processImport seems unnecessarily slow due to graphql.print

[tlivings]

processImport : https://github.com/ardatan/graphql-tools/blob/master/packages/import/src/index.ts#L69

This function:

1. parses a document from a file,
2. iterates through each definition
3. prints the definition to a string
4. appends the string definition to a string of all definitions
5. create a source from the string
6. return the source

This results in unnecessarily bad performance as seen in this attached image:

However, this can simply be boiled down to:

1. parse the document from a file
2. append definitions to a new source
3. return the source

Which results in a reduction of processing time:

Code illustration:

export function processImport(
    filePath: string,
    cwd = cwdFactory(),
    predefinedImports: Record<string, string> = {},
    visitedFiles: VisitedFilesMap = new Map(),
  ): DocumentNode {
    const set = visitFile(filePath, join(cwd + '/root.graphql'), visitedFiles, predefinedImports);

    const document = {
        kind: Kind.DOCUMENT,
        definitions: [],
    };

    for (const defs of set.values()) {
        for (const def of defs) {
            document.definitions.push(def);
        }
    }

    return document;
}

As far as I can tell this is functionally the same without adding the overhead of printing and then re-parsing every definition.

[ardatan]

PRs are welcome!