Unity-Technologies/UnityCsReference · error · ExpressionNotValidException

'{value}' is not valid in the expression

Error message

'{value}' is not valid in the expression

What it means

Thrown inside PopVersionString (VersionRanges.cs:171) while scanning a version-number token (between delimiters or around the comma separator) when a character is neither an allowed version character per IVersionTypeTraits.IsAllowedCharacter (digits, letters, '.', '-', and '/' for UnityVersion; digits, letters, '.', '-' for SemVersion) nor the wildcard '*'. NOTE: the exception message contains only the single offending character, not the whole expression, which makes it harder to locate.

Source

Thrown at Editor/Mono/Scripting/ScriptCompilation/VersionRanges.cs:171

            if (begin > end)
            {
                return null;
            }

            int count = 0;
            while (newBegin <= end)
            {
                var value = expression[newBegin];

                if (value == ',')
                {
                    newBegin++;
                    break;
                }

                if (!versionTypeTraits.IsAllowedCharacter(value) && value != '*')
                {
                    throw new ExpressionNotValidException($"'{value}' is not valid in the expression");
                }

                count++;
                newBegin++;
            }

            return expression.Substring(begin, count);
        }

        private struct ExpressionParsedData
        {
            public TVersion leftVersion;
            public TVersion rightVersion;
            public ExpressionTypeKey GenerateExpressionTypeKey;
        }
    }
}

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Remove interior whitespace: '[1.0, 2.0]' -> '[1.0,2.0]'.
2. Drop unsupported characters from version tokens: '1.0_2' -> '1.0.2'; strip '+build'.
3. Keep only allowed characters (digits, letters, '.', '-', '/', and the '*' wildcard) inside version tokens.
4. If you need a wildcard, use '*' as a body character (e.g. '[1.0,2.*]'); it is the only non-trait character permitted in the token body.

Example fix

// before
"[1.0, 2.0]"   // or "1.0_2"  or "[1.0,2.0+rc1]"
// after
"[1.0,2.0]"    // or "1.0.2"  or "[1.0,2.0]"

// Version-token body chars: digit, letter, '.', '-', '/', and '*' wildcard.
// Reject interior whitespace and punctuation BEFORE parsing.
static readonly char[] k_AllowedBodyExtras = { '.', '-', '/', '*' };
static bool BodyHasOnlyAllowedChars(string expr) {
    if (string.IsNullOrEmpty(expr)) return false;
    foreach (var c in expr) {
        if (c == ',' || c == '[' || c == ']' || c == '(' || c == ')') continue;
        if (char.IsDigit(c) || char.IsLetter(c)) continue;
        if (System.Array.IndexOf(k_AllowedBodyExtras, c) >= 0) continue;
        if (char.IsWhiteSpace(c)) return false;  // interior space — the #1 cause
        return false;
    }
    return true;
}
// Strongest check: run the full k_ValidRange regex, which has no interior spaces.

static bool HasNoInteriorSpaces(string e) =>
    !string.IsNullOrEmpty(e) && !e.Contains(" ") && !e.Contains("\t");

// NOTE: ex.Message contains ONLY the offending char, not the expression.
// Log the expression yourself for context.
try { var def = ranges.GetExpression(expr); }
catch (ExpressionNotValidException ex) {
    ReportToUser($"{expr}: character '{ex.Message}' is not allowed in a version token.");
}

When it happens

Trigger: A disallowed character inside a version token: '_', '+', space, '<', '>', '=', '@', '~', etc. The single most common case is a SPACE AFTER THE COMMA inside a range ('[1.0, 2.0]') — the right-side scan hits the space, which is neither an allowed char nor '*', so it throws with value=' '. Also '1.0_2', '1.0+build', '~1.0', '1.0@2'.

Common situations: Typing '[1.0, 2.0]' with a space after the comma (the Define-Constraints trimmer does not trim interior spaces); appending SemVer build metadata '1.0+001' (not supported by this tokenizer); using an underscore inside a pre-release tag.

Related errors

• Invalid character '{leftSymbol}' in expression
• Invalid character '{rightSymbol}' in expression
• Incomplete expression, missing symbol in start or end
• '{expression}' is not a valid expression
• Unknown expression: {expression}

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/85cfa5699ccbc69f. Report an issue: GitHub.