What causes "bad regex: " in Tencent/matrix?

Pass a non-empty regex string to addClassNamePattern.

Tencent/matrix · error · IllegalArgumentException

bad regex:

Error message

bad regex:

What it means

ExcludedBmps.BuilderWithParams.addClassNamePattern compiles the caller-supplied regex into a Pattern for class-name exclusion rules. A null or empty-string regex is rejected up front with IllegalArgumentException so Pattern.compile never receives invalid input at this point.

Solutions

Pass a non-empty regex string to addClassNamePattern.
Validate config-provided regexes before invoking the builder and skip empty entries.
Default to a sensible pattern or omit the rule entirely when the config value is missing.

Example fix

// before
builder.addClassNamePattern(config.getClassNameRegex(), false);
// after
String regex = config.getClassNameRegex();
if (regex != null && !regex.isEmpty()) {
    builder.addClassNamePattern(regex, false);
}

Defensive patterns

Strategy: validation

Validate before calling

if (regex == null || regex.isEmpty()) { skipRule(); } else { builder.addClassNamePattern(regex, forGCRootOnly); }

Try / catch

try { builder.addClassNamePattern(regex, false); } catch (IllegalArgumentException e) { log.warn("skipping empty regex rule"); }

Prevention

Validate config-sourced regexes before building exclusions
Omit empty rules instead of passing empty strings
Centralize exclusion-pattern construction in one validated helper

When it happens

Trigger: Calling addClassNamePattern(null, ...) or addClassNamePattern("", ...) while building the excluded-references/Bitmap exclusion configuration.

Common situations: Building exclusion config from external config files/remote parameters where the regex key is absent or empty; programmatic builder calls where a variable holding the pattern was never set.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of Tencent/matrix@3b8293bd65 (2026-09-08). Data as JSON: /api/errors/7f5cb27360fab3cd. Report an issue: GitHub.

Appendix: source

Thrown at matrix/matrix-android/matrix-resource-canary/matrix-resource-canary-analyzer/src/main/java/com/tencent/matrix/resource/analyzer/model/ExcludedBmps.java:61

        mClassNamePatterns = Collections.unmodifiableSet(builder.mClassNamePatterns);
    }

    public static Builder builder() {
        return new BuilderWithParams();
    }

    public interface Builder extends ExcludedRefs.Builder {
        Builder addClassNamePattern(String regex, boolean forGCRootOnly);
        ExcludedBmps build();
    }

    static final class BuilderWithParams extends ExcludedRefs.BuilderWithParams implements Builder {
        final Set<PatternInfo> mClassNamePatterns = new HashSet<>();

        @Override
        public Builder addClassNamePattern(String regex, boolean forGCRootOnly) {
            if (regex == null || regex.length() == 0) {
                throw new IllegalArgumentException("bad regex: " + regex);
            }
            mClassNamePatterns.add(new PatternInfo(Pattern.compile(regex), forGCRootOnly));
            return this;
        }

        @Override
        public ExcludedBmps build() {
            return new ExcludedBmps(this);
        }
    }
}

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