Merge pull request #36449 from luksa/env.valueFrom

Automatic merge from submit-queue

Improved validation error message when env.valueFrom contains no (or …

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**What this PR does / why we need it**:
A misleading error message is shown if the user mistypes (or forgets to specify) a field under env.valueFrom. This is the error message: "may not have more than one field specified at a time". But there is only one (misspelled) field specified.


**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:
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```
Improved error message for missing/misspelled field under env.valueFrom
```

pkg/api/validation/validation_test.go

@@ -2446,6 +2446,14 @@ func TestValidateEnv(t *testing.T) {
 			}},
 			expectedError: "[0].valueFrom: Invalid value: \"\": may not be specified when `value` is not empty",
 		},
+		{
+			name: "valueFrom without a source",
+			envs: []api.EnvVar{{
+				Name:      "abc",
+				ValueFrom: &api.EnvVarSource{},
+			}},
+			expectedError: "[0].valueFrom: Invalid value: \"\": must specify one of: `fieldRef`, `resourceFieldRef`, `configMapKeyRef` or `secretKeyRef`",
+		},
 		{
 			name: "valueFrom.fieldRef and valueFrom.secretKeyRef specified",
 			envs: []api.EnvVar{{