Config and starting on grammar.

.vscode/launch.json

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+// A launch configuration that launches the extension inside a new window
+// Use IntelliSense to learn about possible attributes.
+// Hover to view descriptions of existing attributes.
+// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+{
+	"version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Extension",
+            "type": "extensionHost",
+            "request": "launch",
+            "args": [
+                "--extensionDevelopmentPath=${workspaceFolder}"
+            ]
+        }
+    ]
+}

.vscodeignore

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+.vscode/**
+.vscode-test/**
+.gitignore

language-configuration.json

@@ -0,0 +1,25 @@
+{
+    "comments": {
+        "lineComment": "//",
+        "blockComment": [ "/*", "*/" ]
+    },
+    // Symbols used as brackets.
+    "brackets": [
+        ["{", "}"],
+        ["[", "]"],
+        ["(", ")"]
+    ],
+    // Symbols that are auto closed when typing.
+    "autoClosingPairs": [
+        ["{", "}"],
+        ["[", "]"],
+        ["(", ")"],
+        ["\"", "\""],
+    ],
+    // Symbols that can be used to surround a selection.
+    "surroundingPairs": [
+        ["{", "}"],
+        ["(", ")"],
+        ["\"", "\""],
+    ]
+}

package.json

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+{
+    "name": "pdl-language",
+    "displayName": "PDL",
+    "description": "Syntax highlighting for the Packet Description Language.",
+    "version": "0.1.0",
+    "engines": {
+        "vscode": "^1.52.0"
+    },
+    "categories": [
+        "Programming Languages"
+    ],
+    "keywords": [
+        "PDL",
+        "Android"
+    ],
+    "publisher": "Google",
+    "repository": {
+        "type": "git",
+        "url": "https://github.com/google/pdl-language.git"
+    },
+    "license": "Apache-2.0",
+    "contributes": {
+        "languages": [
+            {
+                "id": "pdl",
+                "aliases": [
+                    "PDL",
+                    "pdl"
+                ],
+                "extensions": [
+                    ".pdl"
+                ],
+                "configuration": "./language-configuration.json"
+            }
+        ],
+        "grammars": [
+            {
+                "language": "pdl",
+                "scopeName": "source.pdl",
+                "path": "./syntaxes/pdl.tmLanguage.json"
+            }
+        ]
+    },
+    "devDependencies": {
+        "js-yaml": "^3.14.1"
+    }
+}

syntaxes/pdl.tmLanguage.YAML-tmLanguage

@@ -0,0 +1,237 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+$schema: 'https://raw.githubusercontent.com/martinring/tmlanguage/master/tmlanguage.json'
+fileTypes:
+  - pdl
+scopeName: source.pdl
+name: PDL
+foldingStartMarker: '\{\s*$'
+foldingStopMarker: '^\s*\}'
+patterns:
+  - include: '#main'
+repository:
+  main:
+    patterns:
+      - include: '#comments'
+      - include: '#endianness'
+      - include: '#declaration'
+      - match: '([^\s])'
+        name: invalid.illegal.pdl
+  comments:
+    patterns:
+      - include: '#multi_line_comment'
+      - match: (//).*
+        name: comment.line.double-slash.pdl
+        captures:
+          '1': {name: punctuation.definition.comment.pdl}
+  endianness:
+    patterns:      
+      - match: \b(little_endian_packets|big_endian_packets)\b
+        name: keyword.pdl
+  declaration:
+    patterns:
+      - name: meta.enum.pdl
+        begin: '(enum)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(:)\s*([0-9]+)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.enum.pdl}
+          '2': {name: entity.name.type.enum.pdl}
+          '3': {name: punctuation.separator.pdl}
+          '4': {name: constant.numeric.decimal.pdl}
+          '5': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#enum_body'
+      - name: meta.enum.pdl
+        begin: '(enum)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(:)\s*(0[xX][0-9a-fA-F]+)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.enum.pdl}
+          '2': {name: entity.name.type.enum.pdl}
+          '3': {name: punctuation.separator.pdl}
+          '4': {name: constant.numeric.hex.pdl}
+          '5': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#enum_body'
+      - name: meta.packet.pdl
+        begin: '(packet)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.packet.pdl}
+          '2': {name: entity.name.type.packet.pdl}
+          '3': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#field_list'
+      - name: meta.packet.pdl
+        begin: '(packet)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(:)\s*([a-zA-Z][a-zA-Z0-9_]*)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.packet.pdl}
+          '2': {name: entity.name.type.packet.pdl}
+          '3': {name: punctuation.separator.pdl}
+          '4': {name: entity.name.type.packet.pdl}
+          '5': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#field_list'
+      - name: meta.struct.pdl
+        begin: '(struct)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.struct.pdl}
+          '2': {name: entity.name.type.struct.pdl}
+          '3': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#field_list'
+      - name: meta.struct.pdl
+        begin: '(struct)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(:)\s*([a-zA-Z][a-zA-Z0-9_]*)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.struct.pdl}
+          '2': {name: entity.name.type.struct.pdl}
+          '3': {name: punctuation.separator.pdl}
+          '4': {name: entity.name.type.struct.pdl}
+          '5': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#field_list'
+      - name: meta.group.pdl
+        begin: '(group)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(\{)'
+        beginCaptures:
+          '1': {name: storage.type.group.pdl}
+          '2': {name: entity.name.type.group.pdl}
+          '3': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#field_list'
+      - name: meta.checksum.pdl
+        match: '(checksum)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(:)\s*([0-9]+)\s*(")([^\"]*)(")'
+        captures:
+          '1': {name: storage.type.checksum.pdl}
+          '2': {name: entity.name.type.checksum.pdl}
+          '3': {name: punctuation.separator.pdl}
+          '4': {name: constant.numeric.decimal.pdl}
+          '5': {name: punctuation.definition.string.begin.aidl}
+          '6': {name: string.quoted.double.aidl}
+          '7': {name: punctuation.definition.string.end.aidl}
+      - name: meta.checksum.pdl
+        match: '(checksum)\s+([a-zA-Z][a-zA-Z0-9_]*)\s*(:)\s*(0[xX][0-9a-fA-F]+)\s*(")([^\"]*)(")'
+        captures:
+          '1': {name: storage.type.checksum.pdl}
+          '2': {name: entity.name.type.checksum.pdl}
+          '3': {name: punctuation.separator.pdl}
+          '4': {name: constant.numeric.hex.pdl}
+          '5': {name: punctuation.definition.string.begin.aidl}
+          '6': {name: string.quoted.double.aidl}
+          '7': {name: punctuation.definition.string.end.aidl}
+  enum_body:
+    patterns:
+      - include: '#comments'
+      - match: =
+        name: keyword.operator.assignment.pdl
+      - include: '#integer'
+      - match: ,
+        name: punctuation.separator.pdl
+      - match: '[a-zA-Z][a-zA-Z0-9_]*'
+        name: entity.name.constant.ddl
+  field_list:
+    patterns:
+      - include: '#comments'
+      - match: ':'
+        name: punctuation.separator.pdl
+      - match: (\[)\s*(\+)\s*([0-9]+)(\]) # SIZE_MODIFIER
+        captures:
+          '1': {name: punctuation.pdl}
+          '2': {name: keyword.operator.arithmetic.pdl}
+          '3': {name: constant.numeric.decimal.pdl}
+          '4': {name: punctuation.pdl}
+      - match: (\[)([0-9]+)(\])
+        captures:
+          '1': {name: punctuation.pdl}
+          '2': {name: constant.numeric.decimal.pdl}
+          '3': {name: punctuation.pdl}
+      - match: (\[)(0[xX][0-9a-fA-F]+)(\])
+        captures:
+          '1': {name: punctuation.pdl}
+          '2': {name: constant.numeric.hex.pdl}
+          '3': {name: punctuation.pdl}
+      - begin: '(\{)'
+        beginCaptures:
+          '1': {name: punctuation.section.braces.begin.pdl}
+        end: '(\})'
+        endCaptures:
+          '1': {name: punctuation.section.braces.end.pdl}
+        patterns:
+          - include: '#constraint_list'
+      - match: '(_size_)\s*(\()\s*(_payload_|_body_)\s*(\))\s*(:)'
+        captures:
+          '1': {name: keyword.pdl}
+          '2': {name: punctuation.begin.pdl}
+          '3': {name: keyword.pdl}
+          '4': {name: punctuation.end.pdl}
+          '5': {name: punctuation.separator.pdl}
+      - match: '(_size_|_count_)\s*(\()\s*([a-zA-Z][a-zA-Z0-9_]*)\s*(\))\s*(:)'
+        captures:
+          '1': {name: keyword.pdl}
+          '2': {name: punctuation.begin.pdl}
+          '3': {name: entity.name.pdl}
+          '4': {name: punctuation.end.pdl}
+          '5': {name: punctuation.separator.pdl}
+      - match: '(_payload_)\s*(:)\s*(\[)\s*(\+)\s*([0-9]+)([\]])'
+        captures:
+          '1': {name: keyword.pdl}
+          '2': {name: punctuation.separator.pdl}
+          '3': {name: punctuation.begin.pdl}
+          '4': {name: keyword.operator.arithmetic.pdl}
+          '5': {name: constant.numeric.decimal.pdl}
+          '6': {name: punctuation.end.pdl}
+      - match: _body_
+        name: keyword.pdl
+      - match: '[a-zA-Z][a-zA-Z0-9_]*'
+        name: entity.name.pdl
+      - include: '#integer'
+  integer:
+    patterns:
+      - match: '0[xX][0-9a-fA-F]+'
+        name: constant.numeric.hex.pdl
+      - match: '[0-9]+'
+        name: constant.numeric.decimal.pdl
+  multi_line_comment:
+    patterns:
+      - begin: (/\*\*)
+        beginCaptures:
+          '1': {name: punctuation.definition.comment.aidl}
+        name: comment.block.documentation.aidl
+        end: (\*/)
+        endCaptures:
+          '1': {name: punctuation.definition.comment.aidl}
+      - begin: (/\*)
+        beginCaptures:
+          '1': {name: punctuation.definition.comment.aidl}
+        name: comment.block.aidl
+        end: (\*/)
+        endCaptures:
+          '1': {name: punctuation.definition.comment.aidl}