Checker Diagnostics

Within initializeTypeChecker the following code exists:

// Initialize global symbol table
forEach(host.getSourceFiles(), file => {
    if (!isExternalModule(file)) {
        mergeSymbolTable(globals, file.locals);
    }
});

Which basically merges all the global symbols into the let globals: SymbolTable = {}; (in createTypeChecker) SymbolTable. mergeSymbolTable primarily calls mergeSymbol.