Avoid mixed slashes in Location

wire-schema/src/commonMain/kotlin/com/squareup/wire/schema/Location.kt

@@ -70,7 +70,19 @@ data class Location(
       base: String,
       path: String,
     ): Location {
-      return Location(base.trimEnd('/'), path, -1, -1)
+      return Location(
+        base = base.replace('\\', '/').trimEnd('/'),
+        path = if (path.length >= 3 && path[1] == ':' && path[2] == '\\') {
+          // Preserve the Windows drive root backslash (e.g. "C:\") since okio's path parser
+          // requires a backslash after the volume letter to recognize a Windows absolute path.
+          // TODO(Benoit) Remove this branch once https://github.com/square/okio/pull/1802 is released.
+          path.substring(0, 3) + path.substring(3).replace('\\', '/')
+        } else {
+          path.replace('\\', '/')
+        },
+        line = -1,
+        column = -1,
+      )
     }
   }
 }

wire-schema/src/commonTest/kotlin/com/squareup/wire/schema/LocationTest.kt

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2026 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.squareup.wire.schema
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class LocationTest {
+  @Test
+  fun getWithForwardSlashes() {
+    val location = Location.get("base/dir", "sub/file.proto")
+    assertEquals("base/dir", location.base)
+    assertEquals("sub/file.proto", location.path)
+  }
+
+  @Test
+  fun getTrimsTrailingSlashFromBase() {
+    val location = Location.get("base/dir/", "file.proto")
+    assertEquals("base/dir", location.base)
+  }
+
+  @Test
+  fun getNormalizesWindowsBackslashesInBase() {
+    val location = Location.get("C:\\Users\\username\\protos", "language\\language.proto")
+    assertEquals("C:/Users/username/protos", location.base)
+    assertEquals("language/language.proto", location.path)
+  }
+
+  @Test
+  fun getNormalizesWindowsBackslashesInPath() {
+    val location = Location.get("", "language\\language.proto")
+    assertEquals("language/language.proto", location.path)
+  }
+
+  @Test
+  fun getWithMixedSeparatorsInBase() {
+    val location = Location.get("C:\\Users/username\\protos/", "file.proto")
+    assertEquals("C:/Users/username/protos", location.base)
+  }
+
+  @Test
+  fun getPreservesWindowsDriveRootBackslashInPath() {
+    // okio requires 'C:\' (backslash) to recognize Windows absolute paths; 'C:/' is not supported
+    // in older okio versions. Preserve the root backslash while converting internal separators.
+    val location = Location.get("", "C:\\Users\\protos")
+    assertEquals("C:\\Users/protos", location.path)
+  }
+}