os/env: use libuv v1.12 getenv/setenv API

- Minimum required libuv is now v1.12
- Because `uv_os_getenv` requires allocating, we must manage a map
  (`envmap` in `env.c`) to maintain the old behavior of `os_getenv` .
- free() map-items after removal. khash.h does not make copies of
  anything, so even its keys must be memory-managed by the caller.

closes #8398
closes #9267

2 files changed, 63 insertions, 28 deletions

diff --git a/test/unit/helpers.lua b/test/unit/helpers.lua
index f8143a0125..beb25f25db 100644
--- a/test/unit/helpers.lua
+++ b/test/unit/helpers.lua
@@ -645,16 +645,16 @@ local function itp_child(wr, func)
     s = s:sub(1, hook_msglen - 2)
     sc.write(wr, '>' .. s .. (' '):rep(hook_msglen - 2 - #s) .. '\n')
   end
-  local err, emsg = pcall(init)
-  if err then
+  local status, result = pcall(init)
+  if status then
     collectgarbage('stop')
     child_sethook(wr)
-    err, emsg = pcall(func)
+    status, result = pcall(func)
     debug.sethook()
   end
-  emsg = tostring(emsg)
   sc.write(wr, trace_end_msg)
-  if not err then
+  if not status then
+    local emsg = tostring(result)
     if #emsg > 99999 then
       emsg = emsg:sub(1, 99999)
     end
@@ -668,7 +668,7 @@ local function itp_child(wr, func)
   collectgarbage()
   sc.write(wr, '$\n')
   sc.close(wr)
-  sc.exit(err and 0 or 1)
+  sc.exit(status and 0 or 1)
 end
 
 local function check_child_err(rd)
diff --git a/test/unit/os/env_spec.lua b/test/unit/os/env_spec.lua
index c54d5a9b77..c543551607 100644
--- a/test/unit/os/env_spec.lua
+++ b/test/unit/os/env_spec.lua
@@ -8,17 +8,22 @@ local ffi = helpers.ffi
 local cstr = helpers.cstr
 local to_cstr = helpers.to_cstr
 local NULL = helpers.NULL
+local OK = 0
 
 require('lfs')
 
 local cimp = cimport('./src/nvim/os/os.h')
 
 describe('env.c', function()
+  local function os_env_exists(name)
+    return cimp.os_env_exists(to_cstr(name))
+  end
+
   local function os_setenv(name, value, override)
     return cimp.os_setenv(to_cstr(name), to_cstr(value), override)
   end
 
-  local function os_unsetenv(name, _, _)
+  local function os_unsetenv(name)
     return cimp.os_unsetenv(to_cstr(name))
   end
 
@@ -31,25 +36,44 @@ describe('env.c', function()
     end
   end
 
-  describe('os_setenv', function()
-    local OK = 0
+  itp('os_env_exists', function()
+    eq(false, os_env_exists(''))
+    eq(false, os_env_exists('      '))
+    eq(false, os_env_exists('\t'))
+    eq(false, os_env_exists('\n'))
+    eq(false, os_env_exists('AaあB <= very weird name...'))
 
-    itp('sets an env variable and returns OK', function()
+    local varname = 'NVIM_UNIT_TEST_os_env_exists'
+    eq(false, os_env_exists(varname))
+    eq(OK, os_setenv(varname, 'foo bar baz ...', 1))
+    eq(true, os_env_exists(varname))
+  end)
+
+  describe('os_setenv', function()
+    itp('sets an env var and returns success', function()
       local name = 'NVIM_UNIT_TEST_SETENV_1N'
       local value = 'NVIM_UNIT_TEST_SETENV_1V'
       eq(nil, os.getenv(name))
-      eq(OK, (os_setenv(name, value, 1)))
+      eq(OK, os_setenv(name, value, 1))
       eq(value, os.getenv(name))
+
+      -- Set empty, then set non-empty, then retrieve.
+      eq(OK, os_setenv(name, '', 1))
+      eq('', os.getenv(name))
+      eq(OK, os_setenv(name, 'non-empty', 1))
+      eq('non-empty', os.getenv(name))
     end)
 
-    itp("dosn't overwrite an env variable if overwrite is 0", function()
+    itp("`overwrite` behavior", function()
       local name = 'NVIM_UNIT_TEST_SETENV_2N'
       local value = 'NVIM_UNIT_TEST_SETENV_2V'
       local value_updated = 'NVIM_UNIT_TEST_SETENV_2V_UPDATED'
-      eq(OK, (os_setenv(name, value, 0)))
+      eq(OK, os_setenv(name, value, 0))
       eq(value, os.getenv(name))
-      eq(OK, (os_setenv(name, value_updated, 0)))
+      eq(OK, os_setenv(name, value_updated, 0))
       eq(value, os.getenv(name))
+      eq(OK, os_setenv(name, value_updated, 1))
+      eq(value_updated, os.getenv(name))
     end)
   end)
 
@@ -93,31 +117,42 @@ describe('env.c', function()
   end)
 
   describe('os_getenv', function()
-    itp('reads an env variable', function()
+    itp('reads an env var', function()
       local name = 'NVIM_UNIT_TEST_GETENV_1N'
       local value = 'NVIM_UNIT_TEST_GETENV_1V'
       eq(NULL, os_getenv(name))
       -- Use os_setenv because Lua dosen't have setenv.
       os_setenv(name, value, 1)
       eq(value, os_getenv(name))
+
+      -- Get a big value.
+      local bigval = ('x'):rep(256)
+      eq(OK, os_setenv(name, bigval, 1))
+      eq(bigval, os_getenv(name))
+
+      -- Set non-empty, then set empty.
+      eq(OK, os_setenv(name, 'non-empty', 1))
+      eq('non-empty', os_getenv(name))
+      eq(OK, os_setenv(name, '', 1))
+      eq(NULL, os_getenv(name))
     end)
 
-    itp('returns NULL if the env variable is not found', function()
-      local name = 'NVIM_UNIT_TEST_GETENV_NOTFOUND'
-      return eq(NULL, os_getenv(name))
+    itp('returns NULL if the env var is not found', function()
+      eq(NULL, os_getenv('NVIM_UNIT_TEST_GETENV_NOTFOUND'))
     end)
   end)
 
-  describe('os_unsetenv', function()
-    itp('unsets environment variable', function()
-      local name = 'TEST_UNSETENV'
-      local value = 'TESTVALUE'
-      os_setenv(name, value, 1)
-      os_unsetenv(name)
-      neq(os_getenv(name), value)
-      -- Depending on the platform the var might be unset or set as ''
-      assert.True(os_getenv(name) == nil or os_getenv(name) == '')
-    end)
+  itp('os_unsetenv', function()
+    local name = 'TEST_UNSETENV'
+    local value = 'TESTVALUE'
+    os_setenv(name, value, 1)
+    eq(OK, os_unsetenv(name))
+    neq(os_getenv(name), value)
+    -- Depending on the platform the var might be unset or set as ''
+    assert.True(os_getenv(name) == nil or os_getenv(name) == '')
+    if os_getenv(name) == nil then
+      eq(false, os_env_exists(name))
+    end
   end)
 
   describe('os_getenvname_at_index', function()