Show spelling suggestion in symbol/property name not found error mess…

…ages (Azure#615)

* Implement a levenshtein distance based spell checker

* Provide spelling sugesstion for not found symbol

* Spell checking for property names

* Fix tests

* Fix malformed code

* Remove a bogus test

* Fix levenshtein max boundary

* Address comments

* levenshtein => Levenshtein

src/Bicep.Core.IntegrationTests/TypeSystem/TypeValidationTests.cs

@@ -273,13 +273,36 @@ public void Type_validation_narrowing_on_discriminated_object_types(TypeSymbolVa
   }
 }
 
+output valueA string = myRes.properties.myDisc1.valueA
+output valueB string = myRes.properties.myDisc1.valuuuueB
+";
+
+                var model = GetSemanticModelForTest(program, customTypes);
+                model.GetAllDiagnostics().Should().SatisfyRespectively(
+                    x => x.Should().HaveCodeAndSeverity("BCP053", expectedDiagnosticLevel).And.HaveMessage("The type choiceA does not contain property 'valuuuueB'. Available properties include 'discKey', 'valueA'.")
+                );
+            }
+
+            {
+                // all good
+                var program = @"
+resource myRes 'My.Rp/myType@2020-01-01' = {
+  name: 'steve'
+  properties: {
+    myDisc1: {
+      discKey: 'choiceA'
+      valueA: 'hello'
+    }
+  }
+}
+
 output valueA string = myRes.properties.myDisc1.valueA
 output valueB string = myRes.properties.myDisc1.valueB
 ";
 
                 var model = GetSemanticModelForTest(program, customTypes);
                 model.GetAllDiagnostics().Should().SatisfyRespectively(
-                    x => x.Should().HaveCodeAndSeverity("BCP053", expectedDiagnosticLevel).And.HaveMessage("The type choiceA does not contain property 'valueB'. Available properties include 'discKey', 'valueA'.")
+                    x => x.Should().HaveCodeAndSeverity("BCP083", expectedDiagnosticLevel).And.HaveMessage("The type choiceA does not contain property 'valueB'. Did you mean 'valueA'?")
                 );
             }
         }

src/Bicep.Core.Samples/InvalidExpressions_LF/main.bicep

@@ -199,6 +199,7 @@ var sampleObject = {
 }
 
 var badProperty = sampleObject.myFake
+var badSpelling = sampleObject.myNul
 var badPropertyIndexer = sampleObject['fake']
 var badType = sampleObject.myStr / 32
 var badInnerProperty = sampleObject.myInner.fake

src/Bicep.Core.Samples/InvalidExpressions_LF/main.diagnostics.bicep

@@ -149,7 +149,7 @@ var ternary = null ? 4 : false
 // complex expressions
 var complex = test(2 + 3*4, true || false && null)
 //@[4:11) [BCP028 (Error)] Identifier 'complex' is declared multiple times. Remove or rename the duplicates. |complex|
-//@[14:18) [BCP057 (Error)] The name 'test' does not exist in the current context. |test|
+//@[14:18) [BCP082 (Error)] The name 'test' does not exist in the current context. Did you mean 'test1'? |test|
 //@[36:49) [BCP045 (Error)] Cannot apply operator '&&' to operands of type bool and null. |false && null|
 var complex = -2 && 3 && !4 && 5
 //@[4:11) [BCP028 (Error)] Identifier 'complex' is declared multiple times. Remove or rename the duplicates. |complex|
@@ -220,7 +220,7 @@ output funcvarout array = padLeft
 var fakeFunc = red() + green() * orange()
 //@[15:18) [BCP057 (Error)] The name 'red' does not exist in the current context. |red|
 //@[23:28) [BCP057 (Error)] The name 'green' does not exist in the current context. |green|
-//@[33:39) [BCP057 (Error)] The name 'orange' does not exist in the current context. |orange|
+//@[33:39) [BCP082 (Error)] The name 'orange' does not exist in the current context. Did you mean 'range'? |orange|
 param fakeFuncP string {
   default: blue()
 //@[11:15) [BCP057 (Error)] The name 'blue' does not exist in the current context. |blue|
@@ -255,11 +255,11 @@ var test1 = listKeys('abcd')
 
 // list spelled wrong 
 var test2 = lsitKeys('abcd', '2020-01-01')
-//@[12:20) [BCP057 (Error)] The name 'lsitKeys' does not exist in the current context. |lsitKeys|
+//@[12:20) [BCP082 (Error)] The name 'lsitKeys' does not exist in the current context. Did you mean 'listKeys'? |lsitKeys|
 
 // just 'list' 
 var test3 = list('abcd', '2020-01-01')
-//@[12:16) [BCP057 (Error)] The name 'list' does not exist in the current context. |list|
+//@[12:16) [BCP082 (Error)] The name 'list' does not exist in the current context. Did you mean 'last'? |list|
 
 // cannot compile an expression like this
 var emitLimit = [
@@ -323,6 +323,8 @@ var sampleObject = {
 
 var badProperty = sampleObject.myFake
 //@[31:37) [BCP053 (Error)] The type object does not contain property 'myFake'. Available properties include 'myArr', 'myBool', 'myInner', 'myInt', 'myNull', 'myStr'. |myFake|
+var badSpelling = sampleObject.myNul
+//@[31:36) [BCP083 (Error)] The type object does not contain property 'myNul'. Did you mean 'myNull'? |myNul|
 var badPropertyIndexer = sampleObject['fake']
 //@[38:44) [BCP053 (Error)] The type object does not contain property 'fake'. Available properties include 'myArr', 'myBool', 'myInner', 'myInt', 'myNull', 'myStr'. |'fake'|
 var badType = sampleObject.myStr / 32

src/Bicep.Core.Samples/InvalidExpressions_LF/main.symbols.bicep

@@ -279,6 +279,8 @@ var sampleObject = {
 
 var badProperty = sampleObject.myFake
 //@[4:15) Variable badProperty. Type: error. Declaration start char: 0, length: 37
+var badSpelling = sampleObject.myNul
+//@[4:15) Variable badSpelling. Type: error. Declaration start char: 0, length: 36
 var badPropertyIndexer = sampleObject['fake']
 //@[4:22) Variable badPropertyIndexer. Type: error. Declaration start char: 0, length: 45
 var badType = sampleObject.myStr / 32

src/Bicep.Core.Samples/InvalidExpressions_LF/main.syntax.bicep

@@ -1736,6 +1736,20 @@ var badProperty = sampleObject.myFake
 //@[31:37)   IdentifierSyntax
 //@[31:37)    Identifier |myFake|
 //@[37:38) NewLine |\n|
+var badSpelling = sampleObject.myNul
+//@[0:36) VariableDeclarationSyntax
+//@[0:3)  Identifier |var|
+//@[4:15)  IdentifierSyntax
+//@[4:15)   Identifier |badSpelling|
+//@[16:17)  Assignment |=|
+//@[18:36)  PropertyAccessSyntax
+//@[18:30)   VariableAccessSyntax
+//@[18:30)    IdentifierSyntax
+//@[18:30)     Identifier |sampleObject|
+//@[30:31)   Dot |.|
+//@[31:36)   IdentifierSyntax
+//@[31:36)    Identifier |myNul|
+//@[36:37) NewLine |\n|
 var badPropertyIndexer = sampleObject['fake']
 //@[0:45) VariableDeclarationSyntax
 //@[0:3)  Identifier |var|

src/Bicep.Core.Samples/InvalidExpressions_LF/main.tokens.bicep

@@ -1136,6 +1136,14 @@ var badProperty = sampleObject.myFake
 //@[30:31) Dot |.|
 //@[31:37) Identifier |myFake|
 //@[37:38) NewLine |\n|
+var badSpelling = sampleObject.myNul
+//@[0:3) Identifier |var|
+//@[4:15) Identifier |badSpelling|
+//@[16:17) Assignment |=|
+//@[18:30) Identifier |sampleObject|
+//@[30:31) Dot |.|
+//@[31:36) Identifier |myNul|
+//@[36:37) NewLine |\n|
 var badPropertyIndexer = sampleObject['fake']
 //@[0:3) Identifier |var|
 //@[4:22) Identifier |badPropertyIndexer|

src/Bicep.Core.UnitTests/Text/SpellCheckerTests.cs

@@ -0,0 +1,92 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+using Bicep.Core.Text;
+using FluentAssertions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Bicep.Core.UnitTests.Text
+{
+    [TestClass]
+    public class SpellCheckerTests
+    {
+        [DataTestMethod]
+        [DataRow(null)]
+        [DataRow(new string[0])]
+        public void GetSpellingSuggestion_NullOrEmptyCandidatesEnumerable_ReturnsNull(string[] candidates)
+        {
+            string? result = SpellChecker.GetSpellingSuggestion("foo", candidates);
+
+            result.Should().BeNull();
+        }
+
+        [DataTestMethod]
+        public void GetSpellingSuggestion_EmptyCandidate_ReturnsNull()
+        {
+            var candidates = new [] { "", "" };
+
+            string? result = SpellChecker.GetSpellingSuggestion("foo", candidates);
+
+            result.Should().BeNull();
+        }
+
+        [TestMethod]
+        public void GetSpellingSuggestion_CandidateHasLessThanThreeCharacters_ReturnsNull()
+        {
+            var candidates = new [] { "o", "oo", "oO", "OO" };
+
+            string? result = SpellChecker.GetSpellingSuggestion("ooo", candidates);
+
+            result.Should().BeNull();
+        }
+
+        [DataTestMethod]
+        // maxLengthDifference = 1
+        [DataRow("ooo", "ooooo", "oooooo")]
+        [DataRow("ooooo", "ooo", "ooooooo")]
+        // maxLengthDifference = 2
+        [DataRow("oooooo", "ooo", "ooooooooo", "oooooooooooooo")]
+        [DataRow("oooooooo", "oooo", "ooooo", "ooooooooooo")]
+        public void GetSpellingSuggestion_LengthDifferenceExceedsMax_ReturnsNull(string name, params string[] candidates)
+        {
+            string? result = SpellChecker.GetSpellingSuggestion(name, candidates);
+
+            result.Should().BeNull();
+        }
+
+        [DataTestMethod]
+        // maxLengthDifference = 1, maxDistance = 1
+        [DataRow("ooo", "ooooo", "oooooo", "oxo", "oOO")]
+        [DataRow("ooooo", "ooo", "ooooooo", "oooooo", "oOoOO")]
+        // maxLengthDifference = 2, maxDistance = 2
+        [DataRow("oooooo", "ooo", "ooooooooo", "ooooox", "OOOOOO")]
+        [DataRow("oooooooo", "oooo", "ooooo", "ooooooooooo", "ooooooo", "OoOooOOo")]
+        public void GetSpellingSuggestion_CandidateMatchesNameCaseInsensitively_ReturnsCandidate(string name, params string[] candidates)
+        {
+            string? result = SpellChecker.GetSpellingSuggestion(name, candidates);
+
+            result.Should().Be(candidates[^1]);
+        }
+
+        [DataTestMethod]
+        // maxLengthDifference = 1, maxDistance = 1
+        [DataRow("ooo", "ooooo", "oooooo", "oxx", "oooo", "oxo", "xoo")]
+        [DataRow("ooo", "ooooo", "oooooo", "oxx", "oxo", "xoo", "oooo")]
+        [DataRow("ooo", "ooooo", "oooooo", "oxx", "xoo", "oooo", "oxo")]
+        [DataRow("ooooo", "ooo", "ooooooo", "oxxoo", "oooo", "oooooo", "oxooo")]
+        [DataRow("ooooo", "ooo", "ooooooo", "oxxoo", "oooooo", "oxooo", "oooo")]
+        [DataRow("ooooo", "ooo", "ooooooo", "oxxoo", "oxooo", "oooo", "oooooo")]
+        // maxLengthDifference = 2, maxDistance = 2
+        [DataRow("oooooo", "ooo", "ooooooooo", "oooo", "ooooo", "ooooooo", "ooooox")]
+        [DataRow("oooooo", "ooo", "ooooooooo", "oooo", "ooooooo", "ooooox", "ooooo")]
+        [DataRow("oooooo", "ooo", "ooooooooo", "oooo", "ooooox", "ooooo", "ooooooo")]
+        [DataRow("oooooooo", "oooo", "ooooo", "ooooooooooo", "oooooo", "ooooooo", "ooooooooo", "ooooooox")]
+        [DataRow("oooooooo", "oooo", "ooooo", "ooooooooooo", "oooooo", "ooooooooo", "ooooooox", "ooooooo")]
+        [DataRow("oooooooo", "oooo", "ooooo", "ooooooooooo", "oooooo", "ooooooox", "ooooooo", "ooooooooo")]
+        public void GetSpellingSuggestion_NoCaseInsensitiveMatches_ReturnsFirstCandidateWithSmallestEditDistance(string name, params string[] candidates)
+        {
+            string? result = SpellChecker.GetSpellingSuggestion(name, candidates);
+
+            result.Should().Be(candidates[^3]);
+        }
+    }
+}

src/Bicep.Core.UnitTests/Position/TextCoordinateConverterTests.cs → src/Bicep.Core.UnitTests/Text/TextCoordinateConverterTests.cs

@@ -7,7 +7,7 @@
 using FluentAssertions;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
-namespace Bicep.Core.UnitTests.Position
+namespace Bicep.Core.UnitTests.Text
 {
     [TestClass]
     public class TextCoordinateConverterTests

src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs

@@ -442,6 +442,17 @@ public ErrorDiagnostic ArgumentCountMismatch(int argumentCount, int mininumArgum
                 DiagnosticLevel.Warning,
                 "BCP081",
                 $"Resource type {resourceTypeReference.FormatName()} does not have types available");
+
+            public ErrorDiagnostic SymbolicNameDoesNotExistWithSuggestion(string name, string suggestedName) => new ErrorDiagnostic(
+                TextSpan,
+                "BCP082",
+                $"The name '{name}' does not exist in the current context. Did you mean '{suggestedName}'?");
+
+            public Diagnostic UnknownPropertyWithSuggestion(bool warnInsteadOfError, TypeSymbol type, string badProperty, string suggestedProperty) => new Diagnostic(
+                TextSpan,
+                warnInsteadOfError ? DiagnosticLevel.Warning : DiagnosticLevel.Error,
+                "BCP083",
+                $"The type {type} does not contain property '{badProperty}'. Did you mean '{suggestedProperty}'?");
         }
 
         public static DiagnosticBuilderInternal ForPosition(TextSpan span)

src/Bicep.Core/SemanticModel/FunctionWildcardOverload.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Text.RegularExpressions;
 using Bicep.Core.TypeSystem;
 

src/Bicep.Core/SemanticModel/NameBindingVisitor.cs

@@ -6,6 +6,7 @@
 using Bicep.Core.Diagnostics;
 using Bicep.Core.Parser;
 using Bicep.Core.Syntax;
+using Bicep.Core.Text;
 using Bicep.Core.TypeSystem;
 
 namespace Bicep.Core.SemanticModel
@@ -136,7 +137,16 @@ private Symbol LookupSymbolByName(string name, TextSpan span)
             var foundSymbol = foundSymbols.FirstOrDefault();
             if (foundSymbol == null)
             {
-                return new ErrorSymbol(DiagnosticBuilder.ForPosition(span).SymbolicNameDoesNotExist(name));
+                var nameCandidates = this.declarations.Values
+                    .Concat(this.namespaces.SelectMany(ns => ns.Descendants))
+                    .Select(symbol => symbol.Name)
+                    .ToImmutableSortedSet();
+
+                var suggestedName = SpellChecker.GetSpellingSuggestion(name, nameCandidates);
+
+                return suggestedName != null
+                    ? new ErrorSymbol(DiagnosticBuilder.ForPosition(span).SymbolicNameDoesNotExistWithSuggestion(name, suggestedName))
+                    : new ErrorSymbol(DiagnosticBuilder.ForPosition(span).SymbolicNameDoesNotExist(name));
             }
 
             return ValidateFunctionFlags(foundSymbol, span);

src/Bicep.Core/SemanticModel/Namespaces/AzNamespaceSymbol.cs

@@ -39,8 +39,7 @@ public class AzNamespaceSymbol : NamespaceSymbol
 
             // the use of FunctionPlacementConstraints.Resources prevents use of these functions anywhere where they can't be directly inlined into a resource body
             new FunctionOverload("reference", LanguageConstants.Object, 1, 3, Enumerable.Repeat(LanguageConstants.String, 3), null, FunctionFlags.RequiresInlining),
-            new FunctionWildcardOverload("list*", LanguageConstants.Any, 2, 3, new[] { LanguageConstants.String, LanguageConstants.String, LanguageConstants.Object }, null, new Regex("^list[a-zA-Z]+"), FunctionFlags.RequiresInlining),
-        }.ToImmutableArray();
+            new FunctionWildcardOverload("list*", LanguageConstants.Any, 2, 3, new[] { LanguageConstants.String, LanguageConstants.String, LanguageConstants.Object }, null, new Regex("^list[a-zA-Z]+"), FunctionFlags.RequiresInlining), }.ToImmutableArray();
 
         public AzNamespaceSymbol() : base("az", AzOverloads)
         {