errors: add FatalErrorHandler to handle when an abnormal error occurs on DMDLIB

This patch introduces a FatalErrorHandler for error handling on DMD to make DMD
as a library usable with the semantic analysis.

Signed-off-by: Luís Ferreira <contact@lsferreira.net>

src/dmd/errors.d

@@ -649,15 +649,26 @@ private void _vdeprecationSupplemental(const ref Loc loc, const(char)* format, v
 }
 
 /**
- * Call this after printing out fatal error messages to clean up and exit
- * the compiler.
+ * The type of the fatal error handler
+ * Returns: true if error handling is done, false to do exit(EXIT_FAILURE)
+ */
+alias FatalErrorHandler = bool delegate();
+
+/**
+ * The fatal error handler.
+ * If non-null it will be called for every fatal() call issued by the compiler.
+ */
+__gshared FatalErrorHandler fatalErrorHandler;
+
+/**
+ * Call this after printing out fatal error messages to clean up and exit the
+ * compiler. You can also set a fatalErrorHandler to override this behaviour.
  */
 extern (C++) void fatal()
 {
-    version (none)
-    {
-        halt();
-    }
+    if (fatalErrorHandler && fatalErrorHandler())
+        return;
+
     exit(EXIT_FAILURE);
 }
 

src/dmd/frontend.d

@@ -13,7 +13,7 @@ module dmd.frontend;
 import dmd.astcodegen : ASTCodegen;
 import dmd.dmodule : Module;
 import dmd.globals : CHECKENABLE, Loc, DiagnosticReporting;
-import dmd.errors : DiagnosticHandler, diagnosticHandler, Classification;
+import dmd.errors;
 
 import std.range.primitives : isInputRange, ElementType;
 import std.traits : isNarrowString;
@@ -96,12 +96,14 @@ Initializes the global variables of the DMD compiler.
 This needs to be done $(I before) calling any function.
 
 Params:
-    handler = a delegate to configure what to do with diagnostics (other than printing to console or stderr).
+    diagnosticHandler = a delegate to configure what to do with diagnostics (other than printing to console or stderr).
+    fatalErrorHandler = a delegate to configure what to do with fatal errors (default is to call exit(EXIT_FAILURE)).
     contractChecks = indicates which contracts should be enabled or not
     versionIdentifiers = a list of version identifiers that should be enabled
 */
 void initDMD(
-    DiagnosticHandler handler = null,
+    DiagnosticHandler diagnosticHandler = null,
+    FatalErrorHandler fatalErrorHandler = null,
     const string[] versionIdentifiers = [],
     ContractChecks contractChecks = ContractChecks()
 )
@@ -124,7 +126,8 @@ void initDMD(
     import dmd.objc : Objc;
     import dmd.target : target, defaultTargetOS;
 
-    diagnosticHandler = handler;
+    .diagnosticHandler = diagnosticHandler;
+    .fatalErrorHandler = fatalErrorHandler;
 
     global._init();
 
@@ -175,6 +178,7 @@ void deinitializeDMD()
     import dmd.target : target;
 
     diagnosticHandler = null;
+    fatalErrorHandler = null;
 
     global.deinitialize();
 

test/unit/frontend.d

@@ -216,7 +216,7 @@ unittest
     import dmd.frontend;
     import dmd.globals : global;
 
-    initDMD(null, ["Foo"]);
+    initDMD(null, null, ["Foo"]);
     defaultImportPaths.each!addImport;
 
     auto t = parseModule("test.d", q{