From 646e62ec8102090b4d946f994a3f7669e4bc644b Mon Sep 17 00:00:00 2001
From: i10416 <ito.yo16uh90616@gmail.com>
Date: Sat, 24 Feb 2024 15:13:58 +0900
Subject: [PATCH] fix: cannot find Scala companion module from Java

To find Scala companion mudule from Java, we should strip module suffix
`$`.
This provides workaround for #17255, but it requires some refinment to fully fix it
because not-fully-qualified type like the following example still fails
to compile due to missing symbol.

```java
package example;

public class Bar {
    private static final Foo$ MOD = Foo$.MODULE;
}
```

This is because `pre` in `javaFindMember` for `Foo` in the case above is `<root>`,
not `example` and therefore `pre.findMember` looks for `<root>.Foo` instead
of `example.Foo`.

I'm not sure whether the qualifier is intentionally dropped.
---
 .../dotty/tools/dotc/core/ContextOps.scala    | 22 +++++++++++++------
 .../test/dotc/pos-test-pickling.blacklist     |  1 +
 tests/pos/i17255/Bar.java                     |  6 +++++
 tests/pos/i17255/Foo.scala                    |  5 +++++
 4 files changed, 27 insertions(+), 7 deletions(-)
 create mode 100644 tests/pos/i17255/Bar.java
 create mode 100644 tests/pos/i17255/Foo.scala

diff --git a/compiler/src/dotty/tools/dotc/core/ContextOps.scala b/compiler/src/dotty/tools/dotc/core/ContextOps.scala
index 55fb31fd1916..0511271a5d65 100644
--- a/compiler/src/dotty/tools/dotc/core/ContextOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/ContextOps.scala
@@ -55,11 +55,18 @@ object ContextOps:
     final def javaFindMember(name: Name, pre: Type, lookInCompanion: Boolean, required: FlagSet = EmptyFlags, excluded: FlagSet = EmptyFlags): Denotation =
       assert(ctx.isJava)
       inContext(ctx) {
-
+        import dotty.tools.dotc.core.NameOps.*
         val preSym = pre.typeSymbol
 
         // 1. Try to search in current type and parents.
-        val directSearch = pre.findMember(name, pre, required, excluded)
+        val directSearch =
+          if name.isTypeName && name.endsWith(StdNames.str.MODULE_SUFFIX) then
+            pre.findMember(name.stripModuleClassSuffix, pre, required, excluded) match
+              case NoDenotation => NoDenotation
+              case k: SymDenotation =>
+                k.companionModule.denot
+          else
+            pre.findMember(name, pre, required, excluded)
 
         // 2. Try to search in companion class if current is an object.
         def searchCompanionClass = if lookInCompanion && preSym.is(Flags.Module) then
@@ -81,11 +88,12 @@ object ContextOps:
             val pre1 = bc.companionModule.namedType
             pre1.findMember(name, pre1, required, excluded)
           }.find(_.exists).getOrElse(NoDenotation)
-
-        if preSym.isClass then
-          directSearch orElse searchCompanionClass orElse searchSuperCompanionObjects
-        else
-          directSearch
+        val result =
+          if preSym.isClass then
+            directSearch orElse searchCompanionClass orElse searchSuperCompanionObjects
+          else
+            directSearch
+        result
       }
 
     /** A fresh local context with given tree and owner.
diff --git a/compiler/test/dotc/pos-test-pickling.blacklist b/compiler/test/dotc/pos-test-pickling.blacklist
index b0da78f0a1eb..32f8cdef1386 100644
--- a/compiler/test/dotc/pos-test-pickling.blacklist
+++ b/compiler/test/dotc/pos-test-pickling.blacklist
@@ -29,6 +29,7 @@ i16649-irrefutable.scala
 strict-pattern-bindings-3.0-migration.scala
 i17186b.scala
 i11982a.scala
+i17255
 
 # Tree is huge and blows stack for printing Text
 i7034.scala
diff --git a/tests/pos/i17255/Bar.java b/tests/pos/i17255/Bar.java
new file mode 100644
index 000000000000..35269af2179f
--- /dev/null
+++ b/tests/pos/i17255/Bar.java
@@ -0,0 +1,6 @@
+package example;
+
+
+public class Bar {
+	private static final example.Foo$ MOD = example.Foo$.MODULE$;
+}
\ No newline at end of file
diff --git a/tests/pos/i17255/Foo.scala b/tests/pos/i17255/Foo.scala
new file mode 100644
index 000000000000..9608b43b430f
--- /dev/null
+++ b/tests/pos/i17255/Foo.scala
@@ -0,0 +1,5 @@
+package example
+
+case class Foo(i: Int)
+
+object Foo
\ No newline at end of file