idempotent license report (#11810)

Co-authored-by: Lauri Tulmin <ltulmin@splunk.com>

.github/workflows/build-common.yml

@@ -88,8 +88,7 @@ jobs:
         run: |
           # add any untracked folders that may have been added by generateLicenseReport
           git add licenses
-          # there's always going to one line difference due to the timestamp included in the report
-          if [[ $(git diff --cached --shortstat licenses) == " 1 file changed, 1 insertion(+), 1 deletion(-)" ]]
+          if [[ $(git diff --cached --shortstat licenses) == "" ]]
           then
             echo "Licenses are up-to-date."
           else

javaagent/build.gradle.kts

@@ -2,7 +2,9 @@ import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
 import com.github.jk1.license.filter.LicenseBundleNormalizer
 import com.github.jk1.license.render.InventoryMarkdownReportRenderer
 import org.spdx.sbom.gradle.SpdxSbomTask
+import java.nio.file.Files
 import java.util.UUID
+import java.util.regex.Pattern
 
 plugins {
   id("com.github.jk1.dependency-license-report")
@@ -240,11 +242,29 @@ tasks {
     delete(rootProject.file("licenses"))
   }
 
+  val removeLicenseDate by registering {
+    // removing the license report date makes it idempotent
+    doLast {
+      val filePath = rootDir.toPath().resolve("licenses").resolve("licenses.md")
+      if (Files.exists(filePath)) {
+        val datePattern = Pattern.compile("^_[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2} .*_$")
+        val lines = Files.readAllLines(filePath)
+        // 4th line contains the timestamp of when the license report was generated, replace it with
+        // an empty line
+        if (lines.size > 3 && datePattern.matcher(lines[3]).matches()) {
+          lines[3] = ""
+          Files.write(filePath, lines)
+        }
+      }
+    }
+  }
+
   val generateLicenseReportEnabled =
     gradle.startParameter.taskNames.any { it.equals("generateLicenseReport") }
   named("generateLicenseReport").configure {
     dependsOn(cleanLicenses)
     finalizedBy(":spotlessApply")
+    finalizedBy(removeLicenseDate)
     // disable licence report generation unless this task is explicitly run
     // the files produced by this task are used by other tasks without declaring them as dependency
     // which gradle considers an error

licenses/licenses.md

@@ -1,7 +1,7 @@
 
 # javaagent
 ## Dependency License Report
-_2024-07-19 10:32:38 CEST_
+
 ## Apache License, Version 2.0
 
 **1** **Group:** `com.blogspot.mydailyjava` **Name:** `weak-lock-free` **Version:** `0.18`