Make isOperatorName more precise

Author: mbovel

compiler/src/dotty/tools/dotc/core/NameOps.scala

@@ -7,7 +7,7 @@ import java.nio.CharBuffer
 import scala.io.Codec
 import Int.MaxValue
 import Names.*, StdNames.*, Contexts.*, Symbols.*, Flags.*, NameKinds.*, Types.*
-import util.Chars.{isOperatorPart, digit2int}
+import util.Chars.{isOperatorPart, isIdentifierPart, digit2int}
 import Decorators.*
 import Definitions.*
 import nme.*
@@ -78,9 +78,22 @@ object NameOps {
     def isUnapplyName: Boolean = name == nme.unapply || name == nme.unapplySeq
     def isRightAssocOperatorName: Boolean = name.lastPart.last == ':'
 
-    def isOperatorName: Boolean = name match
-      case name: SimpleName => name.exists(isOperatorPart)
-      case _ => false
+    /** Does this name match `{(letter | digit) '_' } op`?
+      *
+      * See examples in [[NameOpsTest]].
+      */
+    def isOperatorName: Boolean =
+      name match
+        case name: SimpleName =>
+          var i = name.length - 1
+          // Ends with operator characters
+          while i >= 0 && isOperatorPart(name(i)) do i -= 1
+          if i == -1 then return true
+          // Optionnally prefixed with alpha-numeric characters followed by `_`
+          if name(i) != '_' then return false
+          while i >= 0 && isIdentifierPart(name(i)) do i -= 1
+          i == -1
+        case _ => false
 
     /** Is name of a variable pattern? */
     def isVarPattern: Boolean =

compiler/test/dotty/tools/dotc/core/NameOpsTest.scala

@@ -0,0 +1,15 @@
+package dotty.tools.dotc.core
+
+import dotty.tools.dotc.core.NameOps.isOperatorName
+import dotty.tools.dotc.core.Names.{termName, SimpleName}
+
+import org.junit.Test
+
+class NameOpsTest:
+  @Test def isOperatorNamePos: Unit =
+    for name <- List("+", "::", "frozen_=:=", "$_+", "a2_+", "a_b_+") do
+      assert(isOperatorName(termName(name)))
+
+  @Test def isOperatorNameNeg: Unit =
+    for name <- List("foo", "*_*", "<init>", "$reserved", "a*", "2*") do
+      assert(!isOperatorName(termName(name)))