Code Completion

ST LSP provides context-aware completions as you type in .st files.

What Gets Completed

Keywords

All IEC 61131-3 reserved words are available as completions:

IF, THEN, ELSE, ELSIF, END_IF
FOR, TO, BY, DO, END_FOR
WHILE, END_WHILE
CASE, OF, END_CASE
PROGRAM, FUNCTION_BLOCK, FUNCTION, END_PROGRAM, END_FUNCTION_BLOCK, END_FUNCTION
VAR, VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR_GLOBAL, END_VAR
...

Built-in Types

All IEC 61131-3 elementary data types:

Type	Size	Range
BOOL	1 bit	TRUE / FALSE
INT	16 bit	-32768 … 32767
DINT	32 bit	-2147483648 … 2147483647
REAL	32 bit	±3.4×10³⁸
LREAL	64 bit	±1.8×10³⁰⁸
STRING	variable	text
TIME	32 bit	duration
DATE	32 bit	calendar date
…

Standard Function Blocks

IEC 61131-3 standard library FBs, including:

• Timers: TON, TOF, TP
• Counters: CTU, CTD, CTUD
• Bistables: SR, RS
• Edge detectors: R_TRIG, F_TRIG

Local Variables

Variables declared in the current POU’s VAR sections are offered as completions within that POU’s body.

Triggering Completion

Completion triggers automatically after typing or can be invoked manually with Ctrl+Space.

The server registers two trigger characters:

• . (dot) — triggers member completion on function blocks, structs, and enums
• : (colon) — triggers enum-aware completion after :=

Member Completion

Typing . after a variable shows members of its resolved type.

VAR
  fbMotor : FB_Motor;
END_VAR
fbMotor.  (* shows VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, methods, and properties *)

The server resolves the identifier before the dot, looks up its type, and returns matching members. This works through chains of nested types:

fbMotor.stConfig.nMaxSpeed  (* resolves FB_Motor → stConfig's type → nMaxSpeed *)

Pointer dereference syntax is also supported — myPtr^. dereferences the pointer first, then shows members of the pointed-to type.

Visibility Filtering

Access modifiers control which members appear depending on the access context:

Modifier	External (fbVar.)	SUPER^.	THIS^.
(none / public)	Visible	Visible	Visible
INTERNAL	Visible	Visible	Visible
PROTECTED	Hidden	Visible	Visible
PRIVATE	Hidden	Hidden	Visible

• External access (fbVar.) only shows VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, and public methods/properties. Internal variables and private/protected members are excluded.
• THIS^. shows all own members plus inherited members (excluding inherited PRIVATE members).

SUPER^ Completion

Inside a function block that uses EXTENDS, typing SUPER^. shows members inherited from the parent:

FUNCTION_BLOCK FB_Child EXTENDS FB_Parent
VAR END_VAR
  SUPER^.  (* shows FB_Parent's members, walking up the EXTENDS chain *)
END_FUNCTION_BLOCK

SUPER^ walks the entire inheritance chain recursively — grandparent members are included. PRIVATE members from parent FBs are excluded, but PROTECTED members are visible. FINAL methods appear normally (they are callable, just not overridable).

Enum-Aware Completion

After := Assignment

When the left-hand side of := is an enum-typed variable, completion offers only the matching enum values instead of the usual keyword list:

TYPE
  E_Color : (Red, Green, Blue);
END_TYPE
VAR
  eColor : E_Color;
END_VAR
eColor :=   (* shows E_Color.Red, E_Color.Green, E_Color.Blue — no keywords *)

Inside CASE Blocks

When a CASE selector variable has an enum type, completion inside the CASE body offers the enum values:

CASE eColor OF
  (* completion here shows E_Color.Red, E_Color.Green, E_Color.Blue *)
END_CASE

For non-enum variables, the standard keyword and variable completions are returned as usual.