fix(config): references between different sources are consistent when watch

[zhan3333]

Description (what this PR does / why we need it):

Fixed an issue where watch did not work when referencing configuration updates between multiple sources

Which issue(s) this PR fixes (resolves / be part of):

fixes #2801

Other special notes for the reviewers:

/

[zhan3333]

@shenqidebaozi Hi, our project needs to use this function, can we speed up the schedule?

[shenqidebaozi]

@zhan3333 ok

[shenqidebaozi]

@zhan3333 please fix lint

[codecov-commenter]

Codecov Report

Merging #2868 (c20dacf) into main (32b1d13) will increase coverage by 0.12%. The diff coverage is 55.55%.

:exclamation: Current head c20dacf differs from pull request most recent head 2f37620. Consider uploading reports for the commit 2f37620 to get more accurate results

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@@            Coverage Diff             @@
##             main    #2868      +/-   ##
==========================================
+ Coverage   84.50%   84.63%   +0.12%     
==========================================
  Files          88       88              
  Lines        3970     3982      +12     
==========================================
+ Hits         3355     3370      +15     
+ Misses        439      435       -4     
- Partials      176      177       +1     

Impacted Files	Coverage Δ
config/config.go	62.06% <55.55%> (+7.40%)	:arrow_up:

... and 1 file with indirect coverage changes

[zhan3333]

@shenqidebaozi the lint fix has been completed

[zhan3333]

@shenqidebaozi ping

[kratos-ci-bot]

Bot detected the issue body's language is not English, translate it automatically. 👯👭🏻🧑‍🤝‍🧑👫🧑🏿‍🤝‍🧑🏻👩🏾‍🤝‍👨🏿👬🏿

---

@Magic Baoziping

[shenqidebaozi]

could you please provide more detailed background and modification instructions

[zhan3333]

could you please provide more detailed background and modification instructions

Of course @shenqidebaozi

Problem:

When a configuration is referenced across source config, updates to the referenced configuration cannot affect the referenced key.

How it works: config.load() will merge all source config into reader, and when config.next() gets a source configuration change, only that source KVS will be merged into reader.

Because the reference configuration is already processed to a specific value in reader, merge to reader does not trigger an update of the reference configuration.

For example:

source1:

{
    "key": "${key2}"
}

source2:

{
    "key2": "value"
}

After config.Load(), the structure in reader looks like this:

reader:

{
    "key": "value",
    "key2": "value"
}

When source2.key2 value is updated to newValue, the original config.watch() logic merges new KVS with reader to obtain the new reader value:

new reader

{
    "key": "value",
    "key2": "newValue"
}

Clearly, updates to key2 do not affect the value of the reference configuration key, causing the problem.

Solution:

When watch changes, Re-read the sources, this will make the key get the reference configuration value ${key2} again, and create a new reader to replace the config.reader to avoid the merge does not trigger updates when the reference.

[zhan3333]

@shenqidebaozi ping

[kratos-ci-bot]

Bot detected the issue body's language is not English, translate it automatically. 👯👭🏻🧑‍🤝‍🧑👫🧑🏿‍🤝‍🧑🏻👩🏾‍🤝‍👨🏿👬🏿

---

@Magic Baoziping