Additional tests for the identifier parser (#816)

* Add tests for the identifier parser

* docs: Clarify how to delimit identifiers

(cherry picked from commit 0861affeca4d72938f05a2eceddfae2c19199071)

2 files changed, 51 insertions, 10 deletions

diff --git a/doc/markup.rst b/doc/markup.rst
index 1a278da3..a9878837 100644
--- a/doc/markup.rst
+++ b/doc/markup.rst
@@ -859,10 +859,13 @@ Hyperlinked Identifiers
 ~~~~~~~~~~~~~~~~~~~~~~~
 
 Referring to a Haskell identifier, whether it be a type, class,
-constructor, or function, is done by surrounding it with single quotes: ::
+constructor, or function, is done by surrounding it with a combination
+of single quotes and backticks. For example: ::
 
     -- | This module defines the type 'T'.
 
+```T``` is also ok. ``'T``` and ```T'`` are accepted but less common.
+
 If there is an entity ``T`` in scope in the current module, then the
 documentation will hyperlink the reference in the text to the definition
 of ``T`` (if the output format supports hyperlinking, of course; in a
@@ -890,14 +893,6 @@ apostrophes themselves: to hyperlink ``foo'`` one would simply type
 ``'foo''``. To hyperlink identifiers written in infix form, simply put
 them in quotes as always: ``'`elem`'``.
 
-For compatibility with other systems, the following alternative form of
-markup is accepted [3]_: ```T'``.
-
-.. [3]
-   We chose not to use this as the primary markup for identifiers
-   because strictly speaking the ````` character should not be used as a
-   left quote, it is a grave accent.
-
 Emphasis, Bold and Monospaced Text
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/haddock-library/test/Documentation/Haddock/ParserSpec.hs b/haddock-library/test/Documentation/Haddock/ParserSpec.hs
index 86ed3b35..0449c917 100644
--- a/haddock-library/test/Documentation/Haddock/ParserSpec.hs
+++ b/haddock-library/test/Documentation/Haddock/ParserSpec.hs
@@ -86,6 +86,18 @@ spec = do
       it "parses identifiers enclosed within backticks" $ do
         "`foo`" `shouldParseTo` DocIdentifier "foo"
 
+      it "parses identifiers preceded by a backtick and followed by a single quote" $ do
+        "`foo'" `shouldParseTo` DocIdentifier "foo"
+
+      it "parses identifiers preceded by a single quote and followed by a backtick" $ do
+        "'foo`" `shouldParseTo` DocIdentifier "foo"
+
+      it "can parse a constructor identifier" $ do
+        "'Foo'" `shouldParseTo` DocIdentifier "Foo"
+
+      it "can parse a qualified identifier" $ do
+        "'Foo.bar'" `shouldParseTo` DocIdentifier "Foo.bar"
+
       it "parses a word with an one of the delimiters in it as DocString" $ do
           "don't" `shouldParseTo` "don't"
 
@@ -99,9 +111,43 @@ spec = do
       it "doesn't parse empty identifiers" $ do
         "``" `shouldParseTo` "``"
 
-      it "can parse infix identifiers" $ do
+      it "can parse an identifier in infix notation enclosed within backticks" $ do
         "``infix``" `shouldParseTo` "`" <> DocIdentifier "infix" <> "`"
 
+      it "can parse identifiers containing a single quote" $ do
+        "'don't'" `shouldParseTo` DocIdentifier "don't"
+
+      it "can parse identifiers ending with a single quote" $ do
+        "'foo''" `shouldParseTo` DocIdentifier "foo'"
+
+      it "can parse an identifier containing a digit" $ do
+        "'f0'" `shouldParseTo` DocIdentifier "f0"
+
+      it "can parse an identifier containing unicode characters" $ do
+        "'λ'" `shouldParseTo` DocIdentifier "λ"
+
+      it "can parse a single quote followed by an identifier" $ do
+        "''foo'" `shouldParseTo` "'" <> DocIdentifier "foo"
+
+      it "can parse an identifier that starts with an underscore" $ do
+        "'_x'" `shouldParseTo` DocIdentifier "_x"
+
+    context "when parsing operators" $ do
+      it "can parse an operator enclosed within single quotes" $ do
+        "'.='" `shouldParseTo` DocIdentifier ".="
+
+      it "can parse a qualified operator" $ do
+        "'F..'" `shouldParseTo` DocIdentifier "F.."
+
+      it "can parse a constructor operator" $ do
+        "':='" `shouldParseTo` DocIdentifier ":="
+
+      it "can parse a qualified constructor operator" $ do
+        "'F.:='" `shouldParseTo` DocIdentifier "F.:="
+
+      it "can parse a unicode operator" $ do
+        "'∧'" `shouldParseTo` DocIdentifier "∧"
+
     context "when parsing URLs" $ do
       it "parses a URL" $ do
         "<http://example.com/>" `shouldParseTo` hyperlink "http://example.com/" Nothing