Repository: scalameta/scalameta (scala)

Issue:
`illegal start of simple expression` error since 4.8.15
- failure: 4.8.15, 4.9.0
- success: 4.8.14

`build.sbt`


```scala
libraryDependencies += "org.scalameta" %% "scalameta" % "4.8.15"

scalaVersion := "2.13.12"
```

`Main.scala`

```scala
import scala.meta._

object Main {
  def main(args: Array[String]): Unit = {
    val src = Input.String(
"""
  new A {
    def b: C =
      ???
  }
""")
    val p = implicitly[parsers.Parse[Stat]]

    println(p.apply(src, dialects.Scala213Source3).get.structure)
  }
}
```

```
[info] running Main 
[error] <input>:3: error: illegal start of simple expression
[error]     def b: C =
[error]               ^
[error] 	at scala.meta.internal.parsers.ScalametaParser.simpleExpr0(ScalametaParser.scala:2270)
[error] 	at scala.meta.internal.parsers.ScalametaParser.simpleExpr(ScalametaParser.scala:2223)
[error] 	at scala.meta.internal.parsers.ScalametaParser.prefixExpr(ScalametaParser.scala:2206)
[error] 	at scala.meta.internal.parsers.ScalametaParser.postfixExpr(ScalametaParser.scala:2081)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$expr$2(ScalametaParser.scala:1676)
[error] 	at scala.meta.internal.parsers.ScalametaParser.atPosOpt(ScalametaParser.scala:322)
[error] 	at scala.meta.internal.parsers.ScalametaParser.autoPosOpt(ScalametaParser.scala:366)
[error] 	at scala.meta.internal.parsers.ScalametaParser.expr(ScalametaParser.scala:1581)
[error] 	at scala.meta.internal.parsers.ScalametaParser.expr(ScalametaParser.scala:1480)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$funDefRest$1(ScalametaParser.scala:3807)
[error] 	at scala.meta.internal.parsers.ScalametaParser.autoEndPos(ScalametaParser.scala:368)
[error] 	at scala.meta.internal.parsers.ScalametaParser.autoEndPos(ScalametaParser.scala:373)
[error] 	at scala.meta.internal.parsers.ScalametaParser.funDefRest(ScalametaParser.scala:3769)
[error] 	at scala.meta.internal.parsers.ScalametaParser.funDefOrDclOrExtensionOrSecondaryCtor(ScalametaParser.scala:3714)
[error] 	at scala.meta.internal.parsers.ScalametaParser.defOrDclOrSecondaryCtor(ScalametaParser.scala:3544)
[error] 	at scala.meta.internal.parsers.ScalametaParser.nonLocalDefOrDcl(ScalametaParser.scala:3523)
[error] 	at scala.meta.internal.parsers.ScalametaParser$$anonfun$templateStat$1.applyOrElse(ScalametaParser.scala:4495)
[error] 	at scala.meta.internal.parsers.ScalametaParser$$anonfun$templateStat$1.applyOrElse(ScalametaParser.scala:4489)
[error] 	at scala.PartialFunction.$anonfun$runWith$1(PartialFunction.scala:231)
[error] 	at scala.PartialFunction.$anonfun$runWith$1$adapted(PartialFunction.scala:230)
[error] 	at scala.meta.internal.parsers.ScalametaParser.statSeqBuf(ScalametaParser.scala:4440)
[error] 	at scala.meta.internal.parsers.ScalametaParser.getStats$2(ScalametaParser.scala:4479)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$scala$meta$internal$parsers$ScalametaParser$$templateStatSeq$3(ScalametaParser.scala:4480)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$scala$meta$internal$parsers$ScalametaParser$$templateStatSeq$3$adapted(ScalametaParser.scala:4477)
[error] 	at scala.meta.internal.parsers.ScalametaParser.scala$meta$internal$parsers$ScalametaParser$$listBy(ScalametaParser.scala:567
[error] 	at scala.meta.internal.parsers.ScalametaParser.scala$meta$internal$parsers$ScalametaParser$$templateStatSeq(ScalametaParser.scala:4477)
[error] 	at scala.meta.internal.parsers.ScalametaParser.scala$meta$internal$parsers$ScalametaParser$$templateStatSeq(ScalametaParser.scala:4469)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$templateBody$1(ScalametaParser.scala:4322)
[error] 	at scala.meta.internal.parsers.ScalametaParser.inBracesOr(ScalametaParser.scala:260)
[error] 	at scala.meta.internal.parsers.ScalametaParser.inBraces(ScalametaParser.scala:256)
[error] 	at scala.meta.internal.parsers.ScalametaParser.templateBody(ScalametaParser.scala:4322)
[error] 	at scala.meta.internal.parsers.ScalametaParser.templateBodyOpt(ScalametaParser.scala:4326)
[error] 	at scala.meta.internal.parsers.ScalametaParser.templateAfterExtends(ScalametaParser.scala:4269)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$template$1(ScalametaParser.scala:4290)
[error] 	at scala.meta.internal.parsers.ScalametaParser.atPos(ScalametaParser.scala:319)
[error] 	at scala.meta.internal.parsers.ScalametaParser.autoPos(ScalametaParser.scala:365)
[error] 	at scala.meta.internal.parsers.ScalametaParser.template(ScalametaParser.scala:4277)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$simpleExpr0$2(ScalametaParser.scala:2257)
[error] 	at scala.meta.internal.parsers.ScalametaParser.atPos(ScalametaParser.scala:319)
[error] 	at scala.meta.internal.parsers.ScalametaParser.autoPos(ScalametaParser.scala:365)
[error] 	at scala.meta.internal.parsers.ScalametaParser.simpleExpr0(ScalametaParser.scala:2255)
[error] 	at scala.meta.internal.parsers.ScalametaParser.simpleExpr(ScalametaParser.scala:2223)
[error] 	at scala.meta.internal.parsers.ScalametaParser.prefixExpr(ScalametaParser.scala:2206)
[error] 	at scala.meta.internal.parsers.ScalametaParser.postfixExpr(ScalametaParser.scala:2081)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$expr$2(ScalametaParser.scala:1676)
[error] 	at scala.meta.internal.parsers.ScalametaParser.atPosOpt(ScalametaParser.scala:322)
[error] 	at scala.meta.internal.parsers.ScalametaParser.autoPosOpt(ScalametaParser.scala:366)
[error] 	at scala.meta.internal.parsers.ScalametaParser.expr(ScalametaParser.scala:1581)
[error] 	at scala.meta.internal.parsers.ScalametaParser$$anonfun$1.$anonfun$applyOrElse$2(ScalametaParser.scala:4384)
[error] 	at scala.meta.internal.parsers.ScalametaParser.stat(ScalametaParser.scala:4421)
[error] 	at scala.meta.internal.parsers.ScalametaParser$$anonfun$1.applyOrElse(ScalametaParser.scala:4384)
[error] 	at scala.meta.internal.parsers.ScalametaParser$$anonfun$1.applyOrElse(ScalametaParser.scala:4377)
[error] 	at scala.PartialFunction$Lifted.apply(PartialFunction.scala:338)
[error] 	at scala.PartialFunction$Lifted.apply(PartialFunction.scala:334)
[error] 	at scala.meta.internal.parsers.ScalametaParser.entrypointStat(ScalametaParser.scala:4414)
[error] 	at scala.meta.internal.parsers.ScalametaParser.$anonfun$parseStat$1(ScalametaParser.scala:69)
[error] 	at scala.meta.internal.parsers.ScalametaParser.parseRuleAfterBOF(ScalametaParser.scala:59)
[error] 	at scala.meta.internal.parsers.ScalametaParser.parseRule(ScalametaParser.scala:54)
[error] 	at scala.meta.internal.parsers.ScalametaParser.parseStat(ScalametaParser.scala:69)
[error] 	at scala.meta.parsers.Parse$.$anonfun$parseStat$1(Parse.scala:14)
[error] 	at scala.meta.parsers.Parse$$anon$1.apply(Parse.scala:36)
[error] 	at Main$.main(Main.scala:14)
[error] 	at Main.main(Main.scala)
```

Pull request description:
This helps with ignoring cases which are not leading infix at the expense of possible syntax error detection.

Fixes #3571. Fixes scalameta/scalafmt#3786.

Patch:
diff --git a/scalameta/parsers/shared/src/main/scala/scala/meta/internal/parsers/ScannerTokens.scala b/scalameta/parsers/shared/src/main/scala/scala/meta/internal/parsers/ScannerTokens.scala
index 9d321f42f2..d84159c1cf 100644
--- a/scalameta/parsers/shared/src/main/scala/scala/meta/internal/parsers/ScannerTokens.scala
+++ b/scalameta/parsers/shared/src/main/scala/scala/meta/internal/parsers/ScannerTokens.scala
@@ -977,9 +977,9 @@ final class ScannerTokens(val tokens: Tokens)(implicit dialect: Dialect) {
         val commentIndent = multilineCommentIndent(c)
         iter(pos + 1, if (commentIndent < 0) indent else commentIndent, true)
       case t =>
-        if (indent >= 0 && indent < nextIndent) LeadingInfix.InvalidArg
-        else if (canBeLeadingInfixArg(t, pos)) LeadingInfix.Yes
-        else LeadingInfix.InvalidArg
+        if (!canBeLeadingInfixArg(t, pos)) LeadingInfix.No
+        else if (indent >= 0 && indent < nextIndent) LeadingInfix.InvalidArg
+        else LeadingInfix.Yes
     }
     tokens(afterOpPos) match {
       case _: EOL => iter(afterOpPos + 1, 0, false)


Test patch:
diff --git a/tests/shared/src/test/scala/scala/meta/tests/parsers/DefnSuite.scala b/tests/shared/src/test/scala/scala/meta/tests/parsers/DefnSuite.scala
index cd2dde9e3d..3dec258916 100644
--- a/tests/shared/src/test/scala/scala/meta/tests/parsers/DefnSuite.scala
+++ b/tests/shared/src/test/scala/scala/meta/tests/parsers/DefnSuite.scala
@@ -360,4 +360,43 @@ class DefnSuite extends ParseSuite {
     runTestAssert[Stat](code, assertLayout = Some(layout))(tree)
   }
 
+  test("#3571 scala213") {
+    val code =
+      """|new A {
+         |  def b: C =
+         |    ???
+         |}
+         |""".stripMargin
+    val layout =
+      """|new A { def b: C = ??? }
+         |""".stripMargin
+    val tree = Term.NewAnonymous(
+      tpl(
+        List(Init(pname("A"), anon, Nil)),
+        List(Defn.Def(Nil, tname("b"), Nil, Some(pname("C")), tname("???")))
+      )
+    )
+    runTestAssert[Stat](code, layout)(tree)
+  }
+
+  test("#3571 scala213source3") {
+    implicit val Scala213 = scala.meta.dialects.Scala213Source3
+    val code =
+      """|new A {
+         |  def b: C =
+         |    ???
+         |}
+         |""".stripMargin
+    val layout =
+      """|new A { def b: C = ??? }
+         |""".stripMargin
+    val tree = Term.NewAnonymous(
+      tpl(
+        List(Init(pname("A"), anon, Nil)),
+        List(Defn.Def(Nil, tname("b"), Nil, Some(pname("C")), tname("???")))
+      )
+    )
+    runTestAssert[Stat](code, layout)(tree)
+  }
+
 }
diff --git a/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/InfixSuite.scala b/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/InfixSuite.scala
index 05171a662b..3dac9c0880 100644
--- a/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/InfixSuite.scala
+++ b/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/InfixSuite.scala
@@ -440,7 +440,7 @@ class InfixSuite extends BaseDottySuite {
   }
 
   test("scala3 infix syntax 5.2") {
-    runTestError[Stat](
+    val code =
       """|{
          |  println("hello")
          |    ???
@@ -448,11 +448,24 @@ class InfixSuite extends BaseDottySuite {
          |      case 0 => 1
          |    }
          |}
-         |""".stripMargin,
-      """|error: Invalid indented leading infix operator found
-         |    ???
-         |    ^""".stripMargin
+         |""".stripMargin
+    val layout =
+      """|{
+         |  println("hello")
+         |  ???
+         |  ??? match {
+         |    case 0 => 1
+         |  }
+         |}
+         |""".stripMargin
+    val tree = Term.Block(
+      List(
+        Term.Apply(tname("println"), List(str("hello"))),
+        tname("???"),
+        Term.Match(tname("???"), List(Case(int(0), None, int(1))), Nil)
+      )
     )
+    runTestAssert[Stat](code, layout)(tree)
   }
 
   test("scala3 infix syntax 6") {
diff --git a/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/SignificantIndentationSuite.scala b/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/SignificantIndentationSuite.scala
index 3fb4e38f6f..6ed06f7921 100644
--- a/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/SignificantIndentationSuite.scala
+++ b/tests/shared/src/test/scala/scala/meta/tests/parsers/dotty/SignificantIndentationSuite.scala
@@ -3328,4 +3328,23 @@ class SignificantIndentationSuite extends BaseDottySuite {
     runTestAssert[Stat](code, Some(layout))(tree)
   }
 
+  test("#3571 scala3") {
+    val code =
+      """|new A {
+         |  def b: C =
+         |    ???
+         |}
+         |""".stripMargin
+    val layout =
+      """|new A { def b: C = ??? }
+         |""".stripMargin
+    val tree = Term.NewAnonymous(
+      tpl(
+        List(Init(pname("A"), anon, Nil)),
+        List(Defn.Def(Nil, tname("b"), Nil, Some(pname("C")), tname("???")))
+      )
+    )
+    runTestAssert[Stat](code, layout)(tree)
+  }
+
 }