[Opam] Don't generate the dune-site build part when not needed

       Fixes #4849

Signed-off-by: François Bobot <[email protected]>

CHANGES.md

@@ -3,6 +3,9 @@ Unreleased
 
 - Fix plugins with dot in the name (#5182, @bobot, review @rgrinberg)
 
+- Don't generate the dune-site build part when not needed (#4861, @bobot,
+  review @kit-ty-kate)
+
 - Fix installation of implementations of virtual libraries (#5150, fix #3636,
   @rgrinberg)
 

otherlibs/site/test/run.t

@@ -3,26 +3,37 @@ Test embedding of sites locations information
 
   $ mkdir -p a b c
 
-  $ for i in a b d; do
+  $ mkdir -p a
+
+  $ cat >a/dune-project <<EOF
+  > (lang dune 3.0)
+  > (generate_opam_files true)
+  > (using dune_site 0.1)
+  > (name a)
+  > (version 0.a)
+  > (package (name a) (sites (share data)))
+  > EOF
+
+  $ for i in b d; do
   > mkdir -p $i
   > cat >$i/dune-project <<EOF
-  > (lang dune 2.9)
+  > (lang dune 3.0)
   > (generate_opam_files true)
   > (using dune_site 0.1)
   > (name $i)
   > (version 0.$i)
-  > (package (name $i) (sites (share data)))
+  > (package (name $i) (sites (share data)) (depends c))
   > EOF
   > done
 
   $ for i in c; do
   >   mkdir -p $i
   >   cat >$i/dune-project <<EOF
-  > (lang dune 2.9)
+  > (lang dune 3.0)
   > (generate_opam_files true)
   > (using dune_site 0.1)
   > (name $i)
-  > (package (name $i) (sites (share data) (lib plugins)))
+  > (package (name $i) (sites (share data) (lib plugins)) (depends a))
   > EOF
   > done
 
@@ -139,7 +150,7 @@ Test with an opam like installation
   opam-version: "2.0"
   version: "0.a"
   depends: [
-    "dune" {>= "2.9"}
+    "dune" {>= "3.0"}
     "odoc" {with-doc}
   ]
   build: [
@@ -159,9 +170,7 @@ Test with an opam like installation
     ["dune" "install" "-p" name "--create-install-files" name]
   ]
 
-  $ dune subst
-
-  $ dune build -p a --promote-install-files=false @install @runtest @doc
+  $ dune build -p a --promote-install-files=false @install
 
   $ test -e a/a.install
   [1]
@@ -378,11 +387,11 @@ Test %{version:installed-pkg}
   $ for i in f; do
   >   mkdir -p $i
   >   cat >$i/dune-project <<EOF
-  > (lang dune 2.9)
+  > (lang dune 3.0)
   > (using dune_site 0.1)
   > (name $i)
   > (version 0.$i)
-  > (package (name $i) (sites (share data) (lib plugins)))
+  > (package (name $i) (sites (share data) (lib plugins)) (allow_empty))
   > EOF
   > done