Fix using the same previous data table column multiple times in the same cell (spockframework#2084)

Fixes spockframework#2083

Author: Vampire

spock-core/src/main/java/org/spockframework/compiler/WhereBlockRewriter.java

@@ -675,7 +675,7 @@ private void turnIntoSimpleParameterization(List<Expression> column) throws Inva
 
         // otherwise generate the extractors and closure
         List<Statement> statements = new ArrayList<>();
-        List<String> referencedPreviousVariables = previousVariableAccesses.stream().map(VariableExpression::getName).collect(toList());
+        Set<String> referencedPreviousVariables = previousVariableAccesses.stream().map(VariableExpression::getName).collect(toSet());
         generatePreviousColumnExtractorStatements(referencedPreviousVariables, row, statements);
         ReturnStatement providerStatement = new ReturnStatement(providerExpression);
         providerStatement.setSourcePosition(providerExpression);
@@ -702,7 +702,7 @@ private void turnIntoSimpleParameterization(List<Expression> column) throws Inva
     rewriteSimpleParameterization(binExpr, varExpr, true);
   }
 
-  private void generatePreviousColumnExtractorStatements(List<String> referencedPreviousVariables, int row,
+  private void generatePreviousColumnExtractorStatements(Set<String> referencedPreviousVariables, int row,
                                                          List<Statement> statements) {
     for (String referencedPreviousVariable : referencedPreviousVariables) {
       statements.add(new ExpressionStatement(

spock-specs/src/test/groovy/org/spockframework/smoke/ast/DataTablesAstSpec.groovy

@@ -16,6 +16,7 @@ package org.spockframework.smoke.ast
 
 import org.spockframework.EmbeddedSpecification
 import org.spockframework.specs.extension.SpockSnapshotter
+import spock.lang.Issue
 import spock.lang.Snapshot
 import spock.util.Show
 
@@ -83,4 +84,24 @@ class DataTablesAstSpec extends EmbeddedSpecification {
     then:
     snapshotter.assertThat(result.source).matchesSnapshot()
   }
+
+  @Issue('https://github.com/spockframework/spock/issues/2083')
+  def 'using a variable in a cell multiple times compiles'() {
+    given:
+    snapshotter.featureBody()
+
+    when:
+    def result = compiler.transpileFeatureBody '''
+        expect:
+        a + b == result
+
+        where:
+        a | b | result
+        1 | 2 | a + b
+        3 | 4 | a + a // causes the compile error
+    ''', EnumSet.of(Show.METHODS)
+
+    then:
+    snapshotter.assertThat(result.source).matchesSnapshot()
+  }
 }

spock-specs/src/test/resources/snapshots/org/spockframework/smoke/ast/DataTablesAstSpec/using_a_variable_in_a_cell_multiple_times_compiles.groovy

@@ -0,0 +1,49 @@
+package aPackage
+import spock.lang.*
+
+class ASpec extends Specification {
+  def "aFeature"() {
+/*--------- tag::snapshot[] ---------*/
+public void $spock_feature_0_0(java.lang.Object a, java.lang.Object b, java.lang.Object result) {
+    org.spockframework.runtime.ErrorCollector $spock_errorCollector = org.spockframework.runtime.ErrorRethrower.INSTANCE
+    org.spockframework.runtime.ValueRecorder $spock_valueRecorder = new org.spockframework.runtime.ValueRecorder()
+    org.spockframework.runtime.SpockRuntime.callBlockEntered(this, 0)
+    try {
+        org.spockframework.runtime.SpockRuntime.verifyCondition($spock_errorCollector, $spock_valueRecorder.reset(), 'a + b == result', 2, 9, null, $spock_valueRecorder.record($spock_valueRecorder.startRecordingValue(4), $spock_valueRecorder.record($spock_valueRecorder.startRecordingValue(2), $spock_valueRecorder.record($spock_valueRecorder.startRecordingValue(0), a) + $spock_valueRecorder.record($spock_valueRecorder.startRecordingValue(1), b)) == $spock_valueRecorder.record($spock_valueRecorder.startRecordingValue(3), result)))
+    }
+    catch (java.lang.Throwable $spock_condition_throwable) {
+        org.spockframework.runtime.SpockRuntime.conditionFailedWithException($spock_errorCollector, $spock_valueRecorder, 'a + b == result', 2, 9, null, $spock_condition_throwable)}
+    finally {
+    }
+    org.spockframework.runtime.SpockRuntime.callBlockExited(this, 0)
+    this.getSpecificationContext().getMockController().leaveScope()
+}
+
+public java.lang.Object $spock_feature_0_0prov0() {
+    return [1, 3]
+}
+
+public java.lang.Object $spock_feature_0_0prov1(java.util.List $spock_p_a) {
+    return [2, 4]
+}
+
+public java.lang.Object $spock_feature_0_0prov2(java.util.List $spock_p_a, java.util.List $spock_p_b) {
+    return [{ ->
+        java.lang.Object a = $spock_p_a.get(0)
+        java.lang.Object b = $spock_p_b.get(0)
+        return a + b
+    }.call(), { ->
+        java.lang.Object a = $spock_p_a.get(1)
+        return a + a
+    }.call()]
+}
+
+public java.lang.Object $spock_feature_0_0proc(java.lang.Object $spock_p0, java.lang.Object $spock_p1, java.lang.Object $spock_p2) {
+    java.lang.Object a = (( $spock_p0 ) as java.lang.Object)
+    java.lang.Object b = (( $spock_p1 ) as java.lang.Object)
+    java.lang.Object result = (( $spock_p2 ) as java.lang.Object)
+    return new java.lang.Object[]{ a , b , result }
+}
+/*--------- end::snapshot[] ---------*/
+  }
+}