feat: Add CEL-based conditional function execution (#4388) by SurbhiAgarwal1 · Pull Request #4469 · kptdev/kpt

SurbhiAgarwal1 · 2026-04-07T18:29:34Z

Description

This PR adds CEL-based conditional function execution to kpt, implementing #4388.

A new optional condition field is added to the Function type in the Kptfile pipeline. When specified, the CEL expression is evaluated against the current list of KRM resources. If the expression returns false, the function is skipped. If omitted or returns true, the function executes normally.

Motivation

In many real-world scenarios, you want a pipeline function to run only when certain resources exist or meet specific criteria. Without this feature, users had to maintain separate Kptfiles or manually manage which functions run. The condition field makes pipelines more dynamic and reduces the need for workarounds.

Changes

Added condition field to Function type in pkg/api/kptfile/v1/types.go
Added CELEnvironment in pkg/lib/runneroptions/celenv.go using google/cel-go
Integrated condition check in FunctionRunner.Filter() in internal/fnruntime/runner.go
Functions skipped due to condition show [SKIPPED] in CLI output
Added InitCELEnvironment() method to RunnerOptions for proper error handling
Updated all callers of InitDefaults() to also call InitCELEnvironment()
Added E2E testdata for condition-met and condition-not-met cases
Added unit tests for CEL evaluation covering all 3 runtimes (builtin, exec, container)
Updated documentation: kptfile schema reference and book/04-using-functions

Example Usage

pipeline:
  mutators:
    - image: ghcr.io/kptdev/krm-functions-catalog/set-namespace:v0.4
      condition: "resources.exists(r, r.kind == 'ConfigMap' && r.metadata.name == 'env-config')"
      configMap:
        namespace: production

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liamfallon · 2026-04-08T12:51:23Z

Comment from #4391:

Closing this PR in favor of a clean rebase. The branch had accumulated 61 commits including upstream commits from other contributors, making it messy to review.

All the feedback from this review has been addressed in the new PR which has a single clean commit:

Removed unnecessary type alias file (celeval.go)
Grouped constants in const() block
Replaced interface{} with any
Removed panic from InitDefaults, added InitCELEnvironment() error method
Added e2e tests for condition-met and condition-not-met
Added immutability test
Added documentation (kptfile schema + book/04-using-functions)
Removed all unwanted files (krm-functions-catalog, output.txt, etc.)
Fixed diff.patch for renderStatus field

Thank you all for the thorough review!

Copilot

Pull request overview

Copilot reviewed 31 out of 32 changed files in this pull request and generated 6 comments.

Comments suppressed due to low confidence (1)

thirdparty/kyaml/runfn/runfn.go:1

NewFunctionRunner’s error is discarded and SetCondition is called without validating opts.CELEnvironment. This can both (a) mask construction failures and (b) silently ignore the condition at runtime when CELEnvironment is nil (since Filter() only evaluates conditions when celEnv != nil). Handle the err from NewFunctionRunner, and if r.Condition is set, return an error when opts.CELEnvironment is nil (or make SetCondition return an error and enforce it here).

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internal/util/render/executor.go

pkg/lib/runneroptions/runneroptions.go

commands/fn/render/cmdrender.go

documentation/content/en/book/04-using-functions/_index.md

e2e/testdata/live-apply/json-output/config.yaml

e2e/testdata/live-apply/apply-depends-on/config.yaml

Copilot

Pull request overview

Copilot reviewed 29 out of 30 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

documentation/content/en/book/04-using-functions/_index.md:1

Two doc mismatches with the implementation: (1) the CEL resource map normalization in resourceToMap guarantees apiVersion, kind, and metadata keys, but not spec/status—either update the docs or ensure those keys are present; (2) the skipped example says “Successfully executed 1 function(s)” but the new behavior and e2e expectations indicate skipped functions should not count as executed (so this should be 0).

---

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thirdparty/kyaml/runfn/runfn.go

internal/fnruntime/runner.go

Copilot · 2026-04-08T18:09:23Z

internal/fnruntime/runner.go

+			fr.fnResult.ExitCode = 0
+			fr.fnResult.Skipped = true
+			fr.fnResults.Items = append(fr.fnResults.Items, *fr.fnResult)
+			// Return input unchanged - function is skipped
+			fr.skipped = true
+			return input, nil
+		}
+	}


fr.skipped (and fr.fnResult.Skipped) are only ever set to true and never reset in Filter(). If the same FunctionRunner instance is used for more than one Filter() call, WasSkipped() can remain true and fnResult.Skipped can leak across executions. Please reset fr.skipped and fr.fnResult.Skipped at the beginning of Filter() before evaluating the condition.

documentation/content/en/book/04-using-functions/_index.md

liamfallon · 2026-04-08T18:29:02Z

@SurbhiAgarwal1

The tests are failing because we have merged the conditions and renederstatus to kpt recently. I thought that by deleting the diff.patch files, the comparison would just check the output and the tests would pass. However we also need to add the difference in the Kprfile after render to the diff.patch files. Now that I deleted the diff.patch files in the PR, I can't see any option to restore them on the Github GUI.

The following `diff.patch files work for me on the tests locally on my machine:

e2e/testdata/fn-render/condition/condition-met/.expected/diff.patch

diff --git a/Kptfile b/Kptfile
index eb90ac3..d305dc0 100644
--- a/Kptfile
+++ b/Kptfile
@@ -5,4 +5,14 @@ metadata:
 pipeline:
   mutators:
     - image: ghcr.io/kptdev/krm-functions-catalog/no-op
-      condition: "resources.exists(r, r.kind == 'ConfigMap' && r.metadata.name == 'app-config')"
+      condition: resources.exists(r, r.kind == 'ConfigMap' && r.metadata.name == 'app-config')
+status:
+  conditions:
+    - type: Rendered
+      status: "True"
+      reason: RenderSuccess
+  renderStatus:
+    mutationSteps:
+      - image: ghcr.io/kptdev/krm-functions-catalog/no-op
+        exitCode: 0

e2e/testdata/fn-render/condition/condition-not-met/.expected/diff.patch

diff --git a/Kptfile b/Kptfile
index eb90ac3..b055f32 100644
--- a/Kptfile
+++ b/Kptfile
@@ -5,4 +5,14 @@ metadata:
 pipeline:
   mutators:
     - image: ghcr.io/kptdev/krm-functions-catalog/no-op
-      condition: "resources.exists(r, r.kind == 'ConfigMap' && r.metadata.name == 'app-config')"
+      condition: resources.exists(r, r.kind == 'ConfigMap' && r.metadata.name == 'app-config')
+status:
+  conditions:
+    - type: Rendered
+      status: "True"
+      reason: RenderSuccess
+  renderStatus:
+    mutationSteps:
+      - image: ghcr.io/kptdev/krm-functions-catalog/no-op
+        exitCode: 0
+        skipped: true

Can you try restoring the two diff.patch files with the contents above and see if that fixes the tests?

Sorry for mucking with your PR 😢

SurbhiAgarwal1 · 2026-04-08T18:55:19Z

Thank you @liamfallon! I've restored both diff.patch files with exactly the contents you provided in commit df1189f. The tests should pass now. Sorry for the confusion!

SurbhiAgarwal1 · 2026-04-09T05:53:50Z

Hi @liamfallon, I've updated the diff.patch files again using the exact actual output from the CI logs. The tests are still failing with the same diff - it seems the expected diff.patch I have doesn't match what CI produces.

The actual diff CI produces for condition-met is:

index eb90ac3..5ccde1c 100644
@@ -5,4 +5,13 @@
exitCode: 0 with \ No newline at end of file

And for condition-not-met:

index eb90ac3..ac7ae33 100644
@@ -5,4 +5,14 @@
Plus resources.yaml diff: index 7806994..c8cdecf

I've set the diff.patch files to exactly match this output. Could you check if there's something else causing the mismatch? The CI run is #8920 if you want to look at the full logs.

Adds support for CEL expressions in Kptfile pipeline functions via a new 'condition' field. Functions with a condition are only executed if the CEL expression evaluates to true against the current resource list. - Add CELEnvironment in pkg/lib/runneroptions/celenv.go - Integrate condition check in FunctionRunner.Filter (runner.go) - Append skipped result to fnResults when condition is not met - Add 'condition' field to kptfile/v1 Function type - Update all callers of InitDefaults to also call InitCELEnvironment - Add e2e testdata for condition-met and condition-not-met cases - Add unit tests for CEL evaluation and condition checking - Update documentation: kptfile schema and book/04-using-functions - Fix go.mod: mark k8s.io/apiserver as direct dependency Resolves kptdev#4388 Signed-off-by: SurbhiAgarwal1 <agarwalsurbhi1807@gmail.com>

liamfallon · 2026-04-09T06:09:12Z

Hi @SurbhiAgarwal1 , Have a look at this test PR, I just cloned this PR across so that I could push changes directly. I think the tests are running on that one so if you copy the diff.patch files from that PR into this PR I hope it'll work:

#4472

SurbhiAgarwal1 · 2026-04-09T06:10:26Z

Hi @liamfallon, thank you so much for doing that! I've copied the diff.patch files from PR #4472 into this PR. The tests should pass now. Really appreciate you taking the time to debug this!

e2e/testdata/fn-render/condition/condition-met/.expected/diff.patch

…patch

e2e/testdata/fn-render/condition/condition-met/.expected/diff.patch

…patch

liamfallon · 2026-04-09T08:15:04Z

@SurbhiAgarwal1 All tests passing now!

The problems we experienced here are why it is generally not recommended to have text comparison in tests, but to fix all the tests in kpt would be a huge job.

SurbhiAgarwal1 · 2026-04-09T08:35:04Z

Got it, makes sense. Thanks!
Yeah I noticed the text comparison was causing these issues. Glad it’s passing now.
Appreciate the help on this — I’ll keep it in mind if I touch similar tests later.

liamfallon · 2026-04-09T09:30:55Z

If you have time to look at the copilot comments that would be great. We can move to formally review and merge the PR then.

SurbhiAgarwal1 requested review from efiacor, kispaljr, liamfallon and mozesl-nokia as code owners April 7, 2026 18:29

Copilot AI review requested due to automatic review settings April 7, 2026 18:29

dosubot bot added size:XL This PR changes 500-999 lines, ignoring generated files. documentation Improvements or additions to documentation enhancement New feature or request go Pull requests that update Go code labels Apr 7, 2026

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SurbhiAgarwal1 force-pushed the feat/cel-clean-v2 branch from 2037fa3 to b9a1ab1 Compare April 7, 2026 19:39

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SurbhiAgarwal1 force-pushed the feat/cel-clean-v2 branch from abd89dd to df1189f Compare April 8, 2026 18:48

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SurbhiAgarwal1 force-pushed the feat/cel-clean-v2 branch from df1189f to ad63ed9 Compare April 8, 2026 19:04

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SurbhiAgarwal1 force-pushed the feat/cel-clean-v2 branch 2 times, most recently from 298cc5d to 6d4aed1 Compare April 8, 2026 23:04

liamfallon mentioned this pull request Apr 9, 2026

DO NOT MERGE: Test PR to debug cel condition tests #4472

Closed

SurbhiAgarwal1 force-pushed the feat/cel-clean-v2 branch from 6d4aed1 to 26362cc Compare April 9, 2026 05:43

SurbhiAgarwal1 force-pushed the feat/cel-clean-v2 branch from 26362cc to 8daf88e Compare April 9, 2026 06:06

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Update e2e/testdata/fn-render/condition/condition-met/.expected/diff.…

ffba654

…patch

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