[zfs] Optimize enumeration of snapshots

Only generate the list of snapshots when
a) the argument must be a snapshot and nothing else, or
b) the argument as typed contains a literal @, or
c) a snapshot is a valid completion and there is only one dataset
   matching the argument as entered.

Unfortunately, it seems the `zfs` command itself is extremely primitive
and doesn't support listing snapshots by dataset so when we need to
generate completions, we end up needing to enumerate all snapshots
(ever) across all datasets. I'd be very happy to be proven wrong, but I
think the only other way would be manually parse `zdb` output.

See #7472

share/completions/zfs.fish

@@ -289,7 +289,7 @@ complete -c zfs -x -n '__fish_zfs_using_command snapshot; or __fish_zfs_using_co
 complete -c zfs -f -n '__fish_zfs_using_command rollback' -s r -d 'Destroy later snapshot and bookmarks'
 complete -c zfs -f -n '__fish_zfs_using_command rollback' -s R -d 'Recursively destroy later snapshot, bookmarks and clones'
 complete -c zfs -f -n '__fish_zfs_using_command rollback; and __fish_contains_opt -s R' -s f -d 'Force unmounting of clones'
-complete -c zfs -x -n '__fish_zfs_using_command rollback' -d 'Snapshot to roll back to' -a '(__fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command rollback' -d 'Snapshot to roll back to' -a '(__fish_print_zfs_snapshots --force)'
 
 # clone completions
 complete -c zfs -f -n '__fish_zfs_using_command clone' -s p -d 'Create all needed non-existing parent datasets'
@@ -298,7 +298,7 @@ if test $OS = Linux # Only Linux supports the comma-separated format; others nee
 else
     complete -c zfs -x -n '__fish_zfs_using_command clone' -s o -d 'Clone property' -a '(__fish_complete_zfs_rw_properties; __fish_complete_zfs_write_once_properties)'
 end
-complete -c zfs -x -n '__fish_zfs_using_command clone' -d 'Snapshot to clone' -a '(__fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command clone' -d 'Snapshot to clone' -a '(__fish_print_zfs_snapshots --force)'
 
 # promote completions
 complete -c zfs -x -n '__fish_zfs_using_command promote' -d 'Clone to promote' -a '(__fish_print_zfs_filesystems)'
@@ -323,11 +323,11 @@ complete -c zfs -f -n '__fish_zfs_using_command list' -s p -d 'Print parsable (e
 complete -c zfs -x -n '__fish_zfs_using_command list; and __fish_not_contain_opt -s S' -s s -d 'Property to use for sorting output by ascending order' -a '(__fish_complete_zfs_rw_properties; __fish_complete_zfs_write_once_properties; __fish_complete_zfs_ro_properties; echo -e "name\tDataset name")'
 complete -c zfs -x -n '__fish_zfs_using_command list; and __fish_not_contain_opt -s s' -s S -d 'Property to use for sorting output by descending order' -a '(__fish_complete_zfs_rw_properties; __fish_complete_zfs_write_once_properties; __fish_complete_zfs_ro_properties; echo -e "name\tDataset name")'
 complete -c zfs -x -n '__fish_zfs_using_command list' -s t -d 'Dataset type' -a '(__fish_zfs_list_dataset_types)'
-complete -c zfs -x -n '__fish_zfs_using_command list' -d 'Dataset which properties is to be listed' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command list' -d 'Dataset whose properties to list' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
 
 # set completions
 complete -c zfs -x -n '__fish_zfs_using_command set' -d 'Property to set' -a '(__fish_complete_zfs_rw_properties)'
-complete -c zfs -x -n '__fish_zfs_using_command set; and string match -q -r "zfs set \S+ " (commandline -c)' -d 'Dataset which property is to be setted' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command set; and string match -q -r "zfs set \S+ " (commandline -c)' -d 'Dataset whose property to set' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
 
 # get completions
 complete -c zfs -f -n '__fish_zfs_using_command get' -s r -d 'Operate recursively on datasets'
@@ -338,12 +338,12 @@ complete -c zfs -x -n '__fish_zfs_using_command get' -s s -d 'Property source to
 complete -c zfs -f -n '__fish_zfs_using_command get' -s p -d 'Print parsable (exact) values for numbers'
 complete -c zfs -x -n '__fish_zfs_using_command get' -s t -d 'Dataset type' -a '(__fish_append , (__fish_zfs_list_dataset_types))'
 complete -c zfs -x -n '__fish_zfs_using_command get' -d 'Property to get' -a '(__fish_append , (__fish_complete_zfs_rw_properties; __fish_complete_zfs_write_once_properties; __fish_complete_zfs_ro_properties; echo "all"))'
-complete -c zfs -x -n '__fish_zfs_using_command get' -d 'Dataset which properties is to be got' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command get' -d 'Dataset whose property to get' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
 
 # inherit completions
 complete -c zfs -f -n '__fish_zfs_using_command inherit' -s r -d 'Operate recursively on datasets'
 complete -c zfs -f -n '__fish_zfs_using_command inherit' -s S -d 'Revert to the received value if available'
-complete -c zfs -x -n '__fish_zfs_using_command inherit' -d 'Dataset which properties is to be inherited' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command inherit' -d 'Dataset whose properties are to be inherited' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
 
 # upgrade completions
 complete -c zfs -f -n '__fish_zfs_using_command upgrade; and __fish_not_contain_opt -s a -s r -s V' -s v -d 'Verbose mode'
@@ -363,7 +363,7 @@ complete -c zfs -x -n '__fish_zfs_using_command userspace; or __fish_zfs_using_c
 complete -c zfs -x -n '__fish_zfs_using_command userspace' -s t -d 'Identity types to display' -a '(__fish_append , (__fish_zfs_list_userspace_types))'
 complete -c zfs -x -n '__fish_zfs_using_command groupspace' -s t -d 'Identity types to display' -a '(__fish_append , (__fish_zfs_list_groupspace_types))'
 complete -c zfs -f -n '__fish_zfs_using_command userspace; or __fish_zfs_using_command groupspace' -s i -d 'Translate S(amba)ID to POSIX ID'
-complete -c zfs -x -n '__fish_zfs_using_command userspace; or __fish_zfs_using_command groupspace' -d 'Dataset which space usage is to be got' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command userspace; or __fish_zfs_using_command groupspace' -d 'Dataset whose space usage to get' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_snapshots)'
 
 # mount completions
 complete -c zfs -x -n '__fish_zfs_using_command mount' -s o -d 'Temporary mount point property' -a '(__fish_append , (__fish_complete_zfs_mountpoint_properties))'
@@ -393,8 +393,8 @@ if __fish_is_zfs_feature_enabled 'feature@bookmarks'
 end
 
 # send completions
-complete -c zfs -x -n '__fish_zfs_using_command send' -s i -d 'Generate incremental stream from snapshot' -a '(__fish_print_zfs_snapshots; __fish_print_zfs_bookmarks)'
-complete -c zfs -x -n '__fish_zfs_using_command send' -s I -d 'Generate incremental stream from snapshot, even with intermediary snapshots' -a '(__fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command send' -s i -d 'Generate incremental stream from snapshot' -a '(__fish_print_zfs_snapshots --force; __fish_print_zfs_bookmarks)'
+complete -c zfs -x -n '__fish_zfs_using_command send' -s I -d 'Generate incremental stream from snapshot, even with intermediary snapshots' -a '(__fish_print_zfs_snapshots --force)'
 if test $OS = SunOS
     complete -c zfs -f -n '__fish_zfs_using_command send' -s R -l replicate -d 'Include children in replication stream'
     complete -c zfs -f -n '__fish_zfs_using_command send' -s D -l dedup -d 'Generate a deduplicated stream'
@@ -415,7 +415,8 @@ else
     complete -c zfs -f -n '__fish_zfs_using_command send; and __fish_not_contain_opt -s R' -s p -d 'Include dataset properties'
     complete -c zfs -f -n '__fish_zfs_using_command send' -s v -d 'Print verbose information about the stream'
 end
-complete -c zfs -x -n '__fish_zfs_using_command send' -d 'Dataset to send' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
+# Only snapshots (and bookmarks?) may be sent
+complete -c zfs -x -n '__fish_zfs_using_command send' -d 'Dataset to send' -a '(__fish_print_zfs_snapshots --force)'
 
 # receive completions
 complete -c zfs -f -n '__fish_zfs_using_command receive; or __fish_zfs_using_command recv' -s v -d 'Print verbose information about the stream and the time spent processing it'
@@ -430,7 +431,7 @@ end
 if __fish_is_zfs_feature_enabled "feature@extensible_dataset"
     complete -c zfs -f -n '__fish_zfs_using_command receive; or __fish_zfs_using_command recv' -s s -d 'On transfer interruption, store a receive_resume_token for resumption'
 end
-complete -c zfs -x -n '__fish_zfs_using_command receive; or __fish_zfs_using_command recv' -d 'Dataset to receive' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes; __fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command receive; or __fish_zfs_using_command recv' -d 'Dataset to receive' -a '(__fish_print_zfs_filesystems; __fish_print_zfs_volumes;)'
 
 # allow completions
 complete -c zfs -f -n '__fish_zfs_using_command allow; and __fish_not_contain_opt -s d' -s l -d 'Delegate permissions only on the specified dataset'
@@ -467,7 +468,7 @@ complete -c zfs -x -n '__fish_zfs_using_command hold' -d 'Snapshot on which hold
 
 # holds completions
 complete -c zfs -f -n '__fish_zfs_using_command holds' -s r -d 'List holds recursively'
-complete -c zfs -x -n '__fish_zfs_using_command holds' -d 'Snapshot which holds are to be listed' -a '(__fish_print_zfs_snapshots)'
+complete -c zfs -x -n '__fish_zfs_using_command holds' -d 'Snapshot whose holds are to be listed' -a '(__fish_print_zfs_snapshots)'
 
 # release completions
 complete -c zfs -f -n '__fish_zfs_using_command release' -s r -d 'Release hold recursively'
@@ -483,5 +484,5 @@ complete -c zfs -x -n '__fish_zfs_using_command diff' -d 'Source snapshot for th
 if test $OS = SunOS # This is currently only supported under Illumos, but that will probably change
     complete -c zfs -x -n '__fish_zfs_using_command program' -s t -d 'Execution timeout'
     complete -c zfs -x -n '__fish_zfs_using_command program' -s t -d 'Execution memory limit'
-    complete -c zfs -x -n '__fish_zfs_using_command program' -d 'Pool which program will be executed on' -a '(__fish_complete_zfs_pools)'
+    complete -c zfs -x -n '__fish_zfs_using_command program' -d 'Pool program will be executed on' -a '(__fish_complete_zfs_pools)'
 end

share/functions/__fish_print_zfs_snapshots.fish

@@ -1,3 +1,15 @@
 function __fish_print_zfs_snapshots -d "Lists ZFS snapshots"
-    zfs list -t snapshot -o name -H
+    set fast_results (zfs list -o name -H)
+    printf "%s\n" $fast_results
+
+    # Don't retrieve all snapshots for all datasets until an @ is specified,
+    # or if there is only one possible matching dataset. (See #7472)
+    set current_token (commandline --current-token)
+    set filtered_results (string match -e -- $current_token $fast_results)
+    if contains -- --force $argv ||
+        not set -q filtered_results[2] ||
+        string match -eq @ -- $current_token
+
+        zfs list -t snapshot -o name -H
+    end
 end