Add option to ignore failures on steps (#1219)

closes #1181
closes #834 

Adds `ignore_failure` to pipeline steps. When it's set to true,
if the step fails the following steps continue to execute as if no failure had occurred.

---

failure enums idea:
* fail (default) = if other steps run in parallel, wait for them and
then let workflow fail
* cancel = if other steps run in parallel, kill them
* ignore = we mark the step as failed but it wont have any impact

docs/docs/20-usage/20-pipeline-syntax.md

@@ -206,6 +206,20 @@ Woodpecker provides the ability to store named parameters external to the YAML c
 
 For more details check the [secrets docs](./40-secrets.md).
 
+### `failure`
+
+Some of the pipeline steps may be allowed to fail without causing the whole pipeline to report a failure (e.g., a step executing a linting check). To enable this, add `failure: ignore` to your pipeline step. If Woodpecker encounters an error while executing the step, it will report it as failed but still execute the next steps of the pipeline, if any, without affecting the status of the pipeline.
+
+```diff
+ pipeline:
+   backend:
+     image: golang
+     commands:
+       - go build
+       - go test
++    failure: ignore
+```
+
 ### `when` - Conditional Execution
 
 Woodpecker supports defining a list of conditions for a pipeline step by using a `when` block. If at least one of the conditions in the `when` block evaluate to true the step is executed, otherwise it is skipped. A condition can be a check like:

pipeline/backend/types/step.go

@@ -28,6 +28,7 @@ type Step struct {
 	CPUSet       string            `json:"cpu_set,omitempty"`
 	OnFailure    bool              `json:"on_failure,omitempty"`
 	OnSuccess    bool              `json:"on_success,omitempty"`
+	Failure      string            `json:"failure,omitempty"`
 	AuthConfig   Auth              `json:"auth_config,omitempty"`
 	NetworkMode  string            `json:"network_mode,omitempty"`
 	IpcMode      string            `json:"ipc_mode,omitempty"`

pipeline/frontend/metadata.go

@@ -32,6 +32,13 @@ const (
 	EventManual = "manual"
 )
 
+// Different ways to handle failure states
+const (
+	FailureIgnore = "ignore"
+	FailureFail   = "fail"
+	// FailureCancel = "cancel" // Not implemented yet
+)
+
 type (
 	// Metadata defines runtime m.
 	Metadata struct {

pipeline/frontend/yaml/compiler/convert.go

@@ -9,6 +9,7 @@ import (
 	"github.com/rs/zerolog/log"
 
 	backend "github.com/woodpecker-ci/woodpecker/pipeline/backend/types"
+	"github.com/woodpecker-ci/woodpecker/pipeline/frontend"
 	"github.com/woodpecker-ci/woodpecker/pipeline/frontend/yaml"
 	"github.com/woodpecker-ci/woodpecker/pipeline/frontend/yaml/compiler/settings"
 )
@@ -139,6 +140,11 @@ func (c *Compiler) createProcess(name string, container *yaml.Container, section
 	// at least one constraint must include the status failure.
 	onFailure := container.When.IncludesStatus("failure")
 
+	failure := container.Failure
+	if container.Failure == "" {
+		failure = frontend.FailureFail
+	}
+
 	return &backend.Step{
 		Name:         name,
 		Alias:        container.Name,
@@ -167,6 +173,7 @@ func (c *Compiler) createProcess(name string, container *yaml.Container, section
 		AuthConfig:   authConfig,
 		OnSuccess:    onSuccess,
 		OnFailure:    onFailure,
+		Failure:      failure,
 		NetworkMode:  networkMode,
 		IpcMode:      ipcMode,
 	}

pipeline/frontend/yaml/container.go

@@ -41,6 +41,7 @@ type (
 		ExtraHosts    []string               `yaml:"extra_hosts,omitempty"`
 		Group         string                 `yaml:"group,omitempty"`
 		Image         string                 `yaml:"image,omitempty"`
+		Failure       string                 `yaml:"failure,omitempty"`
 		Isolation     string                 `yaml:"isolation,omitempty"`
 		Labels        types.SliceorMap       `yaml:"labels,omitempty"`
 		MemLimit      types.MemStringorInt   `yaml:"mem_limit,omitempty"`

pipeline/pipeline.go

@@ -11,6 +11,7 @@ import (
 	"golang.org/x/sync/errgroup"
 
 	backend "github.com/woodpecker-ci/woodpecker/pipeline/backend/types"
+	"github.com/woodpecker-ci/woodpecker/pipeline/frontend"
 	"github.com/woodpecker-ci/woodpecker/pipeline/multipart"
 )
 
@@ -193,7 +194,11 @@ func (r *Runtime) execAll(steps []*backend.Step) <-chan error {
 			}
 
 			// Return the error after tracing it.
-			return r.traceStep(processState, err, step)
+			err = r.traceStep(processState, err, step)
+			if err != nil && step.Failure == frontend.FailureIgnore {
+				return nil
+			}
+			return err
 		})
 	}
 

pipeline/schema/schema.json

@@ -237,6 +237,12 @@
         "detach": {
           "description": "Detach a step to run in background until pipeline finishes. Read more: https://woodpecker-ci.org/docs/usage/services#detachment",
           "type": "boolean"
+        },
+        "failure": {
+          "description": "How to handle the failure of this step. Read more: https://woodpecker-ci.org/docs/usage/pipeline-syntax#failure",
+          "type": "string",
+          "enum": ["fail", "ignore"],
+          "default": "fail"
         }
       }
     },