make it an error in rhai to have empty ops

fud2/fud-core/src/run.rs

@@ -183,11 +183,6 @@ impl EmitBuild for RulesOp {
             )?;
         }
 
-        // If the sequences of rules was empty, output a phoney rule creating the desired output.
-        if self.cmds.is_empty() {
-            emitter.build_cmd(outputs, "phony", inputs, &[])?;
-        }
-
         Ok(())
     }
 }

fud2/fud-core/src/script/error.rs

@@ -21,6 +21,7 @@ pub(super) enum RhaiSystemErrorKind {
     ExpectedString(String),
     ExpectedShell,
     ExpectedShellDeps,
+    EmptyOp,
 }
 
 impl RhaiSystemError {
@@ -90,6 +91,13 @@ impl RhaiSystemError {
         }
     }
 
+    pub(super) fn empty_op() -> Self {
+        Self {
+            kind: RhaiSystemErrorKind::EmptyOp,
+            position: rhai::Position::NONE,
+        }
+    }
+
     pub(super) fn with_pos(mut self, p: rhai::Position) -> Self {
         self.position = p;
         self
@@ -126,6 +134,9 @@ impl Display for RhaiSystemError {
             RhaiSystemErrorKind::ExpectedShellDeps => {
                 write!(f, "Expected `shell_deps`, got shell. Ops may contain only one of `shell` or `shell_deps` calls, not calls to both")
             }
+            RhaiSystemErrorKind::EmptyOp => {
+                write!(f, "Error: Op must contain at least one call to `shell` or `shell_deps`.")
+            }
         }
     }
 }

fud2/fud-core/src/script/plugin.rs

@@ -352,8 +352,16 @@ impl ScriptContext {
                         c
                     }
                     Some(ShellCommands::Cmds(c)) => c.clone(),
-                    None => vec![],
+
+                    None => {
+                        // If cmds is empty, then the op doesn't do anything and should be considered
+                        // erroneous.
+                        return Err(RhaiSystemError::empty_op()
+                            .with_pos(pos)
+                            .into());
+                    }
                 };
+
                 let op_name = name.clone();
                 let config_vars = config_vars.clone();
                 let op_emitter = crate::run::RulesOp {