fix: when src is not local, basename is not fully describing the filename

[jbedard]

Changes are visible to end-users: no

Test plan

• Covered by existing test cases
• New test cases added

[alexeagle]

is this going to be inconsistent? Shouldn't ALL paths in the sources here become repo-relative?

[jbedard]

You mean throughout all test cases?

By default these sources are relative to the .map file, so no path navigation is needed when the .ts and .map are side-by-side. The exception being when an alternative root is specified (this fix), or when root_dir|out_dir are used to modify the path then we need to navigate there.

[alexeagle]

The build rule that generated this was

rules_swc/examples/source_root/BUILD.bazel

Line 21 in 8864f85

source_root = "../../../debug/source",

right?
I don't see how the relative location for the expected.js needs an extra examples/source_root to navigate back to the in.ts file in this case. It seems like the logic has to be updated to read the value passed to the source_root

[jbedard]

I think either one actually works when there is 1 .map for each .js. The "examples/source_root" path needs to live in one of the two so when you append them you get "examples/source_root/in.ts". But sourcemaps were designed to work with 1 .map for N .js and I think we should align with how that works, in which case the sources needs that path in it.