Copy the flake migration from the flake branch

hydra.nixos.org is already running this rev, and it should be safe to
apply to everyone else. If we make changes to this migration, we'll
need to write another migration anyway.

src/sql/hydra.sql

@@ -54,8 +54,8 @@ create table Jobsets (
     name          text not null,
     project       text not null,
     description   text,
-    nixExprInput  text not null, -- name of the jobsetInput containing the Nix or Guix expression
-    nixExprPath   text not null, -- relative path of the Nix or Guix expression
+    nixExprInput  text, -- name of the jobsetInput containing the Nix or Guix expression
+    nixExprPath   text, -- relative path of the Nix or Guix expression
     errorMsg      text, -- used to signal the last evaluation error etc. for this jobset
     errorTime     integer, -- timestamp associated with errorMsg
     lastCheckedTime integer, -- last time the evaluator looked at this jobset
@@ -70,7 +70,11 @@ create table Jobsets (
     fetchErrorMsg text,
     forceEval     boolean,
     startTime     integer, -- if jobset is currently running
+    type          integer not null default 0, -- 0 == legacy, 1 == flake
+    flake         text,
     check (schedulingShares > 0),
+    check ((type = 0) = (nixExprInput is not null and nixExprPath is not null)),
+    check ((type = 1) = (flake is not null)),
     primary key   (project, name),
     foreign key   (project) references Projects(name) on delete cascade on update cascade
 #ifdef SQLITE
@@ -181,7 +185,8 @@ create table Builds (
 
     -- Copy of the nixExprInput/nixExprPath fields of the jobset that
     -- instantiated this build.  Needed if we want to reproduce this
-    -- build.
+    -- build.  FIXME: this should be stored in JobsetEvals, storing it
+    -- here is denormal.
     nixExprInput  text,
     nixExprPath   text,
 
@@ -522,6 +527,8 @@ create table JobsetEvals (
     nrBuilds      integer,
     nrSucceeded   integer, -- set lazily when all builds are finished
 
+    flake         text, -- immutable flake reference
+
     foreign key   (project) references Projects(name) on delete cascade on update cascade,
     foreign key   (project, jobset) references Jobsets(project, name) on delete cascade on update cascade
 );