[SPARK-34339][CORE][SQL] Expose the number of total paths in Utils.buildLocationMetadata()

### What changes were proposed in this pull request?

This PR proposes to expose the number of total paths in Utils.buildLocationMetadata(), with relaxing space usage a bit (around 10+ chars).

Suppose the first 2 of 5 paths are only fit to the threshold, the outputs between the twos are below:

* before the change: `[path1, path2]`
* after the change: `(5 paths)[path1, path2, ...]`

### Why are the changes needed?

SPARK-31793 silently truncates the paths hence end users can't indicate how many paths are truncated, and even more, whether paths are truncated or not.

### Does this PR introduce _any_ user-facing change?

Yes, the location metadata will also show how many paths are truncated (not shown), instead of silently truncated.

### How was this patch tested?

Modified UTs

Closes #31464 from HeartSaVioR/SPARK-34339.

Authored-by: Jungtaek Lim (HeartSaVioR) <kabhwan.opensource@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -2980,7 +2980,7 @@ private[spark] object Utils extends Logging {
    * exceeds `stopAppendingThreshold`, stop appending paths for saving memory.
    */
   def buildLocationMetadata(paths: Seq[Path], stopAppendingThreshold: Int): String = {
-    val metadata = new StringBuilder("[")
+    val metadata = new StringBuilder(s"(${paths.length} paths)[")
     var index: Int = 0
     while (index < paths.length && metadata.length < stopAppendingThreshold) {
       if (index > 0) {
@@ -2989,6 +2989,12 @@ private[spark] object Utils extends Logging {
       metadata.append(paths(index).toString)
       index += 1
     }
+    if (paths.length > index) {
+      if (index > 0) {
+        metadata.append(", ")
+      }
+      metadata.append("...")
+    }
     metadata.append("]")
     metadata.toString
   }

core/src/test/scala/org/apache/spark/util/UtilsSuite.scala

@@ -1304,16 +1304,11 @@ class UtilsSuite extends SparkFunSuite with ResetSystemProperties with Logging {
 
   test("pathsToMetadata") {
     val paths = (0 to 4).map(i => new Path(s"path$i"))
-    assert(Utils.buildLocationMetadata(paths, 5) == "[path0]")
-    assert(Utils.buildLocationMetadata(paths, 10) == "[path0, path1]")
-    assert(Utils.buildLocationMetadata(paths, 15) == "[path0, path1, path2]")
-    assert(Utils.buildLocationMetadata(paths, 25) == "[path0, path1, path2, path3]")
-
-    // edge-case: we should consider the fact non-path chars including '[' and ", " are accounted
-    // 1. second path is not added due to the addition of '['
-    assert(Utils.buildLocationMetadata(paths, 6) == "[path0]")
-    // 2. third path is not added due to the addition of ", "
-    assert(Utils.buildLocationMetadata(paths, 13) == "[path0, path1]")
+    assert(Utils.buildLocationMetadata(paths, 10) == "(5 paths)[...]")
+    // 11 is the minimum threshold to print at least one path
+    assert(Utils.buildLocationMetadata(paths, 11) == "(5 paths)[path0, ...]")
+    // 11 + 5 + 2 = 18 is the minimum threshold to print two paths
+    assert(Utils.buildLocationMetadata(paths, 18) == "(5 paths)[path0, path1, ...]")
   }
 
   test("checkHost supports both IPV4 and IPV6") {

external/avro/src/test/scala/org/apache/spark/sql/avro/AvroSuite.scala

@@ -2132,7 +2132,7 @@ class AvroV2Suite extends AvroSuite with ExplainSuiteHelper {
            |Output \\[2\\]: \\[value#xL, id#x\\]
            |DataFilters: \\[isnotnull\\(value#xL\\), \\(value#xL > 2\\)\\]
            |Format: avro
-           |Location: InMemoryFileIndex\\[.*\\]
+           |Location: InMemoryFileIndex\\([0-9]+ paths\\)\\[.*\\]
            |PartitionFilters: \\[isnotnull\\(id#x\\), \\(id#x > 1\\)\\]
            |PushedFilers: \\[IsNotNull\\(value\\), GreaterThan\\(value,2\\)\\]
            |ReadSchema: struct\\<value:bigint\\>

sql/core/src/test/scala/org/apache/spark/sql/ExplainSuite.scala

@@ -411,7 +411,7 @@ class ExplainSuite extends ExplainSuiteHelper with DisableAdaptiveExecutionSuite
              |Output \\[2\\]: \\[value#x, id#x\\]
              |DataFilters: \\[isnotnull\\(value#x\\), \\(value#x > 2\\)\\]
              |Format: $fmt
-             |Location: InMemoryFileIndex\\[.*\\]
+             |Location: InMemoryFileIndex\\([0-9]+ paths\\)\\[.*\\]
              |PartitionFilters: \\[isnotnull\\(id#x\\), \\(id#x > 1\\)\\]
              ${pushFilterMaps.get(fmt).get}
              |ReadSchema: struct\\<value:int\\>

sql/core/src/test/scala/org/apache/spark/sql/execution/DataSourceScanExecRedactionSuite.scala

@@ -122,8 +122,6 @@ class DataSourceScanExecRedactionSuite extends DataSourceScanRedactionTest {
 
   test("SPARK-31793: FileSourceScanExec metadata should contain limited file paths") {
     withTempPath { path =>
-      val dir = path.getCanonicalPath
-
       // create a sub-directory with long name so that each root path will always exceed the limit
       // this is to ensure we always test the case for the path truncation
       val dataDirName = Random.alphanumeric.take(100).toList.mkString
@@ -146,6 +144,9 @@ class DataSourceScanExecRedactionSuite extends DataSourceScanRedactionTest {
       // The location metadata should at least contain one path
       assert(location.get.contains(paths.head))
 
+      // The location metadata should have the number of root paths
+      assert(location.get.contains("(10 paths)"))
+
       // The location metadata should have bracket wrapping paths
       assert(location.get.indexOf('[') > -1)
       assert(location.get.indexOf(']') > -1)
@@ -155,7 +156,9 @@ class DataSourceScanExecRedactionSuite extends DataSourceScanRedactionTest {
         location.get.indexOf('[') + 1, location.get.indexOf(']')).split(", ").toSeq
 
       // the only one path should be available
-      assert(pathsInLocation.size == 1)
+      assert(pathsInLocation.size == 2)
+      // indicator ("...") should be available
+      assert(pathsInLocation.exists(_.contains("...")))
     }
   }
 }