add a flag for changing targets gracefully

at the moment an SVD pointer hangs out that messes builds up
when changing targets (sometimes) -- this is the pointer that
includes extra files in the build for targets that have disjoint
RTL sources. add a flag for cleaning this up.

xtask/src/builder.rs

@@ -146,6 +146,7 @@ pub(crate) struct Builder {
     no_image: bool,
     /// when Some, specifies a swap region as offset, size
     swap: Option<(u32, u32)>,
+    change_target: bool,
 }
 
 impl Builder {
@@ -174,6 +175,7 @@ impl Builder {
             dry_run: false,
             no_image: false,
             swap: None,
+            change_target: false,
         }
     }
 
@@ -226,6 +228,11 @@ impl Builder {
         self
     }
 
+    pub fn set_change_target_flag(&mut self) -> &mut Builder {
+        self.change_target = true;
+        self
+    }
+
     /// Set a minimum xous version. This is the minimum Xous version necessary to read
     /// the PDDB that is generated by this build. The purpose of this is so that we can
     /// trim migration code out of the PDDB: when we have a breaking change to the PDDB,
@@ -764,6 +771,15 @@ impl Builder {
                 println!("Dry run requested: only building and not running");
             }
         } else {
+            let svd_spec_path = format!(
+                "target/{}/{}/build/SVD_PATH",
+                self.target.as_ref().expect("target"),
+                self.stream.as_str()
+            );
+            if self.change_target {
+                std::fs::remove_file(&svd_spec_path).ok(); // don't fail if the file does not exist
+            }
+
             // ------ build the kernel ------
             let mut kernel_extra = vec![];
             if self.kernel_disable_defaults {
@@ -823,11 +839,6 @@ impl Builder {
             }
 
             // ---------- extract SVD file path, as computed by utralib ----------
-            let svd_spec_path = format!(
-                "target/{}/{}/build/SVD_PATH",
-                self.target.as_ref().expect("target"),
-                self.stream.as_str()
-            );
             let mut svd_spec_file = OpenOptions::new().read(true).open(svd_spec_path)?;
             let mut svd_path_str = String::new();
             svd_spec_file.read_to_string(&mut svd_path_str)?;

xtask/src/main.rs

@@ -193,6 +193,9 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     if env::args().filter(|x| x == "--offline").count() != 0 {
         builder.add_global_flag("--offline");
     }
+    if env::args().filter(|x| x == "--change-target").count() != 0 {
+        builder.set_change_target_flag();
+    }
 
     // manage an ugly patch we have to do to selectively configure AES for only cramium-soc targets
     match builder::search_in_file("services/aes/Cargo.toml", "default = []") {
@@ -596,6 +599,7 @@ fn print_help() {
     [--gdb-stub]
     [--debug-loader]
     [--offline]
+    [--change-target]
 
 [cratespecs] is a list of 0 or more items of the following syntax:
    [name]                crate 'name' to be built from local source
@@ -620,6 +624,8 @@ be merged in with explicit app/service treatment with the following flags:
 [--debug-loader]         Enable debug printing in the loader
 [--offline]              Avoid network traffic
 [--swap offset:size]     Specify a region for swap memory. The behavior of this depends on the target.
+[--change-target]        Used to clean the cached target/*/*/build/SVD_PATH when changing build targets.
+                         This will also force a full rebuild every time the flag is specified.
 
 - An 'app' must be enumerated in apps/manifest.json.
    A pre-processor configures the launch menu based on the list of specified apps.