Try to find the windows resource compiler on the PATH first

In some situations `cc::windows_registry::find_msvc_tool("link.exe")` returns a
`Tool` with an empty environment (without the Windows SDK tools in the
PATH).  This happens if link.exe itself was found on the PATH, for
example if you're in a VS Developer Command Prompt.

Update the `find_resource_compiler` to more closely follow how
`cc::windows_registry` does it: first try to find "rc.exe" on the PATH
and only if that fails (and also if "link.exe" isn't on the PATH), try
to locate it indirectly via `find_msvc_tool("link.exe")`

Author: lambdageek

compiler/rustc_windows_rc/src/lib.rs

@@ -135,20 +135,30 @@ fn parse_version(version: &str) -> Option<ResourceVersion> {
 /// Find the Windows SDK resource compiler `rc.exe` for the given architecture or target triple.
 /// Returns `None` if the tool could not be found.
 fn find_resource_compiler(arch_or_target: &str) -> Option<path::PathBuf> {
-    find_windows_sdk_tool(arch_or_target, "rc.exe")
+    // If "rc.exe" is on the PATH, use it. Otherwise, try to find the tool in a Windows SDK
+    find_tool_in_env("rc.exe").or_else(|| find_windows_sdk_tool(arch_or_target, "rc.exe"))
 }
 
 /// Find a Windows SDK tool for the given architecture or target triple.
 /// Returns `None` if the tool could not be found.
 fn find_windows_sdk_tool(arch_or_target: &str, tool_name: &str) -> Option<path::PathBuf> {
     // windows_registry::find_tool can only find MSVC tools, not Windows SDK tools, but
-    // cc does include the Windows SDK tools in the PATH environment of MSVC tools.
+    // cc does include the Windows SDK tools in the PATH environment of an MSVC tool, if
+    // the MSVC tool itself was not found via the PATH.
+    if find_tool_in_env("link.exe").is_some() {
+        return None;
+    }
 
     let msvc_linker = windows_registry::find_tool(arch_or_target, "link.exe")?;
     let path = &msvc_linker.env().iter().find(|(k, _)| k == "PATH")?.1;
     find_tool_in_path(tool_name, path)
 }
 
+/// Find a tool in the directories of the PATH environment variable
+fn find_tool_in_env(tool_name: &str) -> Option<path::PathBuf> {
+    env::var_os("PATH").and_then(|p| find_tool_in_path(tool_name, p))
+}
+
 /// Find a tool in the directories in a given PATH-like string.
 fn find_tool_in_path<P: AsRef<ffi::OsStr>>(tool_name: &str, path: P) -> Option<path::PathBuf> {
     env::split_paths(path.as_ref()).find_map(|p| {