docs: better syntax highlighting (#652)

### Summary of Changes

Add rules for [all applicable builtin tokens of
Pygments](https://pygments.org/docs/tokens/) to the lexer to improve
syntax highlighting in the grammar. In particular, syntactic elements
now get highlighted similarly to their Python equivalent, where
possible.

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

docs/lexer/safe_ds_lexer/_safe_ds_lexer.py

@@ -1,41 +1,51 @@
 from pygments.lexer import RegexLexer, words
 from pygments.token import Comment, Keyword, Name, Number, Operator, String, Whitespace
 
-constants = (
+keywords_annotation = ("annotation",)
+
+keywords_class = (
+    "class",
+    "enum",
+)
+
+keywords_constant = (
+    "attr",
+    "val",
+)
+
+keywords_function = (
+    "fun",
+    "pipeline",
+    "segment",
+)
+
+keywords_literal = (
     "false",
     "null",
     "true",
 )
 
-keywords = (
-    "annotation",
+keywords_namespace = (
+    "from",
+    "package",
+)
+
+keywords_generic = (
     "as",
-    "attr",
-    "class",
     "const",
-    "enum",
-    "fun",
+    "import",
     "in",
     "internal",
     "literal",
     "out",
-    "pipeline",
     "private",
     "schema",
-    "segment",
     "static",
     "union",
-    "val",
     "where",
     "yield",
 )
 
-namespace = (
-    "from",
-    "import",
-    "package",
-)
-
 operators = (
     "and",
     "not",
@@ -44,6 +54,21 @@
     "super",
 )
 
+builtins = (
+    "Any",
+    "Nothing",
+    "Boolean",
+    "Number",
+    "Int",
+    "Float",
+    "ListMap",
+    "String",
+)
+
+identifier_fragment = r"[_a-zA-Z][_a-zA-Z0-9]*"
+identifier_regex = rf"{identifier_fragment}|`{identifier_fragment}`"
+qualified_name_regex = rf"({identifier_regex})(\.({identifier_regex}))*"
+
 
 class SafeDsLexer(RegexLexer):
     name = "safe-ds"
@@ -59,17 +84,57 @@ class SafeDsLexer(RegexLexer):
 
     tokens = {
         "root": [
+            # Literals
             (r"\b([0-9]+(\.[0-9]+)?([eE][+-]?[0-9]+)?)\b", Number),
             (r'"|}}', String, "string"),
-            (words(constants, prefix=r"\b", suffix=r"\b"), Keyword.Constant),
-            (words(keywords, prefix=r"\b", suffix=r"\b"), Keyword),
-            (words(namespace, prefix=r"\b", suffix=r"\b"), Keyword.Namespace),
+            # Keywords
+            (
+                words(keywords_annotation, prefix=r"\b", suffix=r"\b"),
+                Keyword,
+                "annotation",
+            ),
+            (words(keywords_class, prefix=r"\b", suffix=r"\b"), Keyword, "class"),
+            (
+                words(keywords_constant, prefix=r"\b", suffix=r"\b"),
+                Keyword.Declaration,
+                "placeholder",
+            ),
+            (words(keywords_function, prefix=r"\b", suffix=r"\b"), Keyword, "function"),
+            (words(keywords_literal, prefix=r"\b", suffix=r"\b"), Keyword.Constant),
+            (
+                words(keywords_namespace, prefix=r"\b", suffix=r"\b"),
+                Keyword.Namespace,
+                "namespace",
+            ),
+            (words(keywords_generic, prefix=r"\b", suffix=r"\b"), Keyword),
+            # Operators
             (words(operators, prefix=r"\b", suffix=r"\b"), Operator.Word),
-            (r"`[_a-zA-Z][_a-zA-Z0-9]*`", Name),
+            # Builtins
+            (words(builtins, prefix=r"\b", suffix=r"\b"), Name.Builtin),
+            # Identifiers
+            (rf"@{identifier_regex}", Name.Decorator),
+            (identifier_regex, Name),
+            # Comments
             (r"//.+?$", Comment.Single),
             (r"/\*[\s\S]*?\*/", Comment.Multiline),
+            # Whitespace
             (r"\s+", Whitespace),
         ],
+        "annotation": [
+            (identifier_regex, Name.Decorator, "#pop"),
+        ],
+        "class": [
+            (identifier_regex, Name.Class, "#pop"),
+        ],
+        "function": [
+            (identifier_regex, Name.Function, "#pop"),
+        ],
+        "namespace": [
+            (qualified_name_regex, Name.Namespace, "#pop"),
+        ],
+        "placeholder": [
+            (identifier_regex, Name.Constant, "#pop"),
+        ],
         "string": [
             (r'([^"{]|\{(?!\{))+', String),
             (r'\{\{|"', String, "#pop"),

tests/resources/validation/other/argument lists/missing required parameter/dont show this error if the argument list is missing altogether.sdstest

@@ -3,7 +3,7 @@ package tests.validation.other.argumentLists.missingRequiredParameter
 // $TEST$ no error r"The parameters? .* must be set here\."
 
 @MyAnnotation
-segment mySegment2(
+segment mySegment3(
     myCallableType: (a: Int, b: Int, c: Int = 0) -> ()
 ) {
     val myBlockLambda = (a: Int, b: Int, c: Int = 0) {};