docs(tvix/eval): builtins.md: note implementation status r/5225

We're getting close to the finish line, folks.

I went through the list of builtins and there are only 33 that
remain unimplemented.  I've marked them, and indicated which are
ready to be implemented vs which are waiting for other things.

We can delete this column from the table once everything is
implemented.

Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: Idfaef93283536288b12e59aef5c3e1cd139bd133
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7140
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

1 files changed, 123 insertions, 116 deletions

diff --git a/tvix/eval/docs/builtins.md b/tvix/eval/docs/builtins.md
index cb0cc828d2..89fe45318a 100644
--- a/tvix/eval/docs/builtins.md
+++ b/tvix/eval/docs/builtins.md
@@ -10,122 +10,129 @@ without documenting their functionality.
 
 See also https://nixos.org/manual/nix/stable/expressions/builtins.html
 
-| name                          | global | arity | pure  |
-|-------------------------------|--------|-------|-------|
-| abort                         | true   | 1     |       |
-| add                           | false  | 2     | true  |
-| addErrorContext               | false  | ?     |       |
-| all                           | false  | 2     | true  |
-| any                           | false  | 2     | true  |
-| appendContext                 | false  | ?     |       |
-| attrNames                     | false  | 1     | true  |
-| attrValues                    | false  |       | true  |
-| baseNameOf                    | true   |       |       |
-| bitAnd                        | false  |       |       |
-| bitOr                         | false  |       |       |
-| bitXor                        | false  |       |       |
-| builtins                      | true   |       |       |
-| catAttrs                      | false  |       |       |
-| compareVersions               | false  |       |       |
-| concatLists                   | false  |       |       |
-| concatMap                     | false  |       |       |
-| concatStringsSep              | false  |       |       |
-| currentSystem                 | false  |       |       |
-| currentTime                   | false  |       | false |
-| deepSeq                       | false  |       |       |
-| derivation                    | true   |       |       |
-| derivationStrict              | true   |       |       |
-| dirOf                         | true   |       |       |
-| div                           | false  |       |       |
-| elem                          | false  |       |       |
-| elemAt                        | false  |       |       |
-| false                         | true   |       |       |
-| fetchGit                      | true   |       |       |
-| fetchMercurial                | true   |       |       |
-| fetchTarball                  | true   |       |       |
-| fetchurl                      | false  |       |       |
-| filter                        | false  |       |       |
-| filterSource                  | false  |       |       |
-| findFile                      | false  |       | false |
-| foldl'                        | false  |       |       |
-| fromJSON                      | false  |       |       |
-| fromTOML                      | true   |       |       |
-| functionArgs                  | false  |       |       |
-| genList                       | false  |       |       |
-| genericClosure                | false  |       |       |
-| getAttr                       | false  |       |       |
-| getContext                    | false  |       |       |
-| getEnv                        | false  |       | false |
-| hasAttr                       | false  |       |       |
-| hasContext                    | false  |       |       |
-| hashFile                      | false  |       | false |
-| hashString                    | false  |       |       |
-| head                          | false  |       |       |
-| import                        | true   |       |       |
-| intersectAttrs                | false  |       |       |
-| isAttrs                       | false  |       |       |
-| isBool                        | false  |       |       |
-| isFloat                       | false  |       |       |
-| isFunction                    | false  |       |       |
-| isInt                         | false  |       |       |
-| isList                        | false  |       |       |
-| isNull                        | true   |       |       |
-| isPath                        | false  |       |       |
-| isString                      | false  |       |       |
-| langVersion                   | false  |       |       |
-| length                        | false  |       |       |
-| lessThan                      | false  |       |       |
-| listToAttrs                   | false  |       |       |
-| map                           | true   |       |       |
-| mapAttrs                      | false  |       |       |
-| match                         | false  |       |       |
-| mul                           | false  |       |       |
-| nixPath                       | false  |       |       |
-| nixVersion                    | false  |       |       |
-| null                          | true   |       |       |
-| parseDrvName                  | false  |       |       |
-| partition                     | false  |       |       |
-| path                          | false  |       | sometimes |
-| pathExists                    | false  |       | false |
-| placeholder                   | true   |       |       |
-| readDir                       | false  |       | false |
-| readFile                      | false  |       | false |
-| removeAttrs                   | true   |       |       |
-| replaceStrings                | false  |       |       |
-| scopedImport                  | true   |       |       |
-| seq                           | false  |       |       |
-| sort                          | false  |       |       |
-| split                         | false  |       |       |
-| splitVersion                  | false  |       |       |
-| storeDir                      | false  |       |       |
-| storePath                     | false  |       |       |
-| stringLength                  | false  |       |       |
-| sub                           | false  |       |       |
-| substring                     | false  |       |       |
-| tail                          | false  |       |       |
-| throw                         | true   |       |       |
-| toFile                        | false  |       |       |
-| toJSON                        | false  |       |       |
-| toPath                        | false  |       |       |
-| toString                      | true   |       |       |
-| toXML                         | false  |       |       |
-| trace                         | false  |       |       |
-| true                          | true   |       |       |
-| tryEval                       | false  |       |       |
-| typeOf                        | false  |       |       |
-| unsafeDiscardOutputDependency | false  |       |       |
-| unsafeDiscardStringContext    | false  |       |       |
-| unsafeGetAttrPos              | false  |       |       |
-| valueSize                     | false  |       |       |
+The `impl` column indicates implementation status in tvix:
+- implemented: "" (empty cell)
+- not yet implemented, but not blocked: `todo`
+- not yet implemented, but blocked by other prerequisites:
+  - `store`: awaiting eval<->store api(s)
+  - `context`: awaiting support for string contexts
+
+| name                          | global | arity | pure  | impl    |
+|-------------------------------|--------|-------|-------|---------|
+| abort                         | true   | 1     |       |         |
+| add                           | false  | 2     | true  |         |
+| addErrorContext               | false  | ?     |       | context |
+| all                           | false  | 2     | true  |         |
+| any                           | false  | 2     | true  |         |
+| appendContext                 | false  | ?     |       | context |
+| attrNames                     | false  | 1     | true  |         |
+| attrValues                    | false  |       | true  |         |
+| baseNameOf                    | true   |       |       |         |
+| bitAnd                        | false  |       |       |         |
+| bitOr                         | false  |       |       |         |
+| bitXor                        | false  |       |       |         |
+| builtins                      | true   |       |       |         |
+| catAttrs                      | false  |       |       |         |
+| compareVersions               | false  |       |       |         |
+| concatLists                   | false  |       |       |         |
+| concatMap                     | false  |       |       |         |
+| concatStringsSep              | false  |       |       |         |
+| currentSystem                 | false  |       |       |         |
+| currentTime                   | false  |       | false |         |
+| deepSeq                       | false  |       |       |         |
+| derivation                    | true   |       |       | store   |
+| derivationStrict              | true   |       |       | store   |
+| dirOf                         | true   |       |       |         |
+| div                           | false  |       |       |         |
+| elem                          | false  |       |       |         |
+| elemAt                        | false  |       |       |         |
+| false                         | true   |       |       |         |
+| fetchGit                      | true   |       |       | store   |
+| fetchMercurial                | true   |       |       | store   |
+| fetchTarball                  | true   |       |       | store   |
+| fetchurl                      | false  |       |       | store   |
+| filter                        | false  |       |       |         |
+| filterSource                  | false  |       |       | store   |
+| findFile                      | false  |       | false | todo    |
+| foldl'                        | false  |       |       |         |
+| fromJSON                      | false  |       |       |         |
+| fromTOML                      | true   |       |       |         |
+| functionArgs                  | false  |       |       |         |
+| genList                       | false  |       |       |         |
+| genericClosure                | false  |       |       | todo    |
+| getAttr                       | false  |       |       |         |
+| getContext                    | false  |       |       | context |
+| getEnv                        | false  |       | false |         |
+| hasAttr                       | false  |       |       |         |
+| hasContext                    | false  |       |       | context |
+| hashFile                      | false  |       | false | todo    |
+| hashString                    | false  |       |       | todo    |
+| head                          | false  |       |       |         |
+| import                        | true   |       |       |         |
+| intersectAttrs                | false  |       |       |         |
+| isAttrs                       | false  |       |       |         |
+| isBool                        | false  |       |       |         |
+| isFloat                       | false  |       |       |         |
+| isFunction                    | false  |       |       |         |
+| isInt                         | false  |       |       |         |
+| isList                        | false  |       |       |         |
+| isNull                        | true   |       |       |         |
+| isPath                        | false  |       |       |         |
+| isString                      | false  |       |       |         |
+| langVersion                   | false  |       |       |         |
+| length                        | false  |       |       |         |
+| lessThan                      | false  |       |       |         |
+| listToAttrs                   | false  |       |       |         |
+| map                           | true   |       |       |         |
+| mapAttrs                      | false  |       |       |         |
+| match                         | false  |       |       |         |
+| mul                           | false  |       |       |         |
+| nixPath                       | false  |       |       | todo    |
+| nixVersion                    | false  |       |       | todo    |
+| null                          | true   |       |       |         |
+| parseDrvName                  | false  |       |       |         |
+| partition                     | false  |       |       |         |
+| path                          | false  |       | sometimes | store |
+| pathExists                    | false  |       | false |         |
+| placeholder                   | true   |       |       | context |
+| readDir                       | false  |       | false |         |
+| readFile                      | false  |       | false |         |
+| removeAttrs                   | true   |       |       |         |
+| replaceStrings                | false  |       |       |         |
+| scopedImport                  | true   |       |       |         |
+| seq                           | false  |       |       |         |
+| sort                          | false  |       |       |         |
+| split                         | false  |       |       | todo    |
+| splitVersion                  | false  |       |       |         |
+| storeDir                      | false  |       |       | store   |
+| storePath                     | false  |       |       | store   |
+| stringLength                  | false  |       |       |         |
+| sub                           | false  |       |       |         |
+| substring                     | false  |       |       |         |
+| tail                          | false  |       |       |         |
+| throw                         | true   |       |       |         |
+| toFile                        | false  |       |       | store   |
+| toJSON                        | false  |       |       | todo    |
+| toPath                        | false  |       |       |         |
+| toString                      | true   |       |       |         |
+| toXML                         | false  |       |       | todo    |
+| trace                         | false  |       |       |         |
+| true                          | true   |       |       |         |
+| tryEval                       | false  |       |       |         |
+| typeOf                        | false  |       |       |         |
+| unsafeDiscardOutputDependency | false  |       |       | context |
+| unsafeDiscardStringContext    | false  |       |       | context |
+| unsafeGetAttrPos              | false  |       |       | todo    |
+| valueSize                     | false  |       |       | todo    |
 
 ## Added after C++ Nix 2.3 (without Flakes enabled)
 
-| name          | global | arity | pure  |
-|---------------|--------|-------|-------|
-| break         | false  | 1     |       |
-| ceil          | false  | 1     | true  |
-| fetchTree     | true   | 1     |       |
-| floor         | false  | 1     | true  |
-| groupBy       | false  | 2     | true  |
-| traceVerbose  | false  | 2     |       |
-| zipAttrsWith  | false  | 2     | true  |
+| name          | global | arity | pure  | impl  |
+|---------------|--------|-------|-------|-------|
+| break         | false  | 1     |       | todo  |
+| ceil          | false  | 1     | true  |       |
+| fetchTree     | true   | 1     |       | todo  |
+| floor         | false  | 1     | true  |       |
+| groupBy       | false  | 2     | true  |       |
+| traceVerbose  | false  | 2     |       | todo  |
+| zipAttrsWith  | false  | 2     | true  | todo  |