Update documentation.

Author: jcbrill

CHANGES.txt

@@ -58,8 +58,11 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
       and then later an environment is constructed with a user specified vswhere
       executable that detects new msvc installations.
     - The vswhere detection of VS2017 (14.1), and later, is now cached at runtime and is
-      only evaluated once using a single vswhere invocation for all installations.
+      only evaluated once using a single vswhere invocation for all msvc versions.
       Previously, the vswhere executable was invoked for each supported msvc version.
+    - The vswhere executable locations for the WinGet and Scoop package managers were
+      added to the default vswhere executable search list after the Chocolatey
+      installation location.
 
   From Mats Wichmann:
 

RELEASE.txt

@@ -35,6 +35,10 @@ CHANGED/ENHANCED EXISTING FUNCTIONALITY
   (14.0).  This behavior was extended to Visual Studio 2017 (14.1) and Visual
   Studio 2008 (8.0).  An express installation of the IDE binary is used when no
   other IDE edition is detected.
+- The vswhere executable locations for the WinGet and Scoop package managers were
+  added to the default vswhere executable search list after the Chocolatey
+  installation location.
+
 
 FIXES
 -----
@@ -79,6 +83,10 @@ IMPROVEMENTS
 - MSVC: Visual Studio 2015 BuildTools (14.0) does not support the sdk version
   argument and does not support the store argument.  Script argument validation now
   takes into account these restrictions.
+- MSVC: The registry detection of VS2015 (14.0), and earlier, is now cached at runtime
+  and is only evaluated once for each msvc version.
+- MSVC: The vswhere detection of VS2017 (14.1), and later, is now cached at runtime and
+  is only evaluated once using a single vswhere invocation for all msvc versions.
 
 PACKAGING
 ---------

SCons/Tool/msvc.xml

@@ -400,24 +400,25 @@ latest version of &MSVC; installed on your system.
 <para>
 The valid values for &cv-MSVC_VERSION; represent major versions
 of the compiler, except that versions ending in <literal>Exp</literal>
-refer to "Express" or "Express for Desktop" Visual Studio editions,
-which require distinct entries because they use a different
-filesystem layout and have feature limitations compared to
-the full version.
+refer to "Express" or "Express for Desktop" Visual Studio editions.
 Values that do not look like a valid compiler version
 <emphasis>string</emphasis> are not supported.
 </para>
 
 <para>
-To have the desired effect, &cv-MSVC_VERSION; must be set by the
-time compiler discovery takes place.
-If the default tools list
-or an explicit tools list including &t-link-msvc; is used,
-discovery takes place as the &consenv; is created,
-so passing it as an argument in the the &f-link-Environment; call
+To have the desired effect, &cv-MSVC_VERSION; must be set before an msvc &f-link-Tool;
+(e.g., &t-link-msvc;) or an msvc-dependent &f-link-Tool; (e.g., &t-link-midl;) is loaded
+into the &consenv;.
+</para>
+
+<para>
+If the default tools list or an explicit tools list is used that includes an
+msvc &f-link-Tool; (e.g., &t-link-msvc;) or an msvc-dependent &f-link-Tool; (e.g., &t-link-midl;);
+the &cv-MSVC_VERSION; is resolved when the &consenv; is created.
+In this case, passing &cv-MSVC_VERSION; as an argument in the &f-link-Environment; call
 is the effective solution.
-Otherwise, &cv-MSVC_VERSION; must be set before the first msvc tool is
-loaded into the environment.
+Otherwise, &cv-MSVC_VERSION; must be set before the first msvc &f-link-Tool; or 
+msvc-dependent &f-link-Tool; is loaded into the environment.
 See the manpage section "Construction Environments" for an example.
 </para>
 
@@ -475,10 +476,10 @@ Visual Studio </literallayout></entry>
       </row>
       <row>
         <entry> <literal>"14.1Exp"</literal> </entry>
-        <entry> 14.1 </entry>
-        <entry> 1910 </entry>
+        <entry> 14.1 or 14.1x </entry>
+        <entry> 191x </entry>
         <entry> Visual Studio 2017 Express </entry>
-        <entry> 15.0 </entry>
+        <entry> 15.x </entry>
       </row>
       <row>
         <entry> <literal>"14.0"</literal> </entry>
@@ -864,34 +865,42 @@ Specify the location of <filename>vswhere.exe</filename>.
 
 <para>
     The <filename>vswhere.exe</filename> executable is distributed with Microsoft Visual Studio and Build
-    Tools since the 2017 edition, but is also available standalone.
+    Tools since the 2017 edition, but is also available as a standalone installation.
     It provides full information about installations of 2017 and later editions.
     With the <option>-legacy</option> argument, <filename>vswhere.exe</filename> can detect installations of the 2010 through 2015
     editions with limited data returned.
-If <envar>VSWHERE</envar> is set, &SCons; will use that location.
 </para>
 <para>
-    Otherwise &SCons; will look in the following locations and set <envar>VSWHERE</envar> to the path of the first <filename>vswhere.exe</filename>
-located.
+    If &cv-VSWHERE; is set to a <filename>vswhere.exe</filename> location, &SCons; will use that location.
+    When &cv-VSWHERE; is undefined, &SCons; will look in the following locations and set &cv-VSWHERE; to the path
+    of the first <filename>vswhere.exe</filename> located:
 </para>
 
 <itemizedlist>
 <listitem><para><literal>%ProgramFiles(x86)%\Microsoft Visual Studio\Installer</literal></para></listitem>
 <listitem><para><literal>%ProgramFiles%\Microsoft Visual Studio\Installer</literal></para></listitem>
 <listitem><para><literal>%ChocolateyInstall%\bin</literal></para></listitem>
+<listitem><para><literal>%LOCALAPPDATA%\Microsoft\WinGet\Links</literal></para></listitem>
+<listitem><para><literal>~\scoop\shims</literal></para></listitem>
+<listitem><para><literal>%SCOOP%\shims</literal></para></listitem>
 </itemizedlist>
 
 <para>
-  Note that <envar>VSWHERE</envar> must be set at the same time or prior to any of &t-link-msvc;, &t-link-msvs; , and/or &t-link-mslink; &f-link-Tool; being initialized.
+  Note that &cv-VSWHERE; must be set prior to the initial &MSVC; compiler discovery.
+  For example, &cv-VSWHERE; must be set at the same time or before the first msvc &f-link-Tool;
+  (e.g., &t-link-msvc;) or msvc-dependent &f-link-Tool; (e.g., &t-link-midl;) is initialized.
+</para>
 
-  Either set it as follows
+<para>
+  Either set it as follows:
 <programlisting>
 env = Environment(VSWHERE='c:/my/path/to/vswhere')
 </programlisting>
 
-or if your &consenv; is created specifying an empty tools list
-(or a list of tools which omits all of default, msvs, msvc, and mslink),
-and also before &f-link-env-Tool; is called to ininitialize any of those tools:
+Or, if your &consenv; is created specifying: (a) an empty tools list, or (b)
+a list of tools which omits all of default, msvc (e.g., &t-link-msvc;), and
+msvc-dependent tools (e.g., &t-link-midl;); and before &f-link-env-Tool;
+is called to initialize any of those tools:
 
 <programlisting>
     env = Environment(tools=[])