implements PR-O1.3

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/PbsFrontendCompiler.java

@@ -12,7 +12,9 @@ import p.studio.compiler.pbs.metadata.PbsReservedMetadataExtractor;
 import p.studio.compiler.pbs.parser.PbsParser;
 import p.studio.compiler.pbs.semantics.PbsDeclarationSemanticsValidator;
 import p.studio.compiler.pbs.semantics.PbsFlowSemanticsValidator;
+import p.studio.compiler.pbs.semantics.PbsSemanticsErrors;
 import p.studio.compiler.source.diagnostics.DiagnosticSink;
+import p.studio.compiler.source.diagnostics.DiagnosticPhase;
 import p.studio.compiler.source.identifiers.FileId;
 import p.studio.utilities.structures.ReadOnlyList;
 
@@ -117,9 +119,13 @@ public final class PbsFrontendCompiler {
         final ReadOnlyList<IRFunction> functions = sourceKind == SourceKind.SDK_INTERFACE
                 ? ReadOnlyList.empty()
                 : lowerFunctions(fileId, ast);
+        final var loweringErrorBaseline = diagnostics.errorCount();
         final ReadOnlyList<IRBackendExecutableFunction> executableFunctions = sourceKind == SourceKind.SDK_INTERFACE
                 ? ReadOnlyList.empty()
-                : lowerExecutableFunctions(fileId, ast, moduleKey, reservedMetadata);
+                : lowerExecutableFunctions(fileId, ast, moduleKey, reservedMetadata, diagnostics);
+        if (diagnostics.errorCount() > loweringErrorBaseline) {
+            return IRBackendFile.empty(fileId);
+        }
         return new IRBackendFile(fileId, functions, executableFunctions, reservedMetadata);
     }
 
@@ -140,7 +146,8 @@ public final class PbsFrontendCompiler {
             final FileId fileId,
             final PbsAst.File ast,
             final String moduleKey,
-            final IRReservedMetadata reservedMetadata) {
+            final IRReservedMetadata reservedMetadata,
+            final DiagnosticSink diagnostics) {
         final var hostByMethodName = new HashMap<String, IRReservedMetadata.HostMethodBinding>();
         for (final var hostBinding : reservedMetadata.hostMethodBindings()) {
             hostByMethodName.put(hostBinding.sourceMethodName(), hostBinding);
@@ -157,8 +164,25 @@ public final class PbsFrontendCompiler {
             final var instructions = new ArrayList<IRBackendExecutableFunction.Instruction>();
             final var callsites = new ArrayList<PbsAst.CallExpr>();
             collectCallsFromBlock(fn.body(), callsites);
+            callsites.sort((a, b) -> {
+                final var deltaStart = Long.compare(a.span().getStart(), b.span().getStart());
+                if (deltaStart != 0) {
+                    return deltaStart;
+                }
+                return Long.compare(a.span().getEnd(), b.span().getEnd());
+            });
             for (final var callExpr : callsites) {
                 final var calleeName = extractSimpleCalleeName(callExpr.callee());
+                if (calleeName == null || calleeName.isBlank()) {
+                    diagnostics.error(
+                            DiagnosticPhase.STATIC_SEMANTICS,
+                            PbsSemanticsErrors.E_SEM_EXEC_LOWERING_UNRESOLVED_CALLEE.name(),
+                            PbsSemanticsErrors.E_SEM_EXEC_LOWERING_UNRESOLVED_CALLEE.name(),
+                            Map.of(),
+                            "executable lowering requires resolvable callee identity",
+                            callExpr.span());
+                    continue;
+                }
                 final var host = hostByMethodName.get(calleeName);
                 if (host != null) {
                     instructions.add(new IRBackendExecutableFunction.Instruction(
@@ -395,7 +419,7 @@ public final class PbsFrontendCompiler {
             case PbsAst.MemberExpr memberExpr -> memberExpr.memberName();
             case PbsAst.BindExpr bindExpr -> bindExpr.functionName();
             case PbsAst.GroupExpr groupExpr -> extractSimpleCalleeName(groupExpr.expression());
-            default -> "<unknown>";
+            default -> null;
         };
     }
 }

prometeu-compiler/frontends/prometeu-frontend-pbs/src/main/java/p/studio/compiler/pbs/semantics/PbsSemanticsErrors.java

@@ -59,4 +59,5 @@ public enum PbsSemanticsErrors {
     E_SEM_HANDLE_NON_RESULT,
     E_SEM_HANDLE_ERROR_MISMATCH,
     E_SEM_HANDLE_ARM_TERMINAL_INVALID,
+    E_SEM_EXEC_LOWERING_UNRESOLVED_CALLEE,
 }

prometeu-compiler/frontends/prometeu-frontend-pbs/src/test/java/p/studio/compiler/pbs/PbsFrontendCompilerTest.java

@@ -98,6 +98,31 @@ class PbsFrontendCompilerTest {
                 i.kind() == p.studio.compiler.models.IRBackendExecutableFunction.InstructionKind.CALL_FUNC));
     }
 
+    @Test
+    void shouldLowerExecutableCallsitesInDeterministicSourceOrder() {
+        final var source = """
+                fn b() -> int { return 1; }
+                fn c() -> int { return 2; }
+                fn a() -> int {
+                  b();
+                  c();
+                  return 0;
+                }
+                """;
+
+        final var diagnostics = DiagnosticSink.empty();
+        final var compiler = new PbsFrontendCompiler();
+        final var fileBackend = compiler.compileFile(new FileId(99), source, diagnostics);
+
+        assertTrue(diagnostics.isEmpty(), "Valid program should not report diagnostics");
+        final var executableA = fileBackend.executableFunctions().stream()
+                .filter(fn -> fn.callableName().equals("a"))
+                .findFirst()
+                .orElseThrow();
+        assertEquals("b", executableA.instructions().get(0).calleeCallableName());
+        assertEquals("c", executableA.instructions().get(1).calleeCallableName());
+    }
+
     @Test
     void shouldNotLowerWhenSyntaxErrorsExist() {
         final var source = """