fix: coerce every expression value kind to a string and drop the format() panic (#1135)

`coerceToString` covered only a few kinds and returned the unconverted `reflect.Value` for the rest, so callers rendered contexts as `<*model.GithubContext Value>` and mangled sized integers and floats the same way. It now returns a string, which makes that placeholder unrepresentable, and is exported as `CoerceToString` so Gitea can drop its own diverging copy. It also takes an already reflected value, so internal callers need no conversion and no guard against the zero `Value`.

`format()` panicked whenever a lone `}` was followed by anything other than another `}`. Only a trailing `}` reached the existing unmatched-brace check, so an expression such as `format('a}b')`, which any workflow can write, took the process down instead. It now returns that same error.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1135
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

act/exprparser/functions.go

@@ -28,8 +28,8 @@ func (impl *interperterImpl) contains(search, item reflect.Value) (bool, error)
 	switch search.Kind() {
 	case reflect.String, reflect.Int, reflect.Float64, reflect.Bool, reflect.Invalid:
 		return strings.Contains(
-			strings.ToLower(impl.coerceToString(search).String()),
-			strings.ToLower(impl.coerceToString(item).String()),
+			strings.ToLower(CoerceToString(search)),
+			strings.ToLower(CoerceToString(item)),
 		), nil
 
 	case reflect.Slice:
@@ -51,15 +51,15 @@ func (impl *interperterImpl) contains(search, item reflect.Value) (bool, error)
 
 func (impl *interperterImpl) startsWith(searchString, searchValue reflect.Value) (bool, error) { //nolint:unparam // pre-existing issue from nektos/act
 	return strings.HasPrefix(
-		strings.ToLower(impl.coerceToString(searchString).String()),
-		strings.ToLower(impl.coerceToString(searchValue).String()),
+		strings.ToLower(CoerceToString(searchString)),
+		strings.ToLower(CoerceToString(searchValue)),
 	), nil
 }
 
 func (impl *interperterImpl) endsWith(searchString, searchValue reflect.Value) (bool, error) { //nolint:unparam // pre-existing issue from nektos/act
 	return strings.HasSuffix(
-		strings.ToLower(impl.coerceToString(searchString).String()),
-		strings.ToLower(impl.coerceToString(searchValue).String()),
+		strings.ToLower(CoerceToString(searchString)),
+		strings.ToLower(CoerceToString(searchValue)),
 	), nil
 }
 
@@ -70,7 +70,7 @@ const (
 )
 
 func (impl *interperterImpl) format(str reflect.Value, replaceValue ...reflect.Value) (string, error) {
-	input := impl.coerceToString(str).String()
+	input := CoerceToString(str)
 	var output strings.Builder
 	replacementIndex := ""
 
@@ -108,7 +108,7 @@ func (impl *interperterImpl) format(str reflect.Value, replaceValue ...reflect.V
 					return "", fmt.Errorf("The following format string references more arguments than were supplied: '%s'", input)
 				}
 
-				output.WriteString(impl.coerceToString(replaceValue[index]).String())
+				output.WriteString(CoerceToString(replaceValue[index]))
 
 				state = passThrough
 
@@ -124,7 +124,7 @@ func (impl *interperterImpl) format(str reflect.Value, replaceValue ...reflect.V
 				state = passThrough
 
 			default:
-				panic("Invalid format parser state")
+				return "", fmt.Errorf("Closing bracket without opening one. The following format string is invalid: '%s'", input)
 			}
 		}
 	}
@@ -143,17 +143,17 @@ func (impl *interperterImpl) format(str reflect.Value, replaceValue ...reflect.V
 }
 
 func (impl *interperterImpl) join(array, sep reflect.Value) (string, error) { //nolint:unparam // pre-existing issue from nektos/act
-	separator := impl.coerceToString(sep).String()
+	separator := CoerceToString(sep)
 	switch array.Kind() {
 	case reflect.Slice:
 		var items []string
 		for i := 0; i < array.Len(); i++ {
-			items = append(items, impl.coerceToString(array.Index(i).Elem()).String())
+			items = append(items, CoerceToString(array.Index(i)))
 		}
 
 		return strings.Join(items, separator), nil
 	default:
-		return strings.Join([]string{impl.coerceToString(array).String()}, separator), nil
+		return strings.Join([]string{CoerceToString(array)}, separator), nil
 	}
 }
 

act/exprparser/functions_test.go

@@ -121,6 +121,7 @@ func TestFunctionJoin(t *testing.T) {
 		{"join(fromJSON('[\"a\", \"b\", null]'), null)", "ab", "join-number"},
 		{"join(fromJSON('[\"a\", \"b\"]'))", "a,b", "join-number"},
 		{"join(fromJSON('[\"a\", \"b\", null]'), 1)", "a1b1", "join-number"},
+		{"join(fromJSON('[1, true, null]'), '-')", "1-true-", "join-mixed-types"},
 	}
 
 	env := &EvaluationEnvironment{}
@@ -230,8 +231,10 @@ func TestFunctionFormat(t *testing.T) {
 		{`format('Hello "{0}" {1} {2} {3} {4}', null, true, -3.14, NaN, Infinity)`, `Hello "" true -3.14 NaN Infinity`, nil, "format-with-primitives"},
 		{`format('Hello "{0}" {1} {2}', fromJSON('[0, true, "abc"]'), fromJSON('[{"a":1}]'), fromJSON('{"a":{"b":1}}'))`, `Hello "Array" Array Object`, nil, "format-with-complex-types"},
 		{"format(true)", "true", nil, "format-with-primitive-args"},
+		{"format('{0}', github)", "Object", nil, "format-with-context"},
 		{"format('echo Hello {0} ${{Test}}', github.undefined_property)", "echo Hello  ${Test}", nil, "format-with-undefined-value"},
 		{"format('{0}}', '{1}', 'World')", nil, "Closing bracket without opening one. The following format string is invalid: '{0}}'", "format-invalid-format-string"},
+		{"format('a}b')", nil, "Closing bracket without opening one. The following format string is invalid: 'a}b'", "format-unmatched-closing-brace"},
 		{"format('{0', '{1}', 'World')", nil, "Unclosed brackets. The following format string is invalid: '{0'", "format-invalid-format-string"},
 		{"format('{2}', '{1}', 'World')", "", "The following format string references more arguments than were supplied: '{2}'", "format-invalid-replacement-reference"},
 		{"format('{2147483648}')", "", "The following format string is invalid: '{2147483648}'", "format-invalid-replacement-reference"},

act/exprparser/interpreter.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"math"
 	"reflect"
+	"strconv"
 	"strings"
 
 	"gitea.com/gitea/runner/act/model"
@@ -429,41 +430,54 @@ func (impl *interperterImpl) coerceToNumber(value reflect.Value) reflect.Value {
 	return reflect.ValueOf(math.NaN())
 }
 
-func (impl *interperterImpl) coerceToString(value reflect.Value) reflect.Value {
-	switch value.Kind() {
-	case reflect.Invalid:
-		return reflect.ValueOf("")
-
-	case reflect.Bool:
-		switch value.Bool() {
-		case true:
-			return reflect.ValueOf("true")
-		case false:
-			return reflect.ValueOf("false")
-		}
-
-	case reflect.String:
-		return value
-
-	case reflect.Int:
-		return reflect.ValueOf(fmt.Sprint(value))
-
-	case reflect.Float64:
-		if math.IsInf(value.Float(), 1) {
-			return reflect.ValueOf("Infinity")
-		} else if math.IsInf(value.Float(), -1) {
-			return reflect.ValueOf("-Infinity")
-		}
-		return reflect.ValueOf(fmt.Sprintf("%.15G", value.Float()))
-
-	case reflect.Slice:
-		return reflect.ValueOf("Array")
-
-	case reflect.Map:
-		return reflect.ValueOf("Object")
+// CoerceToString converts an evaluated expression value to a string the way GitHub does,
+// see https://docs.github.com/en/actions/reference/workflows-and-actions/expressions#operators
+// An already reflected value is accepted as-is, since Interface() would panic on an invalid one.
+func CoerceToString(v any) string {
+	value, ok := v.(reflect.Value)
+	if !ok {
+		value = reflect.ValueOf(v)
 	}
 
-	return value
+	switch value.Kind() {
+	case reflect.Invalid:
+		return ""
+
+	case reflect.Bool:
+		return strconv.FormatBool(value.Bool())
+
+	case reflect.String:
+		return value.String()
+
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return strconv.FormatInt(value.Int(), 10)
+
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		return strconv.FormatUint(value.Uint(), 10)
+
+	case reflect.Float32, reflect.Float64:
+		if math.IsInf(value.Float(), 1) {
+			return "Infinity"
+		} else if math.IsInf(value.Float(), -1) {
+			return "-Infinity"
+		}
+		return fmt.Sprintf("%.15G", value.Float())
+
+	case reflect.Slice, reflect.Array:
+		return "Array"
+
+	// contexts such as `github` are pointers to structs, so they stringify as objects too
+	case reflect.Map, reflect.Struct:
+		return "Object"
+
+	case reflect.Interface, reflect.Pointer:
+		if value.IsNil() {
+			return ""
+		}
+		return CoerceToString(value.Elem())
+	}
+
+	return fmt.Sprintf("%v", value)
 }
 
 func (impl *interperterImpl) compareString(left, right string, kind actionlint.CompareOpNodeKind) (bool, error) {

act/exprparser/interpreter_test.go

@@ -6,6 +6,7 @@ package exprparser
 
 import (
 	"math"
+	"reflect"
 	"testing"
 
 	"gitea.com/gitea/runner/act/model"
@@ -633,3 +634,51 @@ func TestContexts(t *testing.T) {
 		})
 	}
 }
+
+func TestCoerceToString(t *testing.T) {
+	type object struct{ Name string }
+	obj := object{Name: "x"}
+	var nilPointer *object
+	var nilMap map[string]any
+	var nilSlice []any
+
+	table := []struct {
+		input    any
+		expected string
+		name     string
+	}{
+		{nil, "", "null"},
+		{true, "true", "true"},
+		{false, "false", "false"},
+		{"foo", "foo", "string"},
+		{"", "", "empty-string"},
+		{123, "123", "int"},
+		{int64(-9), "-9", "int64"},
+		{uint8(7), "7", "uint8"},
+		{1.0, "1", "float-integral"},
+		{-9.7, "-9.7", "float"},
+		{2.99e-2, "0.0299", "float-exponential"},
+		{1e21, "1E+21", "float-large"},
+		{float32(1.5), "1.5", "float32"},
+		{math.NaN(), "NaN", "nan"},
+		{math.Inf(1), "Infinity", "positive-infinity"},
+		{math.Inf(-1), "-Infinity", "negative-infinity"},
+		{[]any{1, 2}, "Array", "slice"},
+		{nilSlice, "Array", "nil-slice"},
+		{[2]int{1, 2}, "Array", "fixed-size-array"},
+		{map[string]any{"a": 1}, "Object", "map"},
+		{nilMap, "Object", "nil-map"},
+		{obj, "Object", "struct"},
+		{&obj, "Object", "pointer-to-struct"},
+		{nilPointer, "", "nil-pointer"},
+		{&model.GithubContext{Action: "push"}, "Object", "github-context"},
+		{reflect.ValueOf(42), "42", "reflected-value"},
+		{reflect.Value{}, "", "invalid-reflected-value"},
+	}
+
+	for _, tt := range table {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.expected, CoerceToString(tt.input))
+		})
+	}
+}