feat(stdlib): Add Exception.toString (#2143)

compiler/test/stdlib/exception.test.gr

@@ -0,0 +1,22 @@
+module ExceptionTest
+
+from "exception" include Exception
+
+exception Test1
+exception Test2(String)
+// Exception.toString
+assert Exception.toString(Failure("Test")) == "Failure: Test"
+assert Exception.toString(Test1) == "Test1"
+assert Exception.toString(Test2("Test")) == "Test2(\"Test\")"
+
+// Exception.registerPrinter
+let printer = e => {
+  match (e) {
+    Test1 => Some("Test1: This is a test"),
+    Test2(s) => Some("Test2"),
+    _ => None,
+  }
+}
+Exception.registerPrinter(printer)
+assert Exception.toString(Test1) == "Test1: This is a test"
+assert Exception.toString(Test2("Test")) == "Test2"

compiler/test/suites/basic_functionality.re

@@ -377,6 +377,6 @@ describe("basic functionality", ({test, testSkip}) => {
     ~config_fn=smallestFileConfig,
     "smallest_grain_program",
     "",
-    5165,
+    4750,
   );
 });

compiler/test/suites/stdlib.re

@@ -77,6 +77,7 @@ describe("stdlib", ({test, testSkip}) => {
   assertStdlib("bytes.test");
   assertStdlib("buffer.test");
   assertStdlib("char.test");
+  assertStdlib("exception.test");
   assertStdlib("float32.test");
   assertStdlib("float64.test");
   assertStdlib("hash.test");

stdlib/exception.gr

@@ -39,13 +39,15 @@ from "runtime/exception" include Exception
  *
  * @since v0.3.0
  */
-@disableGC
-provide let rec registerPrinter = (printer: Exception => Option<String>) => {
-  // This function _must_ be @disableGC because the printer list uses
-  // unsafe types. Not really a memory leak as this list is never collected
+provide let registerPrinter = Exception.registerPrinter
 
-  // no need to increment refcount on f; we just don't decRef it at the end of the function
-  Exception.printers = WasmI32.fromGrain((printer, Exception.printers))
-  Memory.decRef(WasmI32.fromGrain(registerPrinter))
-  void
-}
+/**
+ * Gets the string representation of the given exception.
+ *
+ * @param e: The exception to stringify
+ *
+ * @returns The string representation of the exception
+ *
+ * @since v0.7.0
+ */
+provide let toString = Exception.toString

stdlib/exception.md

@@ -65,3 +65,28 @@ Exception.registerPrinter(e => {
 throw ExampleError(1) // Error found on line: 1
 ```
 
+### Exception.**toString**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
+
+```grain
+toString : (e: Exception) => String
+```
+
+Gets the string representation of the given exception.
+
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`e`|`Exception`|The exception to stringify|
+
+Returns:
+
+|type|description|
+|----|-----------|
+|`String`|The string representation of the exception|
+

stdlib/pervasives.gr

@@ -236,7 +236,7 @@ provide primitive unbox = "@unbox"
 primitive elideTypeInfo = "@meta.elide_type_info"
 @unsafe
 let setupExceptions = () => {
-  Exception.dangerouslyRegisterPrinter(e => {
+  Exception.registerPrinter(e => {
     match (e) {
       Failure(msg) => Some("Failure: " ++ msg),
       InvalidArgument(msg) => Some("Invalid argument: " ++ msg),
@@ -247,7 +247,7 @@ let setupExceptions = () => {
   // If type information is elided, remove dependency on toString as
   // it will have no effect on exceptions
   if (!elideTypeInfo) {
-    Exception.dangerouslyRegisterBasePrinter(e => Some(toString(e)))
+    Exception.registerBasePrinter(e => toString(e))
   }
 }
 

stdlib/runtime/exception.gr

@@ -1,96 +1,74 @@
-@runtimeMode
+@noPervasives
 module Exception
 
-from "runtime/unsafe/wasmi32" include WasmI32
-use WasmI32.{ (==), (+), (-) }
-
-foreign wasm fd_write:
-  (WasmI32, WasmI32, WasmI32, WasmI32) => WasmI32 from "wasi_snapshot_preview1"
-
-primitive unreachable = "@unreachable"
-
-provide let mut printers = 0n
-
-// These functions are dangerous because they leak runtime memory and perform
-// no GC operations. As such, they should only be called by this module and/or
-// modules that understand these restrictions, namely Pervasives.
-
-provide let dangerouslyRegisterBasePrinter = f => {
-  let mut current = printers
-  while (true) {
-    // There will be at least one printer registered by the time this is called
-    let (_, next) = WasmI32.toGrain(current):
-      (Exception => Option<String>, WasmI32)
-    if (next == 0n) {
-      // Using a tuple in runtime mode is typically disallowed as there is no way
-      // to reclaim the memory, but this function is only called once
-      let newBase = (WasmI32.fromGrain(f), 0n)
-      WasmI32.store(current, WasmI32.fromGrain(newBase), 12n)
-      break
-    }
-    current = next
-  }
-  // We don't decRef the closure or arguments here to avoid a cyclic dep. on Memory.
-  // This is fine, as this function should only be called once.
-  void
-}
-
-provide let dangerouslyRegisterPrinter = f => {
-  printers = WasmI32.fromGrain((f, printers))
-  // We don't decRef the closure or arguments here to avoid a cyclic dep. on Memory.
-  // This is fine, as this function is only called seldomly.
-  void
-}
-
-// avoid cirular dependency on gc
-let incRef = v => {
-  let ptr = WasmI32.fromGrain(v) - 8n
-  WasmI32.store(ptr, WasmI32.load(ptr, 0n) + 1n, 0n)
-  v
-}
+from "runtime/unsafe/panic" include Panic
 
 let _GENERIC_EXCEPTION_NAME = "GrainException"
-
-let exceptionToString = (e: Exception) => {
-  let mut result = _GENERIC_EXCEPTION_NAME
-  let mut current = printers
-  while (true) {
-    if (current == 0n) return result
-    let (printer, next) = WasmI32.toGrain(current):
-      (Exception => Option<String>, WasmI32)
-    // as GC is not available, manually increment the references
-    match (incRef(printer)(incRef(e))) {
-      Some(str) => return str,
-      None => {
-        current = next
+let mut basePrinter = None
+let mut printers = []
+
+/**
+ * Registers a base exception printer. If no other exception printers are
+ * registered, the base printer is used to convert an exception to a string.
+ *
+ * @param printer: The base exception printer to register
+ *
+ * @since v0.7.0
+ */
+provide let registerBasePrinter = (printer: Exception => String) =>
+  basePrinter = Some(printer)
+
+/**
+ * Registers an exception printer. When an exception is thrown, all registered
+ * printers are called in order from the most recently registered printer to
+ * the least recently registered printer. The first `Some` value returned is
+ * used as the exception's string value.
+ *
+ * @param printer: The exception printer to register
+ *
+ * @since v0.7.0
+ */
+provide let registerPrinter = (printer: Exception => Option<String>) =>
+  printers = [printer, ...printers]
+
+/**
+ * Gets the string representation of the given exception.
+ *
+ * @param e: The exception to stringify
+ *
+ * @returns The string representation of the exception
+ *
+ * @since v0.7.0
+ */
+provide let toString = (e: Exception) => {
+  let rec exceptionToString = (e, printers) => {
+    match (printers) {
+      [] => match (basePrinter) {
+        Some(f) => f(e),
+        None => _GENERIC_EXCEPTION_NAME,
+      },
+      [printer, ...rest] => {
+        match (printer(e)) {
+          Some(s) => s,
+          None => exceptionToString(e, rest),
+        }
       },
     }
   }
-  return result
-}
-
-// HACK: Allocate static buffer for printing (40 bytes)
-// Would be nice to have a better way to allocate a static block from
-// the runtime heap, but this is the only module that needs to do it
-let iov = WasmI32.fromGrain([> 0n, 0n, 0n, 0n, 0n, 0n, 0n, 0n, 0n, 0n])
-
-provide let panic = (msg: String) => {
-  let ptr = WasmI32.fromGrain(msg)
-  let written = iov + 32n
-  let lf = iov + 36n
-  WasmI32.store(iov, ptr + 8n, 0n)
-  WasmI32.store(iov, WasmI32.load(ptr, 4n), 4n)
-  WasmI32.store8(lf, 10n, 0n)
-  WasmI32.store(iov, lf, 8n)
-  WasmI32.store(iov, 1n, 12n)
-  fd_write(2n, iov, 2n, written)
-  unreachable()
+  exceptionToString(e, printers)
 }
 
+/**
+ * Throws an uncatchable exception and traps.
+ *
+ * @param e: The exception to throw
+ */
 provide let panicWithException = (e: Exception) => {
-  panic(exceptionToString(e))
+  Panic.panic(toString(e))
 }
 
+// Runtime exceptions
+
 provide exception DivisionByZero
 provide exception ModuloByZero
 provide exception Overflow
@@ -126,4 +104,4 @@ let runtimeErrorPrinter = e => {
   }
 }
 
-dangerouslyRegisterPrinter(runtimeErrorPrinter)
+registerPrinter(runtimeErrorPrinter)

stdlib/runtime/exception.md

@@ -6,33 +6,84 @@ title: Exception
 
 Functions and constants included in the Exception module.
 
-### Exception.**printers**
+### Exception.**registerBasePrinter**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
 
 ```grain
-printers : WasmI32
+registerBasePrinter : (printer: (Exception => String)) => Void
 ```
 
-### Exception.**dangerouslyRegisterBasePrinter**
+Registers a base exception printer. If no other exception printers are
+registered, the base printer is used to convert an exception to a string.
 
-```grain
-dangerouslyRegisterBasePrinter : (f: a) => Void
-```
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`printer`|`Exception => String`|The base exception printer to register|
+
+### Exception.**registerPrinter**
 
-### Exception.**dangerouslyRegisterPrinter**
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
 
 ```grain
-dangerouslyRegisterPrinter : (f: a) => Void
+registerPrinter : (printer: (Exception => Option<String>)) => Void
 ```
 
-### Exception.**panic**
+Registers an exception printer. When an exception is thrown, all registered
+printers are called in order from the most recently registered printer to
+the least recently registered printer. The first `Some` value returned is
+used as the exception's string value.
+
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`printer`|`Exception => Option<String>`|The exception printer to register|
+
+### Exception.**toString**
+
+<details disabled>
+<summary tabindex="-1">Added in <code>next</code></summary>
+No other changes yet.
+</details>
 
 ```grain
-panic : (msg: String) => a
+toString : (e: Exception) => String
 ```
 
+Gets the string representation of the given exception.
+
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`e`|`Exception`|The exception to stringify|
+
+Returns:
+
+|type|description|
+|----|-----------|
+|`String`|The string representation of the exception|
+
 ### Exception.**panicWithException**
 
 ```grain
 panicWithException : (e: Exception) => a
 ```
 
+Throws an uncatchable exception and traps.
+
+Parameters:
+
+|param|type|description|
+|-----|----|-----------|
+|`e`|`Exception`|The exception to throw|
+