Add bring-your-own-buffer versions of `os.lookup_env` and `os.get_env`

And make `core:terminal` use it so that `core:log` can be imported with `-default-to-nil-allocator`,
in which the actual allocator is set up in `main()`.

Windows was tricky because of the utf-8 <> utf-16 conversion, so we use some temporary stack buffers for that purpose,
limiting the non-allocating version there to 512 utf-16 characters each for the key and environment value.

In general the value is (obviously) limited to the size of the supplied buffer, and a `.Buffer_Full` error is returned
if that buffer is insufficient. If the key is not found, the procedure returns `.Env_Var_Not_Found`.

TODO:
- Factor out buffer-backed utf8 + utf16 conversion to `core:sys/util` to more easily apply this pattern.
- Add similar `lookup_env` and `get_env` procedures to `core:os/os2`.

Fixes #5336

9 files changed, 261 insertions, 24 deletions

diff --git a/core/os/env_windows.odin b/core/os/env_windows.odin
index efd002342..6c7759abe 100644
--- a/core/os/env_windows.odin
+++ b/core/os/env_windows.odin
@@ -8,7 +8,7 @@ import "base:runtime"
 // Otherwise the returned value will be empty and the boolean will be false
 // NOTE: the value will be allocated with the supplied allocator
 @(require_results)
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	if key == "" {
 		return
 	}
@@ -29,17 +29,77 @@ lookup_env :: proc(key: string, allocator := context.allocator) -> (value: strin
 	return
 }
 
+// This version of `lookup_env` doesn't allocate and instead requires the user to provide a buffer.
+// Note that it is limited to environment names and values of 512 utf-16 values each
+// due to the necessary utf-8 <> utf-16 conversion.
+@(require_results)
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	key_buf: [513]u16
+	n1 := win32.MultiByteToWideChar(win32.CP_UTF8, win32.MB_ERR_INVALID_CHARS, raw_data(key), i32(len(key)), nil, 0)
+	if n1 == 0 {
+		return "", nil
+	}
+
+	n1 = win32.MultiByteToWideChar(win32.CP_UTF8, win32.MB_ERR_INVALID_CHARS, raw_data(key), i32(len(key)), raw_data(key_buf[:]), n1)
+	if n1 == 0 {
+		return "", nil
+	}
+
+	n2 := win32.GetEnvironmentVariableW(raw_data(key_buf[:]), nil, 0)
+	if n2 == 0 && get_last_error() == ERROR_ENVVAR_NOT_FOUND {
+		return "", .Env_Var_Not_Found
+	}
+
+	val_buf: [513]u16
+	n2 = win32.GetEnvironmentVariableW(raw_data(key_buf[:]), raw_data(val_buf[:]), u32(len(val_buf[:])))
+	if n2 == 0 && get_last_error() == ERROR_ENVVAR_NOT_FOUND {
+		return "", .Env_Var_Not_Found
+	} else if int(n2) > len(buf) {
+		return "", .Buffer_Full
+	}
+
+	n3 := win32.WideCharToMultiByte(win32.CP_UTF8, win32.WC_ERR_INVALID_CHARS, raw_data(val_buf[:]), -1, nil, 0, nil, nil)
+	if n3 == 0 {
+		return
+	} else if int(n3) > len(buf) {
+		return "", .Buffer_Full
+	}
+
+	n4 := win32.WideCharToMultiByte(win32.CP_UTF8, win32.WC_ERR_INVALID_CHARS, raw_data(val_buf[:]), -1, raw_data(buf), n3, nil, nil)
+	if n4 == 0 {
+		return
+	} else if int(n4) > len(buf) {
+		return "", .Buffer_Full
+	}
+
+	for i in 0..<n3 {
+		if buf[i] == 0 {
+			n3 = i
+			break
+		}
+	}
+	return string(buf[:n3]), nil
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
 
 // get_env retrieves the value of the environment variable named by the key
 // It returns the value, which will be empty if the variable is not present
 // To distinguish between an empty value and an unset value, use lookup_env
 // NOTE: the value will be allocated with the supplied allocator
 @(require_results)
-get_env :: proc(key: string, allocator := context.allocator) -> (value: string) {
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
 	value, _ = lookup_env(key, allocator)
 	return
 }
 
+@(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
+
+
 // set_env sets the value of the environment variable named by the key
 set_env :: proc(key, value: string) -> Error {
 	k := win32.utf8_to_wstring(key)
diff --git a/core/os/errors.odin b/core/os/errors.odin
index 691397f4b..bf4cf27ff 100644
--- a/core/os/errors.odin
+++ b/core/os/errors.odin
@@ -35,6 +35,9 @@ General_Error :: enum u32 {
 
 	File_Is_Pipe,
 	Not_Dir,
+
+	// Environment variable not found.
+	Env_Var_Not_Found,
 }
 
 
@@ -82,6 +85,7 @@ error_string :: proc "contextless" (ferr: Error) -> string {
 		case .Pattern_Has_Separator: return "pattern has separator"
 		case .File_Is_Pipe:      return "file is pipe"
 		case .Not_Dir:           return "file is not directory"
+		case .Env_Var_Not_Found: return "environment variable not found"
 		}
 	case io.Error:
 		switch e {
diff --git a/core/os/os_darwin.odin b/core/os/os_darwin.odin
index bbffc46d7..b247b1000 100644
--- a/core/os/os_darwin.odin
+++ b/core/os/os_darwin.odin
@@ -1055,9 +1055,10 @@ flush :: proc(fd: Handle) -> Error {
 }
 
 @(require_results)
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD(ignore = context.temp_allocator == allocator)
 	path_str := strings.clone_to_cstring(key, context.temp_allocator)
+	// NOTE(tetra): Lifetime of 'cstr' is unclear, but _unix_free(cstr) segfaults.
 	cstr := _unix_getenv(path_str)
 	if cstr == nil {
 		return "", false
@@ -1066,11 +1067,39 @@ lookup_env :: proc(key: string, allocator := context.allocator) -> (value: strin
 }
 
 @(require_results)
-get_env :: proc(key: string, allocator := context.allocator) -> (value: string) {
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	if len(key) + 1 > len(buf) {
+		return "", .Buffer_Full
+	} else {
+		copy(buf, key)
+	}
+
+	if value = string(_unix_getenv(cstring(raw_data(buf)))); value == "" {
+		return "", .Env_Var_Not_Found
+	} else {
+		if len(value) > len(buf) {
+			return "", .Buffer_Full
+		} else {
+			copy(buf, value)
+			return string(buf[:len(value)]), nil
+		}
+	}
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
 	value, _ = lookup_env(key, allocator)
 	return
 }
 
+@(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
+
 set_env :: proc(key, value: string) -> Error {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD()
 	key_cstring := strings.clone_to_cstring(key, context.temp_allocator)
diff --git a/core/os/os_freebsd.odin b/core/os/os_freebsd.odin
index f2ee6a496..a4c3c819e 100644
--- a/core/os/os_freebsd.odin
+++ b/core/os/os_freebsd.odin
@@ -827,10 +827,10 @@ access :: proc(path: string, mask: int) -> (bool, Error) {
 }
 
 @(require_results)
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD(ignore = context.temp_allocator == allocator)
-
 	path_str := strings.clone_to_cstring(key, context.temp_allocator)
+	// NOTE(tetra): Lifetime of 'cstr' is unclear, but _unix_free(cstr) segfaults.
 	cstr := _unix_getenv(path_str)
 	if cstr == nil {
 		return "", false
@@ -839,12 +839,40 @@ lookup_env :: proc(key: string, allocator := context.allocator) -> (value: strin
 }
 
 @(require_results)
-get_env :: proc(key: string, allocator := context.allocator) -> (value: string) {
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	if len(key) + 1 > len(buf) {
+		return "", .Buffer_Full
+	} else {
+		copy(buf, key)
+	}
+
+	if value = string(_unix_getenv(cstring(raw_data(buf)))); value == "" {
+		return "", .Env_Var_Not_Found
+	} else {
+		if len(value) > len(buf) {
+			return "", .Buffer_Full
+		} else {
+			copy(buf, value)
+			return string(buf[:len(value)]), nil
+		}
+	}
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
 	value, _ = lookup_env(key, allocator)
 	return
 }
 
 @(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
+
+@(require_results)
 get_current_directory :: proc(allocator := context.allocator) -> string {
 	context.allocator = allocator
 	// NOTE(tetra): I would use PATH_MAX here, but I was not able to find
diff --git a/core/os/os_haiku.odin b/core/os/os_haiku.odin
index 4ce726965..82ead06ab 100644
--- a/core/os/os_haiku.odin
+++ b/core/os/os_haiku.odin
@@ -463,9 +463,10 @@ access :: proc(path: string, mask: int) -> (bool, Error) {
 }
 
 @(require_results)
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD(ignore = context.temp_allocator == allocator)
 	path_str := strings.clone_to_cstring(key, context.temp_allocator)
+	// NOTE(tetra): Lifetime of 'cstr' is unclear, but _unix_free(cstr) segfaults.
 	cstr := _unix_getenv(path_str)
 	if cstr == nil {
 		return "", false
@@ -474,11 +475,40 @@ lookup_env :: proc(key: string, allocator := context.allocator) -> (value: strin
 }
 
 @(require_results)
-get_env :: proc(key: string, allocator := context.allocator) -> (value: string) {
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	if len(key) + 1 > len(buf) {
+		return "", .Buffer_Full
+	} else {
+		copy(buf, key)
+	}
+
+	if value = string(_unix_getenv(cstring(raw_data(buf)))); value == "" {
+		return "", .Env_Var_Not_Found
+	} else {
+		if len(value) > len(buf) {
+			return "", .Buffer_Full
+		} else {
+			copy(buf, value)
+			return string(buf[:len(value)]), nil
+		}
+	}
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
 	value, _ = lookup_env(key, allocator)
 	return
 }
 
+@(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
+
+
 @(private, require_results)
 _processor_core_count :: proc() -> int {
 	info: haiku.system_info
diff --git a/core/os/os_js.odin b/core/os/os_js.odin
index adb0f8061..1870218d3 100644
--- a/core/os/os_js.odin
+++ b/core/os/os_js.odin
@@ -250,11 +250,26 @@ current_thread_id :: proc "contextless" () -> int {
 	return 0
 }
 
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+@(require_results)
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	return "", false
 }
 
-get_env :: proc(key: string, allocator := context.allocator) -> string {
-	value, _ := lookup_env(key, allocator)
-	return value
-}
\ No newline at end of file
+@(require_results)
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	return "", .Env_Var_Not_Found
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
+	value, _ = lookup_env(key, allocator)
+	return
+}
+
+@(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
\ No newline at end of file
diff --git a/core/os/os_linux.odin b/core/os/os_linux.odin
index 84a7f7b32..c14f573bf 100644
--- a/core/os/os_linux.odin
+++ b/core/os/os_linux.odin
@@ -946,7 +946,7 @@ access :: proc(path: string, mask: int) -> (bool, Error) {
 }
 
 @(require_results)
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD(ignore = context.temp_allocator == allocator)
 	path_str := strings.clone_to_cstring(key, context.temp_allocator)
 	// NOTE(tetra): Lifetime of 'cstr' is unclear, but _unix_free(cstr) segfaults.
@@ -958,11 +958,39 @@ lookup_env :: proc(key: string, allocator := context.allocator) -> (value: strin
 }
 
 @(require_results)
-get_env :: proc(key: string, allocator := context.allocator) -> (value: string) {
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	if len(key) + 1 > len(buf) {
+		return "", .Buffer_Full
+	} else {
+		copy(buf, key)
+	}
+
+	if value = string(_unix_getenv(cstring(raw_data(buf)))); value == "" {
+		return "", .Env_Var_Not_Found
+	} else {
+		if len(value) > len(buf) {
+			return "", .Buffer_Full
+		} else {
+			copy(buf, value)
+			return string(buf[:len(value)]), nil
+		}
+	}
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
 	value, _ = lookup_env(key, allocator)
 	return
 }
 
+@(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
+
 set_env :: proc(key, value: string) -> Error {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD()
 	key_cstring := strings.clone_to_cstring(key, context.temp_allocator)
diff --git a/core/os/os_netbsd.odin b/core/os/os_netbsd.odin
index 40b41b133..d1e030e8e 100644
--- a/core/os/os_netbsd.odin
+++ b/core/os/os_netbsd.odin
@@ -874,10 +874,10 @@ access :: proc(path: string, mask: int) -> (bool, Error) {
 }
 
 @(require_results)
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD(ignore = context.temp_allocator == allocator)
-
 	path_str := strings.clone_to_cstring(key, context.temp_allocator)
+	// NOTE(tetra): Lifetime of 'cstr' is unclear, but _unix_free(cstr) segfaults.
 	cstr := _unix_getenv(path_str)
 	if cstr == nil {
 		return "", false
@@ -886,12 +886,40 @@ lookup_env :: proc(key: string, allocator := context.allocator) -> (value: strin
 }
 
 @(require_results)
-get_env :: proc(key: string, allocator := context.allocator) -> (value: string) {
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	if len(key) + 1 > len(buf) {
+		return "", .Buffer_Full
+	} else {
+		copy(buf, key)
+	}
+
+	if value = string(_unix_getenv(cstring(raw_data(buf)))); value == "" {
+		return "", .Env_Var_Not_Found
+	} else {
+		if len(value) > len(buf) {
+			return "", .Buffer_Full
+		} else {
+			copy(buf, value)
+			return string(buf[:len(value)]), nil
+		}
+	}
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
 	value, _ = lookup_env(key, allocator)
 	return
 }
 
 @(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
+
+@(require_results)
 get_current_directory :: proc(allocator := context.allocator) -> string {
 	context.allocator = allocator
 	// NOTE(tetra): I would use PATH_MAX here, but I was not able to find
diff --git a/core/os/os_wasi.odin b/core/os/os_wasi.odin
index a0938e860..4039d247b 100644
--- a/core/os/os_wasi.odin
+++ b/core/os/os_wasi.odin
@@ -240,11 +240,26 @@ exit :: proc "contextless" (code: int) -> ! {
 	wasi.proc_exit(wasi.exitcode_t(code))
 }
 
-lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+@(require_results)
+lookup_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	return "", false
 }
 
-get_env :: proc(key: string, allocator := context.allocator) -> string {
-	value, _ := lookup_env(key, allocator)
-	return value
-}
\ No newline at end of file
+@(require_results)
+lookup_env_buffer :: proc(buf: []u8, key: string) -> (value: string, err: Error) {
+	return "", .Env_Var_Not_Found
+}
+lookup_env :: proc{lookup_env_alloc, lookup_env_buffer}
+
+@(require_results)
+get_env_alloc :: proc(key: string, allocator := context.allocator) -> (value: string) {
+	value, _ = lookup_env(key, allocator)
+	return
+}
+
+@(require_results)
+get_env_buf :: proc(buf: []u8, key: string) -> (value: string) {
+	value, _ = lookup_env(buf, key)
+	return
+}
+get_env :: proc{get_env_alloc, get_env_buf}
\ No newline at end of file