Inconsistent behavior regarding sourcemaps with tsc and deno bundle

[yacinehmito]

In TypeScript, there are three compiler options that relate to source maps:

• sourceMap, which controls whether external source maps should be emitted
• inlineSourceMap, which controls whether inline source maps should be emitted
• inlineSources, which controls whether the original source code should be embedded in the source maps

There are interplay and incompatibilities between these options. Those are not properly taken into account in deno_emit.

I first encountered this when working on #98, which is meant to solve a few source map issues. I found that deno_emit sets inlineSourceMap to true by default and pretty much ignores everything else until it is manually set to false.

I suggested that deno_emit stop emitting inline source maps by default; @dsherret told me that, if it changes, then it is preferable for the default behavior to be consistent with deno bundle, until it is properly sunset.

I ran a program that automatically runs deno bundle, tsc and deno_emit on the same module for all combinations of the aforementioned options and looked at the output. The results are reported in the table below.

My proposal: I think deno_emit should follow the behavior of tsc. By default this will also match deno bundle as deno bundle never emits source maps and tsc doesn't when no options are provided.

---

Legend:

• ⬜️: no source map
• 🔳: inline source map
• 🔲: external source map
• ❌: errors

sourceMap	inlineSourceMap	inlineSources	deno bundle	tsc	deno_emit¹
not set	not set	not set	⬜️	⬜️	🔳
true	not set	not set	⬜️	🔲	🔳
false	not set	not set	⬜️	⬜️	🔳
not set	true	not set	⬜️	🔳	🔳
not set	false	not set	⬜️	⬜️	⬜️
true	true	not set	⬜️	❌²	🔳
true	false	not set	⬜️	🔲	🔲
false	true	not set	⬜️	🔳	🔳
false	false	not set	⬜️	⬜️	⬜️
not set	not set	true	⬜️	❌³	🔳
not set	not set	false	⬜️	⬜️	🔳
true	not set	true	⬜️	🔲	🔳
true	not set	false	⬜️	🔲	🔳
false	not set	true	⬜️	❌³	🔳
false	not set	false	⬜️	⬜️	🔳
not set	true	true	⬜️	🔳	🔳
not set	true	false	⬜️	🔳	🔳
not set	false	true	⬜️	❌³	⬜️
not set	false	false	⬜️	⬜️	⬜️
true	true	true	⬜️	❌²	🔳
true	true	false	⬜️	❌²	🔳
true	false	true	⬜️	🔲	🔲
true	false	false	⬜️	🔲	🔲
false	true	true	⬜️	🔳	🔳
false	true	false	⬜️	🔳	🔳
false	false	true	⬜️	❌³	⬜️
false	false	false	⬜️	⬜️	⬜️

¹ The output of bundle() in deno_emit; this is assuming that the compiler options are properly forwarded, per #98, as the current version always emit inline source maps.

² error TS5053: Option 'sourceMap' cannot be specified with option 'inlineSourceMap'.

³ error TS5051: Option 'inlineSources can only be used when either option '--inlineSourceMap' or option '--sourceMap' is provided.

[yacinehmito]

I think deno_emit should follow the behavior of tsc. By default this will also match deno bundle as deno bundle never emits source maps and tsc doesn't when no options are provided.

@dsherret What do you think? I have already written the tests to ensure this. Waiting for a go to implement.

[yacinehmito]

I implemented it, as it was pretty straightforward.

I say that the defaults are actually set in deno_ast, meaning that there were three possible places to perform the required validation:

• In deno_ast
• In the Rust lib of deno_emit
• In the TS wrapper for deno_emit

I did it in the TS wrapper because it was very easy, but let me know if another place is better.

I'll submit a PR once #97 is merged.

[dsherret]

I did it in the TS wrapper because it was very easy, but let me know if another place is better.

I just looked at the code and that seems good to do. The emit defaults in deno_ast are set for transpiling, so we should probably leave those as-is.