refactor: add plugin.enabled flag

There are places where plugins are loaded explicitly by name
and so conditionally registering codecs leads to KeyErrors.
By adding enabled flag we can gracefully ignore some callbacks
from plugin definitions without breaking anything relying on plugin
existence.

src/chalk_common.nim

@@ -84,6 +84,7 @@ type
                                c: Option[string]) {.cdecl.}
   Plugin* = ref object
     name*:                     string
+    enabled*:                  bool
     configInfo*:               PluginSpec
     getChalkTimeHostInfo*:     ChalkTimeHostCb
     getChalkTimeArtifactInfo*: ChalkTimeArtifactCb

src/plugin_api.nim

@@ -20,6 +20,9 @@ import "."/[config, chalkjson, util]
 # should all be pre-checked.
 
 proc callGetChalkTimeHostInfo*(plugin: Plugin): ChalkDict =
+  if not plugin.enabled:
+    return ChalkDict()
+
   let cb = plugin.getChalkTimeHostInfo
 
   # explicit callback check - otherwise it results in segfault
@@ -31,6 +34,9 @@ proc callGetChalkTimeHostInfo*(plugin: Plugin): ChalkDict =
 
 proc callGetChalkTimeArtifactInfo*(plugin: Plugin, obj: ChalkObj):
          ChalkDict =
+  if not plugin.enabled:
+    return ChalkDict()
+
   let cb = plugin.getChalkTimeArtifactInfo
 
   # explicit callback check - otherwise it results in segfault
@@ -42,6 +48,9 @@ proc callGetChalkTimeArtifactInfo*(plugin: Plugin, obj: ChalkObj):
 
 proc callGetRunTimeArtifactInfo*(plugin: Plugin, obj: ChalkObj, b: bool):
          ChalkDict =
+  if not plugin.enabled:
+    return ChalkDict()
+
   let cb = plugin.getRunTimeArtifactInfo
 
   # explicit callback check - otherwise it results in segfault
@@ -53,6 +62,9 @@ proc callGetRunTimeArtifactInfo*(plugin: Plugin, obj: ChalkObj, b: bool):
 
 proc callGetRunTimeHostInfo*(plugin: Plugin, objs: seq[ChalkObj]):
          ChalkDict =
+  if not plugin.enabled:
+    return ChalkDict()
+
   let cb = plugin.getRunTimeHostInfo
 
   # explicit callback check - otherwise it results in segfault
@@ -594,7 +606,8 @@ proc newPlugin*(
                   getChalkTimeArtifactInfo: ctArtCallback,
                   getRunTimeArtifactInfo:   rtArtCallback,
                   getRunTimeHostInfo:       rtHostCallback,
-                  internalState:            cache)
+                  internalState:            cache,
+                  enabled:                  true)
 
   if not result.checkPlugin(codec = false):
     result = Plugin(nil)
@@ -612,7 +625,8 @@ proc newCodec*(
   handleWrite:        HandleWriteCb       = HandleWritecb(defaultCodecWrite),
   nativeObjPlatforms: seq[string]         =  @[],
   cache:              RootRef             = RootRef(nil),
-  commentStart:       string              = "#"):
+  commentStart:       string              = "#",
+  enabled:            bool                = true):
     Plugin {.discardable, cdecl.} =
 
   result = Plugin(name:                     name,
@@ -627,7 +641,8 @@ proc newCodec*(
                   handleWrite:              handleWrite,
                   nativeObjPlatforms:       nativeObjPlatforms,
                   internalState:            cache,
-                  commentStart:             commentStart)
+                  commentStart:             commentStart,
+                  enabled:                  enabled)
 
   if not result.checkPlugin(codec = true):
     result = Plugin(nil)

src/plugins/codecDocker.nim

@@ -601,9 +601,10 @@ proc dockerExtractChalkMark*(chalk: ChalkObj): ChalkDict {.exportc, cdecl.} =
 proc loadCodecDocker*() =
   # cant use getDockerExePath as that uses codecs to ignore chalk
   # wrappings hence we just check if anything docker is on PATH here
-  if nimutils.findExePath("docker") == "":
+  let enabled = nimutils.findExePath("docker") != ""
+  if not enabled:
     warn("Disabling docker codec as docker command is not available")
-  else:
-    newCodec("docker",
-             rtArtCallback = RunTimeArtifactCb(dockerGetRunTimeArtifactInfo),
-             getChalkId    = ChalkIdCb(dockerGetChalkId))
+  newCodec("docker",
+           rtArtCallback = RunTimeArtifactCb(dockerGetRunTimeArtifactInfo),
+           getChalkId    = ChalkIdCb(dockerGetChalkId),
+           enabled       = enabled)