Merge pull request scala-js#4110 from sjrd/fix-gcc-crash

gzm0 · web-flow · commit fba4b7b44635 · 2020-07-01T11:37:06.000+02:00
Fix scala-js#4098: Avoid `let`/`const` when building the ASTs for GCC.
diff --git a/linker/jvm/src/main/scala/org/scalajs/linker/backend/closure/ClosureAstTransformer.scala b/linker/jvm/src/main/scala/org/scalajs/linker/backend/closure/ClosureAstTransformer.scala
@@ -80,7 +80,17 @@ private class ClosureAstTransformer(featureSet: FeatureSet,
       case Let(ident, mutable, optRhs) =>
         val node = transformName(ident)
         optRhs.foreach(rhs => node.addChildToFront(transformExpr(rhs)))
-        new Node(if (mutable) Token.LET else Token.CONST, node)
+        /* #4098 The following line should be
+         *   new Node(if (mutable) Token.LET else Token.CONST, node)
+         * however, due to an unknown bug in how we build GCC trees or inside
+         * GCC itself, using `let`s and `const`s can result in a crash deep
+         * inside GCC in some obscure cases.
+         * As a workaround, we always emit `var`s instead. This has no visible
+         * semantic change because the Emitter never relies on the specific
+         * semantics of `let`s and `const`s.
+         * TODO We should properly fix this at the root (filed as #4109).
+         */
+        new Node(Token.VAR, node)
       case Skip() =>
         new Node(Token.EMPTY)
       case Block(stats) =>
diff --git a/test-suite/shared/src/test/scala/org/scalajs/testsuite/compiler/RegressionTest.scala b/test-suite/shared/src/test/scala/org/scalajs/testsuite/compiler/RegressionTest.scala
@@ -837,6 +837,13 @@ class RegressionTest {
     assertEquals(6, `class`.foo(5))
   }
 
+  @Test def gcc_crash_with_let_const_issue_4098(): Unit = {
+    val set = new java.util.HashSet[String]()
+    set.remove("")
+    set.remove("1") // only if remove is called twice
+    assertEquals(0, set.size())
+  }
+
 }
 
 object RegressionTest {

Original file line number	Diff line number	Diff line change
`@@ -837,6 +837,13 @@ class RegressionTest {`
`837`	`837`	assertEquals(6, `class`.foo(5))
`838`	`838`	`}`
`839`	`839`
	`840`	`+ @Test def gcc_crash_with_let_const_issue_4098(): Unit = {`
	`841`	`+ val set = new java.util.HashSet[String]()`
	`842`	`+ set.remove("")`
	`843`	`+ set.remove("1") // only if remove is called twice`
	`844`	`+ assertEquals(0, set.size())`
	`845`	`+ }`
	`846`	`+`
`840`	`847`	`}`
`841`	`848`
`842`	`849`	`object RegressionTest {`