More fix-ups upon clarity and correctness

Author: stevapple

Sources/TSCBasic/Process.swift

@@ -474,6 +474,8 @@ public final class Process {
             )
             var searchPaths: [AbsolutePath] = []
 #if os(Windows)
+            // NOTE: `CreateProcess` the Windows system API always searchs System and Windows directories first.
+            // See https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessw#parameters
             var buffer = Array<WCHAR>(repeating: 0, count: Int(MAX_PATH + 1))
             // The 32-bit Windows system directory
             if GetSystemDirectoryW(&buffer, .init(buffer.count)) > 0 {

Sources/TSCBasic/misc.swift

@@ -225,9 +225,9 @@ public func lookupExecutablePath(
         return nil
     }
 #if os(Windows)
-    let isPath = value.contains(":") || value.contains("\\") || value.contains("/")
+    let isFileName = !value.contains(":") && !value.contains("\\") && !value.contains("/")
 #else
-    let isPath = value.contains("/")
+    let isFileName = !value.contains("/")
 #endif
 
     var paths: [AbsolutePath] = []
@@ -241,12 +241,11 @@ public func lookupExecutablePath(
         paths.append(absPath)
     }
 
-    // Ensure the value is not a path.
-    if !isPath {
-        // Try to locate in search paths.
+    if isFileName {
+        // Try to locate file in search paths.
         paths.append(contentsOf: searchPaths.map({ $0.appending(component: value) }))
 #if os(Windows)
-        if !value.contains(".") {
+        if !value.hasSuffix(".") {
             paths.append(contentsOf: searchPaths.map({ $0.appending(component: value + executableFileSuffix) }))
         }
 #endif