resolveDir was added here to solve #2975, in this PR #3003 (comment)

Would you check that this is no longer an issue after removing it? It would be great to add a test based on #2975 to your growing deps test suite (thanks for that by the way!)

resolveDir is removed on purpose.

I can describe the history of this bug.

#2975 and #3254 targets to same bug introduced in 8e1d3d8.

The original purpose of 8e1d3d8 is to aviod duplicated modules by separate entry imports from none-entry imports.

It introduced first version of resolveEntry util function:

function resolveEntry(id: string, isEntry: boolean) {
        const flatId = flattenId(id)
        if (flatId in qualified) {
          return isEntry
            ? {
                path: flatId,
                namespace: 'dep'
              }
            : {
                path: path.resolve(qualified[flatId])
              }
        }
      }

For none-entry import, using qualified[flatId] would make nested dependency like node_modules/package-a/node_modules/package-b never be resolved.

Then #3003 comes to fix. It uses nodejs api require.resolve and resolveDir (provided by esbuild) to resolve none-entry import from sub node_modules directory.

resolveDir introduced in #3003:

      function resolveEntry(id: string, isEntry: boolean, resolveDir: string) {
        const flatId = flattenId(id)
        if (flatId in qualified) {
          return isEntry
            ? {
                path: flatId,
                namespace: 'dep'
              }
            : {
                path: require.resolve(flatId, {
                  paths: [resolveDir]
                })
              }
        }
      }

#3003 has two problems. The more obvious one is flatId + require.resolve = module not found. For scoped packages like @some/package, flatId would be like some_package. And nodejs's require.resolve can't resolve the flatted id.

So we have third version of resolveEntry in #3053:

      function resolveEntry(id: string, isEntry: boolean, resolveDir: string) {
        const flatId = flattenId(id)
        if (flatId in qualified) {
          return isEntry
            ? {
                path: flatId,
                namespace: 'dep'
              }
            : {
                path: require.resolve(qualified[flatId], { // flatId -> qualified[flatId]
                  paths: [resolveDir]
                })
              }
        }
      }

#3053 shouldn't be merged, because it breaks fix of #3003. It resolved scoped package problem, but qualified[flatId] is a absolute path point to node_modules/xx/main-of-xx. The require.resolve and resolveDir are pointless.

Then I comes in #3753:

      function resolveEntry(id: string, isEntry: boolean, resolveDir: string) {
        const flatId = flattenId(id)
        if (flatId in qualified) {
          return isEntry
            ? {
                path: flatId,
                namespace: 'dep'
              }
            : {
                path: require.resolve(id, { // qualified[flatId] -> id
                  paths: [resolveDir]
                })
              }
        }
      }

It looks good, but in 2.4.0-beta.0 beta release we got error reports from #4005 and #4014. The problem is require.resolve behaves different with vite's module resolve function. For packages provide es module ("module" in package.json), it still resolve to "main". It's actually the other one problem introduced in #3003.

And as you see this(#4091) is the most recent fix on the long living bug. As described, I think it's not necessary to process none-entry imports in resolveEntry, so resolveDir is removed.

What a long story= =

And the first version of test case(test-package-a and test-package-b) is very suit to the circumstance of #2975, so I don't think we needs another test case for this.

Indeed, this code is meaningless. Is there a good fix now

{
    path: require.resolve(id, { // qualified[flatId] -> id
      paths: [resolveDir]
    })
  }

Too many issues.

I mean #3053 on third version.

Thanks for taking the time to write down the detailed history of the issue. This is very helpful.