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Support Reader and its variants for no-discarded-pure-expression #103

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Support Reader and its variants for no-discarded-pure-expression #103

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20 changes: 10 additions & 10 deletions README.md
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Expand Up @@ -64,16 +64,16 @@ If your project is a multi-package monorepo, you can follow the instructions

## List of supported rules

| Rule | Description | Fixable | Requires type-checking |
| -------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------ | :-----: | :--------------------: |
| [fp-ts/no-lib-imports](docs/rules/no-lib-imports.md) | Disallow imports from `fp-ts/lib/` | 🔧 | |
| [fp-ts/no-pipeable](docs/rules/no-pipeable.md) | Disallow imports from the `pipeable` module | 🔧 | |
| [fp-ts/no-module-imports](docs/rules/no-module-imports.md) | Disallow imports from fp-ts modules | 🔧 | |
| [fp-ts/no-redundant-flow](docs/rules/no-redundant-flow.md) | Remove redundant uses of `flow` | 🔧 | |
| [fp-ts/prefer-traverse](docs/rules/prefer-traverse.md) | Replace `map` + `sequence` with `traverse` | 💡 | |
| [fp-ts/prefer-chain](docs/rules/prefer-chain.md) | Replace `map` + `flatten` with `chain` | 💡 | |
| [fp-ts/prefer-bimap](docs/rules/prefer-bimap.md) | Replace `map` + `mapLeft` with `bimap` | 💡 | |
| [fp-ts/no-discarded-pure-expression](docs/rules/no-discarded-pure-expression.md) | Disallow expressions returning pure data types (like `Task` or `IO`) in statement position | 💡 | 🦄 |
| Rule | Description | Fixable | Requires type-checking |
| -------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------- | :-----: | :--------------------: |
| [fp-ts/no-lib-imports](docs/rules/no-lib-imports.md) | Disallow imports from `fp-ts/lib/` | 🔧 | |
| [fp-ts/no-pipeable](docs/rules/no-pipeable.md) | Disallow imports from the `pipeable` module | 🔧 | |
| [fp-ts/no-module-imports](docs/rules/no-module-imports.md) | Disallow imports from fp-ts modules | 🔧 | |
| [fp-ts/no-redundant-flow](docs/rules/no-redundant-flow.md) | Remove redundant uses of `flow` | 🔧 | |
| [fp-ts/prefer-traverse](docs/rules/prefer-traverse.md) | Replace `map` + `sequence` with `traverse` | 💡 | |
| [fp-ts/prefer-chain](docs/rules/prefer-chain.md) | Replace `map` + `flatten` with `chain` | 💡 | |
| [fp-ts/prefer-bimap](docs/rules/prefer-bimap.md) | Replace `map` + `mapLeft` with `bimap` | 💡 | |
| [fp-ts/no-discarded-pure-expression](docs/rules/no-discarded-pure-expression.md) | Disallow expressions returning pure data types (like `Task`, `IO`, or `Reader`) in statement position | 💡 | 🦄 |

### Fixable legend:

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11 changes: 6 additions & 5 deletions docs/rules/no-discarded-pure-expression.md
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@@ -1,10 +1,11 @@
# Disallow expressions returning pure data types (like `Task` or `IO`) where `void` or `unknown` is expected or in statement position (fp-ts/no-discarded-pure-expression)
# Disallow expressions returning pure data types (like `Task`, `IO`, or `Reader`) where `void` or `unknown` is expected or in statement position (fp-ts/no-discarded-pure-expression)

Expressions which return a pure data type, such as `IO`, `Task` and their
variants, should normally be passed as an argument, returned, or run.
Expressions which return a pure data type, such as `IO`, `Task`, 'Reader' and
their variants, should normally be passed as an argument, returned, or run.

Failing to do so causes the program represented by `IO` or `Task` to never be
run, leading to surprising behavior which is normally difficult to debug.
Failing to do so causes the program represented by `IO`, `Task`, or `Reader` to
never be run, leading to surprising behavior which is normally difficult to
debug.

This rule covers two common scenarios that are common programming errors:

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40 changes: 25 additions & 15 deletions src/rules/no-discarded-pure-expression.ts
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@@ -1,5 +1,6 @@
import {
ParserServices,
TSESLint,
AST_NODE_TYPES,
} from "@typescript-eslint/experimental-utils";
import { array, option, readonlyArray } from "fp-ts";
Expand Down Expand Up @@ -34,7 +35,8 @@ export default createRule({
create(context) {
const { isFromFpTs, typeOfNode, parserServices } = contextUtils(context);

const pureDataPrefixes = ["Task", "IO"];
const pureDataPrefixes = ["Task", "IO", "Reader"];
const trivialRunPrefixes = ["Task", "IO"];

function isPureDataType(t: ts.Type): boolean {
return (
Expand All @@ -48,6 +50,15 @@ export default createRule({
);
}

function canRunWithoutArgs(t: ts.Type): boolean {
if (t.isUnion()) {
return pipe(t.types, array.every(canRunWithoutArgs));
}
return trivialRunPrefixes.some(
prefix => t.symbol.escapedName.toString().startsWith(prefix)
)
}

function pureDataReturnType(t: ts.Type): Option<ts.Type> {
if (t.isUnion()) {
return pipe(t.types, readonlyArray.findFirstMap(pureDataReturnType));
Expand Down Expand Up @@ -92,6 +103,11 @@ export default createRule({
return isPureDataType(t);
}),
option.fold(constVoid, (t) => {
const addReturn = (fixer: TSESLint.RuleFixer) =>
fixer.insertTextBefore(node.expression, "return ");
const runExpression = (fixer: TSESLint.RuleFixer) =>
fixer.insertTextAfter(node.expression, "()");

context.report({
node: node.expression,
messageId: "pureExpressionInStatementPosition",
Expand All @@ -100,20 +116,14 @@ export default createRule({
? t.types[0]!.symbol.escapedName
: t.symbol.escapedName,
},
suggest: [
{
messageId: "addReturn",
fix(fixer) {
return fixer.insertTextBefore(node.expression, "return ");
},
},
{
messageId: "runExpression",
fix(fixer) {
return fixer.insertTextAfter(node.expression, "()");
},
},
],
suggest: canRunWithoutArgs(t)
? [
{ messageId: "addReturn", fix: addReturn, },
{ messageId: "runExpression", fix: runExpression },
]
: [
{ messageId: "addReturn", fix: addReturn },
],
});
})
);
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88 changes: 88 additions & 0 deletions tests/rules/no-discarded-pure-expression.test.ts
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Expand Up @@ -45,6 +45,22 @@ ruleTester.run("no-discarded-pure-expression", rule, {
}
`,
},
{
code: stripIndent`
import { reader } from "fp-ts"
function ok() {
return reader.of(42)
}
`,
},
{
code: stripIndent`
import { reader } from "fp-ts"
function ok() {
reader.of(42)(null)
}
`,
},
{
parserOptions: { ecmaFeatures: { jsx: true } },
code: stripIndent`
Expand Down Expand Up @@ -250,6 +266,35 @@ ruleTester.run("no-discarded-pure-expression", rule, {
},
],
},
{
code: stripIndent`
import { reader } from "fp-ts"

function woops() {
reader.of(42)
}
`,
errors: [
{
messageId: "pureExpressionInStatementPosition",
data: {
dataType: "Reader",
},
suggestions: [
{
messageId: "addReturn",
output: stripIndent`
import { reader } from "fp-ts"

function woops() {
return reader.of(42)
}
`,
},
],
},
],
},
{
code: stripIndent`
import { task, taskEither } from "fp-ts"
Expand Down Expand Up @@ -310,6 +355,49 @@ ruleTester.run("no-discarded-pure-expression", rule, {
},
],
},
{
code: stripIndent`
import { task, reader } from "fp-ts"

function f(n: number) {
if (n > 1) {
return reader.of("foo")
}
return task.of(42)
}

function woops() {
f(2)
}
`,
errors: [
{
messageId: "pureExpressionInStatementPosition",
data: {
dataType: "Reader",
},
suggestions: [
{
messageId: "addReturn",
output: stripIndent`
import { task, reader } from "fp-ts"

function f(n: number) {
if (n > 1) {
return reader.of("foo")
}
return task.of(42)
}

function woops() {
return f(2)
}
`,
}
],
},
],
},
{
parserOptions: { ecmaFeatures: { jsx: true } },
code: stripIndent`
Expand Down