Fix extension crash triggered by incremental compilation

[mediremi]

This PR fixes an extension crash triggered by syntax errors in the current file when incremental compilation is enabled.

Background

#1167 updated compileContents to use a promisify'd version of child_process.execFile.

As mentioned in the execFile docs, it returns a rejected promise on non-zero exit codes:

If this method is invoked as its util.promisify()ed version, it returns a Promise for an Object with stdout and stderr properties. The returned ChildProcess instance is attached to the Promise as a child property. In case of an error (including any error resulting in an exit code other than 0), a rejected promise is returned, with the same error object given in the callback, but with two additional properties stdout and stderr.

However, compileContents assumes that execFile returns a resolved promise on non-zero exits:

rescript-vscode/server/src/incrementalCompilation.ts

Lines 711 to 715 in adf96f7

	const { stderr } = await execFilePromise(
	entry.project.bscBinaryLocation,
	callArgs,
	{ cwd, signal },
	);

and so ends up rethrowing this error (line 766):

rescript-vscode/server/src/incrementalCompilation.ts

Lines 757 to 767 in adf96f7

	} catch (error: any) {
	if (error.name === "AbortError") {
	getLogger().log(
	`Compilation of ${entry.file.sourceFileName} was aborted.`,
	);
	} else {
	getLogger().error(
	`Unexpected error during compilation of ${entry.file.sourceFileName}: ${error}`,
	);
	throw error;
	}

In turn, this makes the extension crash.

Fix

I added a .catch to check if error.stderr is non-empty, and if so return that. Otherwise, we throw the error so that we don't accidentally swallow e.g. ENOENT errors.

[mediremi]

This import was unused

[nojaf]

Did you run make format?