Better error message for list/array init (#3161)

* Better error message for list/array init

* add comma

src/fsharp/CompileOps.fs

@@ -623,15 +623,11 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
           os.Append(ConstraintSolverMissingConstraintE().Format (NicePrint.stringOfTyparConstraint denv (tpr,tpc))) |> ignore
           if m.StartLine <> m2.StartLine then 
              os.Append(SeeAlsoE().Format (stringOfRange m)) |> ignore
-      | ConstraintSolverTypesNotInEqualityRelation(denv,(TType_measure _ as t1),(TType_measure _ as t2),m,m2,contextInfo) -> 
+      | ConstraintSolverTypesNotInEqualityRelation(denv,(TType_measure _ as t1),(TType_measure _ as t2),m,m2,_) -> 
           // REVIEW: consider if we need to show _cxs (the type parameter constraints)
           let t1, t2, _cxs = NicePrint.minimalStringsOfTwoTypes denv t1 t2
           
-          match contextInfo with
-          | ContextInfo.IfExpression range when range = m -> os.Append(FSComp.SR.ifExpression(t1,t2)) |> ignore
-          | ContextInfo.OmittedElseBranch range when range = m -> os.Append(FSComp.SR.missingElseBranch(t2)) |> ignore
-          | ContextInfo.ElseBranchResult range when range = m -> os.Append(FSComp.SR.elseBranchHasWrongType(t1,t2)) |> ignore
-          | _ -> os.Append(ConstraintSolverTypesNotInEqualityRelation1E().Format t1 t2 )  |> ignore
+          os.Append(ConstraintSolverTypesNotInEqualityRelation1E().Format t1 t2 )  |> ignore
           
           if m.StartLine <> m2.StartLine then
              os.Append(SeeAlsoE().Format (stringOfRange m)) |> ignore
@@ -641,6 +637,11 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
           
           match contextInfo with
           | ContextInfo.IfExpression range when range = m -> os.Append(FSComp.SR.ifExpression(t1,t2)) |> ignore
+          | ContextInfo.CollectionElement (isArray,range) when range = m -> 
+            if isArray then
+                os.Append(FSComp.SR.arrayElementHasWrongType(t1,t2)) |> ignore
+            else
+                os.Append(FSComp.SR.listElementHasWrongType(t1,t2)) |> ignore
           | ContextInfo.OmittedElseBranch range when range = m -> os.Append(FSComp.SR.missingElseBranch(t2)) |> ignore
           | ContextInfo.ElseBranchResult range when range = m -> os.Append(FSComp.SR.elseBranchHasWrongType(t1,t2)) |> ignore
           | _ -> os.Append(ConstraintSolverTypesNotInEqualityRelation2E().Format t1 t2) |> ignore
@@ -667,6 +668,11 @@ let OutputPhasedErrorR (os:StringBuilder) (err:PhasedDiagnostic) =
           let t1,t2,tpcs = NicePrint.minimalStringsOfTwoTypes denv t1 t2
           match contextInfo with
           | ContextInfo.IfExpression range when range = m -> os.Append(FSComp.SR.ifExpression(t1,t2)) |> ignore
+          | ContextInfo.CollectionElement (isArray,range) when range = m -> 
+            if isArray then
+                os.Append(FSComp.SR.arrayElementHasWrongType(t1,t2)) |> ignore
+            else
+                os.Append(FSComp.SR.listElementHasWrongType(t1,t2)) |> ignore
           | ContextInfo.OmittedElseBranch range when range = m -> os.Append(FSComp.SR.missingElseBranch(t2)) |> ignore
           | ContextInfo.ElseBranchResult range when range = m -> os.Append(FSComp.SR.elseBranchHasWrongType(t1,t2)) |> ignore
           | ContextInfo.TupleInRecordFields ->

src/fsharp/ConstraintSolver.fs

@@ -127,6 +127,8 @@ type ContextInfo =
 | RecordFields
 /// The type equation comes from the verification of a tuple in record fields.
 | TupleInRecordFields
+/// The type equation comes from a list or array constructor
+| CollectionElement of bool * range
 /// The type equation comes from a return in a computation expression.
 | ReturnInComputationExpression
 /// The type equation comes from a yield in a computation expression.

src/fsharp/ConstraintSolver.fsi

@@ -62,6 +62,8 @@ type ContextInfo =
 | RecordFields
 /// The type equation comes from the verification of a tuple in record fields.
 | TupleInRecordFields
+/// The type equation comes from a list or array constructor
+| CollectionElement of bool * range
 /// The type equation comes from a return in a computation expression.
 | ReturnInComputationExpression
 /// The type equation comes from a yield in a computation expression.

src/fsharp/FSComp.txt

@@ -16,9 +16,11 @@ undefinedNameSuggestionsIntro,"Maybe you want one of the following:"
 undefinedNameTypeParameter,"The type parameter %s is not defined."
 undefinedNamePatternDiscriminator,"The pattern discriminator '%s' is not defined."
 replaceWithSuggestion,"Replace with '%s'"
+listElementHasWrongType,"All elements of a list constructor expression must have the same type. This expression was expected to have type '%s', but here has type '%s'."
+arrayElementHasWrongType,"All elements of an array constructor expression must have the same type. This expression was expected to have type '%s', but here has type '%s'."
 missingElseBranch,"The 'if' expression is missing an 'else' branch. The 'then' branch has type '%s'. Because 'if' is an expression, and not a statement, add an 'else' branch which returns a value of the same type."
 ifExpression,"The 'if' expression needs to have type '%s' to satisfy context type requirements. It currently has type '%s'."
-elseBranchHasWrongType,"All branches of an 'if' expression must return the same type. This expression was expected to have type '%s' but here has type '%s'."
+elseBranchHasWrongType,"All branches of an 'if' expression must return the same type. This expression was expected to have type '%s', but here has type '%s'."
 commaInsteadOfSemicolonInRecord,"A ';' is used to separate field values in records. Consider replacing ',' with ';'."
 derefInsteadOfNot,"The '!' operator is used to dereference a ref cell. Consider using 'not expr' here."
 buildUnexpectedTypeArgs,"The non-generic type '%s' does not expect any type arguments, but here is given %d type argument(s)"

src/fsharp/TypeChecker.fs

@@ -5715,7 +5715,15 @@ and TcExprUndelayed cenv overallTy env tpenv (expr: SynExpr) =
 
         // Always allow subsumption if a nominal type is known prior to type checking any arguments
         let flex = not (isTyparTy cenv.g argty)
-        let args',tpenv = List.mapFold (TcExprFlex cenv flex argty env) tpenv args
+        let first = ref true
+        let getInitEnv m = 
+            if !first then 
+                first := false
+                env
+            else
+                { env with eContextInfo = ContextInfo.CollectionElement (isArray,m) }
+
+        let args',tpenv = List.mapFold (fun tpenv (x:SynExpr) -> TcExprFlex cenv flex argty (getInitEnv x.Range) tpenv x) tpenv args
         
         let expr = 
             if isArray then Expr.Op(TOp.Array, [argty],args',m)

tests/fsharp/typecheck/sigs/neg20.bsl

@@ -69,35 +69,17 @@ neg20.fs(53,38,53,39): typecheck error FS0001: This expression was expected to h
 but here has type
     'int'    
 
-neg20.fs(60,26,60,33): typecheck error FS0001: This expression was expected to have type
-    'B'    
-but here has type
-    'A'    
+neg20.fs(60,26,60,33): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'B', but here has type 'A'.
 
-neg20.fs(61,27,61,35): typecheck error FS0001: This expression was expected to have type
-    'B1'    
-but here has type
-    'B2'    
+neg20.fs(61,27,61,35): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'B1', but here has type 'B2'.
 
-neg20.fs(62,26,62,33): typecheck error FS0001: This expression was expected to have type
-    'C'    
-but here has type
-    'B'    
+neg20.fs(62,26,62,33): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'C', but here has type 'B'.
 
-neg20.fs(66,25,66,32): typecheck error FS0001: This expression was expected to have type
-    'A'    
-but here has type
-    'B'    
+neg20.fs(66,25,66,32): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'A', but here has type 'B'.
 
-neg20.fs(67,27,67,34): typecheck error FS0001: This expression was expected to have type
-    'B'    
-but here has type
-    'C'    
+neg20.fs(67,27,67,34): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'B', but here has type 'C'.
 
-neg20.fs(70,31,70,38): typecheck error FS0001: This expression was expected to have type
-    'B'    
-but here has type
-    'C'    
+neg20.fs(70,31,70,38): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'B', but here has type 'C'.
 
 neg20.fs(71,34,71,42): typecheck error FS0001: Type mismatch. Expecting a
     'A list'    
@@ -128,7 +110,7 @@ but given a
     'B list'    
 The type 'A' does not match the type 'B'
 
-neg20.fs(83,47,83,54): typecheck error FS0001: All branches of an 'if' expression must return the same type. This expression was expected to have type 'B' but here has type 'C'.
+neg20.fs(83,47,83,54): typecheck error FS0001: All branches of an 'if' expression must return the same type. This expression was expected to have type 'B', but here has type 'C'.
 
 neg20.fs(87,54,87,61): typecheck error FS0001: This expression was expected to have type
     'B'    
@@ -150,10 +132,7 @@ neg20.fs(97,26,97,33): typecheck error FS0001: This expression was expected to h
 but here has type
     'B'    
 
-neg20.fs(99,26,99,33): typecheck error FS0001: This expression was expected to have type
-    'B'    
-but here has type
-    'A'    
+neg20.fs(99,26,99,33): typecheck error FS0001: All elements of a list constructor expression must have the same type. This expression was expected to have type 'B', but here has type 'A'.
 
 neg20.fs(108,12,108,16): typecheck error FS0001: Type mismatch. Expecting a
     'B * B -> 'a'    

tests/fsharp/typecheck/sigs/neg21.bsl

@@ -17,23 +17,11 @@ but given a
     'float<s ^ 4>'    
 The unit of measure 's ^ 3' does not match the unit of measure 's ^ 4'
 
-neg21.fs(19,59,19,67): typecheck error FS0001: Type mismatch. Expecting a
-    'area'    
-but given a
-    'float<m ^ 3>'    
-The unit of measure 'sqrm' does not match the unit of measure 'm ^ 3'
+neg21.fs(19,59,19,67): typecheck error FS0001: The unit of measure 'sqrm' does not match the unit of measure 'm ^ 3'
 
-neg21.fs(20,36,20,44): typecheck error FS0001: Type mismatch. Expecting a
-    'area'    
-but given a
-    'float<m ^ 3>'    
-The unit of measure 'sqrm' does not match the unit of measure 'm ^ 3'
+neg21.fs(20,36,20,44): typecheck error FS0001: The unit of measure 'sqrm' does not match the unit of measure 'm ^ 3'
 
-neg21.fs(21,53,21,59): typecheck error FS0001: Type mismatch. Expecting a
-    'float<s ^ 2>'    
-but given a
-    'float<m>'    
-The unit of measure 's ^ 2' does not match the unit of measure 'm'
+neg21.fs(21,53,21,59): typecheck error FS0001: The unit of measure 's ^ 2' does not match the unit of measure 'm'
 
 neg21.fs(22,17,22,21): typecheck error FS0001: The unit of measure 's ^ 4' does not match the unit of measure 'sqrm'
 

tests/fsharpqa/Source/Warnings/ElseBranchHasWrongType.fs

 // #Warnings
-//<Expects status="Error" span="(7,10)" id="FS0001">All branches of an 'if' expression must return the same type. This expression was expected to have type 'string' but here has type 'int'.</Expects>
+//<Expects status="Error" span="(7,10)" id="FS0001">All branches of an 'if' expression must return the same type. This expression was expected to have type 'string', but here has type 'int'.</Expects>
 
 let test = 100
 let y =

tests/fsharpqa/Source/Warnings/ElseBranchHasWrongType2.fs

 // #Warnings
-//<Expects status="Error" id="FS0001">All branches of an 'if' expression must return the same type. This expression was expected to have type 'string' but here has type 'int'.</Expects>
+//<Expects status="Error" id="FS0001">All branches of an 'if' expression must return the same type. This expression was expected to have type 'string', but here has type 'int'.</Expects>
 
 let test = 100
 let f x = test