Allow leading spaces to bypass console aliases (#13476)

## Summary of the Pull Request

When you create a console alias that overrides an existing command, it
should still be possible to execute the original command by prefixing it
with a space. However, at some point in the past, there was an attempt
to improve the usability by trimming leading spaces, and that ended up
breaking this functionality. This PR reverts that change, so leading
spaces can once again be used to bypass an alias.

## PR Checklist
* [x] Closes #4189
* [x] CLA signed.
* [x] Tests added/passed
* [ ] Documentation updated.
* [ ] Schema updated.
* [x] I've discussed this with core contributors already. Issue number
where discussion took place: #4189

## Validation Steps Performed

I've updated the existing alias unit test for leading spaces to match
the new behavior, i.e. it now confirms that a command with leading
spaces will not match the alias.

I've also manually confirmed that the `doskey` test case reported in
issue #4189 is now working as expected.

src/host/alias.cpp

@@ -817,18 +817,6 @@ void Alias::s_ClearCmdExeAliases()
     CATCH_RETURN();
 }
 
-// Routine Description:
-// - Trims leading spaces off of a string
-// Arguments:
-// - str - String to trim
-void Alias::s_TrimLeadingSpaces(std::wstring& str)
-{
-    // Erase from the beginning of the string up until the first
-    // character found that is not a space.
-    str.erase(str.begin(),
-              std::find_if(str.begin(), str.end(), [](wchar_t ch) { return !std::iswspace(ch); }));
-}
-
 // Routine Description:
 // - Trims trailing \r\n off of a string
 // Arguments:
@@ -1148,9 +1136,6 @@ std::wstring Alias::s_MatchAndCopyAlias(const std::wstring& sourceText,
     // Trim trailing \r\n off of sourceCopy if it has one.
     s_TrimTrailingCrLf(sourceCopy);
 
-    // Trim leading spaces off of sourceCopy if it has any.
-    s_TrimLeadingSpaces(sourceCopy);
-
     // Check if we have an EXE in the list that matches the request first.
     auto exeIter = g_aliasData.find(exeName);
     if (exeIter == g_aliasData.end())

src/host/alias.h

@@ -29,7 +29,6 @@ class Alias
                                             size_t& lineCount);
 
 private:
-    static void s_TrimLeadingSpaces(std::wstring& str);
     static void s_TrimTrailingCrLf(std::wstring& str);
     static std::deque<std::wstring> s_Tokenize(const std::wstring& str);
     static std::wstring s_GetArgString(const std::wstring& str);

src/host/ut_host/AliasTests.cpp

@@ -340,20 +340,18 @@ class AliasTests
         auto rgwchTargetBefore = std::make_unique<wchar_t[]>(cchTarget);
         wcscpy_s(rgwchTargetBefore.get(), cchTarget, rgwchTarget.get());
         size_t cbTargetUsed = 0;
-        const auto cbTargetUsedExpected = cbTarget;
+        const auto cbTargetUsedBefore = cbTargetUsed;
 
         DWORD dwLines = 0;
-        const auto dwLinesExpected = dwLines + 1;
+        const auto dwLinesBefore = dwLines;
 
         // Register the correct alias name before we try.
         std::wstring exe(L"exe.exe");
         std::wstring source(L"Source");
         std::wstring target(L"someTarget");
         Alias::s_TestAddAlias(exe, source, target);
 
-        auto targetExpected = target + L"\r\n";
-
-        // We should be able to match through the leading spaces. They should be stripped.
+        // Leading spaces should bypass the alias. This should not match anything.
         Alias::s_MatchAndCopyAliasLegacy(pwszSource,
                                          cbSource,
                                          rgwchTarget.get(),
@@ -362,9 +360,9 @@ class AliasTests
                                          exe,
                                          dwLines);
 
-        VERIFY_ARE_EQUAL(cbTargetUsedExpected, cbTargetUsed, L"No target bytes should be used.");
-        VERIFY_ARE_EQUAL(String(targetExpected.data(), gsl::narrow<int>(targetExpected.size())), String(rgwchTarget.get(), cchTarget), L"Target string should match expected.");
-        VERIFY_ARE_EQUAL(dwLinesExpected, dwLines, L"Line count be updated to 1.");
+        VERIFY_ARE_EQUAL(cbTargetUsedBefore, cbTargetUsed, L"No bytes should be used if nothing was found.");
+        VERIFY_ARE_EQUAL(String(rgwchTargetBefore.get(), cchTarget), String(rgwchTarget.get(), cchTarget), L"Target string should be unmodified.");
+        VERIFY_ARE_EQUAL(dwLinesBefore, dwLines, L"Line count should pass through.");
     }
 
     TEST_METHOD(TrimTrailing)