Fix resolution of executable names on Windows.

src/runtime/process.cpp

@@ -19,6 +19,7 @@ Author: Jared Roesch
 #include <tchar.h>
 #include <stdio.h>
 #include <strsafe.h>
+#include <shellapi.h>
 #else
 #include <unistd.h>
 #include <fcntl.h>
@@ -108,6 +109,29 @@ static void setup_stdio(SECURITY_ATTRIBUTES * saAttr, HANDLE * theirs, object **
     lean_unreachable();
 }
 
+
+const char* ws = " \t\n\r\f\v";
+
+// trim from end of string (right)
+inline std::string& rtrim(std::string& s, const char* t = ws)
+{
+    s.erase(s.find_last_not_of(t) + 1);
+    return s;
+}
+
+// trim from beginning of string (left)
+inline std::string& ltrim(std::string& s, const char* t = ws)
+{
+    s.erase(0, s.find_first_not_of(t));
+    return s;
+}
+
+// trim from both ends of string (right then left)
+inline std::string& trim(std::string& s, const char* t = ws)
+{
+    return ltrim(rtrim(s, t), t);
+}
+
 // This code is adapted from: https://msdn.microsoft.com/en-us/library/windows/desktop/ms682499(v=vs.85).aspx
 static obj_res spawn(string_ref const & proc_name, array_ref<string_ref> const & args, stdio stdin_mode, stdio stdout_mode,
                      stdio stderr_mode, option_ref<string_ref> const & cwd, array_ref<pair_ref<string_ref, option_ref<string_ref>>> const & env) {
@@ -128,6 +152,36 @@ static obj_res spawn(string_ref const & proc_name, array_ref<string_ref> const &
 
     std::string command = proc_name.to_std_string();
 
+    // remove any whitespace and quotes so we can check if the file exists.
+    trim(command, ws);
+    trim(command, "\"");
+
+    const char* extensions[] = { ".exe", ".com", ".cmd" };
+    const DWORD MAX_SIZE = 32767;
+    char buffer[MAX_SIZE];
+    LPSTR lpFilePart = NULL;
+    DWORD rc = 0;
+    for (auto ext : extensions) {
+        rc = SearchPath(NULL, command.c_str(), ext, MAX_SIZE, buffer, &lpFilePart);
+        if (rc != 0) {
+            break;
+        }
+    }
+
+    if (rc != 0) {
+        // buffer now contains the executable that Windows would have executed if you
+        // typed that name in a terminal window.  This can change the name of the command.
+        // For example, "npm" becomes "C:\Program Files\nodejs\npm.cmd" and not the bash
+        // shell script named "C:\Program Files\nodejs\npm".
+        command = buffer;
+    }
+
+    if (command.find(' ') != std::string::npos || command.find('\t') != std::string::npos) {
+        // path contains whitespace so it needs quotes.
+        command.insert(command.begin(), '"');
+        command += "\"";
+    }
+
     // This needs some thought, on Windows we must pass a command string
     // which is a valid command, that is a fully assembled command to be executed.
     //