1Modules example.com/internalcompat/{a,b} are copies. One could be a fork
2of the other. An external package p exposes a type from a package q
3within the same module.
4
5If gorelease ran apidiff on the two modules instead of on the individual
6packages, then it should not report differences between these packages. The types
7are distinct, but they correspond (in apidiff terminology), which is the
8important property when considering differences between modules. More
9specifically, the fully qualified type names are identical modulo the change
10to the module path.
11
12But at the time gorelease was written, apidiff did not support module
13comparison. If considered at the package level, the two packages
14example.com/internalcompat/a/p and example.com/internalcompat/b/p
15are incompatible, because the packages they refer to are different.
16
17So case 2 below would apply if whole modules were being diffed, but
18it doesn't here because individual packages are being diffed.
19
20There are three use cases to consider:
21
221. One module substitutes for the other via a `replace` directive.
23 Only the replacement module is used, and the package paths are effectively
24 identical, so the types are not distinct.
252. One module subsititutes for the other by rewriting `import` statements
26 globally. All references to the original type become references to the
27 new type, so there is no conflict.
283. One module substitutes for the other by rewriting some `import` statements
29 but not others (for example, those within a specific consumer package).
30 In this case, the types are distinct, and even if there are no changes,
31 the types are not compatible.
View as plain text