Wrong typing of SourceMap.version

[theseanl]

• Rollup Version: 1.16.2
• Operating System (or Browser):
• Node Version: v12.4.0

How Do We Reproduce?

Try using map property of OutputBundle object in generateBundle hook
as a return value { code, map } of a load hook

Expected Behavior

Does not produce any type error.

Actual Behavior

[tsserver 2322] [E] Type '{ file: string; mappings: string; names: string[];   
sources: string[]; sourcesContent: string[]; version: string; toString():       
string; toUrl(): string; }' is not assignable to type 'string |                
ExistingRawSourceMap | { mappings: ""; }'.                                     
Type '{ file: string; mappings: string; names: string[]; sources: string[];  
sourcesContent: string[]; version: string; toString(): string; toUrl(): string 
; }' is not assignable to type 'ExistingRawSourceMap'.                         
Types of property 'version' are incompatible.    

There is a wrong type definition of SourceMap.version in https://github.com/rollup/rollup/blob/master/src/rollup/types.d.ts#L59
magic-string sets the version property as 3, but the type declaration declares its type as string.

This is a propagation of a wrong type declaration of magic-string package, which is fixed in master branch in this Feb but not yet published to NPM: Rich-Harris/magic-string@b6fd47d

This prevents e.g. feeding OutputChunk output from generateBundle as a return value of another rollup plugin's load hook.

In order to resolve this issue, magic-string package must be updated in NPM with the current master branch, its version in rollup must be increased, and the type in src/rollup/type.d.ts must be updated.

[lukastaegert]

Fix at #2976