completionFunc, exists := c.flagCompletionFunctions[flag]
+
+	// If found it here, return now
+	if completionFunc != nil && exists {
+		return completionFunc, exists
+	}
+
+	// If we are already at the root command level, return anyway
+	if !c.HasParent() {
+		return nil, false
+	}
 
-	completionFunc, exists := flagCompletionFunctions[flag]
-	return completionFunc, exists
+	// Or walk up the command tree.
+	return c.Parent().GetFlagCompletion(flag)
 }
 
 // GetFlagCompletionByName returns the completion function for the given flag in the command by name, if available.
@@ -161,7 +173,19 @@ func (c *Command) GetFlagCompletionByName(flagName string) (func(cmd *Command, a
 		return nil, false
 	}
 
-	return GetFlagCompletion(flag)
+	return c.GetFlagCompletion(flag)
+}
+
+// initializeCompletionStorage is (and should be) called in all
+// functions that make use of the command's flag completion functions.
+func (c *Command) initializeCompletionStorage() {
+	if c.flagCompletionMutex == nil {
+		c.flagCompletionMutex = new(sync.RWMutex)
+	}
+
+	if c.flagCompletionFunctions == nil {
+		c.flagCompletionFunctions = make(map[*pflag.Flag]func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective), 0)
+	}
 }
 
 // Returns a string listing the different directive enabled in the specified parameter
@@ -507,9 +531,7 @@ func (c *Command) getCompletions(args []string) (*Command, []string, ShellCompDi
 	// Find the completion function for the flag or command
 	var completionFn func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective)
 	if flag != nil && flagCompletion {
-		flagCompletionMutex.RLock()
-		completionFn = flagCompletionFunctions[flag]
-		flagCompletionMutex.RUnlock()
+		completionFn, _ = finalCmd.GetFlagCompletion(flag)
 	} else {
 		completionFn = finalCmd.ValidArgsFunction
 	}
@@ -833,7 +855,6 @@ to your powershell profile.
 				return cmd.Root().GenPowerShellCompletion(out)
 			}
 			return cmd.Root().GenPowerShellCompletionWithDesc(out)
-
 		},
 	}
 	if haveNoDescFlag {
@@ -873,7 +894,7 @@ func CompDebug(msg string, printToStdErr bool) {
 	// variable BASH_COMP_DEBUG_FILE to the path of some file to be used.
 	if path := os.Getenv("BASH_COMP_DEBUG_FILE"); path != "" {
 		f, err := os.OpenFile(path,
-			os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+			os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
 		if err == nil {
 			defer f.Close()
 			WriteStringAndCheck(f, msg)