Fix if statement non-boolean values

CHANGELOG.md

@@ -14,6 +14,7 @@ All notable changes to this project will be documented in this file.
 ### Fixed
 
 - The `javascript` processor now handles module imports correctly.
+- Bloblang `if` statements now provide explicit errors when query expressions resolve to non-boolean values.
 
 ### Changed
 

internal/bloblang/query/expression.go

@@ -91,7 +91,12 @@ func NewIfFunction(queryFn, ifFn Function, elseIfs []ElseIf, elseFn Function) Fu
 		if err != nil {
 			return nil, fmt.Errorf("failed to check if condition: %w", err)
 		}
-		if queryRes, _ := queryVal.(bool); queryRes {
+
+		queryRes, isBool := queryVal.(bool)
+		if !isBool {
+			return nil, fmt.Errorf("%v resolved to a non-boolean value %v (%T)", queryFn.Annotation(), queryVal, queryVal)
+		}
+		if queryRes {
 			return ifFn.Exec(ctx)
 		}
 
@@ -100,7 +105,11 @@ func NewIfFunction(queryFn, ifFn Function, elseIfs []ElseIf, elseFn Function) Fu
 			if err != nil {
 				return nil, fmt.Errorf("failed to check if condition %v: %w", i+1, err)
 			}
-			if queryRes, _ := queryVal.(bool); queryRes {
+			queryRes, isBool := queryVal.(bool)
+			if !isBool {
+				return nil, fmt.Errorf("%v resolved to a non-boolean value %v (%T)", eFn.QueryFn.Annotation(), queryVal, queryVal)
+			}
+			if queryRes {
 				return eFn.MapFn.Exec(ctx)
 			}
 		}

internal/bloblang/query/expression_test.go

@@ -1,7 +1,6 @@
 package query
 
 import (
-	"errors"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -24,12 +23,12 @@ func TestExpressions(t *testing.T) {
 	}
 
 	tests := map[string]struct {
-		input    Function
-		value    *any
-		output   any
-		err      error
-		messages []easyMsg
-		index    int
+		input       Function
+		value       *any
+		output      any
+		errContains string
+		messages    []easyMsg
+		index       int
 	}{
 		"if false": {
 			input: NewIfFunction(
@@ -107,22 +106,22 @@ func TestExpressions(t *testing.T) {
 				nil,
 				NewLiteralFunction("", "bar"),
 			),
-			err: errors.New("failed to check if condition: variables were undefined"),
+			errContains: "failed to check if condition: variables were undefined",
 		},
 		"match context fails": {
 			input: NewMatchFunction(
 				NewVarFunction("doesnt exist"),
 				NewMatchCase(NewLiteralFunction("", true), NewLiteralFunction("", "foo")),
 			),
-			err: errors.New("variables were undefined"),
+			errContains: "variables were undefined",
 		},
 		"match first case fails": {
 			input: NewMatchFunction(
 				NewLiteralFunction("", "context"),
 				NewMatchCase(NewVarFunction("doesnt exist"), NewLiteralFunction("", "foo")),
 				NewMatchCase(NewLiteralFunction("", true), NewLiteralFunction("", "bar")),
 			),
-			err: errors.New("failed to check match case 0: variables were undefined"),
+			errContains: "failed to check match case 0: variables were undefined",
 		},
 		"match second case fails": {
 			input: NewMatchFunction(
@@ -227,6 +226,15 @@ func TestExpressions(t *testing.T) {
 			}(),
 			output: []any{23},
 		},
+		"non-boolean literal": {
+			input: NewIfFunction(
+				NewLiteralFunction("", "hello world"),
+				NewLiteralFunction("", "foo"),
+				nil,
+				NewLiteralFunction("", "buz"),
+			),
+			errContains: "string literal resolved to a non-boolean value hello world",
+		},
 	}
 
 	for name, test := range tests {
@@ -251,8 +259,9 @@ func TestExpressions(t *testing.T) {
 					Index:    test.index,
 					MsgBatch: msg,
 				}.WithValueFunc(func() *any { return test.value }))
-				if test.err != nil {
-					require.EqualError(t, err, test.err.Error())
+				if test.errContains != "" {
+					require.Error(t, err)
+					require.Contains(t, err.Error(), test.errContains)
 				} else {
 					require.NoError(t, err)
 				}