Raise on abnormal exit in Procss::Status#exit_code (#15241)

spec/std/process/status_spec.cr

@@ -27,7 +27,13 @@ describe Process::Status do
     Process::Status.new(exit_status(128)).exit_code.should eq 128
     Process::Status.new(exit_status(255)).exit_code.should eq 255
 
-    status_for(:interrupted).exit_code.should eq({% if flag?(:unix) %}0{% else %}LibC::STATUS_CONTROL_C_EXIT.to_i32!{% end %})
+    if {{ flag?(:unix) }}
+      expect_raises(RuntimeError, "Abnormal exit has no exit code") do
+        status_for(:interrupted).exit_code
+      end
+    else
+      status_for(:interrupted).exit_code.should eq({% if flag?(:unix) %}0{% else %}LibC::STATUS_CONTROL_C_EXIT.to_i32!{% end %})
+    end
   end
 
   it "#success?" do

src/process/status.cr

@@ -205,9 +205,19 @@ class Process::Status
     {% end %}
   end
 
-  # If `normal_exit?` is `true`, returns the exit code of the process.
+  # Returns the exit code of the process if it exited normally (`#normal_exit?`).
+  #
+  # Raises `RuntimeError` if the status describes an abnormal exit.
+  #
+  # ```
+  # Process.run("true").exit_code                                # => 1
+  # Process.run("exit 123", shell: true).exit_code               # => 123
+  # Process.new("sleep", ["10"]).tap(&.terminate).wait.exit_code # RuntimeError: Abnormal exit has no exit code
+  # ```
   def exit_code : Int32
     {% if flag?(:unix) %}
+      raise RuntimeError.new("Abnormal exit has no exit code") unless normal_exit?
+
       # define __WEXITSTATUS(status) (((status) & 0xff00) >> 8)
       (@exit_status & 0xff00) >> 8
     {% else %}