docs: add complete patch for rules_rust wasip2 support

- Include both triple.bzl and triple_mappings.bzl changes
- Add system constraint mappings for wasip1/wasip2/wasip3
- Update documentation with complete patch instructions
- Fixes 'System wasip2 is not supported' error in CI

Author: avrabe

PATCH_README.md

@@ -4,8 +4,9 @@ This repository uses a fork of rules_rust with minimal patches to support WASI t
 
 ## What's Patched
 
-**File**: `rust/platform/triple.bzl`  
-**Changes**: Added support for 2-component WASI target triples
+**Files**: 
+- `rust/platform/triple.bzl` - Added support for 2-component WASI target triples
+- `rust/platform/triple_mappings.bzl` - Added system constraints for wasip1/wasip2/wasip3
 
 ### The Problem
 rules_rust expects target triples to have 3+ components (e.g., `x86_64-unknown-linux-gnu`), but WASI targets use 2-component format:
@@ -26,14 +27,14 @@ Convert 2-component WASI targets to standard 3-component format:
    cd rules_rust
    ```
 
-2. Apply the patch:
+2. Apply the complete patch:
    ```bash
-   git apply wasip2-support.patch
+   git apply wasip2-complete.patch
    ```
 
 3. Commit and push:
    ```bash
-   git add rust/platform/triple.bzl
+   git add rust/platform/triple.bzl rust/platform/triple_mappings.bzl
    git commit -m "feat: add support for wasm32-wasip2 target triples
 
    - Handle 2-component WASI target triples in triple.bzl

wasip2-complete.patch

@@ -0,0 +1,39 @@
+diff --git a/rust/platform/triple.bzl b/rust/platform/triple.bzl
+index 1234567..abcdefg 100644
+--- a/rust/platform/triple.bzl
++++ b/rust/platform/triple.bzl
+@@ -42,6 +42,17 @@ def triple_from_string(target_triple):
+         )
+ 
+     component_parts = triple.split("-")
++    
++    # Special handling for WASI targets with 2 components
++    if len(component_parts) == 2 and component_parts[0] == "wasm32":
++        if component_parts[1] == "wasip1":
++            # Treat wasm32-wasip1 as wasm32-unknown-wasi
++            component_parts = ["wasm32", "unknown", "wasi"]
++        elif component_parts[1] == "wasip2":
++            # Treat wasm32-wasip2 as wasm32-unknown-wasi  
++            component_parts = ["wasm32", "unknown", "wasi"]
++        elif component_parts[1] == "wasip3":
++            # Future support for wasm32-wasip3
++            component_parts = ["wasm32", "unknown", "wasi"]
++    
+     if len(component_parts) < 3:
+         fail("Expected target triple to contain at least three sections separated by '-'")
+diff --git a/rust/platform/triple_mappings.bzl b/rust/platform/triple_mappings.bzl
+index 2345678..9abcdef 100644
+--- a/rust/platform/triple_mappings.bzl
++++ b/rust/platform/triple_mappings.bzl
+@@ -298,6 +298,8 @@ def system_to_constraints(system):
+         return [
+             constraint_value("@rules_rust//rust/platform/os:wasi"),
+         ]
++    elif system == "wasip1" or system == "wasip2" or system == "wasip3":
++        # Handle 2-component WASI targets that were not normalized
++        return [
++            constraint_value("@rules_rust//rust/platform/os:wasi"),
++        ]
+     elif system == "windows":
+         return [
+             constraint_value("@platforms//os:windows"),