Move the generated checkstyle config to root dir (#66442)

Storing the generated config in the `build` dir meant that it could be
removed for various reasons, which causes e.g. IntelliJ to pop up
dialog, and is a mild annoyance. Instead, write the file to the project
root.

Also inline the path to the suppressions config, which removes a step
from the setup instructions.

.gitignore

@@ -56,3 +56,6 @@ testfixtures_shared/
 
 # These are generated from .ci/jobs.t
 .ci/jobs/
+
+# Generated
+checkstyle_ide.xml

CONTRIBUTING.md

@@ -178,17 +178,13 @@ it is removed due to a `./gradlew clean` or other action.
    3. Check the "+" under "Configuration file"
    4. Set "Description" to "Elasticsearch" (or whatever you want)
    5. Select "Use a local Checkstyle file"
-   6. For the "File", navigate to `build/checkstyle_ide.xml`
+   6. For the "File", enter `checkstyle_ide.xml`
    7. Tick "Store relative to project location"
-   8. Click "Next"
-   9. The Checkstyle config file contains the variable `config_loc`, and
-      IntelliJ will ask for a value. Fill in `buildSrc/src/main/resources`.
-      This allows the config file to reference the exclusions file in that directory.
-   10. Click "Next", then "Finish".
-   11. Click the box next to the new configuration to make it "Active". Without doing this,
-       you'll have to explicitly choose the "Elasticsearch" configuration in the Checkstyle
-       tool window and run the check manually. You can still do this with an active config.
-   12. Click "OK" to apply the new preferences
+   8. Click "Next", then "Finish".
+   9. Click the box next to the new configuration to make it "Active". Without doing this,
+      you'll have to explicitly choose the "Elasticsearch" configuration in the Checkstyle
+      tool window and run the check manually. You can still do this with an active config.
+   10. Click "OK" to apply the new preferences
 
 #### Formatting
 

gradle/ide.gradle

@@ -29,7 +29,7 @@ tasks.register('configureIdeCheckstyle') {
   description = 'Generated a suitable checkstyle config for IDEs'
 
   String checkstyleConfig = 'buildSrc/src/main/resources/checkstyle.xml'
-  String checkstyleIdeConfig = "${buildDir}/checkstyle_ide.xml"
+  String checkstyleIdeConfig = "$rootDir/checkstyle_ide.xml"
 
   inputs.files(file(checkstyleConfig))
   outputs.files(file(checkstyleIdeConfig))
@@ -43,7 +43,7 @@ tasks.register('configureIdeCheckstyle') {
     )
     // Edit the copy so that IntelliJ can copy with it
     modifyXml(checkstyleIdeConfig, { xml ->
-      // This module since it is implemented with custom code
+      // Remove this module since it is implemented with custom code
       xml.module.findAll { it.'@name' == 'org.elasticsearch.gradle.checkstyle.SnippetLengthCheck' }.each { it.parent().remove(it) }
 
       // Move the line length check because the IDE thinks it can't belong under a TreeWalker. Moving the
@@ -52,11 +52,17 @@ tasks.register('configureIdeCheckstyle') {
       Node lineLength = treeWalker.module.find { it.'@name' == 'LineLength' }
       treeWalker.remove(lineLength)
       xml.append(lineLength)
+
+      // Change the checkstyle config to inline the path to the
+      // suppressions config. This removes a configuration step when using
+      // the checkstyle config in an IDE.
+      Node suppressions = xml.module.find { it.'@name' == 'SuppressionFilter' }
+      suppressions.property.findAll { it.'@name' == 'file' }.each { it.'@value' = "buildSrc/src/main/resources/checkstyle_suppressions.xml" }
     },
       "<!DOCTYPE module PUBLIC\n" +
       "  \"-//Puppy Crawl//DTD Check Configuration 1.3//EN\"\n" +
       "  \"http://www.puppycrawl.com/dtds/configuration_1_3.dtd\">\n" +
-      "<!-- Generated automatically from ./checkstyle.xml - do not edit this file directly. -->\n"
+      "<!-- Generated automatically from ${checkstyleConfig} - do not edit this file directly. -->\n"
     )
   }
 }