Add support for multistring in invariant expressions

antlr/src/main/antlr/FSH.g4

@@ -66,7 +66,7 @@ parent:             KW_PARENT name;
 id:                 KW_ID name;
 title:              KW_TITLE STRING;
 description:        KW_DESCRIPTION (STRING | MULTILINE_STRING);
-expression:         KW_EXPRESSION STRING;
+expression:         KW_EXPRESSION (STRING | MULTILINE_STRING);
 xpath:              KW_XPATH STRING;
 severity:           KW_SEVERITY CODE;
 instanceOf:         KW_INSTANCEOF name;

src/fshtypes/Invariant.ts

@@ -51,7 +51,13 @@ export class Invariant extends FshEntity {
       resultLines.push(`* severity = ${this.severity}`);
     }
     if (this.expression) {
-      resultLines.push(`* expression = "${fshifyString(this.expression)}"`);
+      // Expression can be a multiline string.
+      // If it contains newline characters, treat it as a multiline string.
+      if (this.expression.indexOf('\n') > -1) {
+        resultLines.push(`* expression = """${this.expression}"""`);
+      } else {
+        resultLines.push(`* expression = "${fshifyString(this.expression)}"`);
+      }
     }
     if (this.xpath) {
       resultLines.push(`* xpath = "${fshifyString(this.xpath)}"`);

src/import/FSHImporter.ts

@@ -967,7 +967,13 @@ export class FSHImporter extends FSHVisitor {
   }
 
   visitExpression(ctx: pc.ExpressionContext): string {
-    return this.extractString(ctx.STRING());
+    if (ctx.STRING()) {
+      return this.extractString(ctx.STRING());
+    } else if (ctx.MULTILINE_STRING()) {
+      return this.extractMultilineString(ctx.MULTILINE_STRING());
+    }
+    // this can happen due to parsing errors, so just return empty string
+    return '';
   }
 
   visitXpath(ctx: pc.XpathContext): string {

src/import/generated/FSHParser.js

@@ -178,7 +178,7 @@ const serializedATN = [4,1,89,837,2,0,7,0,2,1,7,1,2,2,7,2,2,3,7,3,2,4,7,
 0,0,0,454,453,1,0,0,0,455,63,1,0,0,0,456,457,5,13,0,0,457,458,3,144,72,0,
 458,65,1,0,0,0,459,460,5,14,0,0,460,461,3,144,72,0,461,67,1,0,0,0,462,463,
 5,15,0,0,463,464,5,58,0,0,464,69,1,0,0,0,465,466,5,16,0,0,466,467,7,4,0,
-0,467,71,1,0,0,0,468,469,5,17,0,0,469,470,5,58,0,0,470,73,1,0,0,0,471,472,
+0,467,71,1,0,0,0,468,469,5,17,0,0,469,470,7,4,0,0,470,73,1,0,0,0,471,472,
 5,18,0,0,472,473,5,58,0,0,473,75,1,0,0,0,474,475,5,19,0,0,475,476,5,62,0,
 0,476,77,1,0,0,0,477,478,5,5,0,0,478,479,3,144,72,0,479,79,1,0,0,0,480,481,
 5,20,0,0,481,482,5,62,0,0,482,81,1,0,0,0,483,484,5,21,0,0,484,485,3,144,
@@ -1990,12 +1990,20 @@ export default class FSHParser extends antlr4.Parser {
 	expression() {
 	    let localctx = new ExpressionContext(this, this._ctx, this.state);
 	    this.enterRule(localctx, 72, FSHParser.RULE_expression);
+	    var _la = 0;
 	    try {
 	        this.enterOuterAlt(localctx, 1);
 	        this.state = 468;
 	        this.match(FSHParser.KW_EXPRESSION);
 	        this.state = 469;
-	        this.match(FSHParser.STRING);
+	        _la = this._input.LA(1);
+	        if(!(_la===58 || _la===59)) {
+	        this._errHandler.recoverInline(this);
+	        }
+	        else {
+	        	this._errHandler.reportMatch(this);
+	            this.consume();
+	        }
 	    } catch (re) {
 	    	if(re instanceof antlr4.error.RecognitionException) {
 		        localctx.exception = re;
@@ -6647,6 +6655,10 @@ class ExpressionContext extends antlr4.ParserRuleContext {
 	    return this.getToken(FSHParser.STRING, 0);
 	};
 
+	MULTILINE_STRING() {
+	    return this.getToken(FSHParser.MULTILINE_STRING, 0);
+	};
+
 	enterRule(listener) {
 	    if(listener instanceof FSHListener ) {
 	        listener.enterExpression(this);

src/import/parserContexts.ts

@@ -225,6 +225,7 @@ export interface UsageContext extends ParserRuleContext {
 
 export interface ExpressionContext extends ParserRuleContext {
   STRING(): ParserRuleContext;
+  MULTILINE_STRING(): ParserRuleContext;
 }
 
 export interface XpathContext extends ParserRuleContext {

test/fshtypes/Invariant.test.ts

@@ -60,6 +60,25 @@ describe('Invariant', () => {
       expect(result).toBe(expectedResult);
     });
 
+    it('should produce FSH for an invariant with a multiline expression', () => {
+      const input = new Invariant('inv-3a');
+      input.description = 'This invariant has a multiline expression.';
+      input.severity = new FshCode('error');
+      input.expression =
+        '(cage.exists() and aquarium.exists()) or\n(habitat.exists() and enclosure.exists())';
+      input.xpath = 'f:requirement';
+
+      const expectedResult = [
+        'Invariant: inv-3a',
+        'Description: "This invariant has a multiline expression."',
+        '* severity = #error',
+        '* expression = """(cage.exists() and aquarium.exists()) or\n(habitat.exists() and enclosure.exists())"""',
+        '* xpath = "f:requirement"'
+      ].join(EOL);
+      const result = input.toFSH();
+      expect(result).toBe(expectedResult);
+    });
+
     it('should produce FSH for an invariant with additional rules', () => {
       const input = new Invariant('inv-4');
       input.description = 'This is an important condition.';

test/import/FSHImporter.Invariant.test.ts

@@ -73,6 +73,37 @@ describe('FSHImporter', () => {
         expect(invariant.sourceInfo.file).toBe('Full.fsh');
       });
 
+      it('should parse an invariant with multiline expression', () => {
+        const input = `
+        Invariant: multiline-1
+        Description: "This invariant has a multiline expression."
+        Expression: """
+          (cage.exists() and aquarium.exists()) or
+          (habitat.exists() and enclosure.exists())
+        """
+        Severity: #error
+        `;
+        const result = importSingleText(input, 'Multiline.fsh');
+        expect(result.invariants.size).toBe(1);
+        const invariant = result.invariants.get('multiline-1');
+        expect(invariant.name).toBe('multiline-1');
+        expect(invariant.description).toBe('This invariant has a multiline expression.');
+        expect(invariant.expression).toBe(
+          '(cage.exists() and aquarium.exists()) or\n(habitat.exists() and enclosure.exists())'
+        );
+        const severityCode = new FshCode('error')
+          .withLocation([8, 19, 8, 24])
+          .withFile('Multiline.fsh');
+        expect(invariant.severity).toEqual(severityCode);
+        expect(invariant.sourceInfo.location).toEqual({
+          startLine: 2,
+          startColumn: 9,
+          endLine: 8,
+          endColumn: 24
+        });
+        expect(invariant.sourceInfo.file).toBe('Multiline.fsh');
+      });
+
       it('should only apply each metadata attribute the first time it is declared', () => {
         const input = `
         Invariant: twice-1