RFC: Convention: do no prefix exports with the module's name

Author: aturon

active/0000-no-module-prefixes.md

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+- Start Date: (fill me in with today's date, 2014-10-05)
+- RFC PR: (leave this empty)
+- Rust Issue: (leave this empty)
+
+# Summary
+
+This is a conventions RFC that proposes that the items exported from a module
+should *never* be prefixed with that module name. For example, we should have
+`io::Error`, not `io::IoError`.
+
+(An alternative design is included that special-cases overlap with the
+`prelude`.)
+
+# Motivation
+
+Currently there is no clear prohibition around including the module's name as a
+prefix on an exported item, and it is sometimes done for type names that are
+feared to be "popular" (like `Error` and `Result` being `IoError` and
+`IoResult`) for clarity.
+
+This RFC include two designs: one that entirely rules out such prefixes, and one
+that rules it out *except* for names that overlap with the prelude. Pros/cons
+are given for each.
+
+# Detailed design
+
+The main rule being proposed is very simple: the items exported from a module
+should never be prefixed with the module's name.
+
+Rationale:
+
+* Avoids needless stuttering like `io::IoError`.
+* Any ambiguity can be worked around:
+    * Either qualify by the module, i.e. `io::Error`,
+    * Or rename on import: `use io::Error as IoError`.
+* The rule is extremely simple and clear.
+
+Downsides:
+
+* The name may already exist in the module wanting to export it.
+    * If that's due to explicit imports, those imports can be renamed or
+      module-qualified (see above).
+    * If that's due to a *prelude* conflict, however, confusion may arise due to
+      the conventional *global* meaning of identifiers defined in the prelude
+      (i.e., programmers do not expect prelude imports to be shadowed).
+
+Overall, the RFC author believes that *if* this convention is adopted, confusion
+around redefining prelude names would gradually go away, because (at least for
+things like `Result`) we would come to expect it.
+
+# Alternative design
+
+An alternative rule would be to never prefix an exported item with the module's
+name, *except* for names that are also defined in the prelude, which *must* be
+prefixed by the module's name.
+
+For example, we would have `io::Error` and `io::IoResult`.
+
+Rationale:
+
+* Largely the same as the above, but less decisively.
+* Avoids confusion around prelude-defined names.
+
+Downsides:
+
+* Retains stuttering for some important cases, e.g. custom `Result` types, which
+  are likely to be fairly common.
+* Makes it even more problematic to expand the prelude in the future.