nsis-dev · idleberg · Sep 2, 2026 · Sep 2, 2026 · Sep 2, 2026 · Sep 2, 2026
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -2,7 +2,9 @@ name: Run tests
 
 on:
   push:
+    paths-ignore: ["**.md", LICENSE]
   pull_request:
+    paths-ignore: ["**.md", LICENSE]
   workflow_dispatch:
 
 jobs:
@@ -12,10 +14,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-latest, macos-latest, windows-latest]
         variant: [default, large-strings, advanced-logging]
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
       - name: Setup NSIS
         id: nsis
@@ -37,10 +40,8 @@ jobs:
           [ "$OUT_NSISDIR" = "$NSISDIR" ]
           [ -f "$NSISDIR/Include/MUI2.nsh" ]
 
-          # makensis must come from PATH, i.e. the action put $PREFIX/bin there
-          makensis -VERSION
+          # Unqualified: proves the action put the bin dir on PATH
           info=$(makensis -HDRINFO)
-          echo "$info"
 
           strlen=8192
           [ "$LARGE" = "true" ] || strlen=1024
@@ -66,13 +67,34 @@ jobs:
           makensis test.nsi
           [ -f test.exe ]
 
+  windows-combo-rejected:
+    runs-on: windows-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Setup NSIS with both special builds
+        id: nsis
+        continue-on-error: true
+        uses: ./
+        with:
+          large-strings: true
+          advanced-logging: true
+
+      - name: Check the step failed
+        shell: bash
+        run: '[ "${{ steps.nsis.outcome }}" = failure ]'
+
   pinned-version:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-      - id: nsis
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Setup NSIS
+        id: nsis
         uses: ./
         with:
           version: "3.10"
-      - shell: bash
+
+      - name: Check the pinned version was used
+        shell: bash
         run: '[ "${{ steps.nsis.outputs.version }}" = "3.10" ] && makensis -VERSION | grep -q 3.10'
diff --git a/README.md b/README.md
@@ -6,9 +6,6 @@
 
 Set up [NSIS](https://nsis.sourceforge.io/) in your GitHub workflow.
 
-> [!WARNING]
-> This action currently only supports Linux and macOS runners.
-
 ## Usage
 
 ```yaml
@@ -31,8 +28,13 @@ With build options:
 | Name               | Default  | Description                                                   |
 | ------------------ | -------- | ------------------------------------------------------------- |
 | `version`          | `latest` | NSIS version, e.g. `3.12`. `latest` resolves via SourceForge. |
-| `large-strings`    | `false`  | Build with `NSIS_MAX_STRLEN=8192`.                            |
-| `advanced-logging` | `false`  | Build with `NSIS_CONFIG_LOG=yes`.                             |
+| `large-strings`    | `false`  | `NSIS_MAX_STRLEN=8192`.                                       |
+| `advanced-logging` | `false`  | `NSIS_CONFIG_LOG=yes`.                                        |
+
+> [!NOTE]
+> On Windows, `large-strings` and `advanced-logging` cannot be combined: the
+> action uses upstream's prebuilt special builds and there is no build that
+> ships both. Enabling both fails the step.
 
 ## Outputs
 
@@ -41,8 +43,9 @@ With build options:
 | `version` | Resolved NSIS version.                                    |
 | `nsisdir` | NSIS installation directory (also exported as `NSISDIR`). |
 
-Builds are cached per OS, version and option combination, so only the first run
-pays the compile cost.
+On Linux and macOS, NSIS is built from source; on Windows the action installs
+upstream's prebuilt binaries. Either way the result is cached per OS, version
+and option combination, so only the first run pays the setup cost.
 
 ## License
 

diff --git a/action.yml b/action.yml
@@ -1,15 +1,15 @@
 name: Setup NSIS
-description: Build NSIS from source on Linux and macOS and expose it via NSISDIR
+description: Set up NSIS on Linux, macOS and Windows and expose it via NSISDIR
 
 inputs:
   version:
     description: NSIS version, e.g. 3.12, or "latest"
     default: latest
   large-strings:
-    description: Build with NSIS_MAX_STRLEN=8192
+    description: NSIS_MAX_STRLEN=8192
     default: "false"
   advanced-logging:
-    description: Build with NSIS_CONFIG_LOG=yes
+    description: NSIS_CONFIG_LOG=yes
     default: "false"
 
 outputs:
@@ -18,7 +18,7 @@ outputs:
     value: ${{ steps.vars.outputs.version }}
   nsisdir:
     description: NSIS installation directory
-    value: ${{ steps.vars.outputs.prefix }}/share/nsis
+    value: ${{ steps.vars.outputs.nsisdir }}
 
 runs:
   using: composite
@@ -32,16 +32,38 @@ runs:
         LOG: ${{ inputs.advanced-logging }}
       run: |
         set -euo pipefail
+
         if [ "$VERSION" = latest ]; then
           # SourceForge has no "latest file" URL; its release JSON names the current one
           VERSION=$(curl -fsSL "https://sourceforge.net/projects/nsis/best_release.json" \
             | grep -o 'nsis-[0-9.]*-src\.tar\.bz2' | head -1 | sed 's/^nsis-//;s/-src.*//')
           [ -n "$VERSION" ] || { echo "could not resolve latest NSIS version"; exit 1; }
           echo "resolved latest NSIS version: $VERSION"
         fi
+
+        if [ "${{ runner.os }}" = Windows ]; then
+          # Windows uses upstream's prebuilt binaries, and there is no build that
+          # combines both special builds
+          if [ "$LARGE" = "true" ] && [ "$LOG" = "true" ]; then
+            echo "large-strings and advanced-logging cannot be combined on Windows" >&2
+            exit 1
+          fi
+
+          # Forward slashes: usable from bash and from PATH alike
+          prefix=$(cygpath -m "$HOME/nsis")
+          nsisdir=$prefix
+          bindir=$prefix
+        else
+          prefix=$HOME/nsis
+          nsisdir=$prefix/share/nsis
+          bindir=$prefix/bin
+        fi
+
         echo "version=$VERSION" >> "$GITHUB_OUTPUT"
-        echo "prefix=$HOME/nsis" >> "$GITHUB_OUTPUT"
-        echo "key=nsis-${{ runner.os }}-$VERSION-ls$LARGE-al$LOG" >> "$GITHUB_OUTPUT"
+        echo "prefix=$prefix" >> "$GITHUB_OUTPUT"
+        echo "nsisdir=$nsisdir" >> "$GITHUB_OUTPUT"
+        echo "bindir=$bindir" >> "$GITHUB_OUTPUT"
+        echo "key=nsis-${{ runner.os }}-$VERSION-largeStrings=$LARGE-advancedLogging=$LOG" >> "$GITHUB_OUTPUT"
 
     - name: Restore cached NSIS build
       id: cache
@@ -50,6 +72,36 @@ runs:
         path: ~/nsis
         key: ${{ steps.vars.outputs.key }}
 
+    # Upstream ships prebuilt Windows binaries, including for both special builds,
+    # so there is nothing to compile here
+    - name: Install NSIS (Windows)
+      if: steps.cache.outputs.cache-hit != 'true' && runner.os == 'Windows'
+      shell: bash
+      working-directory: ${{ runner.temp }}
+      env:
+        VERSION: ${{ steps.vars.outputs.version }}
+        LARGE: ${{ inputs.large-strings }}
+        LOG: ${{ inputs.advanced-logging }}
+        PREFIX: ${{ steps.vars.outputs.prefix }}
+      run: |
+        set -euo pipefail
+        base="https://downloads.sourceforge.net/project/nsis/NSIS%20${VERSION%%.*}/$VERSION"
+        curl -fsSLO "$base/nsis-$VERSION.zip"
+        7z x -y -bso0 "nsis-$VERSION.zip"
+
+        mkdir -p "$PREFIX"
+        cp -R "nsis-$VERSION/." "$PREFIX/"
+
+        # Special builds are overlays: makensis.exe plus matching stubs, no top-level dir
+        variant=""
+        [ "$LARGE" = "true" ] && variant="strlen_8192"
+        [ "$LOG" = "true" ] && variant="log"
+
+        if [ -n "$variant" ]; then
+          curl -fsSLO "$base/nsis-$VERSION-$variant.zip"
+          7z x -y -bso0 -o"$PREFIX" "nsis-$VERSION-$variant.zip"
+        fi
+
     - name: Install build dependencies (Linux)
       if: steps.cache.outputs.cache-hit != 'true' && runner.os == 'Linux'
       shell: bash
@@ -67,7 +119,7 @@ runs:
         brew install scons mingw-w64
 
     - name: Download and build NSIS
-      if: steps.cache.outputs.cache-hit != 'true'
+      if: steps.cache.outputs.cache-hit != 'true' && runner.os != 'Windows'
       shell: bash
       working-directory: ${{ runner.temp }}
       env:
@@ -98,6 +150,7 @@ runs:
           STRIP=0
           VERSION="$VERSION"
         )
+
         [ "$LARGE" = "true" ] && args+=(NSIS_MAX_STRLEN=8192)
         [ "$LOG" = "true" ] && args+=(NSIS_CONFIG_LOG=yes)
 
@@ -108,12 +161,12 @@ runs:
     - name: Export NSISDIR and verify
       shell: bash
       env:
-        PREFIX: ${{ steps.vars.outputs.prefix }}
+        NSISDIR: ${{ steps.vars.outputs.nsisdir }}
+        BINDIR: ${{ steps.vars.outputs.bindir }}
       run: |
         set -euo pipefail
-        echo "NSISDIR=$PREFIX/share/nsis" >> "$GITHUB_ENV"
-        echo "$PREFIX/bin" >> "$GITHUB_PATH"
-        export NSISDIR="$PREFIX/share/nsis"
-        echo "makensis v$("$PREFIX/bin/makensis" -VERSION)"
+        echo "NSISDIR=$NSISDIR" >> "$GITHUB_ENV"
+        echo "$BINDIR" >> "$GITHUB_PATH"
+        echo "makensis $("$BINDIR/makensis" -VERSION)"
         echo
-        "$PREFIX/bin/makensis" -HDRINFO
+        "$BINDIR/makensis" -HDRINFO