add tests

Signed-off-by: Arseniy Alekseyev <aalekseyev@janestreet.com>

src/install.ml

@@ -201,7 +201,7 @@ module Entry = struct
         | String_with_vars.Unknown var ->
           Errors.fail (String_with_vars.Var.loc var)
             "Variable %s unavailable while computing [dst]. The extension of \
-             [src] needs to be known earlly to know whether to add an \".exe\" \
+             [src] needs to be known early to know whether to add an \".exe\" \
              suffix on windows." (String_with_vars.Var.describe var)
         | Yes ->
           true
@@ -223,7 +223,7 @@ module Entry = struct
           | None ->
             Errors.fail (String_with_vars.Var.loc var)
               "Variable %s unavailable while computing [dst]. The basename of \
-               [src] needs to be known earlly because it's used to compute [dst]."
+               [src] needs to be known early because it's used to compute [dst]."
               (String_with_vars.Var.describe var)
     in
     match dst with

test/blackbox-tests/test-cases/install-with-var/dune

@@ -2,3 +2,4 @@
  (section man)
  (files (a-man-page.1 as a-man-page.%{context_name}.1) another-man-page.3)
 )
+

test/blackbox-tests/test-cases/install-with-var/foobar.txt

@@ -0,0 +1 @@
+foobar

test/blackbox-tests/test-cases/install-with-var/run.t

@@ -8,3 +8,100 @@
   Installing install/man/man1/a-man-page.default.1
   Installing install/man/man3/another-man-page.3
 
+
+Some variables are restricted in [dst] of [bin] section because evaluating
+them could cause a dependency cycle (also, most of them make no sense in [dst] anyway).
+
+  $ unset FOO
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section bin)
+  >   (files (foobar.txt as "%{env:FOO=foobar}/foo.txt"))
+  >  )
+  > EOF
+
+  $ dune build @install
+  File "dune", line 3, characters 27-42:
+  3 |   (files (foobar.txt as "%{env:FOO=foobar}/foo.txt"))
+                                 ^^^^^^^^^^^^^^^
+  Error: %{env:..} isn't allowed in this position
+  [1]
+
+This is not a problem outside of bin section:
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section man)
+  >   (files (foobar.txt as "%{env:FOO=foobar}/foo.txt"))
+  >  )
+  > EOF
+
+  $ dune build @install
+
+Extension of [src] can't use the restricted variables either because
+addition of .exe suffix to dst on Windows is conditional on the
+extension of [src]:
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section bin)
+  >   (files (%{env:FOO=foobar} as foo.txt))
+  >  )    
+  > EOF
+
+  $ dune build @install
+  File "dune", line 3, characters 12-27:
+  3 |   (files (%{env:FOO=foobar} as foo.txt))
+                  ^^^^^^^^^^^^^^^
+  Error: Variable %{env:..} unavailable while computing [dst]. The extension of [src] needs to be known early to know whether to add an ".exe" suffix on windows.
+  [1]
+
+This is fine if the destination extension is already .exe:
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section bin)
+  >   (files (%{env:FOO=foobar}.txt as foo.exe))
+  >  )    
+  > EOF
+
+  $ dune build @install
+
+Or if the extension of source is clearly not .exe:
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section bin)
+  >   (files (%{env:FOO=foobar}.txt as foo.exe))
+  >  )    
+  > EOF
+
+  $ dune build @install
+
+Exe basename needs to be fully known if dst is missing though:
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section bin)
+  >   (files %{env:FOO=foobar}.txt)
+  >  )    
+  > EOF
+
+  $ dune build @install
+  File "dune", line 3, characters 11-26:
+  3 |   (files %{env:FOO=foobar}.txt)
+                 ^^^^^^^^^^^^^^^
+  Error: Variable %{env:..} unavailable while computing [dst]. The basename of [src] needs to be known early because it's used to compute [dst].
+  [1]
+
+When basename is fully known, all is well:
+
+  $ cat > dune <<EOF
+  >  (install
+  >   (section bin)
+  >   (files %{env:FOO=.}/foobar.txt)
+  >  )    
+  > EOF
+
+  $ dune build @install