Shell: let ports set script memory limits

README.md

@@ -144,6 +144,32 @@ On Windows add `-DCMAKE_C_COMPILER=gcc` (MinGW-w64); the program is
 `build-host/tdsh_host.exe`. `docs/POSIX_HOST.md` and `docs/WINDOWS_HOST.md`
 explain the host ports.
 
+### Memory limits for ports
+
+`TDSH_MAX_VARS`, `TDSH_VAR_NAME_MAX`, `TDSH_VAR_VALUE_MAX` and
+`TDSH_SCRIPT_TASK_STACK` in `tdsh.h` can be set by the build. Their defaults
+are 64 variables, 32-byte name buffers, 256-byte value buffers and 32768
+bytes of stack requested per script worker. The buffers include the final
+NUL. Each script keeps its own copy of the session and its variables.
+
+Apply the same overrides to **every component that includes `tdsh.h`**,
+including the shell core, the platform port and consumers such as TinyDesk.
+The variable limits change the layout of `tdsh_session_t`; mixing defaults
+and overrides between components is incompatible. Set the definitions
+from the build system rather than editing the header. For example, a host
+build with smaller variable tables can use:
+
+```bash
+cmake -S . -B build-small -DTDSH_BUILD_HOST=ON \
+  -DCMAKE_C_FLAGS="-DTDSH_MAX_VARS=48 -DTDSH_VAR_VALUE_MAX=128"
+cmake --build build-small
+ctest --test-dir build-small --output-on-failure
+```
+
+For consumers with C++ sources, pass the same definitions to their C++
+compilation too. Choose the worker stack size for the target and verify
+its margin while running the intended scripts.
+
 ## Scripts
 
 Put commands in a `.tdsh` file and run it with `tdsh run`. The script

include/tdsh.h

@@ -18,19 +18,34 @@ extern "C" {
 #define TDSH_MAX_ARGS      48
 #define TDSH_MAX_PATH      256
 #define TDSH_MAX_REAL_PATH (TDSH_MAX_PATH * 2 + 96)
-#define TDSH_MAX_VARS      64
-#define TDSH_VAR_NAME_MAX  32
+/* The variable table costs TDSH_MAX_VARS * (1 + TDSH_VAR_NAME_MAX +
+ * TDSH_VAR_VALUE_MAX) bytes in every session, including each script's copy.
+ * Buffer sizes include the terminating NUL.  An override must apply to every
+ * component using tdsh.h (core, ports and consumers such as TinyDesk), since
+ * these limits change tdsh_session_t's layout. */
+#ifndef TDSH_MAX_VARS
+#define TDSH_MAX_VARS 64
+#endif
+#ifndef TDSH_VAR_NAME_MAX
+#define TDSH_VAR_NAME_MAX 32
+#endif
+#ifndef TDSH_VAR_VALUE_MAX
 #define TDSH_VAR_VALUE_MAX 256
-#define TDSH_USERNAME_MAX  32
+#endif
+#define TDSH_USERNAME_MAX 32
 
 /* Script files use the .tdsh extension. Each user's startup script, run
  * when the physical console starts as that user: */
-#define TDSH_SCRIPT_EXT           ".tdsh"
-#define TDSH_STARTUP_FILE         ".tdshrc.tdsh"
-#define TDSH_HOSTNAME_MAX         32
-#define TDSH_MAX_COMMANDS         128
-#define TDSH_COPY_BUFFER_SIZE     4096
-#define TDSH_SCRIPT_TASK_STACK    32768
+#define TDSH_SCRIPT_EXT       ".tdsh"
+#define TDSH_STARTUP_FILE     ".tdshrc.tdsh"
+#define TDSH_HOSTNAME_MAX     32
+#define TDSH_MAX_COMMANDS     128
+#define TDSH_COPY_BUFFER_SIZE 4096
+/* Bytes requested for each script worker's stack, in addition to its
+ * session copy and runtime allocations.  Ports may impose their own cap. */
+#ifndef TDSH_SCRIPT_TASK_STACK
+#define TDSH_SCRIPT_TASK_STACK 32768
+#endif
 #define TDSH_SCRIPT_TASK_PRIORITY 4
 
 /* Compatibility defaults used by the ESP-IDF reference port. The portable