From 629b681a298ca4a4f43b4cc1c7aaa3499958c734 Mon Sep 17 00:00:00 2001
From: Julian Smith <jules@op59.net>
Date: Thu, 26 Aug 2021 22:19:08 +0100
Subject: [PATCH] simgear/nasal/code.c:setupFuncall(): improve diagnostic if
 not callable.

If we have an uncallable object error, also show the type and value of the
uncallable object.

To make this work, have upgraded simgear/nasal/lib.c:dosprintf() to be globally
available. Could perhaps rename it and declare in a different header. But it's
C so we don't want to make it part of simgear's general utility functions.
---
 simgear/nasal/code.c  | 26 +++++++++++++++++++++++++-
 simgear/nasal/lib.c   |  6 +-----
 simgear/nasal/nasal.h |  6 ++++++
 3 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/simgear/nasal/code.c b/simgear/nasal/code.c
index 5662de8c..2f920ab0 100644
--- a/simgear/nasal/code.c
+++ b/simgear/nasal/code.c
@@ -328,6 +328,24 @@ static void checkNamedArgs(naContext ctx, struct naCode* c, struct naHash* h)
     }
 }
 
+
+/* This is a C equivalent to NasalRefDescription() in
+flightgear/src/Scripting/NasalSys_private.hxx. */
+static char* NasalRefDescription(naRef val)
+{
+    if (naIsNil(val))           return dosprintf("nil");
+    else if (naIsNum(val))      return dosprintf("num: %f", naNumValue(val).num);
+    else if (naIsString(val))   return dosprintf("string: %s", naStr_data(val));
+    else if (naIsScalar(val))   return dosprintf("scalar");
+    else if (naIsVector(val))   return dosprintf("vector");
+    else if (naIsHash(val))     return dosprintf("hash");
+    else if (naIsFunc(val))     return dosprintf("func");
+    else if (naIsCode(val))     return dosprintf("code");
+    else if (naIsCCode(val))    return dosprintf("ccode");
+    else if (naIsGhost(val))    return dosprintf("ghost");
+    else return dosprintf("?");
+}
+
 static struct Frame* setupFuncall(naContext ctx, int nargs, int mcall, int named)
 {
     naRef *args, func, code, obj = naNil();
@@ -336,7 +354,13 @@ static struct Frame* setupFuncall(naContext ctx, int nargs, int mcall, int named
 
     args = &ctx->opStack[opf];
     func = ctx->opStack[--opf];
-    if(!IS_FUNC(func)) ERR(ctx, "function/method call on uncallable object");
+    if(!IS_FUNC(func)) {
+        char* func_description = NasalRefDescription(func);
+        char* description = dosprintf("function/method call on uncallable object: %s", func_description);
+        ERR(ctx, description);
+        naFree(description);
+        naFree(func_description);
+    }
     code = PTR(func).func->code;
     if(mcall) obj = ctx->opStack[--opf];
     ctx->opFrame = opf;
diff --git a/simgear/nasal/lib.c b/simgear/nasal/lib.c
index 03ae65e0..fcfdf8a2 100644
--- a/simgear/nasal/lib.c
+++ b/simgear/nasal/lib.c
@@ -375,11 +375,7 @@ static naRef f_die(naContext c, naRef me, int argc, naRef* args)
     return naNil(); // never executes
 }
 
-// Wrapper around vsnprintf that will allocate the required size
-// by calling vsnprintf with NULL and 0 - and vsnsprintf will measure the
-// required amount of characters which we then allocate and return
-// Returned buffer should be freed by the caller.
-static char* dosprintf(char* f, ...)
+char* dosprintf(char* f, ...)
 {
     char* buf;
 
diff --git a/simgear/nasal/nasal.h b/simgear/nasal/nasal.h
index 6f3e3bfa..bacef686 100644
--- a/simgear/nasal/nasal.h
+++ b/simgear/nasal/nasal.h
@@ -152,6 +152,12 @@ void naRethrowError(naContext subc);
 int naMember_get(naContext c, naRef obj, naRef field, naRef* out);
 int naMember_cget(naContext c, naRef obj, const char* field, naRef* out);
 
+// Wrapper around vsnprintf that will allocate the required size
+// by calling vsnprintf with NULL and 0 - and vsnsprintf will measure the
+// required amount of characters which we then allocate and return
+// Returned buffer should be freed by the caller with naFree().
+char* dosprintf(char* f, ...);
+
 // Returns a hash containing functions from the Nasal standard library
 // Useful for passing as a namespace to an initial function call
 naRef naInit_std(naContext c);