Fixes #1621: don't force a Chocolatey Python install when Python already exists

docs/packaging/windows-chocolatey/httpie.nuspec

@@ -25,6 +25,10 @@ Main features:
 - Expressive and intuitive syntax
 - Linux, macOS, Windows, and FreeBSD support
 - All that and more in 2 simple commands: `http` + `https`
+
+Requires Python 3.7 or newer. Any existing Python installation is used — including
+one installed from python.org — so Chocolatey will not install a second copy of Python.
+If no Python is found, the installer tells you how to get one (`choco install python3`).
 		</description>
 		<title>HTTPie</title>
 		<authors>HTTPie</authors>
@@ -40,9 +44,13 @@ Main features:
 		<projectSourceUrl>https://github.com/httpie/cli</projectSourceUrl>
 		<docsUrl>https://httpie.io/docs</docsUrl>
 		<bugTrackerUrl>https://github.com/httpie/cli/issues</bugTrackerUrl>
-		<dependencies>
-			<dependency id="python3" version="3.7" />
-		</dependencies>
+		<!--
+			No hard `python3` dependency on purpose: forcing Chocolatey's own Python
+			breaks installs on machines that already have Python from another source
+			(https://github.com/httpie/cli/issues/1621). tools/chocolateyinstall.ps1
+			detects an existing interpreter and reports a clear, actionable error when
+			there is genuinely none.
+		-->
 	</metadata>
 	<files>
 		<file src="tools\**" target="tools" />

docs/packaging/windows-chocolatey/tools/chocolateyinstall.ps1

@@ -1,2 +1,65 @@
-$ErrorActionPreference = 'Stop';
-py -m pip install $env:ChocolateyPackageName==$env:ChocolateyPackageVersion --disable-pip-version-check
+$ErrorActionPreference = 'Stop'
+
+# HTTPie is installed into an existing Python installation via pip, so we need
+# a Python interpreter — but NOT necessarily a Chocolatey-managed one. Declaring
+# a hard `python3` dependency in the .nuspec makes Chocolatey install its own
+# Python even when a perfectly good one is already present (e.g. installed from
+# python.org), and that second install can fail outright, taking the whole
+# `choco install httpie` down with it. See:
+# https://github.com/httpie/cli/issues/1621
+# Instead, we detect whatever Python is already available and only ask the user
+# to install one when there is genuinely none.
+
+$MinimumPythonVersion = [version]'3.7'
+$VersionProbe = 'import sys; sys.stdout.write(".".join(str(part) for part in sys.version_info[:3]))'
+
+function Get-UsablePython {
+    # In order of preference. `py` is the Windows Python launcher: it finds
+    # interpreters registered by any installer, not just Chocolatey's.
+    $candidates = @(
+        @{ Command = 'py'      ; Prefix = @('-3') },
+        @{ Command = 'python'  ; Prefix = @() },
+        @{ Command = 'python3' ; Prefix = @() }
+    )
+
+    foreach ($candidate in $candidates) {
+        $resolved = Get-Command $candidate.Command -CommandType Application -ErrorAction SilentlyContinue | Select-Object -First 1
+        if (-not $resolved) { continue }
+
+        $reported = & $resolved.Path @($candidate.Prefix + @('-c', $VersionProbe)) 2>$null
+        if ($LASTEXITCODE -ne 0 -or [string]::IsNullOrWhiteSpace($reported)) { continue }
+
+        try { $version = [version]$reported.Trim() } catch { continue }
+        if ($version -lt $MinimumPythonVersion) { continue }
+
+        return [pscustomobject]@{
+            Path    = $resolved.Path
+            Prefix  = $candidate.Prefix
+            Version = $version
+        }
+    }
+
+    return $null
+}
+
+$python = Get-UsablePython
+if (-not $python) {
+    throw @"
+HTTPie needs Python $MinimumPythonVersion or newer, but no usable Python interpreter was found on PATH.
+Install Python, then run ``choco install httpie`` again:
+    choco install python3
+Or download an installer from https://www.python.org/downloads/windows/
+(make sure "Add Python to PATH" is enabled).
+"@
+}
+
+Write-Host "Installing HTTPie with Python $($python.Version) from '$($python.Path)'."
+
+& $python.Path @($python.Prefix + @(
+    '-m', 'pip', 'install',
+    "$env:ChocolateyPackageName==$env:ChocolateyPackageVersion",
+    '--disable-pip-version-check'
+))
+if ($LASTEXITCODE -ne 0) {
+    throw "pip failed to install $env:ChocolateyPackageName==$env:ChocolateyPackageVersion (exit code $LASTEXITCODE)."
+}