report first type error

compiler/constrain/src/expr.rs

@@ -355,16 +355,19 @@ pub fn constrain_expr(
             branches,
             final_else,
         } => {
+            let expect_bool = |region| {
                 let bool_type = Type::Variable(Variable::BOOL);
-            let expect_bool = Expected::ForReason(Reason::IfCondition, bool_type, region);
+                Expected::ForReason(Reason::IfCondition, bool_type, region)
+            };
             let mut branch_cons = Vec::with_capacity(2 * branches.len() + 3);
 
             // TODO why does this cond var exist? is it for error messages?
+            let first_cond_region = branches[0].0.region;
             let cond_var_is_bool_con = Eq(
                 Type::Variable(*cond_var),
-                expect_bool.clone(),
+                expect_bool(first_cond_region),
                 Category::If,
-                Region::zero(),
+                first_cond_region,
             );
 
             branch_cons.push(cond_var_is_bool_con);
@@ -376,7 +379,7 @@ pub fn constrain_expr(
                             env,
                             loc_cond.region,
                             &loc_cond.value,
-                            expect_bool.clone(),
+                            expect_bool(loc_cond.region),
                         );
 
                         let then_con = constrain_expr(
@@ -424,7 +427,7 @@ pub fn constrain_expr(
                             env,
                             loc_cond.region,
                             &loc_cond.value,
-                            expect_bool.clone(),
+                            expect_bool(loc_cond.region),
                         );
 
                         let then_con = constrain_expr(

compiler/reporting/src/report.rs

@@ -1,10 +1,12 @@
 use crate::report::ReportText::{Batch, Module, Region, Value};
+use roc_can::expected::{Expected, PExpected};
 use roc_module::symbol::{Interns, ModuleId, Symbol};
 use roc_problem::can::PrecedenceProblem::BothNonAssociative;
 use roc_problem::can::Problem;
 use roc_solve::solve;
 use roc_types::pretty_print::content_to_string;
-use roc_types::subs::{Content, Subs};
+use roc_types::subs::{Content, Subs, Variable};
+use roc_types::types::{write_error_type, Category, ErrorType, PReason, PatternCategory, Reason};
 use std::path::PathBuf;
 
 /// A textual report.
@@ -85,8 +87,7 @@ pub fn type_problem(filename: PathBuf, problem: solve::TypeError) -> Report {
 
     match problem {
         BadExpr(region, category, found, expected) => {
-            dbg!(region, category, found, expected);
-            todo!()
+            return to_expr_report(filename, region, category, found, expected);
         }
         BadPattern(region, category, found, expected) => todo!(),
         CircularType(region, symbol, circ_type) => todo!(),
@@ -98,6 +99,67 @@ pub fn type_problem(filename: PathBuf, problem: solve::TypeError) -> Report {
     }
 }
 
+fn to_expr_report(
+    filename: PathBuf,
+    expr_region: roc_region::all::Region,
+    category: Category,
+    found: ErrorType,
+    expected: Expected<ErrorType>,
+) -> Report {
+    use ReportText::*;
+
+    match expected {
+        Expected::NoExpectation(expected_type) => todo!(),
+        Expected::FromAnnotation(name, arity, sub_context, expected_type) => todo!(),
+        Expected::ForReason(reason, expected_type, region) => {
+            let bad_type = |op_highlight, problem, this_is, further_details| {
+                let mut lines = vec![
+                    plain_text(problem),
+                    Region(region),
+                    add_category(this_is, category),
+                    newline(),
+                    newline(),
+                    plain_text("    "),
+                    ErrorType(found),
+                    newline(),
+                    newline(),
+                    further_details,
+                ];
+
+                Report {
+                    filename,
+                    text: Batch(lines),
+                }
+            };
+            match reason {
+                Reason::IfCondition => bad_type(
+                    Some(expr_region),
+                    "This `if` condition does not evaluate to a boolean value, True or False.",
+                    "It is",
+                    Batch(vec![
+                        plain_text("But I need this `if` condition to be a "),
+                        ReportText::Type(Content::Alias(Symbol::BOOL_BOOL, vec![], Variable::BOOL)),
+                        plain_text(" value."),
+                        newline(),
+                    ]),
+                ),
+                _ => todo!(),
+            }
+        }
+    }
+}
+
+fn add_category(this_is: &str, category: Category) -> ReportText {
+    use Category::*;
+
+    let result = match category {
+        Str => format!("{} a string of type:", this_is),
+        _ => todo!(),
+    };
+
+    plain_text(&*result)
+}
+
 pub fn can_problem(filename: PathBuf, problem: Problem) -> Report {
     let mut texts = Vec::new();
 
@@ -180,6 +242,7 @@ pub enum ReportText {
     /// A type. Render it using roc_types::pretty_print for now, but maybe
     /// do something fancier later.
     Type(Content),
+    ErrorType(ErrorType),
 
     /// Plain text
     Plain(Box<str>),
@@ -322,10 +385,12 @@ impl ReportText {
                 buf.push_str(&interns.module_name(module_id));
             }
             Type(content) => buf.push_str(content_to_string(content, subs, home, interns).as_str()),
+            ErrorType(error_type) => buf.push_str(&write_error_type(home, interns, error_type)),
             Region(region) => {
                 buf.push('\n');
                 buf.push('\n');
 
+                dbg!(region);
                 // widest displayed line number
                 let max_line_number_length = (region.end_line + 1).to_string().len();
 
@@ -460,6 +525,7 @@ impl ReportText {
                 ),
                 Content::Error => {}
             },
+            ErrorType(error_type) => buf.push_str(&write_error_type(home, interns, error_type)),
             Region(region) => {
                 // newline before snippet
                 buf.push('\n');

compiler/reporting/tests/test_reporting.rs

@@ -761,16 +761,21 @@ mod test_reporting {
         report_problem_as(
             indoc!(
                 r#"
-                if 1 then 2 else 3
+                if "foo" then 2 else 3
                 "#
             ),
             indoc!(
                 r#"
-                You cannot mix (!=) and (==) without parentheses
+                This `if` condition does not evaluate to a boolean value, True or False.
 
-                3 ┆      if selectedId != thisId == adminsId then
-                  ┆         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+                1 ┆  if "foo" then 2 else 3
+                  ┆     ^^^^^
 
+                It is a string of type:
+
+                    Str
+
+                But I need this `if` condition to be a Bool value.
                 "#
             ),
         )

compiler/types/src/pretty_print.rs

@@ -24,7 +24,7 @@ static EMPTY_TAG_UNION: &str = "[]";
 ///
 /// Otherwise, parens are unnecessary.
 #[derive(Clone, Copy, Debug, PartialEq)]
-enum Parens {
+pub enum Parens {
     InFn,
     InTypeParam,
     Unnecessary,

compiler/types/src/types.rs

@@ -1,9 +1,10 @@
 use crate::boolean_algebra;
+use crate::pretty_print::Parens;
 use crate::subs::{Subs, VarStore, Variable};
 use inlinable_string::InlinableString;
 use roc_collections::all::{union, ImMap, ImSet, MutMap, MutSet, SendMap};
 use roc_module::ident::{Ident, Lowercase, TagName};
-use roc_module::symbol::Symbol;
+use roc_module::symbol::{Interns, ModuleId, Symbol};
 use roc_parse::operator::{ArgSide, BinOp};
 use roc_region::all::{Located, Region};
 use std::fmt;
@@ -724,6 +725,40 @@ impl ErrorType {
     }
 }
 
+pub fn write_error_type(home: ModuleId, interns: &Interns, error_type: ErrorType) -> String {
+    let mut buf = String::new();
+    write_error_type_help(home, interns, error_type, &mut buf, Parens::Unnecessary);
+
+    buf
+}
+
+fn write_error_type_help(
+    home: ModuleId,
+    interns: &Interns,
+    error_type: ErrorType,
+    buf: &mut String,
+    parens: Parens,
+) {
+    use ErrorType::*;
+
+    match error_type {
+        Infinite => buf.push_str("∞"),
+        Error => buf.push_str("?"),
+        FlexVar(name) => buf.push_str(name.as_str()),
+        RigidVar(name) => buf.push_str(name.as_str()),
+        Type(symbol, arguments) => {
+            buf.push_str(symbol.ident_string(interns));
+
+            for arg in arguments {
+                buf.push(' ');
+
+                write_error_type_help(home, interns, arg, buf, Parens::InTypeParam);
+            }
+        }
+        _ => todo!(),
+    }
+}
+
 #[derive(PartialEq, Eq, Debug, Clone)]
 pub enum TypeExt {
     Closed,