feat: implement hybrid build/download strategy for WASM toolchain

Add support for selective tool building in wasm_toolchain_repository.
This allows users to build specific tools from custom git repositories
while downloading stable releases for others, enabling testing of forked
tools without the overhead of building all tools from source.

Key changes:
- Add _setup_hybrid_tools() function to determine build vs download per tool
- Add helper functions for individual tool downloads
- Fix git clone operations to handle commit hashes properly
- Support custom URLs and per-tool commit specification
- Add "hybrid" as valid strategy option alongside "system", "download", "build"

The hybrid strategy determines build vs download based on whether custom
URLs or commits are provided for each tool. This is particularly useful
for testing fixes in forked repositories while maintaining fast builds
for stable tools.

Author: avrabe

toolchains/wasm_toolchain.bzl

@@ -89,8 +89,10 @@ def _wasm_toolchain_repository_impl(repository_ctx):
         _setup_downloaded_tools(repository_ctx)
     elif strategy == "build":
         _setup_built_tools(repository_ctx)
+    elif strategy == "hybrid":
+        _setup_hybrid_tools(repository_ctx)
     else:
-        fail("Unknown strategy: {}. Must be 'system', 'download', or 'build'".format(strategy))
+        fail("Unknown strategy: {}. Must be 'system', 'download', 'build', or 'hybrid'".format(strategy))
 
     # Create BUILD files for all strategies
     _create_build_files(repository_ctx)
@@ -184,22 +186,42 @@ def _setup_built_tools(repository_ctx):
 
     git_commit = repository_ctx.attr.git_commit
 
+    # Get per-tool commits or use fallback
+    wasm_tools_commit = repository_ctx.attr.wasm_tools_commit or git_commit
+    wac_commit = repository_ctx.attr.wac_commit or git_commit
+    wit_bindgen_commit = repository_ctx.attr.wit_bindgen_commit or git_commit
+
+    # Get custom URLs or use defaults
+    wasm_tools_url = repository_ctx.attr.wasm_tools_url or "https://github.com/bytecodealliance/wasm-tools.git"
+    wac_url = repository_ctx.attr.wac_url or "https://github.com/bytecodealliance/wac.git"  
+    wit_bindgen_url = repository_ctx.attr.wit_bindgen_url or "https://github.com/bytecodealliance/wit-bindgen.git"
+
     # Clone and build wasm-tools
-    repository_ctx.execute([
+    result = repository_ctx.execute([
         "git",
         "clone",
-        "--depth=1",
-        "--branch=" + git_commit,
-        "https://github.com/bytecodealliance/wasm-tools.git",
+        wasm_tools_url,
         "wasm-tools-src",
     ])
-
-    repository_ctx.execute([
+    if result.return_code == 0:
+        result = repository_ctx.execute([
+            "git",
+            "-C",
+            "wasm-tools-src",
+            "checkout",
+            wasm_tools_commit,
+        ])
+    if result.return_code != 0:
+        fail("Failed to clone wasm-tools from {}: {}".format(wasm_tools_url, result.stderr))
+
+    result = repository_ctx.execute([
         "cargo",
         "build",
         "--release",
         "--manifest-path=wasm-tools-src/Cargo.toml",
     ])
+    if result.return_code != 0:
+        fail("Failed to build wasm-tools: {}".format(result.stderr))
 
     repository_ctx.execute([
         "cp",
@@ -208,21 +230,31 @@ def _setup_built_tools(repository_ctx):
     ])
 
     # Clone and build wac
-    repository_ctx.execute([
+    result = repository_ctx.execute([
         "git",
         "clone",
-        "--depth=1",
-        "--branch=" + git_commit,
-        "https://github.com/bytecodealliance/wac.git",
+        wac_url,
         "wac-src",
     ])
-
-    repository_ctx.execute([
+    if result.return_code == 0:
+        result = repository_ctx.execute([
+            "git",
+            "-C",
+            "wac-src",
+            "checkout",
+            wac_commit,
+        ])
+    if result.return_code != 0:
+        fail("Failed to clone wac from {}: {}".format(wac_url, result.stderr))
+
+    result = repository_ctx.execute([
         "cargo",
         "build",
         "--release",
         "--manifest-path=wac-src/Cargo.toml",
     ])
+    if result.return_code != 0:
+        fail("Failed to build wac: {}".format(result.stderr))
 
     repository_ctx.execute([
         "cp",
@@ -231,28 +263,172 @@ def _setup_built_tools(repository_ctx):
     ])
 
     # Clone and build wit-bindgen
-    repository_ctx.execute([
+    result = repository_ctx.execute([
         "git",
         "clone",
-        "--depth=1",
-        "--branch=" + git_commit,
-        "https://github.com/bytecodealliance/wit-bindgen.git",
+        wit_bindgen_url,
         "wit-bindgen-src",
     ])
-
-    repository_ctx.execute([
+    if result.return_code == 0:
+        result = repository_ctx.execute([
+            "git",
+            "-C",
+            "wit-bindgen-src",
+            "checkout",
+            wit_bindgen_commit,
+        ])
+    if result.return_code != 0:
+        fail("Failed to clone wit-bindgen from {}: {}".format(wit_bindgen_url, result.stderr))
+
+    result = repository_ctx.execute([
         "cargo",
         "build",
         "--release",
         "--manifest-path=wit-bindgen-src/Cargo.toml",
     ])
+    if result.return_code != 0:
+        fail("Failed to build wit-bindgen: {}".format(result.stderr))
 
     repository_ctx.execute([
         "cp",
         "wit-bindgen-src/target/release/wit-bindgen",
         "wit-bindgen",
     ])
 
+def _setup_hybrid_tools(repository_ctx):
+    """Setup tools using hybrid build/download strategy"""
+    
+    # Determine which tools to build vs download based on custom URLs/commits
+    build_wasm_tools = repository_ctx.attr.wasm_tools_url != "" or repository_ctx.attr.wasm_tools_commit != ""
+    build_wac = repository_ctx.attr.wac_url != "" or repository_ctx.attr.wac_commit != ""
+    build_wit_bindgen = repository_ctx.attr.wit_bindgen_url != "" or repository_ctx.attr.wit_bindgen_commit != ""
+    
+    # Get commits and URLs for tools we're building
+    git_commit = repository_ctx.attr.git_commit
+    wasm_tools_commit = repository_ctx.attr.wasm_tools_commit or git_commit
+    wac_commit = repository_ctx.attr.wac_commit or git_commit
+    wit_bindgen_commit = repository_ctx.attr.wit_bindgen_commit or git_commit
+    
+    wasm_tools_url = repository_ctx.attr.wasm_tools_url or "https://github.com/bytecodealliance/wasm-tools.git"
+    wac_url = repository_ctx.attr.wac_url or "https://github.com/bytecodealliance/wac.git"
+    wit_bindgen_url = repository_ctx.attr.wit_bindgen_url or "https://github.com/bytecodealliance/wit-bindgen.git"
+    
+    # Build or download wasm-tools
+    if build_wasm_tools:
+        result = repository_ctx.execute([
+            "git", "clone", wasm_tools_url, "wasm-tools-src",
+        ])
+        if result.return_code == 0:
+            result = repository_ctx.execute([
+                "git", "-C", "wasm-tools-src", "checkout", wasm_tools_commit,
+            ])
+        if result.return_code != 0:
+            fail("Failed to clone wasm-tools from {}: {}".format(wasm_tools_url, result.stderr))
+        
+        result = repository_ctx.execute([
+            "cargo", "build", "--release", "--manifest-path=wasm-tools-src/Cargo.toml",
+        ])
+        if result.return_code != 0:
+            fail("Failed to build wasm-tools: {}".format(result.stderr))
+        
+        repository_ctx.execute(["cp", "wasm-tools-src/target/release/wasm-tools", "wasm-tools"])
+    else:
+        _download_wasm_tools(repository_ctx)
+    
+    # Build or download wac
+    if build_wac:
+        result = repository_ctx.execute([
+            "git", "clone", wac_url, "wac-src",
+        ])
+        if result.return_code == 0:
+            result = repository_ctx.execute([
+                "git", "-C", "wac-src", "checkout", wac_commit,
+            ])
+        if result.return_code != 0:
+            fail("Failed to clone wac from {}: {}".format(wac_url, result.stderr))
+        
+        result = repository_ctx.execute([
+            "cargo", "build", "--release", "--manifest-path=wac-src/Cargo.toml",
+        ])
+        if result.return_code != 0:
+            fail("Failed to build wac: {}".format(result.stderr))
+        
+        repository_ctx.execute(["cp", "wac-src/target/release/wac", "wac"])
+    else:
+        _download_wac(repository_ctx)
+    
+    # Build or download wit-bindgen
+    if build_wit_bindgen:
+        result = repository_ctx.execute([
+            "git", "clone", wit_bindgen_url, "wit-bindgen-src",
+        ])
+        if result.return_code == 0:
+            result = repository_ctx.execute([
+                "git", "-C", "wit-bindgen-src", "checkout", wit_bindgen_commit,
+            ])
+        if result.return_code != 0:
+            fail("Failed to clone wit-bindgen from {}: {}".format(wit_bindgen_url, result.stderr))
+        
+        result = repository_ctx.execute([
+            "cargo", "build", "--release", "--manifest-path=wit-bindgen-src/Cargo.toml",
+        ])
+        if result.return_code != 0:
+            fail("Failed to build wit-bindgen: {}".format(result.stderr))
+        
+        repository_ctx.execute(["cp", "wit-bindgen-src/target/release/wit-bindgen", "wit-bindgen"])
+    else:
+        _download_wit_bindgen(repository_ctx)
+
+def _download_wasm_tools(repository_ctx):
+    """Download wasm-tools only"""
+    platform = _detect_host_platform(repository_ctx)
+    version = repository_ctx.attr.version
+    platform_suffix = _get_platform_suffix(platform)
+    
+    wasm_tools_url = "https://github.com/bytecodealliance/wasm-tools/releases/download/v{}/wasm-tools-{}-{}.tar.gz".format(
+        version, version, platform_suffix,
+    )
+    
+    repository_ctx.download_and_extract(
+        url = wasm_tools_url,
+        stripPrefix = "wasm-tools-{}-{}".format(version, platform_suffix),
+    )
+
+def _download_wac(repository_ctx):
+    """Download wac only"""
+    platform = _detect_host_platform(repository_ctx)
+    platform_suffix = _get_platform_suffix(platform)
+    
+    wac_version = "0.7.0"
+    wac_platform_map = {
+        "aarch64-macos": "aarch64-apple-darwin",
+        "x86_64-macos": "x86_64-apple-darwin", 
+        "x86_64-linux": "x86_64-unknown-linux-musl",
+        "aarch64-linux": "aarch64-unknown-linux-musl",
+        "x86_64-windows": "x86_64-pc-windows-gnu",
+    }
+    wac_platform = wac_platform_map.get(platform_suffix, "x86_64-unknown-linux-musl")
+    wac_url = "https://github.com/bytecodealliance/wac/releases/download/v{}/wac-cli-{}".format(
+        wac_version, wac_platform,
+    )
+    
+    repository_ctx.download(url = wac_url, output = "wac", executable = True)
+
+def _download_wit_bindgen(repository_ctx):
+    """Download wit-bindgen only"""
+    platform = _detect_host_platform(repository_ctx)
+    platform_suffix = _get_platform_suffix(platform)
+    
+    wit_bindgen_version = "0.43.0"
+    wit_bindgen_url = "https://github.com/bytecodealliance/wit-bindgen/releases/download/v{}/wit-bindgen-{}-{}.tar.gz".format(
+        wit_bindgen_version, wit_bindgen_version, platform_suffix,
+    )
+    
+    repository_ctx.download_and_extract(
+        url = wit_bindgen_url,
+        stripPrefix = "wit-bindgen-{}-{}".format(wit_bindgen_version, platform_suffix),
+    )
+
 def _get_platform_suffix(platform):
     """Get platform suffix for download URLs"""
     platform_suffixes = {
@@ -324,18 +500,30 @@ wasm_toolchain_repository = repository_rule(
     implementation = _wasm_toolchain_repository_impl,
     attrs = {
         "strategy": attr.string(
-            doc = "Tool acquisition strategy: 'system', 'download', or 'build'",
+            doc = "Tool acquisition strategy: 'system', 'download', 'build', or 'hybrid'",
             default = "system",
-            values = ["system", "download", "build"],
+            values = ["system", "download", "build", "hybrid"],
         ),
         "version": attr.string(
             doc = "Version to use (for download/build strategies)",
             default = "1.235.0",
         ),
         "git_commit": attr.string(
-            doc = "Git commit/tag to build from (for build strategy)",
+            doc = "Git commit/tag to build from (for build strategy) - fallback for all tools",
             default = "main",
         ),
+        "wasm_tools_commit": attr.string(
+            doc = "Git commit/tag for wasm-tools (overrides git_commit)",
+            default = "",
+        ),
+        "wac_commit": attr.string(
+            doc = "Git commit/tag for wac (overrides git_commit)",
+            default = "",
+        ),
+        "wit_bindgen_commit": attr.string(
+            doc = "Git commit/tag for wit-bindgen (overrides git_commit)",
+            default = "",
+        ),
         "wasm_tools_url": attr.string(
             doc = "Custom download URL for wasm-tools (optional)",
             default = "",