Fix declaring a variable inside the case target expression

* Fixes #3377

Author: eregon

CHANGELOG.md

@@ -13,6 +13,7 @@ Bug fixes:
 * Fix some C API functions which were failing when called with Ruby values represented as Java primitives (#3352, @eregon).
 * Fix `IO.select([io], nil, [io])` on macOS, it was hanging due to a bug in macOS `poll(2)` (#3346, @eregon, @andrykonchin).
 * Run context cleanup such as showing the output of tools when `SignalException` and `Interrupt` escape (@eregon).
+* Handle a new variable inside the `case` target expression correctly (#3377, @eregon).
 
 Compatibility:
 

spec/ruby/language/case_spec.rb

@@ -399,6 +399,22 @@ def ===(o)
       :called
     end.should == :called
   end
+
+  it "supports declaring variables in the case target expression" do
+    def test(v)
+      case new_variable_in_expression = v
+      when true
+        # This extra block is a test that `new_variable_in_expression` is declared outside of it and not inside
+        self.then { new_variable_in_expression }
+      else
+        # Same
+        self.then { new_variable_in_expression.casecmp?("foo") }
+      end
+    end
+
+    self.test("bar").should == false
+    self.test(true).should == true
+  end
 end
 
 describe "The 'case'-construct with no target expression" do

src/main/java/org/truffleruby/parser/BodyTranslator.java

@@ -693,8 +693,6 @@ protected ArgumentsAndBlockTranslation translateArgumentsAndBlock(SourceIndexLen
     public RubyNode visitCaseNode(CaseParseNode node) {
         final SourceIndexLength sourceSection = node.getPosition();
 
-        RubyNode elseNode = translateNodeOrNil(sourceSection, node.getElseNode());
-
         /* There are two sorts of case - one compares a list of expressions against a value, the other just checks a
          * list of expressions for truth. */
 
@@ -710,6 +708,8 @@ public RubyNode visitCaseNode(CaseParseNode node) {
             /* Build an if expression from the whens and else. Work backwards because the first if contains all the
              * others in its else clause. */
 
+            RubyNode elseNode = translateNodeOrNil(sourceSection, node.getElseNode());
+
             for (int n = node.getCases().size() - 1; n >= 0; n--) {
                 final WhenParseNode when = (WhenParseNode) node.getCases().get(n);
 
@@ -746,6 +746,8 @@ public RubyNode visitCaseNode(CaseParseNode node) {
             // A top-level block assigns the temp then runs the if
             ret = sequence(sourceSection, Arrays.asList(assignTemp, ifNode));
         } else {
+            RubyNode elseNode = translateNodeOrNil(sourceSection, node.getElseNode());
+
             for (int n = node.getCases().size() - 1; n >= 0; n--) {
                 final WhenParseNode when = (WhenParseNode) node.getCases().get(n);
 

src/main/java/org/truffleruby/parser/YARPTranslator.java

@@ -865,7 +865,6 @@ public RubyNode visitCaseNode(Nodes.CaseNode node) {
         // - the other just checks a list of expressions for truth.
 
         final RubyNode rubyNode;
-        RubyNode elseNode = translateNodeOrNil(node.consequent);
 
         if (node.predicate != null) {
             // Evaluate the case expression and store it in a local
@@ -875,6 +874,8 @@ public RubyNode visitCaseNode(Nodes.CaseNode node) {
 
             // Build an if expression from `when` and `else` branches.
             // Work backwards to make the first if contain all the others in its `else` clause.
+            RubyNode elseNode = translateNodeOrNil(node.consequent);
+
             final Nodes.Node[] conditions = node.conditions;
 
             for (int n = conditions.length - 1; n >= 0; n--) {
@@ -936,6 +937,8 @@ public RubyNode visitCaseNode(Nodes.CaseNode node) {
             // Build an if expression from `when` and `else` branches.
             // Work backwards to make the first if contain all the others in its `else` clause.
 
+            RubyNode elseNode = translateNodeOrNil(node.consequent);
+
             final Nodes.Node[] conditions = node.conditions;
 
             for (int n = node.conditions.length - 1; n >= 0; n--) {