Allow repeated invocation (#37)

* Workaround for repeated invocations

As noted in the comment, repeated invocations of this action might have
caused environment variables to overflow. This cute hack avoid this,
allowing to reconfigure environment.

* Note caveats in README

While this approach mostly works, I still have reservations so let's
leave some cautionary notes.

* Test repeated reconfiguration on CI

Well, let's build our "Hello, world!" four times, for four different
architectures, because why not.

.github/workflows/main.yml

@@ -18,13 +18,42 @@ jobs:
         uses: actions/checkout@v2
       - name: Download Internet
         run: npm install
-      - name: Enable Developer Command Prompt
+      - name: Enable Developer Command Prompt (amd64)
         uses: ./
-      - name: Compile and run some C code
+        with:
+          arch: amd64
+      - name: Compile and run some C code (amd64)
         shell: cmd
         run: |
           cl.exe hello.c
           hello.exe
+      - name: Enable Developer Command Prompt (amd64_x86)
+        uses: ./
+        with:
+          arch: amd64_x86
+      - name: Compile and run some C code (x86)
+        shell: cmd
+        run: |
+          cl.exe hello.c
+          hello.exe
+      - name: Enable Developer Command Prompt (amd64_arm)
+        uses: ./
+        with:
+          arch: amd64_arm
+      - name: Compile some C code (arm)
+        shell: cmd
+        run: |
+          cl.exe hello.c
+          dumpbin /headers hello.exe
+      - name: Enable Developer Command Prompt (amd64_arm64)
+        uses: ./
+        with:
+          arch: amd64_arm64
+      - name: Compile some C code (arm64)
+        shell: cmd
+        run: |
+          cl.exe hello.c
+          dumpbin /headers hello.exe
   audit:
     name: npm audit
     runs-on: windows-latest

README.md

@@ -87,6 +87,48 @@ If you experience compilation errors where `link` complains about unreasonable c
 Recommended workaround is to remove `/usr/bin/link` if that interferes with your builds.
 If this is not acceptable, please file an issue, then we'll figure out something better.
 
+### Reconfiguration
+
+You can invoke `ilammy/msvc-dev-cmd` multiple times during your jobs with different inputs
+to reconfigure the environment for building with different settings
+(e.g., to target multiple architectures).
+
+```yaml
+jobs:
+  release:
+    steps:
+      # ...
+      - name: Configure build for amd64
+        uses: ilammy/msvc-dev-cmd@v1
+        with:
+          arch: amd64
+
+      - run: build # (for amd64)
+
+      - name: Configure build for x86
+        uses: ilammy/msvc-dev-cmd@v1
+        with:
+          arch: amd64_x86
+
+      - run: build # (for x86)
+
+      - name: Configure build for ARM64
+        uses: ilammy/msvc-dev-cmd@v1
+        with:
+          arch: amd64_arm64
+
+      - run: build # (for ARM64)
+
+      # ...
+```
+
+This mostly works but it's not really recommended
+since Developer Command Prompt was not meant for recursive reconfiguration.
+That said, if it does not work for you, please file an issue.
+
+Consider using [`strategy.matrix`](https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstrategymatrix)
+to execute different build configuration in parallel, independent environments.
+
 ## License
 
 MIT, see [LICENSE](LICENSE).

index.js

@@ -55,6 +55,21 @@ function findVcvarsall() {
     throw new Error('Microsoft Visual Studio not found')
 }
 
+function isPathVariable(name) {
+    const pathLikeVariables = ['PATH', 'INCLUDE', 'LIB', 'LIBPATH']
+    return pathLikeVariables.indexOf(name.toUpperCase()) != -1
+}
+
+function filterPathValue(path) {
+    let paths = path.split(';')
+    // Remove duplicates by keeping the first occurance and preserving order.
+    // This keeps path shadowing working as intended.
+    function unique(value, index, self) {
+        return self.indexOf(value) === index
+    }
+    return paths.filter(unique).join(';')
+}
+
 function main() {
     if (process.platform != 'win32') {
         core.info('This is not a Windows virtual environment, bye!')
@@ -139,11 +154,18 @@ function main() {
         if (!string.includes('=')) {
             continue;
         }
-        const [name, new_value] = string.split('=')
-        const old_value = old_env_vars[name]
+        let [name, new_value] = string.split('=')
+        let old_value = old_env_vars[name]
         // For new variables "old_value === undefined".
         if (new_value !== old_value) {
             core.info(`Setting ${name}`)
+            // Special case for a bunch of PATH-like variables: vcvarsall.bat
+            // just prepends its stuff without checking if its already there.
+            // This makes repeated invocations of this action fail after some
+            // point, when the environment variable overflows. Avoid that.
+            if (isPathVariable(name)) {
+                new_value = filterPathValue(new_value)
+            }
             core.exportVariable(name, new_value)
         }
     }