Fish completion using Go completion

Signed-off-by: Marc Khouzam <marc.khouzam@montreal.ca>

fish_completions.go

@@ -0,0 +1,172 @@
+package cobra
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+func genFishComp(buf *bytes.Buffer, name string, includeDesc bool) {
+	compCmd := CompRequestCmd
+	if includeDesc {
+		compCmd = CompWithDescRequestCmd
+	}
+	buf.WriteString(fmt.Sprintf("# fish completion for %-36s -*- shell-script -*-\n", name))
+	buf.WriteString(fmt.Sprintf(`
+function __%[1]s_debug
+    set file "$BASH_COMP_DEBUG_FILE"
+    if test -n "$file"
+        echo "$argv" >> $file
+    end
+end
+
+function __%[1]s_perform_completion
+    __%[1]s_debug "Starting __%[1]s_perform_completion with: $argv"
+
+    set args (string split -- " " "$argv")
+    set lastArg "$args[-1]"
+
+    __%[1]s_debug "args: $args"
+    __%[1]s_debug "last arg: $lastArg"
+
+    set emptyArg ""
+    if test -z "$lastArg"
+        __%[1]s_debug "Setting emptyArg"
+        set emptyArg \"\"
+    end
+    __%[1]s_debug "emptyArg: $emptyArg"
+
+    set requestComp "$args[1] %[2]s $args[2..-1] $emptyArg"
+    __%[1]s_debug "Calling $requestComp"
+
+    set results (eval $requestComp 2> /dev/null)
+    set comps $results[1..-2]
+    set directiveLine $results[-1]
+
+    # For Fish, when completing a flag with an = (e.g., <program> -n=<TAB>)
+    # completions must be prefixed with the flag
+    set flagPrefix (string match -r -- '-.*=' "$lastArg")
+
+    __%[1]s_debug "Comps: $comps"
+    __%[1]s_debug "DirectiveLine: $directiveLine"
+    __%[1]s_debug "flagPrefix: $flagPrefix"
+
+    for comp in $comps
+        printf "%%s%%s\n" "$flagPrefix" "$comp"
+    end
+
+    printf "%%s\n" "$directiveLine"
+end
+
+# This function does three things:
+# 1- Obtain the completions and store them in the global __%[1]s_comp_results
+# 2- Set the __%[1]s_comp_do_file_comp flag if file completion should be performed
+#    and unset it otherwise
+# 3- Return true if the completion results are not empty
+function __%[1]s_prepare_completions
+    # Start fresh
+    set --erase __%[1]s_comp_do_file_comp
+    set --erase __%[1]s_comp_results
+
+    # Check if the command-line is already provided.  This is useful for testing.
+    if not set --query __%[1]s_comp_commandLine
+        set __%[1]s_comp_commandLine (commandline)
+    end
+    __%[1]s_debug "commandLine is: $__%[1]s_comp_commandLine"
+
+    set results (__%[1]s_perform_completion "$__%[1]s_comp_commandLine")
+    set --erase __%[1]s_comp_commandLine
+    __%[1]s_debug "Completion results: $results"
+
+    if test -z "$results"
+        __%[1]s_debug "No completion, probably due to a failure"
+        # Might as well do file completion, in case it helps
+        set --global __%[1]s_comp_do_file_comp 1
+        return 0
+    end
+
+    set directive (string sub --start 2 $results[-1])
+    set --global __%[1]s_comp_results $results[1..-2]
+
+    __%[1]s_debug "Completions are: $__%[1]s_comp_results"
+    __%[1]s_debug "Directive is: $directive"
+
+    if test -z "$directive"
+        set directive 0
+    end
+
+    set compErr (math (math --scale 0 $directive / %[3]d) %% 2)
+    if test $compErr -eq 1
+        __%[1]s_debug "Received error directive: aborting."
+        # Might as well do file completion, in case it helps
+        set --global __%[1]s_comp_do_file_comp 1
+        return 0
+    end
+
+    set nospace (math (math --scale 0 $directive / %[4]d) %% 2)
+    set nofiles (math (math --scale 0 $directive / %[5]d) %% 2)
+
+    __%[1]s_debug "nospace: $nospace, nofiles: $nofiles"
+
+    # Important not to quote the variable for count to work
+    set numComps (count $__%[1]s_comp_results)
+    __%[1]s_debug "numComps: $numComps"
+
+    if test $numComps -eq 1; and test $nospace -ne 0
+        # To support the "nospace" directive we trick the shell
+        # by outputting an extra, longer completion.
+        __%[1]s_debug "Adding second completion to perform nospace directive"
+        set --append __%[1]s_comp_results $__%[1]s_comp_results[1].
+    end
+
+    if test $numComps -eq 0; and test $nofiles -eq 0
+        __%[1]s_debug "Requesting file completion"
+        set --global __%[1]s_comp_do_file_comp 1
+    end
+
+    # If we don't want file completion, we must return true even if there
+    # are no completions found.  This is because fish will perform the last
+    # completion command, even if its condition is false, if no other
+    # completion command was triggered
+    return (not set --query __%[1]s_comp_do_file_comp)
+end
+
+# Remove any pre-existing completions for the program since we will be handling all of them
+# TODO this cleanup is not sufficient.  Fish completions are only loaded once the user triggers
+# them, so the below deletion will not work as it is run too early.  What else can we do?
+complete -c %[1]s -e
+
+# The order in which the below two lines are defined is very important so that __%[1]s_prepare_completions
+# is called first.  It is __%[1]s_prepare_completions that sets up the __%[1]s_comp_do_file_comp variable.
+#
+# This completion will be run second as complete commands are added FILO.
+# It triggers file completion choices when __%[1]s_comp_do_file_comp is set.
+complete -c %[1]s -n 'set --query __%[1]s_comp_do_file_comp'
+
+# This completion will be run first as complete commands are added FILO.
+# The call to __%[1]s_prepare_completions will setup both __%[1]s_comp_results abd __%[1]s_comp_do_file_comp.
+# It provides the program's completion choices.
+complete -c %[1]s -n '__%[1]s_prepare_completions' -f -a '$__%[1]s_comp_results'
+
+`, name, compCmd, BashCompDirectiveError, BashCompDirectiveNoSpace, BashCompDirectiveNoFileComp))
+}
+
+// GenFishCompletion generates fish completion file and writes to the passed writer.
+func (c *Command) GenFishCompletion(w io.Writer, includeDesc bool) error {
+	buf := new(bytes.Buffer)
+	genFishComp(buf, c.Name(), includeDesc)
+	_, err := buf.WriteTo(w)
+	return err
+}
+
+// GenFishCompletionFile generates fish completion file.
+func (c *Command) GenFishCompletionFile(filename string, includeDesc bool) error {
+	outFile, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+	defer outFile.Close()
+
+	return c.GenFishCompletion(outFile, includeDesc)
+}

fish_completions.md

@@ -0,0 +1,7 @@
+## Generating Fish Completions for your own cobra.Command
+
+Cobra supports native Fish completions generated from the root `cobra.Command`.  You can use the `command.GenFishCompletion()` or `command.GenFishCompletionFile()` functions. You must provide these functions with a parameter indicating if the completions should be annotated with a description; Cobra will provide the description automatically based on usage information.  You can choose to make this option configurable by your users.
+
+### Limitations
+
+* Custom completions implemented using the `ValidArgsFunction` and `RegisterFlagCompletionFunc()` are supported automatically but the ones implemented in Bash scripting are not.