feat(citations): add Org 9.5 citation support with BibTeX source, completions, and go-to-source

docs/configuration.org

@@ -2311,6 +2311,7 @@ these types:
 - Planning keywords (=DEADLINE=, =SCHEDULED=, =CLOSED=)
 - Orgfile special keywords (=#+TITLE=, =#+BEGIN_SRC=, =#+ARCHIVE=, etc.)
 - Hyperlinks (=* - headlines=, =# - headlines with CUSTOM_ID property=, =headlines matching title=)
+- Citation keys (inside =[cite:...]= blocks after =@=)
 
 Autocompletion is context aware, which means that for example
 tags autocompletion will kick in only when cursor is at the end of
@@ -2540,6 +2541,162 @@ require('orgmode').setup({
 })
 #+end_src
 
+*** Citations
+:PROPERTIES:
+:CUSTOM_ID: citations
+:END:
+Orgmode supports [[https://orgmode.org/manual/Citation-handling.html][Org 9.5 citations]] using the =[cite:@key]= syntax.
+For example:
+
+#+begin_src org
+See [cite:@smith2020] for details, or [cite/t:@jones2021;@doe2022] for a
+textual citation.
+#+end_src
+
+The citation key under the cursor can be followed to its bibliography entry
+using the same =org_open_at_point= mapping (=<Leader>oo= by default) that is
+used for hyperlinks.
+
+Citation key autocompletion is provided via the standard =omnifunc= (triggered
+by =<C-x><C-o>= in insert mode). Completion is active inside any =[cite:...]=
+or =[cite/style:...]=, after the =@= character.
+
+**** Bibliography files
+:PROPERTIES:
+:CUSTOM_ID: citations-bibliography-files
+:END:
+The built-in BibTeX source reads citation keys from =.bib= files.  Two
+discovery mechanisms are available (both can be used simultaneously):
+
+***** Global bibliography
+:PROPERTIES:
+:CUSTOM_ID: org_cite_global_bibliography
+:END:
+Set =citations.org_cite_global_bibliography= to a path or list of paths that
+are always searched, regardless of which file is open:
+
+#+begin_src lua
+require('orgmode').setup({
+  citations = {
+    org_cite_global_bibliography = {
+      '~/references/global.bib',
+      '~/references/books.bib',
+    },
+  },
+})
+#+end_src
+
+A single string is also accepted:
+
+#+begin_src lua
+require('orgmode').setup({
+  citations = {
+    org_cite_global_bibliography = '~/references/global.bib',
+  },
+})
+#+end_src
+
+***** File-local bibliography
+:PROPERTIES:
+:CUSTOM_ID: citations-file-local-bibliography
+:END:
+Any =.org= file can declare its own bibliography with one or more
+=#+bibliography:= directives.  Paths are resolved relative to the org file:
+
+#+begin_src org
+#+bibliography: refs.bib
+#+bibliography: /absolute/path/to/extra.bib
+
+* Introduction
+See [cite:@smith2020] for background.
+#+end_src
+
+**** Custom citation sources
+:PROPERTIES:
+:CUSTOM_ID: citations-custom-sources
+:END:
+Additional citation sources can be registered via =citations.sources=.  Each
+source is a table (or object) that implements the =OrgCitationSource=
+interface:
+
+- =get_name()= (required) — return a unique name string for the source.
+- =get_items()= (required) — return a list of =OrgCitationItem= tables.
+  Each item must have a =key= field, and may optionally have =label= and
+  =description= fields used in completion menus.
+- =follow(key)= (optional) — navigate to the entry for =key=; return =true=
+  if handled, =false= to fall through to the next source.
+
+#+begin_src lua
+require('orgmode').setup({
+  citations = {
+    sources = {
+      {
+        get_name = function() return 'my_source' end,
+        get_items = function()
+          return {
+            { key = 'smith2020', description = 'Smith et al. 2020' },
+            { key = 'jones2021' },
+          }
+        end,
+        follow = function(self, key)
+          vim.notify('Citation: ' .. key)
+          return true
+        end,
+      },
+    },
+  },
+})
+#+end_src
+
+***** Example: Zotero Local API
+:PROPERTIES:
+:CUSTOM_ID: citations-zotero-local-api
+:END:
+[[https://www.zotero.org][Zotero]] exposes a local HTTP API on =http://localhost:23119= (requires the
+Zotero desktop application to be running).  The example below defines a
+custom source that queries the local API for all library items and exposes
+their citation keys for completion.
+#+begin_src lua
+local ZoteroSource = {}
+
+function ZoteroSource:get_name()
+  return 'zotero'
+end
+
+function ZoteroSource:get_items()
+  local curl = require('plenary.curl')
+  local res = curl.get {
+    url = 'http://localhost:23119/api/users/0/items?format=json',
+    accept = 'application/json',
+  }
+  if res.status == 200 then
+    local data = vim.json.decode(res.body or '') or {}
+    local items = {}
+    for _, entry in ipairs(data) do
+      local d = entry.data or {}
+      if d.citationKey then
+        local creators = d.creators or {}
+        local author = (creators[1] or {}).lastName or ''
+        local year = (d.date or ''):match('%d%d%d%d') or ''
+        table.insert(items, {
+          key = d.citationKey,
+          description = author .. year .. ' ' .. (d.title or ''),
+        })
+      end
+    end
+    return items
+  else
+    return {}
+  end
+end
+
+require('orgmode').setup({
+  citations = {
+    sources = { ZoteroSource },
+  },
+})
+#+end_src
+
 *** Notifications
 :PROPERTIES:
 :CUSTOM_ID: notifications

lua/orgmode/colors/highlights.lua

@@ -67,6 +67,8 @@ function M.link_highlights()
     ['@org.latex'] = '@markup.math',
     ['@org.latex_env'] = '@markup.environment',
     ['@org.footnote'] = '@markup.link.url',
+    ['@org.citation'] = '@markup.link',
+    ['@org.citation.reference'] = '@markup.link.url',
     -- Other
     ['@org.table.delimiter'] = '@punctuation.special',
     ['@org.table.heading'] = '@markup.heading',

lua/orgmode/config/defaults.lua

@@ -96,6 +96,10 @@ local DefaultConfig = {
   hyperlinks = {
     sources = {},
   },
+  citations = {
+    sources = {},
+    org_cite_global_bibliography = {},
+  },
   mappings = {
     disable_all = false,
     org_return_uses_meta_return = false,

lua/orgmode/init.lua

@@ -12,6 +12,7 @@ local auto_instance_keys = {
   notifications = true,
   completion = true,
   links = true,
+  citations = true,
 }
 
 ---@class Org
@@ -27,6 +28,7 @@ local auto_instance_keys = {
 ---@field org_mappings OrgMappings
 ---@field notifications OrgNotifications
 ---@field links OrgLinks
+---@field citations OrgCitations
 local Org = {}
 setmetatable(Org, {
   __index = function(tbl, key)
@@ -60,6 +62,7 @@ function Org:init()
     })
     :load_sync(true, 20000)
   self.links = require('orgmode.org.links'):new({ files = self.files })
+  self.citations = require('orgmode.org.citations'):new({ files = self.files })
   self.agenda = require('orgmode.agenda'):new({
     files = self.files,
     highlighter = self.highlighter,
@@ -68,12 +71,14 @@ function Org:init()
   self.capture = require('orgmode.capture'):new({
     files = self.files,
   })
-  self.completion = require('orgmode.org.autocompletion'):new({ files = self.files, links = self.links })
+  self.completion =
+    require('orgmode.org.autocompletion'):new({ files = self.files, links = self.links, citations = self.citations })
   self.org_mappings = require('orgmode.org.mappings'):new({
     capture = self.capture,
     agenda = self.agenda,
     files = self.files,
     links = self.links,
+    citations = self.citations,
     completion = self.completion,
   })
   self.clock = require('orgmode.clock'):new({

lua/orgmode/org/autocompletion/init.lua

@@ -1,6 +1,7 @@
 ---@class OrgCompletion
 ---@field files OrgFiles
 ---@field links OrgLinks
+---@field citations OrgCitations
 ---@field private sources OrgCompletionSource[]
 ---@field private sources_by_name table<string, OrgCompletionSource>
 ---@field private fuzzy_match? boolean does completeopt has fuzzy option
@@ -10,11 +11,12 @@ local OrgCompletion = {
 }
 OrgCompletion.__index = OrgCompletion
 
----@param opts { files: OrgFiles, links: OrgLinks }
+---@param opts { files: OrgFiles, links: OrgLinks, citations: OrgCitations }
 function OrgCompletion:new(opts)
   local this = setmetatable({
     files = opts.files,
     links = opts.links,
+    citations = opts.citations,
     sources = {},
     sources_by_name = {},
     fuzzy_match = vim.tbl_contains(vim.opt_local.completeopt:get(), 'fuzzy'),
@@ -31,6 +33,7 @@ function OrgCompletion:setup_builtin_sources()
   self:add_source(require('orgmode.org.autocompletion.sources.directives'):new())
   self:add_source(require('orgmode.org.autocompletion.sources.properties'):new({ completion = self }))
   self:add_source(require('orgmode.org.autocompletion.sources.hyperlinks'):new({ completion = self }))
+  self:add_source(require('orgmode.org.autocompletion.sources.citations'):new({ completion = self }))
 end
 
 ---@param source OrgCompletionSource

lua/orgmode/org/autocompletion/sources/citations.lua

@@ -0,0 +1,39 @@
+---@class OrgCompletionCitations:OrgCompletionSource
+---@field completion OrgCompletion
+---@field private pattern vim.regex
+local OrgCompletionCitations = {}
+OrgCompletionCitations.__index = OrgCompletionCitations
+
+---@param opts { completion: OrgCompletion }
+function OrgCompletionCitations:new(opts)
+  return setmetatable({
+    completion = opts.completion,
+    pattern = vim.regex([=[\[cite[/:][^\]]*@\zs[^ \]]*$]=]),
+  }, OrgCompletionCitations)
+end
+
+---@return string
+function OrgCompletionCitations:get_name()
+  return 'citations'
+end
+
+---@param context OrgCompletionContext
+---@return number | nil
+function OrgCompletionCitations:get_start(context)
+  return self.pattern:match_str(context.line)
+end
+
+---@param _ OrgCompletionContext
+---@return string[]
+function OrgCompletionCitations:get_results(_)
+  local citations = self.completion.citations
+  if not citations then
+    return {}
+  end
+  local items = citations:get_items()
+  return vim.tbl_map(function(item)
+    return item.key
+  end, items)
+end
+
+return OrgCompletionCitations

lua/orgmode/org/autocompletion/sources/directives.lua

@@ -34,6 +34,7 @@ function OrgCompletionDirectives:get_results(_)
     '#+begin_example',
     '#+end_src',
     '#+end_example',
+    '#+bibliography',
   }
 end
 

lua/orgmode/org/citations/_meta.lua

@@ -0,0 +1,11 @@
+---@meta
+
+---@class OrgCitationItem
+---@field key string The citation key (e.g. "smith2020")
+---@field label? string Optional display label used in completion menus
+---@field description? string Optional human-readable description (author, title, year, etc.)
+
+---@class OrgCitationSource
+---@field get_name fun(self: OrgCitationSource): string Return the unique name of this source
+---@field get_items fun(self: OrgCitationSource): OrgCitationItem[] Return all citation items
+---@field follow? fun(self: OrgCitationSource, key: string): boolean Navigate to the entry for the given key; return true if handled