Control flow for constructor initialized properties by ahejlsberg · Pull Request #37920 · microsoft/TypeScript · GitHub

With this PR we use control flow analysis of this.xxx assignments in constructors to determine the types of properties that have no type annotations or initializers.

In .ts files we perform control flow analysis for properties declared with no type annotation or initializer when in noImplicitAny mode.
In .js files we perform control flow analysis for properties declared with no JSDoc type annotation or initializer, and properties with no explicit declaration but at least one this.xxx assignment in the constructor.

In the following example, control flow analysis determines the type of x to be string | number based on the this.x assignments in the constructor:

// Compile with --noImplicitAny
class C {
    x;  // string | number
    constructor(b: boolean) {
        if (b) {
            this.x = 'hello';
        }
        else {
            this.x = 42;
        }
    }
}

In .js files we would previously determine the type of a property with no explicit declaration from local analysis of all this.xxx assignments seen in the constructor and methods of the class. This analysis is less precise than control flow analysis, but we still use it as a fallback. With the increased precision of control flow analysis we now correctly discover properties that are conditionally (as opposed to definitely) initialized in constructors. We're also able to handle assignments of values that depend on previous assignment to the same property, as well as other scenarios that previously were deemed circular.

The baseline changes are mostly because constructor declared properties are now considered to have type any when they are assignment targets in the constructor body. This an effect of how CFA auto-typing works.

Fixes #37900.

…ents

Anders Hejlsberg (@ahejlsberg) do we have a test for the declaration emit of a property like this? afaik none of the cases in tests/cases/conformance/jsdoc/declarations/jsDeclarationsClasses.ts are that complex.

Wesley Wigham (@weswigham) Best I can tell there are several classes in that test that now have property types computed by CFA with no changes in baselines. I wouldn't expect any either since declaration emit just uses getTypeOfSymbol.

TypeScript Bot (@typescript-bot) user test this

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the parallelized community code test suite on this PR at df98d9c. You can monitor the build here.

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

Nathan Shively-Sanders (@sandersn) I'm looking at the user test suite baseline changes, and so far things seem reasonable. The increased precision of CFA causes more errors in places as expected, for example when CFA discovers that a property is conditionally (instead of definitely) initialized in the constructor or that a property has an auto-type array type.

The chrome-devtools errors are insanely hard to verify because there's no indentation in the code, but best I can tell they're to be expected.

I ran a before/after perf comparison of 10 runs of chrome-devtools-frontend, since it's a nice big code base with lots of functions.

Here's the average of 10 runs:

Before, time: 15.94 s
After, time: 16.21 s
1.66% slower.

Before, memory: 751.06 MB
After, memory: 757.27 MB
0.82% more memory.

Not that much difference actually.

(Anders Hejlsberg (@ahejlsberg) only one file in chrome-devtools-frontend is indentation-free, and it's a checked-in dependency. I always just skip that one.)

TypeScript Bot (@typescript-bot) user test this

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the parallelized community code test suite on this PR at 728d9cb. You can monitor the build here.

Nathan Shively-Sanders (@sandersn) Fixed some over eager widening in auto-typed assignments. User test baselines now look good. More errors because we figure out more types, but the errors are to be expected and some of them actually reveal questionable logic.

I tried to get some perf numbers by running tsc on chrome-devtools-frontend but there is so much variability in the numbers that I can't really see any appreciable difference.

…lizer

TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) run dt

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the extended test suite on this PR at ab993c2. You can monitor the build here.

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the parallelized Definitely Typed test suite on this PR at ab993c2. You can monitor the build here.

Heya Anders Hejlsberg (@ahejlsberg), I've started to run the parallelized community code test suite on this PR at ab993c2. You can monitor the build here.

Thinking of mixins, shouldn't we iterate through the base types list and get the property from the first base type which has it, rather than only checking the first base type?

No, classes never have more than one base class, mixins or not.

Anders Hejlsberg (ahejlsberg) added 2 commits April 12, 2020 15:27

Use CFA to determine types of properties declared by this.xxx assignm…

2fbab38

…ents

Accept new baselines

957d9e6

Anders Hejlsberg (ahejlsberg) mentioned this pull request Apr 12, 2020

this-property assignments should use autoType to get control flow narrowing #37900

Closed

Anders Hejlsberg (ahejlsberg) added 2 commits April 14, 2020 10:13

Also use CFA in constructor functions

6e0274a

Accept new baselines

df98d9c

Fix lint error

0c9c76a

TypeScript Bot (typescript-bot) mentioned this pull request Apr 14, 2020

🤖 User test baselines have changed for controlFlowConstructorProperties typescript-bot/TypeScript#21

Open

Only widen fresh literal types in CFA of assignment to auto-typed

728d9cb

Anders Hejlsberg (ahejlsberg) added 4 commits April 20, 2020 20:33

Auto-typing for declared properties with no type annotation or initia…

fa6fee8

…lizer

Add optionality if declaration includes '?' modifier

e6d7607

Always use CFA for properties with no initializer in .js files

33cbb82

Small fix

ab993c2

Anders Hejlsberg (ahejlsberg) changed the title Control flow for constructor properties Control flow for constructor initialized properties Apr 21, 2020

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request Apr 21, 2020

Design Meeting Notes, 4/17/2020 #38096

Closed

Nathan Shively-Sanders (sandersn) self-assigned this Apr 21, 2020

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request Apr 24, 2020

Design Meeting Notes, 4/24/2020 #38168

Closed

Wesley Wigham (weswigham) reviewed Apr 28, 2020

View reviewed changes

Wesley Wigham (weswigham) approved these changes Apr 28, 2020

View reviewed changes

Anders Hejlsberg (ahejlsberg) merged commit 3919042 into master Apr 28, 2020

Anders Hejlsberg (ahejlsberg) deleted the controlFlowConstructorProperties branch April 28, 2020 23:59

Anders Hejlsberg (ahejlsberg) added this to the TypeScript 4.0 milestone Apr 29, 2020

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request May 12, 2020

TypeScript 4.0 Iteration Plan #38510

Closed

Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025

+                      // Return the inherited type of the given property or undefined if property doesn't exist in a base class.
+                      function getTypeOfPropertyInBaseClass(property: Symbol) {
+                          const classType = getDeclaringClass(property);
+                          const baseClassType = classType && getBaseTypes(classType)[0];

Control flow for constructor initialized properties by ahejlsberg · Pull Request #37920 · microsoft/TypeScript · GitHub

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Control flow for constructor initialized properties - #37920

Control flow for constructor initialized properties#37920Anders Hejlsberg (ahejlsberg) merged 10 commits intomastermicrosoft/TypeScript:masterfrom controlFlowConstructorPropertiesmicrosoft/TypeScript:controlFlowConstructorPropertiesCopy head branch name to clipboard

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Control flow for constructor initialized properties#37920
Anders Hejlsberg (ahejlsberg) merged 10 commits into
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