Proposal to resolve some confusion about stages in Hadrian

The current situation with hadrian is that

1. We build libraries required to build the stage2 compiler with stage1 and place them in _build/stage1.
2. The stage2 compiler is built with stage1 and then placed in _build/stage1.
3. Executables built using the stage2 compiler such as haddock then also

use the libraries built by the stage1 compiler even though they are being built with the stage2 compiler.

However, this is problematic because when you want to build a stage3 compiler, we want to actually build the libraries again using the stage2 compiler and place them in _build/stage2. If we follow the existing logic for executables built using the stage2 compiler then in order to build a stage3 compiler we would just reuse all the libraries from _build/stage1 which seems incorrect.

The proposal is simply thus:

1. When building an executable at stageN, we use libraries also built at stageN. Concretely, if we want to build haddock, a stage2 executable, then we also have to build all the libraries it needs with the stage2 compiler and install them into a package database in _build/stage2.
2. The definition of "build" can be configured. By default, in order to "build" a stage2 library we copy it from the stage1 database but it is configurable to rebuild it with the stage2 compiler as we would want to for stage3.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	snowleopard
Operating system
Architecture