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feat(core): present reason for cyclic references (#2061)
To help people debugging cyclic references, we now trace the "reason" a cyclic reference got added, so that we can present the conflicting references instead of just presenting an error. Fix the order of the error message, which was the wrong way around. Clean up references a little: - Split out `Reference` and `CfnReference`, which got conflated in an undesirable way. `Reference` is now officially the base class for all references, and `CfnReference` is only one implementation of it for CloudFormation references. - Make 'scope' required for references, the only place where it was potentially empty was for CFN Pseudo Parameters, refactored those to not use classes anymore (because there's no need to). - Get rid of 'Ref', the class wasn't being very useful. - Make a dependency Construct => Stack lazy (it was conflicting at load time with the Stack => Construct dependency which is more important).
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,115 @@ | ||
| import { Reference } from "./reference"; | ||
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| const CFN_REFERENCE_SYMBOL = Symbol('@aws-cdk/cdk.CfnReference'); | ||
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| /** | ||
| * A Token that represents a CloudFormation reference to another resource | ||
| * | ||
| * If these references are used in a different stack from where they are | ||
| * defined, appropriate CloudFormation `Export`s and `Fn::ImportValue`s will be | ||
| * synthesized automatically instead of the regular CloudFormation references. | ||
| * | ||
| * Additionally, the dependency between the stacks will be recorded, and the toolkit | ||
| * will make sure to deploy producing stack before the consuming stack. | ||
| * | ||
| * This magic happens in the prepare() phase, where consuming stacks will call | ||
| * `consumeFromStack` on these Tokens and if they happen to be exported by a different | ||
| * Stack, we'll register the dependency. | ||
| */ | ||
| export class CfnReference extends Reference { | ||
| /** | ||
| * Check whether this is actually a Reference | ||
| */ | ||
| public static isCfnReference(x: Token): x is CfnReference { | ||
| return (x as any)[CFN_REFERENCE_SYMBOL] === true; | ||
| } | ||
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| /** | ||
| * What stack this Token is pointing to | ||
| */ | ||
| private readonly producingStack?: Stack; | ||
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| /** | ||
| * The Tokens that should be returned for each consuming stack (as decided by the producing Stack) | ||
| */ | ||
| private readonly replacementTokens: Map<Stack, Token>; | ||
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| private readonly originalDisplayName: string; | ||
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| constructor(value: any, displayName: string, target: Construct) { | ||
| if (typeof(value) === 'function') { | ||
| throw new Error('Reference can only hold CloudFormation intrinsics (not a function)'); | ||
| } | ||
| // prepend scope path to display name | ||
| super(value, `${target.node.id}.${displayName}`, target); | ||
| this.originalDisplayName = displayName; | ||
| this.replacementTokens = new Map<Stack, Token>(); | ||
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| this.producingStack = target.node.stack; | ||
| Object.defineProperty(this, CFN_REFERENCE_SYMBOL, { value: true }); | ||
| } | ||
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| public resolve(context: ResolveContext): any { | ||
| // If we have a special token for this consuming stack, resolve that. Otherwise resolve as if | ||
| // we are in the same stack. | ||
| const token = this.replacementTokens.get(context.scope.node.stack); | ||
| if (token) { | ||
| return token.resolve(context); | ||
| } else { | ||
| return super.resolve(context); | ||
| } | ||
| } | ||
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| /** | ||
| * Register a stack this references is being consumed from. | ||
| */ | ||
| public consumeFromStack(consumingStack: Stack, consumingConstruct: IConstruct) { | ||
| if (this.producingStack && this.producingStack !== consumingStack && !this.replacementTokens.has(consumingStack)) { | ||
| // We're trying to resolve a cross-stack reference | ||
| consumingStack.addDependency(this.producingStack, `${consumingConstruct.node.path} -> ${this.target.node.path}.${this.originalDisplayName}`); | ||
| this.replacementTokens.set(consumingStack, this.exportValue(this, consumingStack)); | ||
| } | ||
| } | ||
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| /** | ||
| * Export a Token value for use in another stack | ||
| * | ||
| * Works by mutating the producing stack in-place. | ||
| */ | ||
| private exportValue(tokenValue: Token, consumingStack: Stack): Token { | ||
| const producingStack = this.producingStack!; | ||
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| if (producingStack.env.account !== consumingStack.env.account || producingStack.env.region !== consumingStack.env.region) { | ||
| throw new Error('Can only reference cross stacks in the same region and account.'); | ||
| } | ||
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| // Ensure a singleton "Exports" scoping Construct | ||
| // This mostly exists to trigger LogicalID munging, which would be | ||
| // disabled if we parented constructs directly under Stack. | ||
| // Also it nicely prevents likely construct name clashes | ||
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| const exportsName = 'Exports'; | ||
| let stackExports = producingStack.node.tryFindChild(exportsName) as Construct; | ||
| if (stackExports === undefined) { | ||
| stackExports = new Construct(producingStack, exportsName); | ||
| } | ||
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| // Ensure a singleton CfnOutput for this value | ||
| const resolved = producingStack.node.resolve(tokenValue); | ||
| const id = 'Output' + JSON.stringify(resolved); | ||
| let output = stackExports.node.tryFindChild(id) as CfnOutput; | ||
| if (!output) { | ||
| output = new CfnOutput(stackExports, id, { value: tokenValue }); | ||
| } | ||
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| // We want to return an actual FnImportValue Token here, but Fn.importValue() returns a 'string', | ||
| // so construct one in-place. | ||
| return new Token({ 'Fn::ImportValue': output.obtainExportName() }); | ||
| } | ||
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| } | ||
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| import { CfnOutput } from "./cfn-output"; | ||
| import { Construct, IConstruct } from "./construct"; | ||
| import { Stack } from "./stack"; | ||
| import { ResolveContext, Token } from "./token"; |
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