public String invoke()

in core/src/main/java/hudson/FilePath.java [2746:2848]
72 lines of code
22 McCabe index (conditional complexity)

            public String invoke(File dir, VirtualChannel channel) throws IOException, InterruptedException {
                if(fileMasks.startsWith("~"))
                    return Messages.FilePath_TildaDoesntWork();

                StringTokenizer tokens = new StringTokenizer(fileMasks,",");

                while(tokens.hasMoreTokens()) {
                    final String fileMask = tokens.nextToken().trim();
                    if(hasMatch(dir,fileMask,caseSensitive))
                        continue;   // no error on this portion
                    
                    // JENKINS-5253 - if we can get some match in case insensitive mode
                    // and user requested case sensitive match, notify the user
                    if (caseSensitive && hasMatch(dir, fileMask, false)) {
                        return Messages.FilePath_validateAntFileMask_matchWithCaseInsensitive(fileMask);
                    }

                    // in 1.172 we introduced an incompatible change to stop using ' ' as the separator
                    // so see if we can match by using ' ' as the separator
                    if(fileMask.contains(" ")) {
                        boolean matched = true;
                        for (String token : Util.tokenize(fileMask))
                            matched &= hasMatch(dir,token,caseSensitive);
                        if(matched)
                            return Messages.FilePath_validateAntFileMask_whitespaceSeparator();
                    }

                    // a common mistake is to assume the wrong base dir, and there are two variations
                    // to this: (1) the user gave us aa/bb/cc/dd where cc/dd was correct
                    // and (2) the user gave us cc/dd where aa/bb/cc/dd was correct.

                    {// check the (1) above first
                        String f=fileMask;
                        while(true) {
                            int idx = findSeparator(f);
                            if(idx==-1)     break;
                            f=f.substring(idx+1);

                            if(hasMatch(dir,f,caseSensitive))
                                return Messages.FilePath_validateAntFileMask_doesntMatchAndSuggest(fileMask,f);
                        }
                    }

                    {// check the (2) above next as this is more expensive.
                        // Try prepending "**/" to see if that results in a match
                        FileSet fs = Util.createFileSet(reading(dir),"**/"+fileMask);
                        fs.setCaseSensitive(caseSensitive);
                        DirectoryScanner ds = fs.getDirectoryScanner(new Project());
                        if(ds.getIncludedFilesCount()!=0) {
                            // try shorter name first so that the suggestion results in least amount of changes
                            String[] names = ds.getIncludedFiles();
                            Arrays.sort(names,SHORTER_STRING_FIRST);
                            for( String f : names) {
                                // now we want to decompose f to the leading portion that matched "**"
                                // and the trailing portion that matched the file mask, so that
                                // we can suggest the user error.
                                //
                                // this is not a very efficient/clever way to do it, but it's relatively simple

                                StringBuilder prefix = new StringBuilder();
                                while(true) {
                                    int idx = findSeparator(f);
                                    if(idx==-1)     break;

                                    prefix.append(f, 0, idx).append('/');
                                    f=f.substring(idx+1);
                                    if(hasMatch(dir,prefix+fileMask,caseSensitive))
                                        return Messages.FilePath_validateAntFileMask_doesntMatchAndSuggest(fileMask, prefix+fileMask);
                                }
                            }
                        }
                    }

                    {// finally, see if we can identify any sub portion that's valid. Otherwise bail out
                        String previous = null;
                        String pattern = fileMask;

                        while(true) {
                            if(hasMatch(dir,pattern,caseSensitive)) {
                                // found a match
                                if(previous==null)
                                    return Messages.FilePath_validateAntFileMask_portionMatchAndSuggest(fileMask,pattern);
                                else
                                    return Messages.FilePath_validateAntFileMask_portionMatchButPreviousNotMatchAndSuggest(fileMask,pattern,previous);
                            }

                            int idx = findSeparator(pattern);
                            if(idx<0) {// no more path component left to go back
                                if(pattern.equals(fileMask))
                                    return Messages.FilePath_validateAntFileMask_doesntMatchAnything(fileMask);
                                else
                                    return Messages.FilePath_validateAntFileMask_doesntMatchAnythingAndSuggest(fileMask,pattern);
                            }

                            // cut off the trailing component and try again
                            previous = pattern;
                            pattern = pattern.substring(0,idx);
                        }
                    }
                }

                return null; // no error
            }