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| author | Bryan C. Mills <bcmills@google.com> | 2021-01-28 09:10:57 -0500 |
|---|---|---|
| committer | Bryan C. Mills <bcmills@google.com> | 2021-02-18 21:09:46 +0000 |
| commit | eb982727e33263c0bb67de607beb44c5e0bd2bea (patch) | |
| tree | e052fc775be98c4661657747d3a778a1850ce574 /src/cmd/go/internal/mvs/mvs_test.go | |
| parent | 3b7277d3651b5c5856c5b0879ba3fb7a5f279508 (diff) | |
| download | go-eb982727e33263c0bb67de607beb44c5e0bd2bea.tar.gz go-eb982727e33263c0bb67de607beb44c5e0bd2bea.zip | |
cmd/go/internal/mvs: fix Downgrade to match Algorithm 4
mvs.Downgrade is pretty clearly intended to match Algorithm 4 from the
MVS blog post (https://research.swtch.com/vgo-mvs#algorithm_4).
Per the blog post:
“Downgrading one module may require downgrading other modules, but we
want to downgrade as few other modules as possible. … To avoid an
unnecessary downgrade to E 1.1, we must also add a new requirement on
E 1.2. We can apply Algorithm R to find the minimal set of new
requirements to write to go.mod.”
mvs.Downgrade does not match that behavior today: it fails to retain
the selected versions of transitive dependencies that are not implied
by downgraded direct dependencies of the target (module E in the
post). This bug is currently masked by the fact that we only call
Downgrade today with a *modload.mvsReqs, for which the Required method
happens to return the complete build list — rather than only the
direct dependencies as documented for the mvs.Reqs interface.
For #36460
Change-Id: If9c8f413b156b5f67c02787d9359394e169951b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/287633
Trust: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Diffstat (limited to 'src/cmd/go/internal/mvs/mvs_test.go')
| -rw-r--r-- | src/cmd/go/internal/mvs/mvs_test.go | 19 |
1 files changed, 6 insertions, 13 deletions
diff --git a/src/cmd/go/internal/mvs/mvs_test.go b/src/cmd/go/internal/mvs/mvs_test.go index b8ff3bd8c2..742e396e0d 100644 --- a/src/cmd/go/internal/mvs/mvs_test.go +++ b/src/cmd/go/internal/mvs/mvs_test.go @@ -32,8 +32,7 @@ build A: A B1 C2 D4 E2 F1 upgrade* A: A B1 C4 D5 E2 F1 G1 upgrade A C4: A B1 C4 D4 E2 F1 G1 build A2: A2 B1 C4 D4 E2 F1 G1 -# BUG: selected versions E2 and F1 are not preserved. -downgrade A2 D2: A2 C4 D2 +downgrade A2 D2: A2 C4 D2 E2 F1 G1 name: trim A: B1 C2 @@ -216,8 +215,7 @@ A: B2 B1: C1 B2: C2 build A: A B2 C2 -# BUG: build list from downgrade omits selected version C1. -downgrade A C1: A B1 +downgrade A C1: A B1 C1 name: down2 A: B2 E2 @@ -231,9 +229,7 @@ E2: D2 E1: F1: build A: A B2 C2 D2 E2 F2 -# BUG: selected versions C1 and D1 are not preserved, and -# requested version F1 is not selected. -downgrade A F1: A B1 E1 +downgrade A F1: A B1 C1 D1 E1 F1 # https://research.swtch.com/vgo-mvs#algorithm_4: # “[D]owngrades are constrained to only downgrade packages, not also upgrade @@ -252,8 +248,7 @@ C2: D1: D2: build A: A B2 C1 D2 -# BUG: requested version D1 is not selected. -downgrade A D1: A +downgrade A D1: A D1 # https://research.swtch.com/vgo-mvs#algorithm_4: # “Unlike upgrades, downgrades must work by removing requirements, not adding @@ -270,10 +265,8 @@ B2: D2 C1: D1: D2: -build A: A B2 D2 -# BUG: requested version D1 is not selected, -# and selected version C1 is omitted from the returned build list. -downgrade A D1: A B1 +build A: A B2 D2 +downgrade A D1: A B1 C1 D1 name: downcycle A: A B2 |