More flexible citation key syntax jgm#6026

MANUAL.txt

@@ -4825,14 +4825,21 @@ Each citation must have a key, composed of '@' + the citation
 identifier from the database, and may optionally have a prefix,
 a locator, and a suffix.  The citation key must begin with a letter, digit,
 or `_`, and may contain alphanumerics, `_`, and internal punctuation
-characters (`:.#$%&-+?<>~/`).  Here are some examples:
+characters (`:.#$%&-+?<>~/`).  Alternatively arbitrary citation keys
+can be given inbetween `{` and `}`. Inside them `}` and `\` can be escaped
+using `\`. Here are some examples:
 
     Blah blah [see @doe99, pp. 33-35; also @smith04, chap. 1].
 
     Blah blah [@doe99, pp. 33-35, 38-39 and *passim*].
 
     Blah blah [@smith04; @doe99].
 
+You can also use citation keys directly without brackets:
+
+    Blah blah @smith04.
+    @{A more complex cite key}
+
 `pandoc-citeproc` detects locator terms in the [CSL locale files].
 Either abbreviated or unabbreviated forms are accepted. In the `en-US`
 locale, locator terms can be written in either singular or plural forms,

doc/org.md

@@ -127,7 +127,9 @@ the citation identifier from the database, and may optionally
 have a prefix, a locator, and a suffix. The citation key must
 begin with a letter, digit, or `_`, and may contain
 alphanumerics, `_`, and internal punctuation characters
-(`:.#$%&-+?<>~/`). Here are some examples:
+(`:.#$%&-+?<>~/`). Alternatively arbitrary citation keys can be
+given inbetween `{` and `}`. Inside them `}` and `\` can be
+escaped using `\`.
 
 ### Simple citation
 
@@ -137,6 +139,8 @@ ID prefixed by '@'.
 
 Example:
 
+    @citekey
+    @{this is a citekey}
     [prefix @citekey suffix]
     [see @doe2000 pp. 23-42]
     [@doe2000 p. 5; to a lesser extend @doe2005]

src/Text/Pandoc/Parsing.hs

@@ -1468,12 +1468,14 @@ citeKey = try $ do
   guard =<< notAfterString
   suppress_author <- option False (True <$ char '-')
   char '@'
-  firstChar <- alphaNum <|> char '_' <|> char '*' -- @* for wildcard in nocite
-  let regchar = satisfy (\c -> isAlphaNum c || c == '_')
-  let internal p = try $ p <* lookAhead regchar
-  rest <- many $ regchar <|> internal (oneOf ":.#$%&-+?<>~/") <|>
-                 try (oneOf ":/" <* lookAhead (char '/'))
-  let key = firstChar:rest
+  key <-
+    do firstChar <- alphaNum <|> char '_' <|> char '*' -- @* for wildcard in nocite
+       let regchar = satisfy (\c -> isAlphaNum c || c == '_')
+       let internal p = try $ p <* lookAhead regchar
+       rest <- many $ regchar <|> internal (oneOf ":.#$%&-+?<>~/") <|>
+                      try (oneOf ":/" <* lookAhead (char '/'))
+       pure $ firstChar:rest
+    <|> char '{' *> many (noneOf "}\\" <|> char '\\' *> anyChar) <* char '}'
   return (suppress_author, T.pack key)