[SPARK-27259][CORE] Allow setting -1 as length for FileBlock

[praneetsharma]

What changes were proposed in this pull request?

This PR aims to update the validation check on length from length >= 0 to length >= -1 in order to allow set -1 to keep the default value.

Why are the changes needed?

At Apache Spark 2.2.0, SPARK-18702 adds class FileBlock with the default length value, -1, initially.

There is no way to set filePath only while keeping length is -1.

  def set(filePath: String, startOffset: Long, length: Long): Unit = {
     require(filePath != null, "filePath cannot be null")
     require(startOffset >= 0, s"startOffset ($startOffset) cannot be negative")
     require(length >= 0, s"length ($length) cannot be negative")
     inputBlock.set(new FileBlock(UTF8String.fromString(filePath), startOffset, length))
   }

For compressed files (like GZ), the size of split can be set to -1. This was allowed till Spark 2.1 but regressed starting with spark 2.2.x. Please note that split length of -1 also means the length was unknown - a valid scenario. Thus, split length of -1 should be acceptable like pre Spark 2.2.

Does this PR introduce any user-facing change?

No

How was this patch tested?

This is updating the corner case on the requirement check. Manually check the code.

[dongjoon-hyun]

Hi, @praneetsharma .
Could you give us the valid reference for the following claim?

Please note that split length of -1 also means the length was unknown - a valid scenario.

I'm just wondering if we have an official reference for the following.

Certain custom InputFormats set split size to be -1 for compressed files like GZ.

[dongjoon-hyun]

ok to test

[SparkQA]

Test build #112132 has finished for PR 26123 at commit c67bcf3.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #112133 has finished for PR 26123 at commit 840f1ce.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #112131 has finished for PR 26123 at commit 53ae391.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[dongjoon-hyun]

+1, LGTM. Thank you, @praneetsharma .
Merged to master/3.0-preview/2.4.