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hsmusic-wiki - HSMusic - static wiki software cataloguing collaborative creation
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-rw-r--r--src/data/composite/control-flow/exposeConstant.js2
-rw-r--r--src/data/composite/things/flash-act/index.js1
-rw-r--r--src/data/composite/things/flash-act/withFlashSide.js22
-rw-r--r--src/data/composite/things/flash/withFlashAct.js100
-rw-r--r--src/data/composite/things/track/index.js1
-rw-r--r--src/data/composite/things/track/inheritFromOriginalRelease.js51
-rw-r--r--src/data/composite/things/track/withAlbum.js100
-rw-r--r--src/data/composite/things/track/withAlwaysReferenceByDirectory.js31
-rw-r--r--src/data/composite/things/track/withContainingTrackSection.js47
-rw-r--r--src/data/composite/things/track/withPropertyFromAlbum.js13
-rw-r--r--src/data/composite/things/track/withPropertyFromOriginalRelease.js86
-rw-r--r--src/data/composite/wiki-data/index.js1
-rw-r--r--src/data/composite/wiki-data/withResolvedContribs.js22
-rw-r--r--src/data/composite/wiki-data/withReverseContributionList.js14
-rw-r--r--src/data/composite/wiki-data/withReverseReferenceList.js10
-rw-r--r--src/data/composite/wiki-data/withUniqueReferencingThing.js51
-rw-r--r--src/data/composite/wiki-properties/contributionList.js10
17 files changed, 279 insertions, 283 deletions
diff --git a/src/data/composite/control-flow/exposeConstant.js b/src/data/composite/control-flow/exposeConstant.js
index e043547..e76699c 100644
--- a/src/data/composite/control-flow/exposeConstant.js
+++ b/src/data/composite/control-flow/exposeConstant.js
@@ -12,7 +12,7 @@ export default templateCompositeFrom({
   compose: false,
 
   inputs: {
-    value: input.staticValue(),
+    value: input.staticValue({acceptsNull: true}),
   },
 
   steps: () => [
diff --git a/src/data/composite/things/flash-act/index.js b/src/data/composite/things/flash-act/index.js
new file mode 100644
index 0000000..40fecd2
--- /dev/null
+++ b/src/data/composite/things/flash-act/index.js
@@ -0,0 +1 @@
+export {default as withFlashSide} from './withFlashSide.js';
diff --git a/src/data/composite/things/flash-act/withFlashSide.js b/src/data/composite/things/flash-act/withFlashSide.js
new file mode 100644
index 0000000..64daa1f
--- /dev/null
+++ b/src/data/composite/things/flash-act/withFlashSide.js
@@ -0,0 +1,22 @@
+// Gets the flash act's side. This will early exit if flashSideData is missing.
+// If there's no side whose list of flash acts includes this act, the output
+// dependency will be null.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {withUniqueReferencingThing} from '#composite/wiki-data';
+
+export default templateCompositeFrom({
+  annotation: `withFlashSide`,
+
+  outputs: ['#flashSide'],
+
+  steps: () => [
+    withUniqueReferencingThing({
+      data: 'flashSideData',
+      list: input.value('acts'),
+    }).outputs({
+      ['#uniqueReferencingThing']: '#flashSide',
+    }),
+  ],
+});
diff --git a/src/data/composite/things/flash/withFlashAct.js b/src/data/composite/things/flash/withFlashAct.js
index ada2dcf..652b8bf 100644
--- a/src/data/composite/things/flash/withFlashAct.js
+++ b/src/data/composite/things/flash/withFlashAct.js
@@ -1,108 +1,22 @@
 // Gets the flash's act. This will early exit if flashActData is missing.
-// By default, if there's no flash whose list of flashes includes this flash,
-// the output dependency will be null; set {notFoundMode: 'exit'} to early
-// exit instead.
-//
-// This step models with Flash.withAlbum.
+// If there's no flash whose list of flashes includes this flash, the output
+// dependency will be null.
 
 import {input, templateCompositeFrom} from '#composite';
-import {is} from '#validators';
 
-import {exitWithoutDependency, withResultOfAvailabilityCheck}
-  from '#composite/control-flow';
-import {withPropertyFromList} from '#composite/data';
+import {withUniqueReferencingThing} from '#composite/wiki-data';
 
 export default templateCompositeFrom({
   annotation: `withFlashAct`,
 
-  inputs: {
-    notFoundMode: input({
-      validate: is('exit', 'null'),
-      defaultValue: 'null',
-    }),
-  },
-
   outputs: ['#flashAct'],
 
   steps: () => [
-    // null flashActData is always an early exit.
-
-    exitWithoutDependency({
-      dependency: 'flashActData',
-      mode: input.value('null'),
-    }),
-
-    // empty flashActData conditionally exits early or outputs null.
-
-    withResultOfAvailabilityCheck({
-      from: 'flashActData',
-      mode: input.value('empty'),
-    }).outputs({
-      '#availability': '#flashActDataAvailability',
-    }),
-
-    {
-      dependencies: [input('notFoundMode'), '#flashActDataAvailability'],
-      compute(continuation, {
-        [input('notFoundMode')]: notFoundMode,
-        ['#flashActDataAvailability']: flashActDataIsAvailable,
-      }) {
-        if (flashActDataIsAvailable) return continuation();
-        switch (notFoundMode) {
-          case 'exit': return continuation.exit(null);
-          case 'null': return continuation.raiseOutput({'#flashAct': null});
-        }
-      },
-    },
-
-    withPropertyFromList({
-      list: 'flashActData',
-      property: input.value('flashes'),
-    }),
-
-    {
-      dependencies: [input.myself(), '#flashActData.flashes'],
-      compute: (continuation, {
-        [input.myself()]: track,
-        ['#flashActData.flashes']: flashLists,
-      }) => continuation({
-        ['#flashActIndex']:
-          flashLists.findIndex(flashes => flashes.includes(track)),
-      }),
-    },
-
-    // album not found conditionally exits or outputs null.
-
-    withResultOfAvailabilityCheck({
-      from: '#flashActIndex',
-      mode: input.value('index'),
+    withUniqueReferencingThing({
+      data: 'flashActData',
+      list: input.value('flashes'),
     }).outputs({
-      '#availability': '#flashActAvailability',
+      ['#uniqueReferencingThing']: '#flashAct',
     }),
-
-    {
-      dependencies: [input('notFoundMode'), '#flashActAvailability'],
-      compute(continuation, {
-        [input('notFoundMode')]: notFoundMode,
-        ['#flashActAvailability']: flashActIsAvailable,
-      }) {
-        if (flashActIsAvailable) return continuation();
-        switch (notFoundMode) {
-          case 'exit': return continuation.exit(null);
-          case 'null': return continuation.raiseOutput({'#flashAct': null});
-        }
-      },
-    },
-
-    {
-      dependencies: ['flashActData', '#flashActIndex'],
-      compute: (continuation, {
-        ['flashActData']: flashActData,
-        ['#flashActIndex']: flashActIndex,
-      }) => continuation.raiseOutput({
-        ['#flashAct']:
-          flashActData[flashActIndex],
-      }),
-    },
   ],
 });
diff --git a/src/data/composite/things/track/index.js b/src/data/composite/things/track/index.js
index cc723a2..8959de9 100644
--- a/src/data/composite/things/track/index.js
+++ b/src/data/composite/things/track/index.js
@@ -9,3 +9,4 @@ export {default as withContainingTrackSection} from './withContainingTrackSectio
 export {default as withHasUniqueCoverArt} from './withHasUniqueCoverArt.js';
 export {default as withOtherReleases} from './withOtherReleases.js';
 export {default as withPropertyFromAlbum} from './withPropertyFromAlbum.js';
+export {default as withPropertyFromOriginalRelease} from './withPropertyFromOriginalRelease.js';
diff --git a/src/data/composite/things/track/inheritFromOriginalRelease.js b/src/data/composite/things/track/inheritFromOriginalRelease.js
index 27ed138..38ab06b 100644
--- a/src/data/composite/things/track/inheritFromOriginalRelease.js
+++ b/src/data/composite/things/track/inheritFromOriginalRelease.js
@@ -1,8 +1,6 @@
-// Early exits with a value inherited from the original release, if
-// this track is a rerelease, and otherwise continues with no further
-// dependencies provided. If allowOverride is true, then the continuation
-// will also be called if the original release exposed the requested
-// property as null.
+// Early exits with the value for the same property as specified on the
+// original release, if this track is a rerelease, and otherwise continues
+// without providing any further dependencies.
 //
 // Like withOriginalRelease, this will early exit (with notFoundValue) if the
 // original release is specified by reference and that reference doesn't
@@ -10,41 +8,34 @@
 
 import {input, templateCompositeFrom} from '#composite';
 
-import withOriginalRelease from './withOriginalRelease.js';
+import {exposeDependency, raiseOutputWithoutDependency}
+  from '#composite/control-flow';
+
+import withPropertyFromOriginalRelease
+  from './withPropertyFromOriginalRelease.js';
 
 export default templateCompositeFrom({
   annotation: `inheritFromOriginalRelease`,
 
   inputs: {
-    property: input({type: 'string'}),
-    allowOverride: input({type: 'boolean', defaultValue: false}),
-    notFoundValue: input({defaultValue: null}),
+    notFoundValue: input({
+      defaultValue: null,
+    }),
   },
 
   steps: () => [
-    withOriginalRelease({
+    withPropertyFromOriginalRelease({
+      property: input.thisProperty(),
       notFoundValue: input('notFoundValue'),
     }),
 
-    {
-      dependencies: [
-        '#originalRelease',
-        input('property'),
-        input('allowOverride'),
-      ],
-
-      compute: (continuation, {
-        ['#originalRelease']: originalRelease,
-        [input('property')]: originalProperty,
-        [input('allowOverride')]: allowOverride,
-      }) => {
-        if (!originalRelease) return continuation();
-
-        const value = originalRelease[originalProperty];
-        if (allowOverride && value === null) return continuation();
-
-        return continuation.exit(value);
-      },
-    },
+    raiseOutputWithoutDependency({
+      dependency: '#isRerelease',
+      mode: input.value('falsy'),
+    }),
+
+    exposeDependency({
+      dependency: '#originalValue',
+    }),
   ],
 });
diff --git a/src/data/composite/things/track/withAlbum.js b/src/data/composite/things/track/withAlbum.js
index cbd16dc..03b840d 100644
--- a/src/data/composite/things/track/withAlbum.js
+++ b/src/data/composite/things/track/withAlbum.js
@@ -1,108 +1,22 @@
 // Gets the track's album. This will early exit if albumData is missing.
-// By default, if there's no album whose list of tracks includes this track,
-// the output dependency will be null; set {notFoundMode: 'exit'} to early
-// exit instead.
-//
-// This step models with Flash.withFlashAct.
+// If there's no album whose list of tracks includes this track, the output
+// dependency will be null.
 
 import {input, templateCompositeFrom} from '#composite';
-import {is} from '#validators';
 
-import {exitWithoutDependency, withResultOfAvailabilityCheck}
-  from '#composite/control-flow';
-import {withPropertyFromList} from '#composite/data';
+import {withUniqueReferencingThing} from '#composite/wiki-data';
 
 export default templateCompositeFrom({
   annotation: `withAlbum`,
 
-  inputs: {
-    notFoundMode: input({
-      validate: is('exit', 'null'),
-      defaultValue: 'null',
-    }),
-  },
-
   outputs: ['#album'],
 
   steps: () => [
-    // null albumData is always an early exit.
-
-    exitWithoutDependency({
-      dependency: 'albumData',
-      mode: input.value('null'),
-    }),
-
-    // empty albumData conditionally exits early or outputs null.
-
-    withResultOfAvailabilityCheck({
-      from: 'albumData',
-      mode: input.value('empty'),
-    }).outputs({
-      '#availability': '#albumDataAvailability',
-    }),
-
-    {
-      dependencies: [input('notFoundMode'), '#albumDataAvailability'],
-      compute(continuation, {
-        [input('notFoundMode')]: notFoundMode,
-        ['#albumDataAvailability']: albumDataIsAvailable,
-      }) {
-        if (albumDataIsAvailable) return continuation();
-        switch (notFoundMode) {
-          case 'exit': return continuation.exit(null);
-          case 'null': return continuation.raiseOutput({'#album': null});
-        }
-      },
-    },
-
-    withPropertyFromList({
-      list: 'albumData',
-      property: input.value('tracks'),
-    }),
-
-    {
-      dependencies: [input.myself(), '#albumData.tracks'],
-      compute: (continuation, {
-        [input.myself()]: track,
-        ['#albumData.tracks']: trackLists,
-      }) => continuation({
-        ['#albumIndex']:
-          trackLists.findIndex(tracks => tracks.includes(track)),
-      }),
-    },
-
-    // album not found conditionally exits or outputs null.
-
-    withResultOfAvailabilityCheck({
-      from: '#albumIndex',
-      mode: input.value('index'),
+    withUniqueReferencingThing({
+      data: 'albumData',
+      list: input.value('tracks'),
     }).outputs({
-      '#availability': '#albumAvailability',
+      ['#uniqueReferencingThing']: '#album',
     }),
-
-    {
-      dependencies: [input('notFoundMode'), '#albumAvailability'],
-      compute(continuation, {
-        [input('notFoundMode')]: notFoundMode,
-        ['#albumAvailability']: albumIsAvailable,
-      }) {
-        if (albumIsAvailable) return continuation();
-        switch (notFoundMode) {
-          case 'exit': return continuation.exit(null);
-          case 'null': return continuation.raiseOutput({'#album': null});
-        }
-      },
-    },
-
-    {
-      dependencies: ['albumData', '#albumIndex'],
-      compute: (continuation, {
-        ['albumData']: albumData,
-        ['#albumIndex']: albumIndex,
-      }) => continuation.raiseOutput({
-        ['#album']:
-          albumData[albumIndex],
-      }),
-    },
   ],
 });
diff --git a/src/data/composite/things/track/withAlwaysReferenceByDirectory.js b/src/data/composite/things/track/withAlwaysReferenceByDirectory.js
index fac8e21..e01720b 100644
--- a/src/data/composite/things/track/withAlwaysReferenceByDirectory.js
+++ b/src/data/composite/things/track/withAlwaysReferenceByDirectory.js
@@ -7,11 +7,15 @@ import {input, templateCompositeFrom} from '#composite';
 import find from '#find';
 import {isBoolean} from '#validators';
 
-import {exitWithoutDependency, exposeUpdateValueOrContinue}
-  from '#composite/control-flow';
 import {withPropertyFromObject} from '#composite/data';
 import {withResolvedReference} from '#composite/wiki-data';
 
+import {
+  exitWithoutDependency,
+  exposeDependencyOrContinue,
+  exposeUpdateValueOrContinue,
+} from '#composite/control-flow';
+
 export default templateCompositeFrom({
   annotation: `withAlwaysReferenceByDirectory`,
 
@@ -22,6 +26,29 @@ export default templateCompositeFrom({
       validate: input.value(isBoolean),
     }),
 
+    // withAlwaysReferenceByDirectory is sort of a fragile area - we can't
+    // find the track's album the normal way because albums' track lists
+    // recurse back into alwaysReferenceByDirectory!
+    withResolvedReference({
+      ref: 'dataSourceAlbum',
+      data: 'albumData',
+      find: input.value(find.album),
+    }).outputs({
+      '#resolvedReference': '#album',
+    }),
+
+    withPropertyFromObject({
+      object: '#album',
+      property: input.value('alwaysReferenceTracksByDirectory'),
+    }),
+
+    // Falsy mode means this exposes true if the album's property is true,
+    // but continues if the property is false (which is also the default).
+    exposeDependencyOrContinue({
+      dependency: '#album.alwaysReferenceTracksByDirectory',
+      mode: input.value('falsy'),
+    }),
+
     // Remaining code is for defaulting to true if this track is a rerelease of
     // another with the same name, so everything further depends on access to
     // trackData as well as originalReleaseTrack.
diff --git a/src/data/composite/things/track/withContainingTrackSection.js b/src/data/composite/things/track/withContainingTrackSection.js
index b2e5f2b..eaac14d 100644
--- a/src/data/composite/things/track/withContainingTrackSection.js
+++ b/src/data/composite/things/track/withContainingTrackSection.js
@@ -1,63 +1,42 @@
 // Gets the track section containing this track from its album's track list.
-// If notFoundMode is set to 'exit', this will early exit if the album can't be
-// found or if none of its trackSections includes the track for some reason.
 
 import {input, templateCompositeFrom} from '#composite';
 import {is} from '#validators';
 
+import {raiseOutputWithoutDependency} from '#composite/control-flow';
+
 import withPropertyFromAlbum from './withPropertyFromAlbum.js';
 
 export default templateCompositeFrom({
   annotation: `withContainingTrackSection`,
 
-  inputs: {
-    notFoundMode: input({
-      validate: is('exit', 'null'),
-      defaultValue: 'null',
-    }),
-  },
-
   outputs: ['#trackSection'],
 
   steps: () => [
     withPropertyFromAlbum({
       property: input.value('trackSections'),
-      notFoundMode: input('notFoundMode'),
+    }),
+
+    raiseOutputWithoutDependency({
+      dependency: '#album.trackSections',
+      output: input.value({'#trackSection': null}),
     }),
 
     {
       dependencies: [
         input.myself(),
-        input('notFoundMode'),
         '#album.trackSections',
       ],
 
-      compute(continuation, {
+      compute: (continuation, {
         [input.myself()]: track,
         [input('notFoundMode')]: notFoundMode,
         ['#album.trackSections']: trackSections,
-      }) {
-        if (!trackSections) {
-          return continuation.raiseOutput({
-            ['#trackSection']: null,
-          });
-        }
-
-        const trackSection =
-          trackSections.find(({tracks}) => tracks.includes(track));
-
-        if (trackSection) {
-          return continuation.raiseOutput({
-            ['#trackSection']: trackSection,
-          });
-        } else if (notFoundMode === 'exit') {
-          return continuation.exit(null);
-        } else {
-          return continuation.raiseOutput({
-            ['#trackSection']: null,
-          });
-        }
-      },
+      }) => continuation({
+        ['#trackSection']:
+          trackSections.find(({tracks}) => tracks.includes(track))
+            ?? null,
+      }),
     },
   ],
 });
diff --git a/src/data/composite/things/track/withPropertyFromAlbum.js b/src/data/composite/things/track/withPropertyFromAlbum.js
index b236a6e..d41390f 100644
--- a/src/data/composite/things/track/withPropertyFromAlbum.js
+++ b/src/data/composite/things/track/withPropertyFromAlbum.js
@@ -1,7 +1,5 @@
 // Gets a single property from this track's album, providing it as the same
-// property name prefixed with '#album.' (by default). If the track's album
-// isn't available, then by default, the property will be provided as null;
-// set {notFoundMode: 'exit'} to early exit instead.
+// property name prefixed with '#album.' (by default).
 
 import {input, templateCompositeFrom} from '#composite';
 import {is} from '#validators';
@@ -15,11 +13,6 @@ export default templateCompositeFrom({
 
   inputs: {
     property: input.staticValue({type: 'string'}),
-
-    notFoundMode: input({
-      validate: is('exit', 'null'),
-      defaultValue: 'null',
-    }),
   },
 
   outputs: ({
@@ -27,9 +20,7 @@ export default templateCompositeFrom({
   }) => ['#album.' + property],
 
   steps: () => [
-    withAlbum({
-      notFoundMode: input('notFoundMode'),
-    }),
+    withAlbum(),
 
     withPropertyFromObject({
       object: '#album',
diff --git a/src/data/composite/things/track/withPropertyFromOriginalRelease.js b/src/data/composite/things/track/withPropertyFromOriginalRelease.js
new file mode 100644
index 0000000..fd37f6d
--- /dev/null
+++ b/src/data/composite/things/track/withPropertyFromOriginalRelease.js
@@ -0,0 +1,86 @@
+// Provides a value inherited from the original release, if applicable, and a
+// flag indicating if this track is a rerelase or not.
+//
+// Like withOriginalRelease, this will early exit (with notFoundValue) if the
+// original release is specified by reference and that reference doesn't
+// resolve to anything.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {withResultOfAvailabilityCheck} from '#composite/control-flow';
+import {withPropertyFromObject} from '#composite/data';
+
+import withOriginalRelease from './withOriginalRelease.js';
+
+export default templateCompositeFrom({
+  annotation: `inheritFromOriginalRelease`,
+
+  inputs: {
+    property: input({type: 'string'}),
+
+    notFoundValue: input({
+      defaultValue: null,
+    }),
+  },
+
+  outputs: ({
+    [input.staticValue('property')]: property,
+  }) =>
+    ['#isRerelease'].concat(
+      (property
+        ? ['#original.' + property]
+        : ['#originalValue'])),
+
+  steps: () => [
+    withOriginalRelease({
+      notFoundValue: input('notFoundValue'),
+    }),
+
+    withResultOfAvailabilityCheck({
+      from: '#originalRelease',
+    }),
+
+    {
+      dependencies: [
+        '#availability',
+        input.staticValue('property'),
+      ],
+
+      compute: (continuation, {
+        ['#availability']: availability,
+        [input.staticValue('property')]: property,
+      }) =>
+        (availability
+          ? continuation()
+          : continuation.raiseOutput(
+              Object.assign(
+                {'#isRerelease': false},
+                (property
+                  ? {['#original.' + property]: null}
+                  : {'#originalValue': null})))),
+    },
+
+    withPropertyFromObject({
+      object: '#originalRelease',
+      property: input('property'),
+    }),
+
+    {
+      dependencies: [
+        '#value',
+        input.staticValue('property'),
+      ],
+
+      compute: (continuation, {
+        ['#value']: value,
+        [input.staticValue('property')]: property,
+      }) =>
+        continuation.raiseOutput(
+          Object.assign(
+            {'#isRerelease': true},
+            (property
+              ? {['#original.' + property]: value}
+              : {'#originalValue': value}))),
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-data/index.js b/src/data/composite/wiki-data/index.js
index 3ccfa75..b4cf6d1 100644
--- a/src/data/composite/wiki-data/index.js
+++ b/src/data/composite/wiki-data/index.js
@@ -13,3 +13,4 @@ export {default as withResolvedReferenceList} from './withResolvedReferenceList.
 export {default as withReverseContributionList} from './withReverseContributionList.js';
 export {default as withReverseReferenceList} from './withReverseReferenceList.js';
 export {default as withThingsSortedAlphabetically} from './withThingsSortedAlphabetically.js';
+export {default as withUniqueReferencingThing} from './withUniqueReferencingThing.js';
diff --git a/src/data/composite/wiki-data/withResolvedContribs.js b/src/data/composite/wiki-data/withResolvedContribs.js
index 77b0f96..9526638 100644
--- a/src/data/composite/wiki-data/withResolvedContribs.js
+++ b/src/data/composite/wiki-data/withResolvedContribs.js
@@ -1,7 +1,8 @@
 // Resolves the contribsByRef contained in the provided dependency,
 // providing (named by the second argument) the result. "Resolving"
-// means mapping the "who" reference of each contribution to an artist
-// object, and filtering out those whose "who" doesn't match any artist.
+// means mapping the artist reference of each contribution to an artist
+// object, and filtering out those whose artist reference doesn't match
+// any artist.
 
 import {input, templateCompositeFrom} from '#composite';
 import find from '#find';
@@ -46,29 +47,30 @@ export default templateCompositeFrom({
 
     withPropertiesFromList({
       list: input('from'),
-      properties: input.value(['who', 'what']),
+      properties: input.value(['artist', 'annotation']),
       prefix: input.value('#contribs'),
     }),
 
     withResolvedReferenceList({
-      list: '#contribs.who',
+      list: '#contribs.artist',
       data: 'artistData',
       find: input.value(find.artist),
       notFoundMode: input('notFoundMode'),
     }).outputs({
-      ['#resolvedReferenceList']: '#contribs.who',
+      ['#resolvedReferenceList']: '#contribs.artist',
     }),
 
     {
-      dependencies: ['#contribs.who', '#contribs.what'],
+      dependencies: ['#contribs.artist', '#contribs.annotation'],
 
       compute(continuation, {
-        ['#contribs.who']: who,
-        ['#contribs.what']: what,
+        ['#contribs.artist']: artist,
+        ['#contribs.annotation']: annotation,
       }) {
-        filterMultipleArrays(who, what, (who, _what) => who);
+        filterMultipleArrays(artist, annotation, (artist, _annotation) => artist);
         return continuation({
-          ['#resolvedContribs']: stitchArrays({who, what}),
+          ['#resolvedContribs']:
+            stitchArrays({artist, annotation}),
         });
       },
     },
diff --git a/src/data/composite/wiki-data/withReverseContributionList.js b/src/data/composite/wiki-data/withReverseContributionList.js
index eccb58b..91e125e 100644
--- a/src/data/composite/wiki-data/withReverseContributionList.js
+++ b/src/data/composite/wiki-data/withReverseContributionList.js
@@ -11,7 +11,8 @@
 
 import {input, templateCompositeFrom} from '#composite';
 
-import {exitWithoutDependency} from '#composite/control-flow';
+import {exitWithoutDependency, raiseOutputWithoutDependency}
+  from '#composite/control-flow';
 
 import inputWikiData from './inputWikiData.js';
 
@@ -32,10 +33,17 @@ export default templateCompositeFrom({
   outputs: ['#reverseContributionList'],
 
   steps: () => [
+    // Early exit with an empty array if the data list isn't available.
     exitWithoutDependency({
       dependency: input('data'),
       value: input.value([]),
+    }),
+
+    // Raise an empty array (don't early exit) if the data list is empty.
+    raiseOutputWithoutDependency({
+      dependency: input('data'),
       mode: input.value('empty'),
+      output: input.value({'#reverseContributionList': []}),
     }),
 
     {
@@ -58,10 +66,10 @@ export default templateCompositeFrom({
           for (const referencingThing of data) {
             const referenceList = referencingThing[list];
 
-            // Destructuring {who} is the only unique part of the
+            // Destructuring {artist} is the only unique part of the
             // withReverseContributionList implementation, compared to
             // withReverseReferneceList.
-            for (const {who: referencedThing} of referenceList) {
+            for (const {artist: referencedThing} of referenceList) {
               if (cacheRecord.has(referencedThing)) {
                 cacheRecord.get(referencedThing).push(referencingThing);
               } else {
diff --git a/src/data/composite/wiki-data/withReverseReferenceList.js b/src/data/composite/wiki-data/withReverseReferenceList.js
index 2d7a421..8cd540a 100644
--- a/src/data/composite/wiki-data/withReverseReferenceList.js
+++ b/src/data/composite/wiki-data/withReverseReferenceList.js
@@ -13,7 +13,8 @@
 
 import {input, templateCompositeFrom} from '#composite';
 
-import {exitWithoutDependency} from '#composite/control-flow';
+import {exitWithoutDependency, raiseOutputWithoutDependency}
+  from '#composite/control-flow';
 
 import inputWikiData from './inputWikiData.js';
 
@@ -34,10 +35,17 @@ export default templateCompositeFrom({
   outputs: ['#reverseReferenceList'],
 
   steps: () => [
+    // Early exit with an empty array if the data list isn't available.
     exitWithoutDependency({
       dependency: input('data'),
       value: input.value([]),
+    }),
+
+    // Raise an empty array (don't early exit) if the data list is empty.
+    raiseOutputWithoutDependency({
+      dependency: input('data'),
       mode: input.value('empty'),
+      output: input.value({'#reverseReferenceList': []}),
     }),
 
     {
diff --git a/src/data/composite/wiki-data/withUniqueReferencingThing.js b/src/data/composite/wiki-data/withUniqueReferencingThing.js
new file mode 100644
index 0000000..61c1061
--- /dev/null
+++ b/src/data/composite/wiki-data/withUniqueReferencingThing.js
@@ -0,0 +1,51 @@
+// Like withReverseReferenceList, but this is specifically for special "unique"
+// references, meaning this thing is referenced by exactly one or zero things
+// in the data list.
+
+import {input, templateCompositeFrom} from '#composite';
+
+import {exitWithoutDependency, raiseOutputWithoutDependency}
+  from '#composite/control-flow';
+
+import inputWikiData from './inputWikiData.js';
+import withReverseReferenceList from './withReverseReferenceList.js';
+
+export default templateCompositeFrom({
+  annotation: `withUniqueReferencingThing`,
+
+  inputs: {
+    data: inputWikiData({allowMixedTypes: false}),
+    list: input({type: 'string'}),
+  },
+
+  outputs: ['#uniqueReferencingThing'],
+
+  steps: () => [
+    // Early exit with null (not an empty array) if the data list
+    // isn't available.
+    exitWithoutDependency({
+      dependency: input('data'),
+    }),
+
+    withReverseReferenceList({
+      data: input('data'),
+      list: input('list'),
+    }),
+
+    raiseOutputWithoutDependency({
+      dependency: '#reverseReferenceList',
+      mode: input.value('empty'),
+      output: input.value({'#uniqueReferencingThing': null}),
+    }),
+
+    {
+      dependencies: ['#reverseReferenceList'],
+      compute: (continuation, {
+        ['#reverseReferenceList']: reverseReferenceList,
+      }) => continuation({
+        ['#uniqueReferencingThing']:
+          reverseReferenceList[0],
+      }),
+    },
+  ],
+});
diff --git a/src/data/composite/wiki-properties/contributionList.js b/src/data/composite/wiki-properties/contributionList.js
index 8fde2ca..aad12a2 100644
--- a/src/data/composite/wiki-properties/contributionList.js
+++ b/src/data/composite/wiki-properties/contributionList.js
@@ -3,15 +3,15 @@
 // into one property. Update value will look something like this:
 //
 //   [
-//     {who: 'Artist Name', what: 'Viola'},
-//     {who: 'artist:john-cena', what: null},
+//     {artist: 'Artist Name', annotation: 'Viola'},
+//     {artist: 'artist:john-cena', annotation: null},
 //     ...
 //   ]
 //
 // ...typically as processed from YAML, spreadsheet, or elsewhere.
-// Exposes as the same, but with the "who" replaced with matches found in
-// artistData - which means this always depends on an `artistData` property
-// also existing on this object!
+// Exposes as the same, but with the artist property replaced with matches
+// found in artistData - which means this always depends on an `artistData`
+// property also existing on this object!
 //
 
 import {input, templateCompositeFrom} from '#composite';