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Symbols and Declarations Linking between a node and a symbol is performed by a few functions. One function that is used to bind the SourceFile node to the source file Symbol (in case of an external module) is the addDeclarationToSymbol function

Note : the Symbol for an external module source file is setup as flags : SymbolFlags.ValueModule and name: '"' + removeFileExtension(file.fileName) + '"').

function addDeclarationToSymbol(symbol: Symbol, node: Declaration, symbolFlags: SymbolFlags) { symbol.flags |= symbolFlags;

node.symbol = symbol;

if (!symbol.declarations) {
    symbol.declarations = [];
}
symbol.declarations.push(node);

if (symbolFlags & SymbolFlags.HasExports && !symbol.exports) {
    symbol.exports = {};
}

if (symbolFlags & SymbolFlags.HasMembers && !symbol.members) {
    symbol.members = {};
}

if (symbolFlags & SymbolFlags.Value && !symbol.valueDeclaration) {
    symbol.valueDeclaration = node;
}

} The important linking portions:

Creates a link to the Symbol from the AST node (node.symbol). Adds the node as one of the declarations of the Symbol (symbol.declarations). Declaration Declaration is just a node with an optional name. In types.ts

interface Declaration extends Node { _declarationBrand: any; name?: DeclarationName; }