Improve type-checking of struct declarations/expressions

src/checker.ts

@@ -9,7 +9,7 @@ import {
   SyntaxKind,
   TypeExpression
 } from "./cst";
-import { ArityMismatchDiagnostic, BindingNotFoudDiagnostic, describeType, Diagnostics, UnificationFailedDiagnostic } from "./diagnostics";
+import { ArityMismatchDiagnostic, BindingNotFoudDiagnostic, describeType, Diagnostics, FieldDoesNotExistDiagnostic, FieldMissingDiagnostic, UnificationFailedDiagnostic } from "./diagnostics";
 import { assert, isEmpty } from "./util";
 import { LabeledDirectedHashGraph, LabeledGraph, strongconnect } from "yagl"
 
@@ -743,21 +743,13 @@ export class Checker {
           return new TAny();
         }
         const recordType = this.instantiate(scheme, node);
-        const type = this.createTypeVar();
+        assert(recordType.kind === TypeKind.Record);
+        const fields = new Map();
         for (const member of node.members) {
           switch (member.kind) {
             case SyntaxKind.StructExpressionField:
             {
-              this.addConstraint(
-                new CEqual(
-                  new TLabeled(
-                    member.name.text,
-                    this.inferExpression(member.expression)
-                  ),
-                  type,
-                  member,
-                )
-              );
+              fields.set(member.name.text, this.inferExpression(member.expression));
               break;
             }
             case SyntaxKind.PunnedStructExpressionField:
@@ -770,19 +762,14 @@ export class Checker {
               } else {
                 fieldType = this.instantiate(scheme, member);
               }
-              this.addConstraint(
-                new CEqual(
-                  fieldType,
-                  type,
-                  member
-                )
-              );
+              fields.set(member.name.text, fieldType);
               break;
             }
             default:
               throw new Error(`Unexpected ${member}`);
           }
         }
+        const type = new TRecord(recordType.decl, fields);
         this.addConstraint(
           new CEqual(
             recordType,
@@ -1342,6 +1329,7 @@ export class Checker {
 
         case ConstraintKind.Equal:
         {
+          // constraint.dump();
           if (!this.unify(constraint.left, constraint.right, solution, constraint)) {
             errorCount++;
             if (errorCount === MAX_TYPE_ERROR_COUNT) {
@@ -1423,9 +1411,10 @@ export class Checker {
     }
 
     if (left.kind === TypeKind.Labeled && right.kind === TypeKind.Labeled) {
-      //const remaining = new Set(right.fields.keys());
       let success = false;
-
+      // This works like an ordinary union-find algorithm where an additional
+      // property 'fields' is carried over from the child nodes to the
+      // ever-changing root node.
       const root = left.find();
       right.parent = root;
       if (root.fields === undefined) {
@@ -1447,12 +1436,12 @@ export class Checker {
       return success;
     }
 
-
-    if (left.kind === TypeKind.Record && right.kind === TypeKind.Labeled) {
-      let success = true;
-      if (right.fields === undefined) {
-        right.fields = new Map([ [ right.name, right.type ] ]);
+    if (left.kind === TypeKind.Record && right.kind === TypeKind.Record) {
+      if (left.decl !== right.decl) {
+        this.diagnostics.add(new UnificationFailedDiagnostic(left, right, [...constraint.getNodes()]));
+        return false;
       }
+      let success = true;
       const remaining = new Set(right.fields.keys());
       for (const [fieldName, fieldType] of left.fields) {
         if (right.fields.has(fieldName)) {
@@ -1460,13 +1449,29 @@ export class Checker {
             success = false;
           }
           remaining.delete(fieldName);
+        } else {
+          this.diagnostics.add(new FieldMissingDiagnostic(right, fieldName));
+          success = false;
         }
       }
       for (const fieldName of remaining) {
+        this.diagnostics.add(new FieldDoesNotExistDiagnostic(left, fieldName));
+      }
+      return success;
+    }
+
+    if (left.kind === TypeKind.Record && right.kind === TypeKind.Labeled) {
+      let success = true;
+      if (right.fields === undefined) {
+        right.fields = new Map([ [ right.name, right.type ] ]);
+      }
+      for (const [fieldName, fieldType] of left.fields) {
         if (left.fields.has(fieldName)) {
-          if (!this.unify(left.fields.get(fieldName)!, right.fields.get(fieldName)!, solution, constraint)) {
+          if (!this.unify(fieldType, left.fields.get(fieldName)!, solution, constraint)) {
             success = false;
           }
+        } else {
+          this.diagnostics.add(new FieldMissingDiagnostic(right, fieldName));
         }
       }
       return success;

src/diagnostics.ts

@@ -1,4 +1,5 @@
 
+import { describe } from "yargs";
 import { TypeKind, type Type, type TArrow } from "./checker";
 import { Syntax, SyntaxKind, TextFile, TextPosition, TextRange, Token } from "./cst";
 import { countDigits } from "./util";
@@ -135,7 +136,7 @@ export class UnexpectedTokenDiagnostic {
   public format(): string {
     return ANSI_FG_RED + ANSI_BOLD + 'fatal: ' + ANSI_RESET
          + `expected ${describeExpected(this.expected)} but got ${describeActual(this.actual)}\n\n`
-         + printExcerpt(this.file, this.actual.getRange()) + '\n';
+         + printNode(this.actual) + '\n';
   }
 
 }
@@ -152,10 +153,9 @@ export class BindingNotFoudDiagnostic {
   }
 
   public format(): string {
-    const file = this.node.getSourceFile().getFile();
     return ANSI_FG_RED + ANSI_BOLD + 'error: ' + ANSI_RESET 
          + `binding '${this.name}' was not found.\n\n`
-         + printExcerpt(file, this.node.getRange()) + '\n';
+         + printNode(this.node) + '\n';
   }
 
 }
@@ -229,16 +229,14 @@ export class UnificationFailedDiagnostic {
 
   public format(): string {
     const node = this.nodes[0];
-    const file = node.getSourceFile().getFile();
     let out = ANSI_FG_RED + ANSI_BOLD + `error: ` + ANSI_RESET
         + `unification of ` + ANSI_FG_GREEN + describeType(this.left) + ANSI_RESET
         + ' and ' + ANSI_FG_GREEN + describeType(this.right) + ANSI_RESET + ' failed.\n\n'
-        + printExcerpt(file, node.getRange()) + '\n';
+        + printNode(node) + '\n';
     for (let i = 1; i < this.nodes.length; i++) {
       const node = this.nodes[i];
-      const file = node.getSourceFile().getFile();
       out += '  ... in an instantiation of the following expression\n\n'
-      out += printExcerpt(file, node.getRange(), { indentation: i === 0 ? '  ' : '    ' }) + '\n';
+      out += printNode(node, { indentation: i === 0 ? '  ' : '    ' }) + '\n';
     }
     return out;
   }
@@ -267,12 +265,52 @@ export class ArityMismatchDiagnostic {
 
 }
 
+export class FieldMissingDiagnostic {
+
+  public readonly level = Level.Error;
+
+  public constructor(
+    public recordType: TRecord,
+    public fieldName: string,
+  ) {
+
+  }
+
+  public format(): string {
+    return ANSI_FG_RED + ANSI_BOLD + 'error: ' + ANSI_RESET 
+         + `field '${this.fieldName}' is missing from `
+         + describeType(this.recordType) + '\n\n';
+  }
+
+}
+
+export class FieldDoesNotExistDiagnostic {
+
+  public readonly level = Level.Error;
+
+  public constructor(
+    public recordType: TRecord,
+    public fieldName: string,
+  ) {
+
+  }
+
+  public format(): string {
+    return ANSI_FG_RED + ANSI_BOLD + 'error: ' + ANSI_RESET 
+        + `field '${this.fieldName}' does not exist on type `
+        +  describeType(this.recordType) + '\n\n';
+  }
+
+}
+
 export type Diagnostic
   = UnexpectedCharDiagnostic
   | BindingNotFoudDiagnostic
   | UnificationFailedDiagnostic
   | UnexpectedTokenDiagnostic
   | ArityMismatchDiagnostic
+  | FieldMissingDiagnostic
+  | FieldDoesNotExistDiagnostic
 
 export interface Diagnostics {
   add(diagnostic: Diagnostic): void;
@@ -309,6 +347,16 @@ export class ConsoleDiagnostics {
 
 }
 
+interface PrintExcerptOptions {
+  indentation?: string;
+  extraLineCount?: number;
+}
+
+function printNode(node: Syntax, options?: PrintExcerptOptions): string {
+  const file = node.getSourceFile().getFile();
+  return printExcerpt(file, node.getRange(), options);
+}
+
 function printExcerpt(file: TextFile, span: TextRange, { indentation = '  ', extraLineCount = 2 } = {}): string {
   let out = '';
   const content = file.text;