Implement priority overrides for injected routes and redirects

.changeset/smooth-cobras-help.md

@@ -0,0 +1,20 @@
+---
+'astro': minor
+---
+
+Reworks route priority processing to allow for more flexible and intuitive redirects and route injection
+
+- Priority order for project routes, injected routes and redirects are now all the same.
+- Injected routes and redirects can now specify if they should be prioritized above,
+  with or below project routes. This is done by adding a `priority` property to the route
+  object in `injectRoute` and in the `redirects` property in `astro.config.mjs`.
+- Now more specific routes always take priority over less specific routes.  
+  Example: `/blog/[...slug]` will take priority over `/[...slug]`
+- Static redirects now have a lower priority than all project routed, even if the routes are dynamic,
+  matching the already documented behavior.  
+  Example: `/blog (redirect)` will no longer override a `/[slug]` route by default, this can be re-enabled
+  using the new `priority` field. 
+- Collision detection between routes can now detect coliisions between similar dynamic routes
+  of any kind (project routes, injected routes and redirects).  
+  Example: `/blog/[page]` will now be detected as a collision with `/blog/[slug]`
+- Colision detection is now reported as a warning for backward compatibility with all the previous false negatives.

packages/astro/src/@types/astro.ts

@@ -1555,10 +1555,19 @@ export interface AstroUserConfig {
  */
 export type InjectedScriptStage = 'before-hydration' | 'head-inline' | 'page' | 'page-ssr';
 
+/**
+ * IDs for different priorities of injected routes and redirects:
+ * - "above-project": Override any project route in case of conflict.
+ * - "same-as-project": Behave the same as if the route was defined in the project, following the same priority rules.
+ * - "below-project": Only match if no project route matches.
+ */
+export type RoutePriorityOverride = 'above-project' | 'same-as-project' | 'below-project';
+
 export interface InjectedRoute {
 	pattern: string;
 	entrypoint: string;
 	prerender?: boolean;
+	priority?: RoutePriorityOverride;
 }
 
 export interface ResolvedInjectedRoute extends InjectedRoute {
@@ -2385,6 +2394,7 @@ type RedirectConfig =
 	| {
 			status: ValidRedirectStatus;
 			destination: string;
+			priority?: RoutePriorityOverride;
 	  };
 
 export interface RouteData {

packages/astro/src/core/config/schema.ts

@@ -173,6 +173,7 @@ export const AstroConfigSchema = z.object({
 						z.literal(308),
 					]),
 					destination: z.string(),
+					priority: z.enum(['above-project', 'same-as-project', 'below-project']).optional(),
 				}),
 			])
 		)