cli fails generating artifacts

[santino]

Issue workflow progress

Progress of the issue based on the Contributor Workflow

• 1. The issue provides a reproduction available on Github, Stackblitz or CodeSandbox

Make sure to fork this template and run yarn generate in the terminal.

Please make sure Mesh package versions under package.json matches yours.

• 2. A failing test has been provided
• 3. A local solution has been provided
• 4. A pull request is pending review

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Describe the bug
Since the release of v0.78.12 the cli package has an issue that causes a failure on generating the Typescript artifacts.
This happens when working with a single data source and a transform in wrap mode.
This is the output:

💡 🕸️  Mesh Generating the unified schema
💡 🕸️  Mesh - Source1 Dereferencing the bundle
💡 🕸️  Mesh - Source1 Creating the GraphQL Schema from dereferenced schema
💡 🕸️  Mesh Generating artifacts
💡 🕸️  Mesh Generating index file in TypeScript
💥 🕸️  Mesh TypeError: Cannot read properties of undefined (reading 'get')
    at generateTsArtifacts (/Users/user/projects/mesh-project/node_modules/@graphql-mesh/cli/bin.js:251:70)
    at Object.handler (/Users/user/projects/mesh-project/node_modules/@graphql-mesh/cli/bin.js:1033:19)

To Reproduce
Steps to reproduce the behavior:

• Have a Mesh service that works on a single data source (hence no stitching required)
• Define a transform at the source level that supports both bare and wrap mode (e.g. naming convention, filterSchema, etc.)
• Omit the mode property in the transform config (or set it to wrap)
• Run the server

Expected behavior
The artifacts are generated correctly and the server runs as normal.

[santino]

Hey @ardatan, I thought I'd summarise my findings on this issue.

This happens because merger-bare is applied by default, at the root level, to the Mesh Config.
Merger-bare does not seem to play nice when used in a single data source (no merging actually required) and at least one wrap mode transform.
In a scenario like this, merger-stitching should be user as a default instead; so this seems to be the first thing to fix.
In fact, if I explicitly apply merger: stitching to the Mesh Config .yaml file, things work again as expected.

Clearly, this is just the initial part of the issue, because developers might still need to user merger: bare and it should just work.

The actual error is generated by generateTsArtifacts which expects a unified schema as first argument.
Then it tries to access the get property out of unifiedSchema.extensions.sourceMap, like this:

const transformedSchema = unifiedSchema.extensions.sourceMap.get(rawSource);

The problem, in this case, is that with this configuration (single data-source with merger-bare and wrap-mode transform) the extensions property in the unified schema resolves to [Object: null prototype] {} and so the sourceMap property is undefined.
Instead, in the case of a single source with merger-bare and bare-mode transform, the same extensions property does have sourceMap.get and so generateTsArtifacts can get the transformedSchema.

Hope this helps.