refactor: use the shared expression evaluation layer

Gitea carries a copy of this evaluation layer, as
modules/actions/jobparser/evaluator.go says itself: "copied from
runner.expressionEvaluator, to avoid unnecessary dependencies". It now
lives in gitea.dev/actionslib/pkg/expreval, so both sides split
sub-expressions, interpolate, keep the type of a lone expression and
apply the default status check the same way.

expressionEvaluator keeps the logging and the mask of every single
evaluation, which is what the shared Evaluator takes a function for.

Signed-off-by: Lunny Xiao <xiaolunwen@gmail.com>

act/runner/expression.go

@@ -7,7 +7,6 @@ package runner
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"maps"
 	"path"
@@ -21,9 +20,9 @@ import (
 
 	_ "embed"
 
+	"gitea.dev/actionslib/pkg/expreval"
 	"gitea.dev/actionslib/pkg/exprparser"
 	"gitea.dev/actionslib/pkg/model"
-	"github.com/rhysd/actionlint"
 	"go.yaml.in/yaml/v4"
 )
 
@@ -235,137 +234,16 @@ func (ee expressionEvaluator) evaluate(ctx context.Context, in string, defaultSt
 	return evaluated, err
 }
 
-func (ee expressionEvaluator) evaluateScalarYamlNode(ctx context.Context, node *yaml.Node) (*yaml.Node, error) {
-	var in string
-	if err := node.Decode(&in); err != nil {
-		return nil, err
-	}
-	if !strings.Contains(in, "${{") || !strings.Contains(in, "}}") {
-		return nil, nil //nolint:nilnil // pre-existing issue from nektos/act
-	}
-	res, err := ee.evaluateScalar(ctx, in)
-	if err != nil {
-		return nil, err
-	}
-	ret := &yaml.Node{}
-	if err := ret.Encode(res); err != nil {
-		return nil, err
-	}
-	return ret, err
-}
-
-func (ee expressionEvaluator) evaluateMappingYamlNode(ctx context.Context, node *yaml.Node) (*yaml.Node, error) {
-	var ret *yaml.Node
-	// GitHub has this undocumented feature to merge maps, called insert directive
-	insertDirective := regexp.MustCompile(`\${{\s*insert\s*}}`)
-	for i := 0; i < len(node.Content)/2; i++ {
-		changed := func() error {
-			if ret == nil {
-				ret = &yaml.Node{}
-				if err := ret.Encode(node); err != nil {
-					return err
-				}
-				ret.Content = ret.Content[:i*2]
-			}
-			return nil
-		}
-		k := node.Content[i*2]
-		v := node.Content[i*2+1]
-		ev, err := ee.evaluateYamlNodeInternal(ctx, v)
-		if err != nil {
-			return nil, err
-		}
-		if ev != nil {
-			if err := changed(); err != nil {
-				return nil, err
-			}
-		} else {
-			ev = v
-		}
-		var sk string
-		// Merge the nested map of the insert directive
-		if k.Decode(&sk) == nil && insertDirective.MatchString(sk) {
-			if ev.Kind != yaml.MappingNode {
-				return nil, fmt.Errorf("failed to insert node %v into mapping %v unexpected type %v expected MappingNode", ev, node, ev.Kind)
-			}
-			if err := changed(); err != nil {
-				return nil, err
-			}
-			ret.Content = append(ret.Content, ev.Content...)
-		} else {
-			ek, err := ee.evaluateYamlNodeInternal(ctx, k)
-			if err != nil {
-				return nil, err
-			}
-			if ek != nil {
-				if err := changed(); err != nil {
-					return nil, err
-				}
-			} else {
-				ek = k
-			}
-			if ret != nil {
-				ret.Content = append(ret.Content, ek, ev)
-			}
-		}
-	}
-	return ret, nil
-}
-
-func (ee expressionEvaluator) evaluateSequenceYamlNode(ctx context.Context, node *yaml.Node) (*yaml.Node, error) {
-	var ret *yaml.Node
-	for i := 0; i < len(node.Content); i++ {
-		v := node.Content[i]
-		// Preserve nested sequences
-		wasseq := v.Kind == yaml.SequenceNode
-		ev, err := ee.evaluateYamlNodeInternal(ctx, v)
-		if err != nil {
-			return nil, err
-		}
-		if ev != nil {
-			if ret == nil {
-				ret = &yaml.Node{}
-				if err := ret.Encode(node); err != nil {
-					return nil, err
-				}
-				ret.Content = ret.Content[:i]
-			}
-			// GitHub has this undocumented feature to merge sequences / arrays
-			// We have a nested sequence via evaluation, merge the arrays
-			if ev.Kind == yaml.SequenceNode && !wasseq {
-				ret.Content = append(ret.Content, ev.Content...)
-			} else {
-				ret.Content = append(ret.Content, ev)
-			}
-		} else if ret != nil {
-			ret.Content = append(ret.Content, v)
-		}
-	}
-	return ret, nil
-}
-
-func (ee expressionEvaluator) evaluateYamlNodeInternal(ctx context.Context, node *yaml.Node) (*yaml.Node, error) {
-	switch node.Kind {
-	case yaml.ScalarNode:
-		return ee.evaluateScalarYamlNode(ctx, node)
-	case yaml.MappingNode:
-		return ee.evaluateMappingYamlNode(ctx, node)
-	case yaml.SequenceNode:
-		return ee.evaluateSequenceYamlNode(ctx, node)
-	default:
-		return nil, nil //nolint:nilnil // pre-existing issue from nektos/act
-	}
+// shared returns the evaluation layer of the shared library, bound to this context so the
+// evaluation of every single expression is still logged and masked here.
+func (ee expressionEvaluator) shared(ctx context.Context) expreval.Evaluator {
+	return expreval.New(func(in string, defaultStatusCheck exprparser.DefaultStatusCheck) (any, error) {
+		return ee.evaluate(ctx, in, defaultStatusCheck)
+	})
 }
 
 func (ee expressionEvaluator) EvaluateYamlNode(ctx context.Context, node *yaml.Node) error {
-	ret, err := ee.evaluateYamlNodeInternal(ctx, node)
-	if err != nil {
-		return err
-	}
-	if ret != nil {
-		return ret.Decode(node)
-	}
-	return nil
+	return ee.shared(ctx).EvaluateYamlNode(node)
 }
 
 func (ee expressionEvaluator) Interpolate(ctx context.Context, in string) string {
@@ -377,138 +255,16 @@ func (ee expressionEvaluator) Interpolate(ctx context.Context, in string) string
 	return out
 }
 
-// interpolate evaluates every part on its own, so a malformed one cannot restructure its neighbours
 func (ee expressionEvaluator) interpolate(ctx context.Context, in string) (string, error) {
-	parts, err := splitSubExpressions(in)
-	if err != nil {
-		return "", err
-	}
-	if len(parts) == 1 && !parts[0].isExpr {
-		return in, nil
-	}
-	var out strings.Builder
-	out.Grow(len(in))
-	for _, part := range parts {
-		if !part.isExpr {
-			out.WriteString(part.text)
-			continue
-		}
-		evaluated, err := ee.evaluate(ctx, part.text, exprparser.DefaultStatusCheckNone)
-		if err != nil {
-			return "", err
-		}
-		out.WriteString(exprparser.CoerceToString(evaluated))
-	}
-	return out.String(), nil
-}
-
-// evaluateScalar keeps the type of a lone expression, so `${{ fromJSON('[1,2]') }}` stays an array
-func (ee expressionEvaluator) evaluateScalar(ctx context.Context, in string) (any, error) {
-	parts, err := splitSubExpressions(in)
-	if err != nil {
-		return nil, err
-	}
-	if len(parts) == 1 && parts[0].isExpr {
-		return ee.evaluate(ctx, parts[0].text, exprparser.DefaultStatusCheckNone)
-	}
-	return ee.interpolate(ctx, in)
+	return ee.shared(ctx).Interpolate(in)
 }
 
 // EvalBool evaluates an expression against given evaluator. An `if:` is an expression even without
 // `${{ }}`, while literal text around one makes the whole value a string.
 func EvalBool(ctx context.Context, evaluator ExpressionEvaluator, expr string, defaultStatusCheck exprparser.DefaultStatusCheck) (bool, error) {
-	parts, err := splitSubExpressions(expr)
-	if err != nil {
-		return false, err
-	}
-	if len(parts) == 1 {
-		evaluated, err := evaluator.evaluate(ctx, parts[0].text, defaultStatusCheck)
-		if err != nil {
-			return false, err
-		}
-		return exprparser.IsTruthy(evaluated), nil
-	}
-
-	// mixed content is a string, so the status check applies to it separately
-	if defaultStatusCheck != exprparser.DefaultStatusCheckNone && !callsStatusFunction(parts) {
-		status, err := evaluator.evaluate(ctx, "", defaultStatusCheck)
-		if err != nil {
-			return false, err
-		}
-		if !exprparser.IsTruthy(status) {
-			return false, nil
-		}
-	}
-	interpolated, err := evaluator.interpolate(ctx, expr)
-	if err != nil {
-		return false, err
-	}
-	return exprparser.IsTruthy(interpolated), nil
-}
-
-// callsStatusFunction reports whether any part calls a status function. A part that does not parse
-// counts as one, so the evaluation reports it against the real values.
-func callsStatusFunction(parts []exprPart) bool {
-	for _, part := range parts {
-		if !part.isExpr {
-			continue
-		}
-		// The lexer needs the closing `}}` that the scanner strips.
-		exprNode, err := actionlint.NewExprParser().Parse(actionlint.NewExprLexer(part.text + "}}"))
-		if err != nil || exprparser.CallsStatusFunction(exprNode) {
-			return true
-		}
-	}
-	return false
-}
-
-type exprPart struct {
-	text   string
-	isExpr bool
-}
-
-// splitSubExpressions splits in the way GitHub's template reader does, leaving a value without a
-// complete expression literal.
-func splitSubExpressions(in string) ([]exprPart, error) {
-	if !strings.Contains(in, "${{") || !strings.Contains(in, "}}") {
-		return []exprPart{{text: in}}, nil
-	}
-
-	parts := make([]exprPart, 0, 2*strings.Count(in, "${{")+1)
-	for {
-		start := strings.Index(in, "${{")
-		if start < 0 {
-			if in != "" {
-				parts = append(parts, exprPart{text: in})
-			}
-			return parts, nil
-		}
-		if start > 0 {
-			parts = append(parts, exprPart{text: in[:start]})
-		}
-		rest := in[start+len("${{"):]
-		end := indexExprEnd(rest)
-		if end < 0 {
-			return nil, errors.New("unclosed expression")
-		}
-		parts = append(parts, exprPart{text: strings.TrimSpace(rest[:end]), isExpr: true})
-		in = rest[end+len("}}"):]
-	}
-}
-
-// indexExprEnd returns the offset of the `}}` ending an expression, or -1. A quote toggles string
-// state, so a `}}` inside a string does not end it.
-func indexExprEnd(in string) int {
-	inString := false
-	for i := range len(in) {
-		switch {
-		case in[i] == '\'':
-			inString = !inString
-		case !inString && in[i] == '}' && i+1 < len(in) && in[i+1] == '}':
-			return i
-		}
-	}
-	return -1
+	return expreval.New(func(in string, dsc exprparser.DefaultStatusCheck) (any, error) {
+		return evaluator.evaluate(ctx, in, dsc)
+	}).EvalBool(expr, defaultStatusCheck)
 }
 
 func getEvaluatorInputs(ctx context.Context, rc *RunContext, step step, ghc *model.GithubContext) map[string]any {