refactor: Convert ANTLR DateExpression parser to a recursive decent parser #1615

Author: rholshausen

core/model/src/main/kotlin/au/com/dius/pact/core/model/generators/DateExpression.kt

@@ -10,8 +10,6 @@ import au.com.dius.pact.core.support.generators.expressions.DateExpressionParser
 import au.com.dius.pact.core.support.generators.expressions.DateOffsetType
 import au.com.dius.pact.core.support.generators.expressions.Operation
 import mu.KLogging
-import org.antlr.v4.runtime.CharStreams
-import org.antlr.v4.runtime.CommonTokenStream
 import java.time.DayOfWeek
 import java.time.Month
 import java.time.OffsetDateTime
@@ -142,17 +140,11 @@ object DateExpression : KLogging() {
   }
 
   private fun parseDateExpression(expression: String): Result<ParsedDateExpression, String> {
-    val charStream = CharStreams.fromString(expression)
-    val lexer = DateExpressionLexer(charStream)
-    val tokens = CommonTokenStream(lexer)
-    val parser = DateExpressionParser(tokens)
-    val errorListener = ErrorListener()
-    parser.addErrorListener(errorListener)
-    val result = parser.expression()
-    return if (errorListener.errors.isNotEmpty()) {
-      Err("Error parsing expression: ${errorListener.errors.joinToString(", ")}")
-    } else {
-      Ok(ParsedDateExpression(result.dateBase, result.adj))
+    val lexer = DateExpressionLexer(expression)
+    val parser = DateExpressionParser(lexer)
+    return when (val result = parser.expression()) {
+      is Err -> Err("Error parsing expression: ${result.error}")
+      is Ok -> Ok(ParsedDateExpression(result.value.first, result.value.second.toMutableList()))
     }
   }
 }

core/model/src/test/groovy/au/com/dius/pact/core/model/generators/DateExpressionSpec.groovy

@@ -1,6 +1,5 @@
-package au.com.dius.pact.model.generators
+package au.com.dius.pact.core.model.generators
 
-import au.com.dius.pact.core.model.generators.DateExpression
 import spock.lang.Specification
 import spock.lang.Unroll
 
@@ -55,8 +54,8 @@ class DateExpressionSpec extends Specification {
         where:
 
         expression | expected
-        '+'        | 'Error parsing expression: line 1:1 mismatched input \'<EOF>\' expecting INT'
-        'now +'    | 'Error parsing expression: line 1:5 mismatched input \'<EOF>\' expecting INT'
+        '+'        | 'Error parsing expression: Was expecting an integer at index 1'
+        'now +'    | 'Error parsing expression: Was expecting an integer at index 5'
         'tomorr'   | /^Error parsing expression.*/
     }
 }

core/model/src/test/groovy/au/com/dius/pact/core/model/generators/DateTimeExpressionSpec.groovy

@@ -1,6 +1,5 @@
-package au.com.dius.pact.model.generators
+package au.com.dius.pact.core.model.generators
 
-import au.com.dius.pact.core.model.generators.DateTimeExpression
 import spock.lang.Specification
 import spock.lang.Unroll
 
@@ -102,12 +101,12 @@ class DateTimeExpressionSpec extends Specification {
         where:
 
         expression      | expected
-        '+'             | 'Error parsing expression: line 1:1 mismatched input \'<EOF>\' expecting INT'
-        'now +'         | 'Error parsing expression: line 1:5 mismatched input \'<EOF>\' expecting INT'
+        '+'             | 'Error parsing expression: Was expecting an integer at index 1'
+        'now +'         | 'Error parsing expression: Was expecting an integer at index 5'
         'tomorr'        | /^Error parsing expression.*/
         'now @ +'       | 'Error parsing expression: line 1:7 mismatched input \'<EOF>\' expecting INT'
-        '+ @ +'         | 'Error parsing expression: line 1:2 mismatched input \'<EOF>\' expecting INT, Error parsing expression: line 1:5 mismatched input \'<EOF>\' expecting INT'
-        'now+ @ now +'  | 'Error parsing expression: line 1:5 mismatched input \'<EOF>\' expecting INT, Error parsing expression: line 1:12 mismatched input \'<EOF>\' expecting INT'
+        '+ @ +'         | 'Error parsing expression: Was expecting an integer at index 2, Error parsing expression: line 1:5 mismatched input \'<EOF>\' expecting INT'
+        'now+ @ now +'  | 'Error parsing expression: Was expecting an integer at index 5, Error parsing expression: line 1:12 mismatched input \'<EOF>\' expecting INT'
         'now @ now +'   | 'Error parsing expression: line 1:11 mismatched input \'<EOF>\' expecting INT'
         'now @ noo'     | /^Error parsing expression.*/
     }

core/support/src/main/antlr/au/com/dius/pact/core/support/generators/expressions/DateExpression.g4

@@ -19,13 +19,11 @@ data class Version(
   }
 
   companion object {
-    val INT = Regex("^\\d+")
-
     @JvmStatic
     fun parse(version: String): Result<Version, String> {
       val lexer = StringLexer(version)
 
-      val major = when (val result = parseInt(lexer)) {
+      val major = when (val result = lexer.parseInt()) {
         is Ok -> result.value
         is Err -> return result
       }
@@ -35,15 +33,15 @@ data class Version(
         return Err(err)
       }
 
-      val minor = when (val result = parseInt(lexer)) {
+      val minor = when (val result = lexer.parseInt()) {
         is Ok -> result.value
         is Err -> return result
       }
 
       return when {
         lexer.peekNextChar() == '.' -> {
           lexer.advance()
-          when (val result = parseInt(lexer)) {
+          when (val result = lexer.parseInt()) {
             is Ok -> if (lexer.empty) {
               Ok(Version(major, minor, result.value))
             } else {
@@ -64,12 +62,5 @@ data class Version(
         else -> "Was expecting a '$c' at index ${lexer.index - 1} but got '$ch'"
       }
     }
-
-    private fun parseInt(lexer: StringLexer): Result<Int, String> {
-      return when (val result = lexer.matchRegex(INT)) {
-        null -> Err("Was expecting an integer at index ${lexer.index}")
-        else -> Ok(result.toInt())
-      }
-    }
   }
 }