Add DUNE_TARGET_EXEC

Signed-off-by: Romain Beauxis <[email protected]>

Author: toots

bin/common.ml

@@ -877,7 +877,12 @@ module Builder = struct
       Arg.(
         value
         & opt (some string) None
-        & info [ "target-exec" ] ~docs ~docv:"TOOLCHAIN=CMD" ~doc:(Some doc))
+        & info
+            [ "target-exec" ]
+            ~docs
+            ~docv:"TOOLCHAIN=CMD"
+            ~doc:(Some doc)
+            ~env:(Cmd.Env.info ~doc "DUNE_TARGET_EXEC"))
     and+ build_dir =
       let doc = "Specified build directory. _build if unspecified" in
       Arg.(

test/blackbox-tests/test-cases/custom-cross-compilation/target-exec.t

@@ -116,6 +116,27 @@ Build with -x test_toolchain and --target-exec test_toolchain=test_toolchain_wra
   Args: $TESTCASE_ROOT/_build/default.test_toolchain/hello.exe --hello-arg1 --hello-arg2
   ---- HELLO END ----
 
+Build with -x test_toolchain and environment variable DUNE_TARGET_EXEC=test_toolchain=test_toolchain_wrapper.sh
+(should use target binary ./hello.exe wrapped with the wrapper)
+
+  $ PATH="$PWD/bin:$PATH" DUNE_TARGET_EXEC=test_toolchain=test_toolchain_wrapper.sh dune build @runhello -x test_toolchain --force
+  ---- HELLO START ----
+  Hello from OCaml!
+  PWD: $TESTCASE_ROOT/_build/default
+  Args: ./hello.exe --hello-arg1 --hello-arg2
+  ---- HELLO END ----
+  
+  === TEST_TOOLCHAIN WRAPPER START ===
+  WRAPPER PWD: $TESTCASE_ROOT/_build/default.test_toolchain
+  WRAPPER executing: $TESTCASE_ROOT/_build/default.test_toolchain/hello.exe --hello-arg1 --hello-arg2
+  === WRAPPER EXEC ===
+  ---- HELLO START ----
+  Hello from OCaml!
+  PWD: $TESTCASE_ROOT/_build/default.test_toolchain
+  Args: $TESTCASE_ROOT/_build/default.test_toolchain/hello.exe --hello-arg1 --hello-arg2
+  ---- HELLO END ----
+  
+
 
 Build with -x test_toolchain and --target-exec with arguments
 (should use target binary ./hello.exe wrapped with the wrapper)