Custom ValueSource erroneously tracks files etc used in obtain() when ValueSource parameters are passed in

[cloudshiftchris]

When creating a custom ValueSource with parameters, and using other ValueSource instances for those parameters, the inputs are erroneously tracked.

Expected Behavior

As documented, ValueSource implementations should not track files, environment variables, etc.

Current Behavior

Gradle erroneously tracks ValueSource inputs, resulting in unexpectedly dirty configuration caches.

Context

This causes the configuration cache to miss 100% of the time.

This is due to a collision of events:
- Gradle fingerprints the input parameters to the ValueSource;
- this results in beforeValueObtained() event being fired, which DISABLES input tracking
- ...and then afterValueObtained() is fired, which ENABLES input tracking, just in time to drop into the obtain()
method of our custom ValueSource

Steps to Reproduce

Reproduced here. Consistently reproducible in configurations where a ValueSource is used as a parameter to a ValueSource

Your Environment

MacOS, Gradle 7.5.1, Java 17

[cloudshiftchris]

At a minimum it should be documented that ValueSources should not be used as parameters to ValueSources; this is likely insufficient as it's not directly evident what constitutes a 'ValueSource' - it's intuitive to pass in providers.gradleProperty, for example.

A hard error when this is detected would be a good initial step.

Ideally the inputTracking state would be smart enough to support these use cases.

[cloudshiftchris]

Added additional diagnostic output to show the input tracking state:

        beforeValueObtained()  // input tracking turned off (entering custom MyValueSource)
        beforeValueObtained()  // input tracking turned off (entering environment variable)
        afterValueObtained()   // input tracking turned on  (exiting environment variable)
        valueObtained(): class org.gradle.api.internal.provider.sources.EnvironmentVariableValueSource org.gradle.api.internal.provider.sources.EnvironmentVariableValueSource$Inject@46d4f344

        // whoops; inside our ValueSource with input tracking turned on
        In value source
        Test file @ /Users/chrislee/.cloudshift/test.properties

        afterValueObtained()   // input tracking turned on (exiting custom MyValueSource)
        valueObtained(): class Build_gradle$MyValueSource Build_gradle$MyValueSource$Inject@6383cdd1

[cloudshiftchris]

This looks to be fixable in org.gradle.configurationcache.fingerprint.ConfigurationCacheFingerprintWriter by changing the ThreadLocal to a counter (e.g. ThreadLocal) to support nested ValueSources, with a state of '0' -> input tracking enabled and < 0 (assuming beforeValueObtained() decrements counter) -> input tracking disabled.

[mlopatkin]

This will be fixed in 7.6 RC1. There is some follow-up work to do, tracked in #22494. Big thanks to @cloudshiftchris for finding the root cause!