fix: resolve generic TO_STRING/TO_WSTRING to the correct monomorphization

book/src/libraries/external_functions.md

@@ -19,6 +19,58 @@ At compilation time, the function `log` will be defined as an externally availab
 
 > Note: At linking time, a `log` function with a compatible signature must be available on the system.
 
+## Generic Functions
+
+A `FUNCTION` can be made generic by declaring one or more type parameters with a
+type-nature constraint, e.g. `<T: ANY_INT>`. The type parameters may be used as the type
+of inputs, outputs and the return value:
+
+```iecst
+FUNCTION MAX <T: ANY_ELEMENTARY> : T
+VAR_INPUT
+    in1 : T;
+    in2 : T;
+END_VAR
+END_FUNCTION
+```
+
+A generic function is never called directly. Every call is resolved to a concrete
+*monomorphization* whose name is the generic function's name followed by `__<TYPE>` for
+the resolved type argument. For example, `MAX(aDint, bDint)` resolves to `MAX__DINT`.
+
+The compiler does not synthesize the body of a monomorphization; each one must be
+*provided*, as one of:
+
+- an ordinary `FUNCTION` with the mangled name (an ST body),
+- an `{external}` declaration of the mangled name (implemented elsewhere, e.g. in C or
+  Rust, resolved at link time), or
+- a compiler builtin.
+
+Calling a generic with a type for which no monomorphization is provided is reported as an
+unresolved reference (`E048`).
+
+### Monomorphizations returning aggregate types
+
+When a generic function returns an aggregate type (`STRING`, `WSTRING`, an array or a
+struct), its monomorphization must be **declared in `ST`** — either as a body or as an
+`{external}` declaration. A symbol that exists only at link time (with no `ST`
+declaration) is enough for a scalar return, but not for an aggregate return: an
+aggregate-returning generic call whose monomorphization is not declared is reported as
+`E048` at compile time rather than failing at link time or run time.
+
+For example, the standard `TO_STRING <T: ANY> : STRING` conversion declares a
+monomorphization for every supported source type (`TO_STRING__DINT`, `TO_STRING__REAL`,
+…). Calling `TO_STRING` with a type that has no such declaration is a compile error:
+
+```iecst
+TYPE Point : STRUCT x, y : DINT; END_STRUCT END_TYPE
+
+FUNCTION main : DINT
+VAR s : STRING; p : Point; END_VAR
+    s := TO_STRING(p);   // error[E048]: Could not resolve reference to TO_STRING__Point
+END_FUNCTION
+```
+
 ## Calling C functions
 
 `ST` code can call into foreign functions natively.

libs/stdlib/iec61131-st/to_string.st

@@ -93,6 +93,161 @@ FUNCTION TO_STRING__WSTRING : STRING[__STRING_LENGTH]
     WSTRING_TO_STRING_EXT(in, TO_STRING__WSTRING);
 END_FUNCTION
 
+// Numeric, bit-string and date/time monomorphizations of the generic TO_STRING, each
+// delegating to the corresponding typed <T>_TO_STRING conversion function.
+
+FUNCTION TO_STRING__DINT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DINT;
+    END_VAR
+
+    TO_STRING__DINT := DINT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LINT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LINT;
+    END_VAR
+
+    TO_STRING__LINT := LINT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__USINT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : USINT;
+    END_VAR
+
+    TO_STRING__USINT := USINT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__UINT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : UINT;
+    END_VAR
+
+    TO_STRING__UINT := UINT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__UDINT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : UDINT;
+    END_VAR
+
+    TO_STRING__UDINT := UDINT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__ULINT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : ULINT;
+    END_VAR
+
+    TO_STRING__ULINT := ULINT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__BYTE : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : BYTE;
+    END_VAR
+
+    TO_STRING__BYTE := BYTE_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__DWORD : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DWORD;
+    END_VAR
+
+    TO_STRING__DWORD := DWORD_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LWORD : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LWORD;
+    END_VAR
+
+    TO_STRING__LWORD := LWORD_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__REAL : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : REAL;
+    END_VAR
+
+    TO_STRING__REAL := REAL_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LREAL : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LREAL;
+    END_VAR
+
+    TO_STRING__LREAL := LREAL_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__TIME : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : TIME;
+    END_VAR
+
+    TO_STRING__TIME := TIME_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LTIME : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LTIME;
+    END_VAR
+
+    TO_STRING__LTIME := LTIME_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__DATE : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DATE;
+    END_VAR
+
+    TO_STRING__DATE := DATE_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LDATE : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LDATE;
+    END_VAR
+
+    TO_STRING__LDATE := LDATE_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__DT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DT;
+    END_VAR
+
+    TO_STRING__DT := DT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LDT : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LDT;
+    END_VAR
+
+    TO_STRING__LDT := LDT_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__TOD : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : TOD;
+    END_VAR
+
+    TO_STRING__TOD := TOD_TO_STRING(in);
+END_FUNCTION
+
+FUNCTION TO_STRING__LTOD : STRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LTOD;
+    END_VAR
+
+    TO_STRING__LTOD := LTOD_TO_STRING(in);
+END_FUNCTION
+
 // -----------------------------------------------------------------------------------------------------------
 FUNCTION TO_WSTRING<T: ANY> : WSTRING[__STRING_LENGTH]
     VAR_INPUT
@@ -122,4 +277,127 @@ FUNCTION TO_WSTRING__WCHAR : WSTRING[__STRING_LENGTH]
     END_VAR
 
     TO_WSTRING__WCHAR := WCHAR_TO_WSTRING(in);
-END_FUNCTION
+END_FUNCTION
+
+// Numeric, bit-string and date/time monomorphizations of the generic TO_WSTRING, each
+// delegating to the corresponding typed <T>_TO_WSTRING conversion function.
+
+FUNCTION TO_WSTRING__DINT : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DINT;
+    END_VAR
+
+    TO_WSTRING__DINT := DINT_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LINT : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LINT;
+    END_VAR
+
+    TO_WSTRING__LINT := LINT_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__BYTE : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : BYTE;
+    END_VAR
+
+    TO_WSTRING__BYTE := BYTE_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__DWORD : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DWORD;
+    END_VAR
+
+    TO_WSTRING__DWORD := DWORD_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LWORD : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LWORD;
+    END_VAR
+
+    TO_WSTRING__LWORD := LWORD_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__REAL : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : REAL;
+    END_VAR
+
+    TO_WSTRING__REAL := REAL_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LREAL : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LREAL;
+    END_VAR
+
+    TO_WSTRING__LREAL := LREAL_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__TIME : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : TIME;
+    END_VAR
+
+    TO_WSTRING__TIME := TIME_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LTIME : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LTIME;
+    END_VAR
+
+    TO_WSTRING__LTIME := LTIME_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__DATE : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DATE;
+    END_VAR
+
+    TO_WSTRING__DATE := DATE_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LDATE : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LDATE;
+    END_VAR
+
+    TO_WSTRING__LDATE := LDATE_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__DT : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : DT;
+    END_VAR
+
+    TO_WSTRING__DT := DT_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LDT : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LDT;
+    END_VAR
+
+    TO_WSTRING__LDT := LDT_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__TOD : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : TOD;
+    END_VAR
+
+    TO_WSTRING__TOD := TOD_TO_WSTRING(in);
+END_FUNCTION
+
+FUNCTION TO_WSTRING__LTOD : WSTRING[__STRING_LENGTH]
+    VAR_INPUT
+        in : LTOD;
+    END_VAR
+
+    TO_WSTRING__LTOD := LTOD_TO_WSTRING(in);
+END_FUNCTION