always give a target with commands the first prereqs

2 files changed, 23 insertions, 8 deletions

diff --git a/src/makefile/input.rs b/src/makefile/input.rs
index 03e7f18..5dda538 100644
--- a/src/makefile/input.rs
+++ b/src/makefile/input.rs
@@ -1163,8 +1163,8 @@ cursed:
     #[test]
     fn dependency_prepending_appending() -> R {
         let file = "
-test: a
 test: b
+test: a
 \techo hi
 test: c
         ";
diff --git a/src/makefile/target.rs b/src/makefile/target.rs
index 8f56506..c12f666 100644
--- a/src/makefile/target.rs
+++ b/src/makefile/target.rs
@@ -2,6 +2,7 @@ use std::cell::{Cell, RefCell};
 use std::collections::HashMap;
 use std::fmt;
 use std::fs::metadata;
+use std::mem;
 use std::rc::Rc;
 use std::time::SystemTime;
 
@@ -23,13 +24,27 @@ pub struct Target {
 impl Target {
     pub fn extend(&mut self, other: Target) {
         assert_eq!(&self.name, &other.name);
-        self.prerequisites.extend(other.prerequisites);
-        assert!(self.commands.is_empty() || other.commands.is_empty());
-        self.commands.extend(other.commands);
-        assert!(self.stem.is_none() || other.stem.is_none());
-        self.stem = self.stem.take().or(other.stem);
-        let already_updated = self.already_updated.get() || other.already_updated.get();
-        self.already_updated.set(already_updated);
+        match (self.commands.is_empty(), other.commands.is_empty()) {
+            (false, false) => {
+                // both targets have commands, so replace this entirely
+                *self = other;
+            }
+            (true, false) => {
+                // this target doesn't have commands, but the other one does,
+                // so it's the real one
+                let mut other = other;
+                mem::swap(self, &mut other);
+                self.extend(other);
+            }
+            (false, true) | (true, true) => {
+                // this target might have commands, but the other one doesn't,
+                // so append non-command stuff
+                self.prerequisites.extend(other.prerequisites);
+                self.stem = self.stem.take().or(other.stem);
+                let already_updated = self.already_updated.get() || other.already_updated.get();
+                self.already_updated.set(already_updated);
+            }
+        }
     }
 
     fn modified_time(&self) -> Option<SystemTime> {