feat(Bazel): Add variable parsing to bazel StarlarkParser

Signed-off-by: Mateusz Los <mateusz.los@extern.wenovate.de>

Author: losmateusz1

plugins/package-managers/bazel/src/main/kotlin/StarlarkParser.kt

@@ -195,12 +195,16 @@ internal class Lexer(private val input: String) {
 internal class Parser(input: String) {
     private val lexer = Lexer(input)
     private var currentToken: Token = lexer.nextToken()
+    private var lookaheadToken: Token = lexer.nextToken()
+    private val variables = mutableMapOf<String, String>()
 
     private fun eat(type: TokenType) {
-        require(currentToken.type == type) {
-            "Unexpected token '${currentToken.value}' (${currentToken.type}) at ${lexer.locationInfo()}, expected: $type"
-        }
-        currentToken = lexer.nextToken()
+        val message = "Unexpected token '${currentToken.value}' (${currentToken.type})" +
+            " at ${lexer.locationInfo()}, expected: $type"
+        require(currentToken.type == type) { message }
+
+        currentToken = lookaheadToken
+        lookaheadToken = lexer.nextToken()
     }
 
     private fun parseKeyValue(): Pair<String, String> {
@@ -211,6 +215,9 @@ internal class Parser(input: String) {
 
         if (currentToken.type in setOf(TokenType.STRING, TokenType.NUMBER, TokenType.BOOLEAN)) {
             eat(currentToken.type)
+        } else if (currentToken.type == TokenType.IDENTIFIER) {
+            value = variables[currentToken.value] ?: currentToken.value
+            eat(TokenType.IDENTIFIER)
         } else if (currentToken.type == TokenType.LBRACKET) { // Skip lists for now.
             while (currentToken.type != TokenType.RBRACKET) {
                 eat(currentToken.type)
@@ -223,6 +230,16 @@ internal class Parser(input: String) {
         return key to value
     }
 
+    private fun parseVariableAssignment() {
+        val name = currentToken.value
+        eat(TokenType.IDENTIFIER)
+        eat(TokenType.EQUALS)
+        if (currentToken.type in setOf(TokenType.STRING, TokenType.NUMBER, TokenType.BOOLEAN)) {
+            variables[name] = currentToken.value
+            eat(currentToken.type)
+        }
+    }
+
     private fun parseBazelDepDirective(): BazelDepDirective {
         eat(TokenType.IDENTIFIER)
         eat(TokenType.LPAREN)
@@ -268,9 +285,14 @@ internal class Parser(input: String) {
         var moduleDirective: ModuleDirective? = null
 
         while (currentToken.type != TokenType.EOF) {
-            when (currentToken.value) {
-                "module" -> moduleDirective = parseModuleDirective()
-                "bazel_dep" -> dependencies.add(parseBazelDepDirective())
+            when {
+                currentToken.value == "module" -> moduleDirective = parseModuleDirective()
+
+                currentToken.value == "bazel_dep" -> dependencies.add(parseBazelDepDirective())
+
+                currentToken.type == TokenType.IDENTIFIER && lookaheadToken.type == TokenType.EQUALS ->
+                    parseVariableAssignment()
+
                 else -> eat(currentToken.type) // Skip unknown tokens.
             }
         }