diff --git a/extensions/csharp/syntaxes/csharp.tmLanguage.json b/extensions/csharp/syntaxes/csharp.tmLanguage.json
index 17abddbfec0..5fd726114a5 100644
--- a/extensions/csharp/syntaxes/csharp.tmLanguage.json
+++ b/extensions/csharp/syntaxes/csharp.tmLanguage.json
@@ -4,7 +4,7 @@
 		"If you want to provide a fix or improvement, please create a pull request against the original repository.",
 		"Once accepted there, we are happy to receive an update request."
 	],
-	"version": "https://github.com/dotnet/csharp-tmLanguage/commit/b68631155b9ba9886fb3ef8f9a94e4c731b41f3d",
+	"version": "https://github.com/dotnet/csharp-tmLanguage/commit/542a4e220e58813ea67cdd91b3a454e6e4491aab",
 	"name": "C#",
 	"scopeName": "source.cs",
 	"patterns": [
@@ -556,7 +556,7 @@
 		},
 		"storage-modifier": {
 			"name": "storage.modifier.cs",
-			"match": "(?<!\\.)\\b(new|public|protected|internal|private|abstract|virtual|override|sealed|static|partial|readonly|volatile|const|extern|async|unsafe)\\b"
+			"match": "(?<!\\.)\\b(new|public|protected|internal|private|abstract|virtual|override|sealed|static|partial|readonly|volatile|const|extern|async|unsafe|ref)\\b"
 		},
 		"class-declaration": {
 			"begin": "(?=\\bclass\\b)",
@@ -616,7 +616,7 @@
 			]
 		},
 		"delegate-declaration": {
-			"begin": "(?x)\n(?:\\b(delegate)\\b)\\s+\n(?<type-name>\n  (?:\n    (?:ref\\s+)?   # ref return\n    (?:\n      (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n      (?<name-and-type-args> # identifier + type arguments (if any)\n        \\g<identifier>\\s*\n        (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n      )\n      (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n      (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n    )\n    (?:\\s*\\?\\s*)? # nullable suffix?\n    (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n  )\n)\\s+\n(\\g<identifier>)\\s*\n(<([^<>]+)>)?\\s*\n(?=\\()",
+			"begin": "(?x)\n(?:\\b(delegate)\\b)\\s+\n(?<type-name>\n  (?:\n    (?:ref\\s+(?:readonly\\s+)?)?   # ref return\n    (?:\n      (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n      (?<name-and-type-args> # identifier + type arguments (if any)\n        \\g<identifier>\\s*\n        (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n      )\n      (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n      (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n    )\n    (?:\\s*\\?\\s*)? # nullable suffix?\n    (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n  )\n)\\s+\n(\\g<identifier>)\\s*\n(<([^<>]+)>)?\\s*\n(?=\\()",
 			"beginCaptures": {
 				"1": {
 					"name": "keyword.other.delegate.cs"
@@ -1001,7 +1001,7 @@
 			]
 		},
 		"property-declaration": {
-			"begin": "(?x)\n(?!.*\\b(?:class|interface|struct|enum|event)\\b)\\s*\n(?<return-type>\n  (?<type-name>\n    (?:\n      (?:ref\\s+)?   # ref return\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\\s+\n)\n(?<interface-name>\\g<type-name>\\s*\\.\\s*)?\n(?<property-name>\\g<identifier>)\\s*\n(?=\\{|=>|$)",
+			"begin": "(?x)\n(?!.*\\b(?:class|interface|struct|enum|event)\\b)\\s*\n(?<return-type>\n  (?<type-name>\n    (?:\n      (?:ref\\s+(?:readonly\\s+)?)?   # ref return\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\\s+\n)\n(?<interface-name>\\g<type-name>\\s*\\.\\s*)?\n(?<property-name>\\g<identifier>)\\s*\n(?=\\{|=>|$)",
 			"beginCaptures": {
 				"1": {
 					"patterns": [
@@ -1044,7 +1044,7 @@
 			]
 		},
 		"indexer-declaration": {
-			"begin": "(?x)\n(?<return-type>\n  (?<type-name>\n    (?:\n      (?:ref\\s+)?   # ref return\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\\s+\n)\n(?<interface-name>\\g<type-name>\\s*\\.\\s*)?\n(?<indexer-name>this)\\s*\n(?=\\[)",
+			"begin": "(?x)\n(?<return-type>\n  (?<type-name>\n    (?:\n      (?:ref\\s+(?:readonly\\s+)?)?   # ref return\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\\s+\n)\n(?<interface-name>\\g<type-name>\\s*\\.\\s*)?\n(?<indexer-name>this)\\s*\n(?=\\[)",
 			"beginCaptures": {
 				"1": {
 					"patterns": [
@@ -1217,7 +1217,7 @@
 			]
 		},
 		"method-declaration": {
-			"begin": "(?x)\n(?<return-type>\n  (?<type-name>\n    (?:\n      (?:ref\\s+)?   # ref return\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\\s+\n)\n(?<interface-name>\\g<type-name>\\s*\\.\\s*)?\n(\\g<identifier>)\\s*\n(<([^<>]+)>)?\\s*\n(?=\\()",
+			"begin": "(?x)\n(?<return-type>\n  (?<type-name>\n    (?:\n      (?:ref\\s+(?:readonly\\s+)?)?   # ref return\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\\s+\n)\n(?<interface-name>\\g<type-name>\\s*\\.\\s*)?\n(\\g<identifier>)\\s*\n(<([^<>]+)>)?\\s*\n(?=\\()",
 			"beginCaptures": {
 				"1": {
 					"patterns": [
@@ -1353,7 +1353,7 @@
 			]
 		},
 		"operator-declaration": {
-			"begin": "(?x)\n(?<type-name>\n  (?:\n    (?:ref\\s+)?   # ref return\n    (?:\n      (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n      (?<name-and-type-args> # identifier + type arguments (if any)\n        \\g<identifier>\\s*\n        (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n      )\n      (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n      (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n    )\n    (?:\\s*\\?\\s*)? # nullable suffix?\n    (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n  )\n)\\s*\n(?<operator-keyword>(?:\\b(?:operator)))\\s*\n(?<operator>(?:\\+|-|\\*|/|%|&|\\||\\^|\\<\\<|\\>\\>|==|!=|\\>|\\<|\\>=|\\<=|!|~|\\+\\+|--|true|false))\\s*\n(?=\\()",
+			"begin": "(?x)\n(?<type-name>\n  (?:\n    (?:ref\\s+(?:readonly\\s+)?)?   # ref return\n    (?:\n      (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n      (?<name-and-type-args> # identifier + type arguments (if any)\n        \\g<identifier>\\s*\n        (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n      )\n      (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n      (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n    )\n    (?:\\s*\\?\\s*)? # nullable suffix?\n    (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n  )\n)\\s*\n(?<operator-keyword>(?:\\b(?:operator)))\\s*\n(?<operator>(?:\\+|-|\\*|/|%|&|\\||\\^|\\<\\<|\\>\\>|==|!=|\\>|\\<|\\>=|\\<=|!|~|\\+\\+|--|true|false))\\s*\n(?=\\()",
 			"beginCaptures": {
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@@ -1386,7 +1386,7 @@
 			]
 		},
 		"conversion-operator-declaration": {
-			"begin": "(?x)\n(?<explicit-or-implicit-keyword>(?:\\b(?:explicit|implicit)))\\s*\n(?<operator-keyword>(?:\\b(?:operator)))\\s*\n(?<type-name>\n  (?:\n    (?:ref\\s+)?   # ref return\n    (?:\n      (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n      (?<name-and-type-args> # identifier + type arguments (if any)\n        \\g<identifier>\\s*\n        (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n      )\n      (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n      (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n    )\n    (?:\\s*\\?\\s*)? # nullable suffix?\n    (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n  )\n)\\s*\n(?=\\()",
+			"begin": "(?x)\n(?<explicit-or-implicit-keyword>(?:\\b(?:explicit|implicit)))\\s*\n(?<operator-keyword>(?:\\b(?:operator)))\\s*\n(?<type-name>\n  (?:\n    (?:ref\\s+(?:readonly\\s+)?)?   # ref return\n    (?:\n      (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n      (?<name-and-type-args> # identifier + type arguments (if any)\n        \\g<identifier>\\s*\n        (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n      )\n      (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n      (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n    )\n    (?:\\s*\\?\\s*)? # nullable suffix?\n    (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n  )\n)\\s*\n(?=\\()",
 			"beginCaptures": {
 				"1": {
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@@ -2150,22 +2150,25 @@
 			]
 		},
 		"local-variable-declaration": {
-			"begin": "(?x)\n(?:\n  (?:(\\bref)\\s+)?(\\bvar\\b)| # ref local\n  (?<type-name>\n    (?:\n      (?:ref\\s+)?   # ref local\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\n)\\s+\n(\\g<identifier>)\\s*\n(?=,|;|=|\\))",
+			"begin": "(?x)\n(?:\n  (?:(\\bref)\\s+(?:(\\breadonly)\\s+)?)?(\\bvar\\b)| # ref local\n  (?<type-name>\n    (?:\n      (?:ref\\s+(?:readonly\\s+)?)?   # ref local\n      (?:\n        (?:(?<identifier>@?[_[:alpha:]][_[:alnum:]]*)\\s*\\:\\:\\s*)? # alias-qualification\n        (?<name-and-type-args> # identifier + type arguments (if any)\n          \\g<identifier>\\s*\n          (?<type-args>\\s*<(?:[^<>]|\\g<type-args>)+>\\s*)?\n        )\n        (?:\\s*\\.\\s*\\g<name-and-type-args>)* | # Are there any more names being dotted into?\n        (?<tuple>\\s*\\((?:[^\\(\\)]|\\g<tuple>)+\\))\n      )\n      (?:\\s*\\?\\s*)? # nullable suffix?\n      (?:\\s*\\[(?:\\s*,\\s*)*\\]\\s*)* # array suffix?\n    )\n  )\n)\\s+\n(\\g<identifier>)\\s*\n(?=,|;|=|\\))",
 			"beginCaptures": {
 				"1": {
 					"name": "storage.modifier.cs"
 				},
 				"2": {
-					"name": "keyword.other.var.cs"
+					"name": "storage.modifier.cs"
 				},
 				"3": {
+					"name": "keyword.other.var.cs"
+				},
+				"4": {
 					"patterns": [
 						{
 							"include": "#type"
 						}
 					]
 				},
-				"8": {
+				"9": {
 					"name": "entity.name.variable.local.cs"
 				}
 			},
@@ -3611,6 +3614,9 @@
 				{
 					"include": "#ref-modifier"
 				},
+				{
+					"include": "#readonly-modifier"
+				},
 				{
 					"include": "#tuple-type"
 				},
@@ -3635,6 +3641,10 @@
 			"name": "storage.modifier.cs",
 			"match": "\\b(ref)\\b"
 		},
+		"readonly-modifier": {
+			"name": "storage.modifier.cs",
+			"match": "\\b(readonly)\\b"
+		},
 		"tuple-type": {
 			"begin": "\\(",
 			"beginCaptures": {