Create type aliases for unresolved type symbols by ahejlsberg · Pull Request #45976 · microsoft/TypeScript · GitHub

With this PR we create type aliases for unresolved symbols such that quick info and error messages list back the unresolved name instead of just any.

In this example where ItemData is not defined:

function foo(items: ItemData[]) {
    let item = items[0];
}

hovering over item and items now shows ItemData and ItemData[] where previously we'd just show any and any[]. Furthermore, hovering over the unresolved ItemData reference shows type ItemData = /*unresolved*/ any.

Fixes #45893.

Largely looks good, though I think this needs fourslash and possibly syntax server tests, specifically for

find all references
go to definition (at least the fact that it doesn't work)
quick info

Would be helpful to leave a comment on this one (pun intended).

Suggested change

      
                        const options = { removeComments: type !== unresolvedType };
          
                        // The unresolved type gets a synthesized comment on `any` 
          
                        // to hint to users that it's not a plain `any`.
          
                        // Otherwise, we always strip comments out.
          
                        const options = { removeComments: type !== unresolvedType };

Sure, I'll add a comment.

Why not just this? Seems like it'd be cheaper too.

Suggested change

      
                        return type === errorType || !!(type.flags & TypeFlags.Any && type.aliasSymbol);
          
                        return type === errorType || type === unresolvedType;

No, that wouldn't work. I'll add a clarifying comment, but basically we want to identify the special TypeFlags.Any types produced by getTypeForTypeAliasReference for an unresolved symbol. The sole purpose of unresolvedType is to act as the declared type for the special type alias symbols we create for unresolved names. The type is never actually returned by anything because getTypeForTypeAliasReference maps it into a special TypeFlags.Any type with an aliasSymbol.

Is there some way to make the type writer a little smarter here so that the team can differentiate between an unresolved and a concrete type?

We certainly have the ability to tell the difference, but what did you have in mind in terms of output? Remember that we're often dealing with composed types, e.g. for var v: Promise<await[]> we can't easily attach a comment to the await identifier in the output.

A parenthesized type might work like (/*unresolved*/ await)

I'm not really sure we want to do that. We're already generate an error at every reference to an unresolved symbol, I don't think we also want the extra noise in the type baselines.

I guess this doesn't technically fix #38836 because this only applies to types, right?

Right, this doesn't fix #38836. One complication there would be what scope to introduce the unknown value symbols into. Should they be locals of the innermost enclosing function, or just globals like we do for the type symbols? The latter typically makes sense for types, but less clear for unresolved value symbols.

or just globals like we do for the type symbols

I think just a global scope makes enough sense; if you do have a bunch of unresolved variables spread throughout your codebase, it's convenient to find-all-references, and likely to be a global anyhow; if it's mostly local (e.g. a user forgot to locally declare it), it doesn't really matter where you put it. But I'd understand if we wanted to take it one step at a time.

Looks like there's a few conflicts that need to be resolved.

# Conflicts: # src/compiler/checker.ts # tests/cases/fourslash/findReferencesJSXTagName.ts # tests/cases/fourslash/tsxFindAllReferences10.ts

Anders Hejlsberg (ahejlsberg) added 3 commits September 20, 2021 14:26

Create type aliases for unresolved type symbols

981cbb3

Accept new baselines

17332e1

Update fourslash tests

3d34ca7

TypeScript Bot (typescript-bot) assigned Anders Hejlsberg (ahejlsberg) Sep 20, 2021

TypeScript Bot (typescript-bot) added Author: Team For Milestone Bug PRs that fix a bug with a specific milestone labels Sep 20, 2021

Anders Hejlsberg (ahejlsberg) requested review from Daniel Rosenwasser (DanielRosenwasser) and Andrew Branch (andrewbranch) September 20, 2021 23:54

Daniel Rosenwasser (DanielRosenwasser) requested changes Sep 21, 2021

View reviewed changes

Unresolved import aliases create tagged unresolved symbols

8f828c4

Anders Hejlsberg (ahejlsberg) added 4 commits September 22, 2021 17:49

Add comments

891f961

Merge branch 'main' into fix45893

e949c85

# Conflicts: # src/compiler/checker.ts # tests/cases/fourslash/findReferencesJSXTagName.ts # tests/cases/fourslash/tsxFindAllReferences10.ts

Accept new baselines

5314074

Add fourslash tests

9d01571

Andrew Branch (andrewbranch) approved these changes Sep 23, 2021

View reviewed changes

Anders Hejlsberg (ahejlsberg) merged commit a4f9bf0 into main Sep 23, 2021

Anders Hejlsberg (ahejlsberg) deleted the fix45893 branch September 23, 2021 20:21

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

                           const typeNode = nodeBuilder.typeToTypeNode(type, enclosingDeclaration, toNodeBuilderFlags(flags) | NodeBuilderFlags.IgnoreErrors | (noTruncation ? NodeBuilderFlags.NoTruncation : 0), writer);
                           if (typeNode === undefined) return Debug.fail("should always get typenode");
-                          const options = { removeComments: true };
+                          const options = { removeComments: type !== unresolvedType };

                  // Legal to use 'await' in a type context.
                  var v: await;
-              >v : any
+              >v : await

	return type === errorType \|\| !!(type.flags & TypeFlags.Any && type.aliasSymbol);
	return type === errorType \|\| type === unresolvedType;

Create type aliases for unresolved type symbols by ahejlsberg · Pull Request #45976 · microsoft/TypeScript · GitHub

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Create type aliases for unresolved type symbols - #45976

Create type aliases for unresolved type symbols#45976Anders Hejlsberg (ahejlsberg) merged 8 commits intomainmicrosoft/TypeScript:mainfrom fix45893microsoft/TypeScript:fix45893Copy head branch name to clipboard

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Anders Hejlsberg (ahejlsberg) commented Sep 22, 2021

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Daniel Rosenwasser (DanielRosenwasser) commented Sep 22, 2021

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Create type aliases for unresolved type symbols#45976
Anders Hejlsberg (ahejlsberg) merged 8 commits into
mainfrom
fix45893

Daniel Rosenwasser (DanielRosenwasser) left a comment •
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Daniel Rosenwasser (DanielRosenwasser) commented Sep 21, 2021 •
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