docs(prqlc-c): replace stale Go cgo snippet, fix linker flags (#5956)

Author: prql-bot

prqlc/bindings/prqlc-c/README.md

@@ -7,86 +7,28 @@ allows embedding in languages that support FFI — for example, Golang.
 
 ## Linking
 
-See [examples/minimal-c/Makefile](examples/minimal-c/Makefile).
+See [examples/minimal-c/Makefile](examples/minimal-c/Makefile) for the canonical
+link flags used to build the bundled C example.
 
-Copy the `.a` and `.so` files in a convenient place and add the following
-compile flags to Go (cgo):
+To link against the static library from another build system, point the linker
+at the directory containing `libprqlc_c.a` and add `prqlc_c` plus its system
+dependencies, for example:
 
-`CGO_LDFLAGS="-L/path/to/libprqlc_c.a -lprqlc -pthread -ldl" go build`
+`CGO_LDFLAGS="-L/path/to/target/release -lprqlc_c -pthread -ldl -lm" go build`
 
-## Examples
-
-For a minimal example, see
-[examples/minimal-c/main.c](examples/minimal-c/main.c).
-
-Below is an example from an actual application that is using PRQL in Go.
-
-```go
-package prql
-
-/*
-
-
-#include <stdlib.h>
-
-int to_sql(char *prql_query, char *sql_query);
-int to_json(char *prql_query, char *json_query);
-
-*/
-import "C"
+(On macOS, also add `-framework CoreFoundation`.)
 
-import (
-    "errors"
-    "strings"
-    "unsafe"
-)
-
-// ToSQL converts a PRQL query to SQL
-func ToSQL(prql string) (string, error) {
-    // buffer length should not be less than 1K because we may get an error
-    // from the PRQL compiler with a very short query
-    cStringBufferLength := 1024
-
-    // allocate a buffer 3 times the length of the PRQL query to store the
-    // generated SQL query
-    if len(prql)*3 > cStringBufferLength {
-        cStringBufferLength = len(prql) * 3
-    }
-
-    // preallocate the buffer
-    cstr := C.CString(strings.Repeat(" ", cStringBufferLength))
-    defer C.free(unsafe.Pointer(cstr))
-
-    // convert the PRQL query to SQL
-    res := C.to_sql(C.CString(prql), cstr)
-    if res == 0 {
-        return C.GoString(cstr), nil
-    }
-
-    return "", errors.New(C.GoString(cstr))
-}
-
-// ToJSON converts a PRQL query to JSON
-func ToJSON(prql string) (string, error) {
-    // buffer length should not be less than 1K because we may get an error
-    cStringBufferLength := 1024
-    if len(prql)*3 > cStringBufferLength {
-        cStringBufferLength = len(prql) * 10
-    }
-
-    // preallocate the buffer
-    cstr := C.CString(strings.Repeat(" ", cStringBufferLength))
-    defer C.free(unsafe.Pointer(cstr))
+## Examples
 
-    // convert the PRQL query to SQL
-    res := C.to_json(C.CString(prql), cstr)
-    if res == 0 {
-        return C.GoString(cstr), nil
-    }
+- [examples/minimal-c/main.c](examples/minimal-c/main.c) — minimal C example
+  covering `compile`, custom `Options`, error handling, and the staged
+  `prql_to_pl` / `pl_to_rq` entry points.
+- [examples/minimal-cpp](examples/minimal-cpp) — the same flow using the
+  generated C++ header.
+- [examples/minimal-zig](examples/minimal-zig) — a Zig example using `@cImport`
+  against `prqlc.h`.
 
-    return "", errors.New(C.GoString(cstr))
-}
-```
+The full FFI surface is documented inline in [prqlc.h](prqlc.h).
 
 ## Development