@@ -65,8 +65,7 @@ func startPty(cmd *exec.Cmd) (PTY, error) {
6565 false ,
6666 // https://docs.microsoft.com/en-us/windows/win32/procthread/process-creation-flags#create_unicode_environment
6767 windows .CREATE_UNICODE_ENVIRONMENT | windows .EXTENDED_STARTUPINFO_PRESENT ,
68- // Environment variables can come later!
69- createEnvBlock ([]string {"SYSTEMROOT=" + os .Getenv ("SYSTEMROOT" )}),
68+ createEnvBlock (addCriticalEnv (dedupEnvCase (true , cmd .Env ))),
7069 dirPtr ,
7170 & startupInfo .StartupInfo ,
7271 & processInfo ,
@@ -103,3 +102,46 @@ func createEnvBlock(envv []string) *uint16 {
103102
104103 return & utf16 .Encode ([]rune (string (b )))[0 ]
105104}
105+
106+ // dedupEnvCase is dedupEnv with a case option for testing.
107+ // If caseInsensitive is true, the case of keys is ignored.
108+ func dedupEnvCase (caseInsensitive bool , env []string ) []string {
109+ out := make ([]string , 0 , len (env ))
110+ saw := make (map [string ]int , len (env )) // key => index into out
111+ for _ , kv := range env {
112+ eq := strings .Index (kv , "=" )
113+ if eq < 0 {
114+ out = append (out , kv )
115+ continue
116+ }
117+ k := kv [:eq ]
118+ if caseInsensitive {
119+ k = strings .ToLower (k )
120+ }
121+ if dupIdx , isDup := saw [k ]; isDup {
122+ out [dupIdx ] = kv
123+ continue
124+ }
125+ saw [k ] = len (out )
126+ out = append (out , kv )
127+ }
128+ return out
129+ }
130+
131+ // addCriticalEnv adds any critical environment variables that are required
132+ // (or at least almost always required) on the operating system.
133+ // Currently this is only used for Windows.
134+ func addCriticalEnv (env []string ) []string {
135+ for _ , kv := range env {
136+ eq := strings .Index (kv , "=" )
137+ if eq < 0 {
138+ continue
139+ }
140+ k := kv [:eq ]
141+ if strings .EqualFold (k , "SYSTEMROOT" ) {
142+ // We already have it.
143+ return env
144+ }
145+ }
146+ return append (env , "SYSTEMROOT=" + os .Getenv ("SYSTEMROOT" ))
147+ }
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