Auto merge of #24051 - TheGoddessInari:fix_windows, r=jdm

build_commands: Make Visual Studio detection not assume environment

<!-- Please describe your changes on the following line: -->
Ever since 681d7b165a, servo breaks building if you're not running Visual Studio 2015 or 2017 in the default location on C:.

I rewrote the PR to not assume environment, similarly to #23098.

We need to stop meeting like this. 🦊

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because 681d7b165a didn't. Realistically, there should be environment tests for Visual Studio 2015, 2017, and 2019, but I won't have the time for it soon.

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python/servo/build_commands.py

@@ -249,22 +249,15 @@ class MachCommands(CommandBase):
             env["CXXFLAGS"] += "-mmacosx-version-min=10.10"
 
         if 'windows' in host:
+            vsinstalldir = os.environ.get('VSINSTALLDIR')
             vcinstalldir = None
-            msbuildinstalldir = None
-            vs_version = "15.0"
-            editions = ["Enterprise", "Professional", "Community", "BuildTools"]
-            prog_files = os.environ.get("ProgramFiles(x86)")
-            base_vs_path = os.path.join(prog_files, "Microsoft Visual Studio", "2017")
-
-            for edition in editions:
-                # C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin
-                # C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\amd64
-                msbuildinstalldir = os.path.join(base_vs_path, edition, "MSBuild", vs_version, "Bin")
-                if os.path.exists(msbuildinstalldir):
-                    break
+            vs_version = os.environ.get('VisualStudioVersion')
+            if vsinstalldir and vs_version:
+                msbuild_version = get_msbuild_version(vs_version)
             else:
-                print("Can't find MSBuild.exe installation at %s." % base_vs_path)
-                sys.exit(1)
+                (vsinstalldir, vs_version, msbuild_version) = find_highest_msvc_version()
+            msbuildinstalldir = os.path.join(vsinstalldir, "MSBuild",
+                                             msbuild_version, "Bin")
 
         if host != target_triple and 'windows' in target_triple:
             if os.environ.get('VisualStudioVersion'):
@@ -272,13 +265,9 @@ class MachCommands(CommandBase):
                       "Please run `python mach build [arguments]` to bypass automatic "
                       "Visual Studio shell.")
                 sys.exit(1)
-
-            for edition in editions:
-                vcinstalldir = os.path.join(base_vs_path, edition, "VC")
-                if os.path.exists(vcinstalldir):
-                    break
-            else:
-                print("Can't find Visual Studio 2017 installation at %s." % base_vs_path)
+            vcinstalldir = os.environ.get("VCINSTALLDIR", "") or os.path.join(vsinstalldir, "VC")
+            if not os.path.exists(vcinstalldir):
+                print("Can't find Visual C++ %s installation at %s." % (vs_version, vcinstalldir))
                 sys.exit(1)
 
         if uwp:
@@ -989,7 +978,7 @@ def package_msvc_dlls(servo_exe_dir, target, vcinstalldir, vs_version):
         "msvcp140.dll",
         "vcruntime140.dll",
     ]
-    if target_arch != "aarch64":
+    if target_arch != "aarch64" and vs_version in ("14.0", "15.0"):
         msvc_deps += ["api-ms-win-crt-runtime-l1-1-0.dll"]
 
     # Check if it's Visual C++ Build Tools or Visual Studio 2015
@@ -1040,3 +1029,34 @@ def package_msvc_dlls(servo_exe_dir, target, vcinstalldir, vs_version):
     for msvc_dll in missing:
         print("DLL file `{}` not found!".format(msvc_dll))
     return not missing
+
+
+def get_msbuild_version(vs_version):
+    if vs_version in ("15.0", "14.0"):
+        msbuild_version = vs_version
+    else:
+        msbuild_version = "Current"
+    return msbuild_version
+
+
+def find_highest_msvc_version():
+    editions = ["Enterprise", "Professional", "Community", "BuildTools"]
+    prog_files = os.environ.get("ProgramFiles(x86)")
+    base_vs_path = os.path.join(prog_files, "Microsoft Visual Studio")
+
+    vs_versions = ["2019", "2017"]
+    versions = {
+        ("2019", "vs"): "16.0",
+        ("2017", "vs"): "15.0",
+    }
+
+    for version in vs_versions:
+        for edition in editions:
+            vs_version = versions[version, "vs"]
+            msbuild_version = get_msbuild_version(vs_version)
+
+            vsinstalldir = os.path.join(base_vs_path, version, edition)
+            if os.path.exists(vsinstalldir):
+                return (vsinstalldir, vs_version, msbuild_version)
+    print("Can't find MSBuild.exe installation under %s." % base_vs_path)
+    sys.exit(1)