Apply variable overrides for exec

Fixes #9995

src/exec.cpp

@@ -1072,6 +1072,11 @@ bool exec_job(parser_t &parser, const shared_ptr<job_t> &j, const io_chain_t &bl
             return false;
         }
 
+        // Apply foo=bar variable assignments
+        for (const auto &assignment : j->processes.front()->variable_assignments) {
+            parser.vars().set(assignment.variable_name, ENV_LOCAL | ENV_EXPORT, assignment.values);
+        }
+
         internal_exec(parser.vars(), j.get(), block_io);
         // internal_exec only returns if it failed to set up redirections.
         // In case of an successful exec, this code is not reached.

tests/checks/exec.fish

@@ -1,4 +1,5 @@
-#RUN: %fish %s
+#RUN: %fish -C 'set -l fish %fish' %s
+
 exec cat <nosuchfile
 #CHECKERR: warning: An error occurred while redirecting file 'nosuchfile'
 #CHECKERR: warning: Path 'nosuchfile' does not exist
@@ -10,7 +11,10 @@ not exec cat <nosuchfile
 echo "neg failed: $status"
 #CHECK: neg failed: 0
 
+# See that variable overrides are applied to exec'd processes
+$fish --no-config -c 'foo=bar exec env' | grep foo=bar
+# CHECK: foo=bar
+
 # This needs to be last, because it actually runs exec.
 exec cat </dev/null
 echo "not reached"
-