Formatting & Appearance

ST LSP enhances the visual presentation of Structured Text code through document formatting, semantic syntax highlighting, and code lens annotations.

Document Formatting

Use Format Document (Shift+Alt+F) or enable Format on Save to automatically format an entire .st file. The formatter works on the token stream (not the AST) for robustness on partially-written code.

Keyword Uppercasing

All IEC 61131-3 keywords are converted to uppercase:

(* Before formatting *)
function_block myController
var_input
    enable : bool;
end_var

if enable then
    run();
end_if

end_function_block

(* After formatting *)
FUNCTION_BLOCK myController
VAR_INPUT
    enable : BOOL;
END_VAR

IF enable THEN
    run();
END_IF

END_FUNCTION_BLOCK

Indentation

The formatter applies consistent two-space (or tab-based) indentation following IEC 61131-3 structure:

Token	Effect
END_IF, END_FOR, END_WHILE, END_VAR, ELSE, ELSIF	Decrease indent before
END_PROGRAM, END_FUNCTION_BLOCK, END_TYPE	Reset to column 0
PROGRAM, FUNCTION_BLOCK, FUNCTION, METHOD, TYPE	Increase indent after
THEN, DO, REPEAT, VAR*, STRUCT	Increase indent (if last token on line)

Operator Spacing

The formatter ensures consistent spacing around operators and punctuation:

Rule	Example
Space around binary operators	a := b + c (not a:=b+c)
No space before ;, ,, ), ]	foo(a, b);
No space after (, [	arr[0]
No space around .	timer.Q
Unary minus treated correctly	x := -1; vs x := a - 1;

Comments (inline // and block (* *)) are preserved exactly as written.

Semantic Tokens

ST LSP provides semantic syntax highlighting on top of the standard TextMate grammar. Symbols are coloured by their actual meaning — not just their syntax — so variable names, type names, keywords, and function blocks each get a distinct colour.

Token Types

Token type	What is highlighted
keyword	Control flow, declarations, operators
type	Built-in types, custom TYPEs, ALIASes
function	PROGRAM, FUNCTION_BLOCK, FUNCTION names
variable	VAR, VAR_GLOBAL declarations
parameter	VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT
enumMember	Enum value names
property	FB PROPERTY declarations
method	FB METHOD declarations
interface	INTERFACE declarations
comment	// and (* *) comments
string	Quoted string literals
number	Integer and real literals

Token Modifiers

Modifier	Meaning
declaration	The site where the symbol is declared
abstract	ABSTRACT method in an FB
defaultLibrary	Built-in type or standard library FB

Note: Semantic token colours follow your VS Code theme. Themes that support semantic highlighting (most modern themes do) will automatically apply distinct colours per token type.

Code Lens

Code lens annotations appear above INTERFACE and FUNCTION_BLOCK declarations, showing relationship statistics computed from the workspace index:

INTERFACE — how many FBs implement it:

(* 3 implementations *)
INTERFACE I_Sensor
    METHOD GetValue : REAL;
END_INTERFACE

FUNCTION_BLOCK — how many FBs extend it:

(* 2 children *)
FUNCTION_BLOCK BasePump
END_FUNCTION_BLOCK

METHOD — how many extending FBs override it:

FUNCTION_BLOCK BasePump
    (* overridden in 1 FB *)
    METHOD Run : BOOL
    END_METHOD
END_FUNCTION_BLOCK

Click the code lens annotation to jump to the list of implementations, children, or overrides.

Note: Code lens counts are computed from the workspace index. If the count appears stale, save any modified files to trigger re-indexing.